LOW←TECH MAGAZINE

How to Build a Bike Generator with Control Panel

2022-03-06T00:00:00+01:00

Image: the bike generator in the living room.

Article

Introduction
The bike generator
- The flywheel
- Maximum power production
The art of pedal power: what are the challenges?
The dashboard: how to address these challenges?
- Matching the voltage: buck and boost converters
- Matching the current: switchable circuits and dimmers
How to use the bike: experiments
Alternative configurations: Bike generator with a work table
Hybrid human/solar power system

Introduction

Summary

Many people have built pedal power generators and published the manuals online and in books. However, when we set out to make a pedal power generator ourselves, we found that these manuals are incomplete when making the bike generator practical to use. The focus is on building the power source itself, with comparatively little attention to what happens with the power that comes out of it.

To try and make human power production more useful, we built not just a pedal power generator but also a control panel in the form of a “dashboard” attached to the handlebars. The dashboard allows powering or charging a wide diversity of devices – no matter what voltage they run on. Furthermore, multiple devices can be powered simultaneously, allowing the cyclist to adjust the resistance on the pedals for an optimal workout.

We also tried to improve the bike generator itself. Although there are good manuals available, we wanted a power source that is easy to build (no welding or complex tools required), comfortable to pedal, as compact as possible, and not an eyesore. The bike generator is set up in a small living room and used regularly. We found the solution in a vintage exercise bike with a flywheel, an approach we have not seen before.

Trial and Error

The bike generator and dashboard were designed and made in collaboration with Marie Verdeil as part of her internship at Low-tech Magazine. We could not find the technical information we were looking for, so we followed a trial-and-error approach. That was time-consuming and costly, but we gained insight and learned lessons. We made lots of mistakes that you can avoid.

We are not engineers, and we welcome technical feedback concerning further improvements. Based on that feedback and more experiments with the bike generator – which is now in use for one month – we will update and expand the manual. Our design can be adjusted and adapted to your needs. We appreciate a donation if you find our work interesting.

Newcomers to this website may want to read some earlier articles that this bike generator project is building further upon: The short history of pedal powered machines (2011), Pedal powered farms and factories: the forgotten future of the stationary bicycle (2011), Bike generators are not sustainable (2011), How to go off-grid in your apartment (2016), Slow electricity: the return of DC Power? (2016), Could we run modern society on human power alone? (2017), and How much energy do we need? (2018).

The Bike Generator

There are many ways to build a bicycle generator, and each has its advantages and disadvantages. We based our pedal power plant on a vintage exercise bicycle from the 1950s. Our bike was made by Spanish brand BH but similar vintage models can be found anywhere in the industrialised world.

Image: The exercise bike dating from the 1950s. It has a heavy flywheel in front.

The Flywheel

Our approach has several advantages. The first and most important is that old exercise bikes have a large flywheel in front. Bike generators without flywheels – which are the majority these days – are likely to end up gathering dust in the garage because they are tiring and uncomfortable to pedal.

A flywheel is essential because pedalling a stationary bicycle is a different experience from riding a bike on the road. The power that our feet put on the pedals peaks every 180 degrees of crank rotation. On the road, this has little effect because of the inertia of the cyclist.

In contrast, on a stationary bike, this uneven power output results in jerky motion and additional stress on parts. The flywheel solves this by its large mass and rotational speed. It evens out the difference between power peaks and makes for comfortable pedalling. The rider tires less quickly and can generate more energy. A flywheel also produces a more steady voltage.

Our approach also makes it possible to build a pedal power generator with simple tools and basic skills. There is no need to cut or weld metal – the bike remains like it is. ¹ Neither is there a need to build a support structure – the bicycle already has one. We only had to add a so-called friction drive – a small roller attached to the generator shaft and pressed against the flywheel.

Image: The friction drive – a small roller attached to the generator shaft and pressed against the flywheel.

Our method also results in a very compact bike generator. It is just over 1m long. Finally, and although this is a matter of personal taste, it results in a bike generator that is beautiful to behold. The bicycle was bought from someone in a neighbouring village who had it standing in the living room as a decoration.

As a disadvantage, one could mention that a friction drive is less energy efficient than a gear or belt drive. However, the higher efficiency of the flywheel compensates for that. Only a combination of flywheel and gear or belt drive would do better – but that would be more difficult to build. Another disadvantage is that our machine has no switchable gears – more on that later.

Maximum Power Production

The power output (W) of a bike generator corresponds to the voltage (V) multiplied by the current (A). We obtained roughly 100 watts (12V, 8-9A) of power during a short and heavy workout. During a moderate effort – which we can sustain for a longer time – power production is between 45 and 75 watts. The power output not only depends on the bike but also on the person who operates it. Athletes could produce more power, while couch potatoes would (initially!) generate less. ² ³

We measured the power output right after the generator. However, you need to put more power on the pedals to obtain that power output. To start with, no generator is 100% efficient. Our generator achieves its maximum efficiency (75-78%) at a power output of more than 6A (72W). Efficiency decreases when you produce less power: it drops to 60% at 3A and less than 45% at 2A. Second, there are energy losses in the drive train between the pedals and the generator. We cannot measure these, but according to the data we found, a friction drive introduces on average 15% of extra energy losses.

Taking into account efficiency losses in both generator and friction drive, you need to put at least 150 watts on the pedals to obtain a power output of 100 watts. There are additional energy losses in the bicycle drive train. In theory, bicycle gears have low energy losses, at most a few percent. In practice, however, these energy losses can be high. We proved this unintentionally. Power production doubled after we thoroughly cleaned and oiled the bicycle train. We made the mistake of cleaning the bike only at the very end. That forced adjustments to the control panel to manage the higher currents that suddenly came through it.

The Art of Pedal Power: What Are the Challenges?

As a power cyclist, you have to match the voltage (V) and the current (A) of the device you are powering or charging. However, this is easier said than done. Electric devices run on different voltages and they have very different power demands. The voltage refers to how fast you pedal and the current to how hard you pedal.

Image: the bike generator in operation.

1. Matching the voltage

A bike generator produces low voltage DC power, similar to a solar PV system (12/24V). The voltage output depends on how fast the bike generator spins. The pedalling rate and the gear ratio determine the generator speed. The manual explains in detail how to set up the correct gear ratio. In short, you need to measure the outer diameter of three parts (pedal sprocket, flywheel sprocket, flywheel) and use those data to calculate the correct spindle size for the intended voltage output.

Once you have set the gear ratio, you could produce a lower or a higher voltage by pedalling slower or faster, respectively. That makes it possible to power devices on different voltages. However, assuming your generator provides 12V at average pedalling speed, you would have to pedal in extreme slow motion to produce 5V, and it will be hard to keep your feet at the pedals to provide 24V. Gears would make it easier to vary the voltage output, but our bike has none.

Running an appliance straight from the generator can be a practical solution if it needs roughly 12V. The flywheel helps to maintain a relatively steady voltage output. However, electronic devices and batteries require a precise voltage. Otherwise, they may not work or get damaged. Furthermore, running an appliance straight from the generator prevents you from powering or charging several devices with different voltages simultaneously – which is a solution to the next problem.

2. Matching the current

Electric and electronic devices can have very different power demands – even if they work on the same voltage. Unfortunately, it’s much harder to adjust the current than the voltage. How hard you have to pedal depends entirely on the device you are powering. In some cases, this results in an optimal resistance. More often, the resistance at the pedals is either too low or too high.

At one extreme, resistance on the pedals is almost zero when charging a smartphone or a relatively small lead-acid battery. At the other extreme, resistance on the pedals is too high when powering a kettle or a refrigerator. Some devices have varying current demands. For example, the printer demands between 25 and 70 watts of power, depending on what it’s doing exactly. There are peaks in power demand following startup and between pages, and printing images requires more effort than printing text.

3. Charging batteries

Off-grid solar PV systems often charge lead-acid batteries. Human power does not depend on the weather and the time of day, but it can be practical to store human energy in a battery for future use.

Based on 100 watts of power production, it’s easy to make overly optimistic calculations about the time you need to charge a battery. For example, if it takes 100 watt-hours to charge a battery, you can do that in one hour. Right? Wrong. Even if you could sustain a power output of 100 watts for an hour, the battery limits how much power you can put into it. It’s not possible to do a short workout to charge the battery faster than it allows you to.

Lead-acid batteries charge between 10 and 25% of their maximum capacity – and we obtained 10% for all batteries tested. For large batteries, this is not a problem. Charging one lead-acid car battery (roughly 60-80Ah) requires you to get 85-115 watts out of the generator, which is a heavy workout. A full charge (12V to 13V) will take five hours, not including charge & discharge losses.

However, for smaller lead-acid batteries, the low power demand is problematic. There is little or no resistance on the pedals (so no real workout), it is very inefficient (the generator has high energy losses), and still, it takes as much time as charging a much larger battery. For example, recharging a 12V battery with a storage capacity of 14Ah (similar to the one powering the solar-powered website) requires only 1.4A. That is not much of a workout (20W).

The same problem occurs with USB devices. The most cited use of a pedal power generator is charging a smartphone. However, recharging a smartphone requires very little power (5-10W) compared to what the bike can produce. (Some newer models allow faster charging). You may think charging a 10Wh phone battery would take only 6 minutes at a maximum power output of 100W, but it takes just as long as when you plug it into a wall socket. A much smaller hand-powered charger would be sufficient to charge a smartphone, but then you don’t have your hands free.

The Dashboard: How to Address These Challenges?

To overcome all these problems, we built a control panel that distributes the power from the bike generator into switchable circuits with different voltages for the operation of various devices. You can use these circuits separately or in combination, which allows you to adjust the resistance at the pedals precisely for the optimal workout. You can also control some devices directly by lowering their power demand.

Image: The control panel.

Image: The control panel seen from the side.

1. Matching the voltage: Buck and boost converters

There is no need to pedal faster or slower to match the voltage of different devices. Instead, you can use buck converters and boost converters - electronic modules that convert a fluctuating voltage input into a steady voltage output.

Buck converters have a higher input voltage than the output voltage (they step down the voltage), while boost converters have a higher output voltage than input voltage (they step up the voltage). You can adjust the output voltage by turning a tiny screw on the module. There’s more information on buck and boost converters in the manual.

2. Matching the current: Switchable circuits & dimmers

You can build one electric circuit using only one buck or boost converter. You can then adjust the voltage by turning the tiny screw every time you power a device that requires a different voltage. However, building multiple switchable circuits with different voltages brings advantages. Not only can you easily switch between different types of appliances without the need for a screwdriver, but you can also adjust the resistance at the pedals by running several circuits simultaneously.

The control panel includes:

Two circuits for powering or charging USB devices (5V)
Three circuits for powering 12V appliances
One circuit for charging lead-acid batteries (14.4V)
One circuit for powering mains appliances (220V here in the EU)
One unregulated circuit where the voltage output matches the voltage input

Image: The front of the control panel.

Image: The back of the control panel.

If there is insufficient power demand, you can increase the resistance on the pedals by switching on more circuits. That will also increase the efficiency of the generator. To address the low power demand of batteries, you can keep the 5V and 14.4V circuits always open. That introduces a basic electric load of roughly 20W (two to five USB devices and a 14Ah lead-acid battery). For a heavier workout, increase the load by opening other circuits and powering more devices. This approach does not shorten the time it takes to charge batteries. However, it makes your effort more worthwhile.

A dashboard with nothing but 5V USB circuits is another option. More so, you use the control panel in that way with small changes. You can hook up a handful of devices to a single USB output, with a maximum power use of 10 watts (5V/2A). Our dashboard has two 5V circuits – one serves primarily for dashboard lighting, but you can add a USB distributor hub to it for another 10W of devices.

You can add six additional USB power outputs by plugging USB connectors into the three 12V outputs, at least when you add three female 12V connectors. That brings total power demand to 80 watts — enough to recharge 10 to 15 smartphones simultaneously. There’s no shortage of USB devices these days: phones, tablets, ebooks, power banks, bicycle lights, cameras, wireless headphones, AA battery chargers, and so on.

Dimmer

If there is too much power demand, you can switch off one or more circuits. For some more powerful 12V devices, the dashboard also allows you to lower the current and thus the resistance on the pedals directly by using a variable resistor or potentiometer (better known as a dimmer).

When you “dim” appliances like the electric kettle or the Peltier refrigerator, they work just as well, only slower. Without a potentiometer, only athletes could power these devices (100-120W). If you plan to charge large lead-acid batteries, you can also add a dimmer to the 14.4V circuit. However, dimming does not work for all devices. A laptop, for example, will shut down if it does not receive the power it needs.

By switching between and combining different circuits - and by finetuning the current on the 12V circuit - you can adjust the resistance at the pedals as precisely as on an exercise bike. That optimizes endurance but also power production.

How to Use the Bike: Experiments

A bike generator is best suited for powering electric devices directly – without storing the energy into a battery first. That avoids charge and discharge losses (up to 30% in lead-acid batteries) and reduces the complexity and the costs of setting up a practical human power plant. For this purpose, the control panel has several 12V circuits and a 220V circuit.

Image: Some of the appliances that we tested: air compressor, lights, Peltier refrigerator, dot-matrixprinter, electric kettle, soldering iron.

Among the 12V devices that we powered directly are an experimental Peltier refrigerator, a water kettle, laptops – powered by a 12V adapter, and without battery or with the battery at 100% – lights, a soldering iron, a power drill, and a sander. Many more 12V devices exist, mainly aimed at truck drivers and car drivers, sailors, caravan dwellers (and low-tech tinkerers who wire their apartment as if it was a sailboat).

These are all the devices we have powered or charged so far:

All types of USB devices (5V)
Lead-acid batteries of different sizes (14.4V)
Peltier refrigerator (12V)
Electric kettle (12V)
Soldering iron (12V)
Corded power drill (12V)
Corded sanding machine (12V)
Air compressor (12V)
Model railway (12V)
Sewing machine (220V)
Dot-matrix printer (220V)
Stereo amplifier + cd-player (220V)
Laptops (12V, 220V)
Lighting (5V, 12V, 220V)
Fans (5V, 12V, 220V)

Powering the lights is often more practical with a battery because that allows you to enjoy lighting without having to pedal at the same time. However, it’s perfectly doable to read a book on the bike while providing the lights in real-time, especially in winter – it takes little effort, it’s healthier than sitting still, and it keeps you warm. Other appliances that are well suited for “direct drive” human power production are power tools and heating and cooling devices.

1. Corded Power Tools

Although 12V power tools are widely used, they are almost always powered by lithium-ion batteries. You could recharge these batteries with human power. However, that will take a long time, is not much of a workout, and introduces significant energy losses. Therefore, it makes sense to convert these devices into corded power tools. In this way, you only need to produce power when you need it, with much higher efficiency. Furthermore, there is no more need to wait for batteries to charge – the tool is always ready to use.

Converting a battery-powered tool to a corded tool can be pretty straightforward. After removing the battery, locate the positive and the negative contacts and solder two wires to them. Note that you only get one chance to decide which one is positive or negative. For the power drill, this was very easy to figure out. For the sander, we asked advice because the wiring is more complicated. 12V power tools with missing or dead batteries usually sell cheap on the second-hand market.

A corded power drill is perhaps the most versatile tool. You can use it with a whisk (to beat eggs), a stiff brush (to remove paint or clean objects), a grinding wheel (to sharpen knives), or a polishing wheel (to make chrome or other metals and materials shine). Precision tools for jewelry or model making also combine well with direct pedal power. We are still in the early testing phase for converting and using corded 12V power tools.

Hand vs. Foot-powered Tools

Compared to human-powered mechanical hand tools, human-powered electric equipment is less energy efficient. Going electric introduces extra energy losses – in the generator, the buck converter, the wires, and the drive train. However, this is more than compensated for by a more energy-efficient use of the human power source. Our legs are roughly four times stronger than our arms.

Going electric is also more ergonomic because it spares hand joints and muscles. Fixing dozens of screws by hand may be more sustainable than using a power drill, but it can ruin your wrist. A bike generator thus allows you to work faster and more ergonomically without relying on an external energy source.

Mechanical hand tools keep some advantages: they are silent, more portable, and less energy-intensive to manufacture. A third option combines these advantages: pedal-powered mechanical equipment. However, it’s challenging to build a compact stationary bicycle that can power many different tools. We designed the bike generator to be as compact and multifunctional as possible.

Power tools can have high power demands, but this should not stop you. The sander only needs 30 watts at most, but our power drill can demand up to 20A of current – which is too high for the bicycle generator and control panel (12V×20A=240W). However, the machine will rarely require that power unless you use it to drill through hard materials.

The power demand of a power tool will increase whenever the torque increases, so you feel when the drill bit has gone through the material or when the screw has been fixed or loosened. You can handle the tool as precisely with your feet as you can with your hands.

2. Electric Kettle

Electric heating and cooling are energy-intensive. Alternatives, such as direct solar heat and fire, are more sustainable. However, heating and cooling can easily be included in your exercise routine and provide results.

We apply this principle with an electric kettle and an experimental Peltier refrigerator. Both appliances are very well insulated. Consequently, converting human power into heat or cold becomes another (very cheap and sustainable) form of energy storage – without all the drawbacks of batteries.

Electric kettles that run on grid power are often very powerful and boil water in a matter of minutes or even seconds. Boiling water using a bicycle generator will take a lot more time, but it’s perfectly possible. We acquired a commercial 12V electric kettle with a vacuum insulated reservoir of one litre. During a test, boiling water for one cup of tea took slightly more than one hour at an average power production of 60W.

The electric kettle can also prepare hot water bottles for thermal comfort. That requires more water than a cup of tea, but with a lower temperature of around 60 degrees celsius. During a test, heating one litre of water for a (small) hot water bottle took 1 hour and 30 minutes at an average power production of 60 watts.

Following this effort, the last thing you need is a hot water bottle. Stronger still, during that effort, you are a space heater with an output of several hundreds of watts, and you may be able to increase the air temperature in a small room. However, the vacuum insulated kettle can be put into a fireless cooker and used hours later when you are inactive and need warmth.

3. Peltier Refrigerator

Commercial 12V refrigerators are expensive. After researching thermoelectric generators (TEGs), the idea of a Peltier refrigerator was born. A Peltier refrigerator is essentially a well-insulated fireless cooker with a TEG mounted on top. If power is applied, the module will get hot on one side and cold on the other, cooling the box interior. TEG cooling is not particularly efficient. However, it’s silent, works without problematic cooling gases, and is the easiest way to make a refrigerator yourself.

The TEG refrigerator is an early prototype, which needs further testing and improvements. Powering one TEG at full power requires roughly 60 watts (12V×5A), measured right after the generator. That is a good workout, and the dimmer allows to lower the resistance at the pedals precisely. However, it quickly became apparent that one TEG is not enough for the size of the cooling space. We will add a second one for a heavier workout (60-100 watts).

Mains Appliances (220V)

Our dashboard also includes a 220V circuit. That makes it compatible with grid-powered devices (110V in the US, 240V in the UK). The 220V circuit requires an inverter. The inverter is too large to include in the dashboard, so we placed it in a box on the luggage rack that we built in front.

A 220V socket is not necessary. Many 220V appliances have 12V (or 24V) alternatives which are more energy efficient for decentralised power production. However, we included a 220V circuit for powering devices that have not (yet) been replaced by or converted to low voltage alternatives: the dot-matrix printer, the sewing machine, the stereo system, and the router.

The dot-matrix printer and the sewing machine are challenging to operate because of their rapidly changing power demand. For example, to avoid the voltage dropping below 12V at high power peaks while printing, you need to pedal very fast (around 20V) to provide sufficient inertia to the flywheel. A supercapacitor may be able to solve this — this is something we will try in the coming months. A foot-powered mechanical sewing machine and printer would be much more energy-efficient — but much less space-efficient.

Alternative configurations: Bike generator with a work desk

The control panel is designed to power a wide diversity of devices, but you can follow a similar approach with different results. For example, if you only want to charge lead-acid batteries, one 14.4V circuit is enough. You can use a buck and boost converter to create any voltage you need, for example, to build a 3V, 6V, 9V, or 24V circuit.

However, if you mainly want to run 24V appliances, it’s a better idea to adjust the gear ratio. Same if you only want to charge 14.4V lead-acid batteries on a 12V system: adjust the gear ratio to generate 16-17V (to compensate for energy losses in the buck converter).

Image: The 220V power output.

Image: The luggage rack and the power outlets (unregulated, 3x12V, 14.4V, 5V USB).

Image: Inside the box: the inverter, the wind charge controller, the lead-acid battery.

Our choice to have a large dashboard on the handlebars has advantages and disadvantages. To have the control panel on the bike itself makes it easy to read and manipulate. It also makes the bike generator portable. If the neighbour needs emergency power, you pick up the bike, and you are there in a minute. On the downside, having the dashboard on the bike adds vibrations, which increase noise and energy losses. It also makes it necessary to adjust the voltage output from the buck and boost converters from time to time.

Most importantly, having such a large control panel on the bike prevents you from placing a large desk on top of the handlebars instead. That could be useful to operate power tools or a laptop while simultaneously providing power. Our present set-up is not ideal for using power tools. It requires two people - one to cycle and one to operate the power tool. Likewise, you can power another person’s laptop, but you can’t power yours while using it.

We plan to build a bike generator with a smaller dashboard — one 12V circuit and two USB ports — and a large workspace on the handlebars. Such a bike generator harks back to similar (mechanical) bicycle machines from the early twentieth century. Another option is to screw the control panel to the wall or put it on a shelf — and place the bike generator next to it. The inverter, lead-acid battery, and wind charge controller – now on the “luggage rack” – can also move away from the bike.

Hybrid Solar/Human Power System

Some of you may think that our bike generator is more of a gimmick than a practical power source for the household. In part, this is true. Our human power plant is the perfect exercise machine – power production is motivating. It is also practical in emergencies, especially if enough people power is available – it can produce up to 2.4 kWh per day. However, it won’t provide enough energy daily – not even for a low-tech household. In practice, there are not enough people willing to cycle.

On the other hand, a bike generator is an excellent addition to an off-the-grid solar PV system, at least in a low-energy household. The power output of the bicycle generator does not depend on the weather, the seasons, or the time of day. Human power can provide extra energy during bad weather, which reduces the need for expensive and unsustainable batteries. That is especially useful in winter, when the solar PV system produces much less power, and when the effort required to operate the bike also keeps you warm. There is enough solar power in summer — when it’s often too hot to use a stationary bicycle.

Image: The bike generator stands right next to the solar PV systems. The ultimate plan is to integrate both power systems.

With a power production of 50-100 watts, the bike generator is more powerful than the two solar panels that are standing on the balcony next to it: the 50 watts solar panel that is powering the lights in the living room and the 30 watts solar panel that runs the solar-powered website. The solar panels rarely – if ever – reach their maximum power production, and during bad weather, they produce much less power than the bike generator. With dark clouds overhead, energy production almost drops to zero, and if this lasts for two days, the lights and the website go down. One or two hours per day on the bike generator could fix this. Alternatively, pedal power could operate power tools or other devices without draining the energy storage from the solar PV system.

It’s also possible to use the dashboard with a solar panel instead of a bike generator. It suffices to replace the wind charge controller with a solar charge controller. You can then use solar energy to power devices directly — without necessarily using a solar charge controller and battery. Replace the wind charge controller with a hybrid solar/wind charge controller, and you can use both energy sources to charge batteries and power devices directly. Solar and human power can also be combined, increasing the power output.

Combining solar and human power should make it possible to take further steps towards an off-grid urban household. The plan is to add another 50W solar panel, take more devices off the grid (most notably the refrigerator) and keep the battery storage as it is.

Manual: The Bike Generator

Image: The friction drive.

What type of generator do you need?

To convert the mechanical energy of the flywheel into electricity, you need a 12V/24V permanent magnet DC generator with a maximum power output of about 150-250 watts. Not any generator will do. You need one that runs at a relatively low speed (<5000 no-load rpm) to obtain 12 or 24V with a practical gear ratio (see further). Many generators need to run at higher speeds to generate 12V or 24V, and you won’t be able to produce more than a few volts at an average pedalling rate.

Be sure to get a brushed DC motor. Brushless DC motors won’t work because they need a very high rotation speed. Note that a generator is a motor working in reverse. When searching online, “DC motor” will give you more results than “DC generator”. Car alternators also work, and many pedal power plants use them because they are cheap and easy to obtain. However, they are very inefficient and require a 9V battery to start.

You can scavenge DC generators from discarded electric scooters or bicycles, but we bought a brand new one: the Ampflow Pancake Motor P40-250. It has a no-load RPM of 1700 at 12V and a maximum power output of 250 watts. You can tighten it securely to a metal or wooden surface, which saves a lot of trouble.

How to calculate the gear ratio and spindle size?

The voltage created by the generator is directly proportional to the rotating speed of the generator (the RPM or “rounds per minute”). However, the rotating speed of the generator is not a given. It depends on how fast you pedal (the RPM of the pedals). It also depends on the gear ratio between the pedals and the generator. The average RPM of the pedals on a stationary bike – a comfortable pedalling rate that you can sustain for a long time – is roughly 60 RPM. It can be calculated precisely by a tachometer or using low-tech tricks. ⁴

Our bike generator uses a friction drive. It consists of a small wheel (the spindle) attached to the generator shaft that will spin in contact with the flywheel. Calculating the gear ratio involves measuring the outer diameter of four parts: the pedal sprocket, the flywheel sprocket, the flywheel, and the spindle. The first three are known, while the latter was for us to figure out. The spindle size you need depends on the specifications of your generator and on the exact voltage that you would like to produce. Figuring this out can be mind-boggling unless someone provides you with the right formula (thank you, Gabriel Verdeil!).

First, you need to find the “no-load RPM” of your generator. This information should be provided by the manufacturer. Our generator has a no-load RPM of 3400 at 24V. This ratio is proportional — you can calculate the required no-load RPM for any voltage you want. For example, at 12V it’s 1700 RPM (3400/24×12), and at 16V it’s 2267 RPM (3400/24×16). Next, measure the outer diameter of the pedal sprocket, the flywheel sprocket, and the flywheel. Whether you use mm, cm, or any other unit doesn’t matter but be consistent. Now you have all the data you need to calculate the spindle size. Below is the formula, followed by the calculation for our specific case (assuming 60 RPM at the pedals):

Spindle diameter = (PS×W×RPM pedals)/(WS×RPM generator)

PS = pedal sprocket diameter
W = flywheel diameter
RPM pedals = how fast you pedal
WS = flywheel sprocket diameter
RPM generator = the no-load RPM of the generator

Spindle diameter for our configuration (in mm) to produce different voltages:

12V = (190×525×60)/(60×1700) = 58.68mm spindle diameter.
13V = (190×525×60)/(60×1842) = 54.15 mm spindle diameter.
14V = (190×525×60)/(60×1983) = 50.30 mm spindle diameter.
15V = (190×525×60)/(60×2125) = 46.94 mm spindle diameter.
16V = (190×525×60)/(60×2267) = 44.00 mm spindle diameter.
17V = (190×525×60)/(60×2408) = 41.42 mm spindle diameter.
24V = (190×525×60)/(60×3400) = 29.34 mm spindle diameter.

The exact voltage you need – and thus the exact spindle size – depends on what exactly you want to do with the bike. We address this in detail in the manual for the control panel. Imagine you want to charge lead-acid batteries (which require 14.4V). You use a buck converter (which steps down the input voltage), so you will need to produce close to 17V to make up for the losses in the voltage conversion. That results in a spindle diameter of 41.42mm. This configuration shows in the illustration below.

You can use the formula in different ways. You can use it to calculate the minimum RPM at the pedals for a given spindle; to calculate the generator RPM based on a given RPM at the pedals and spindle size; and to calculate the voltage that will be produced by a given configuration. Find the formulas below, followed by an example based on the configuration illustrated above:

Calculate the minimum RPM at the pedals for a given spindle size (S):

RPM generator/[(PS×W)/(FS×S]
2260/[(190×525)/(60×41)] = 55.81 RPM at the pedals.

Calculate the generator RPM for a given spindle size and RPM at the pedals:

(PS/FS)×(W/S)×RPM at the pedals
(190/60)×(525/41)×55 = 40.61 (gear ratio)×56 = 2274 RPM

Calculate the voltage for a given RPM at the generator:

Generator RPM×No load RPM ratio
2274×(3400/24) = 16.1V

What type of spindle do you need?

Figuring out the spindle size is only half of the work. It can be challenging to find a spindle with the correct diameter, made from the required materials, and compatible with the generator shaft. We tried a dozen spindles until we got the right one. A flywheel has a hard surface and requires a soft spindle made of rubber or polyurethane. We found that a solid metal and rubber buffer allowed optimal friction with our flywheel. We took it to a metal workshop where they drilled a 10 mm hole into the piece.

Image: A sample of our test spindles.

Other options are small solid polyurethane wheels and rubber suspensions. Skate wheels have a larger inside diameter which is not ideal for an 8-10mm shaft. Be careful to choose a material that can handle friction: some plastic tends to heat up and melt. Keep in mind: this is a trial and error process. You won’t get this right from the first time. Another route you could take is to design a custom lathed piece, as is described in magnificientrevolution.org’s tutorial. A universal mounting hub can help attach wheels featuring bolt holes, such as robot wheels.

Buying a DC generator with a pre-installed spindle seems the easiest solution. For example, Pedal Power Generator offers a 360W generator with a spindle size of 37.5 mm. However, you can’t choose a spindle with a different diameter. That means you cannot control the output voltage unless you replace the sprockets in the bicycle drive train. In our case, a 37.5mm spindle would produce 18V, which is too much.

How to fix the spindle to the generator?

The generator comes with an integrated sprocket or pulley drive. You need to remove it to attach the spindle. A nylon lock nut with a reverse tread holds the sprocket or pulley drive. You need to unscrew it to the right. You probably need a clamp to manage this.

Image: The generator with a threaded shaft arbor.

Image: The generator with the 41mm spindle.

Our generator features an 8 mm shaft, while our spindle fits on a 10 mm shaft. Therefore, we use a two-part spindle featuring a “shaft arbor” and a wheel. To properly attach the spindle, you can take advantage of the D-cut on the shaft (a “round shaft with drive flat”). Our first try was a threaded fixation, but that did not work. Because of the reversed thread, it will come loose when the generator starts spinning.

We found that a threaded shaft arbor with set screws was the most versatile solution to test different wheels. We fixed the shaft arbor with grub screws placed on the flat section of the shaft. It’s an M10 threaded rod. You can secure a wheel on it with a couple of washers and a nut. A Bore Rigid Coupling could also serve as a small spindle. You can also use it to attach the generator’s shaft to another axle with a wheel. However, we found this was not ideal for our setup because the set screws stick out of the coupling, damaging the flywheel.

How to fix the friction drive to the bike?

We screwed the generator to a wooden board and then pressed it against the flywheel using a wood support structure. The board is attached to the bike with a strong door hinge. That allows adapting the angle at which the spindle is in contact with the flywheel. The stand is resting on a cork wedge that buffers the vibrations. See our first prototype for another method.

Image: The friction drive.

Manual: The Control Panel

Buck and boost converters, dimmers

Buck converters and boost converters are electronic modules that convert a fluctuating voltage input into a steady voltage output. Buck converters have a higher input voltage than the output voltage (they step down the voltage), while boost converters have a higher output voltage than input voltage (they step up the voltage).

You can adjust the output voltage by turning a tiny screw on the module. Some buck and boost converters come with a small digital screen that shows the output voltage. If this is not the case, you can use a multimeter to adjust the voltage output.

Note that you need either a buck or a boost converter. Do NOT use a buck/boost converter. This is a sort of micro bench supply that requires the output voltage to be adjusted every time the system is powered up. This is unpractical and risks damage to your appliances. In contrast, a buck or boost converter remembers the output voltage whenever you start it up.

Also, do NOT buy a voltage regulator. This device allows you to regulate the output voltage but only in relation to the input voltage. If the voltage input changes, so will the voltage output. You want a buck or boost converter, in which the voltage input can fluctuate but the voltage output is stable.

Finally, you should check the maximum current rating before buying a buck or boost converter. Some only take 2A, which is not powerful enough for a bike generator. You need at least one that can take 5A and preferably one that can take 10A or 15A, depending on your power output.

Buck or boost converter?

Whether you opt for a buck or a boost converter depends on the voltage produced by the generator — and by the voltage of the device(s) you want to power or charge. If the bike generator puts out 12V and you want to charge 5V USB devices, you need to step down the volume and thus use a buck converter. These small modules with a USB connector convert a fluctuating voltage input into a steady 5V voltage output. ⁵

If you want to power 12V devices or recharge lead-acid batteries (14.4V), both a buck and a boost converter could work. If you opt for a buck converter, the bike generator needs to have a voltage output that is slightly above 12V or 14.4V (13-14V and 16-17V, respectively). This higher input voltage is necessary to compensate for energy losses in the power conversion. If you use a boost converter, the voltage output of the generator needs to stay below 12V or 14.4V.

A buck converter will never exceed the chosen voltage output, no matter how many volts the generator produces. In contrast, a boost converter guarantees you a minimum voltage output, but it does not set a maximum output voltage. If you pedal too fast, the voltage output may exceed the set voltage output and damage the appliance or battery you are powering or recharging.

For our first dashboard prototype, we used only buck converters. We used a boost converter to charge lead-acid batteries for the next version. The generator needs to produce 16-17V to obtain a voltage output of 14.4V with a buck converter. That is fine if you only want to charge lead-acid batteries because you can then adjust the gear ratio to produce 16-17V at a comfortable pedalling speed. However, if you optimize the gear ratio for lower voltages, you have to pedal very fast whenever you include the charging of batteries in your workout.

Wind charge controller

The bike generator needs to supply 14.4V to charge lead-acid batteries — the maximum voltage that a lead-acid battery needs. In principle, all you need is a buck or boost converter, but there’s one caveat: you may overcharge the battery, which can lead to an explosion.

You can avoid this risk in a low-tech way – by keeping an eye on the amperemeter. Once the current drops to 3% of the rated storage capacity of the battery (in Ah), the battery is fully recharged — and you should stop pedalling. Because you are the power source and thus certainly present and awake, this approach is less risky than charging a lead-acid battery from a DC power supply or a solar panel without a charge controller.

However, it’s a good idea to add more security. A solar charge controller provides this security in a solar PV system. It cuts the power input whenever the voltage rises above 14.4V. However, a solar charge controller does not work when coupled to a bike generator. Instead, you need a wind charge controller, which operates the other way around.

Instead of cutting the load to zero, a wind charge controller suddenly increases it and “brakes”. If you use a buck converter, the wind charge controller will rarely activate the break because the buck converter will limit the voltage output to 14.4V. It will only brake when you threaten to overcharge the battery. If you use a boost converter, the wind charge controller will brake whenever you accidentally exceed a voltage output of 14.4V.

Wind charge controllers have three green wires to connect to the power source. You can take any two of these three wires and connect them to the plus and the minus of the power input – it doesn’t matter which goes where.

Most wind charge controllers commercially available are way too powerful for a pedal power generator, so get the smallest one you can find. We sent two charge controllers back to the manufacturer. One wind charge controller with a screen came without a manual, and nobody could figure out how it works. The only hybrid wind/solar controller that we tried, for now, was dangerous. The solar panel overcharged the battery. It also maintained the electric brake for half an hour whenever we crossed the threshold, thus blocking human power production.

Wires, Connectors, Diodes, Fuses, On/Off Switches

You need wires, connectors, diodes, fuses, and on-off buttons to connect everything. All these parts can confuse you, so here’s what you need to know.

Wires

The control panel includes roughly ten meters of electric cable. However, the main thing to worry about is not the length but the thickness of the cable. Opt for too thin wires, and your dashboard may catch fire during a heavy workout. Making the right choice can be confusing because there are several standards. We wired the dashboard with a 20AWG 0.52mm2 cable, which takes 11A. A better option would have been an 18AWG 0.82mm2 cable, which takes 16A. Take care when stripping the wires: if you cut too deep the cable can take less current.

Connectors

Wires can be connected using very different methods. We choose lever connectors — bulky and expensive but handy. They help to connect wires securely without soldering or screws. These connectors come with two to ten pins. Wiring the dashboard can become disorderly. Make sure you don’t cut the cables too short.

Fuses

You can build a bike generator and controller without fuses, but it’s not a good idea. A fuse will break the electric circuit when you exceed a current threshold, preventing fire and damage to components. We placed a 12A fuse at the entrance of the dashboard (our max power production is 8-9A). We also added fuses to most of the devices we power.

On-off switches

Switchable circuits require on-off buttons. Our dashboard has nine of them. We wanted switches that light up when active because that quickly shows which electric circuits are in operation when starting the pedal power generator. However, lights make wiring the on-off switches more complex.

We bought switches with the wires already attached because we preferred not to solder the connections. However, we had to solder them anyways because the thick wires took too much space. On-off buttons without lights and with prefixed thinner wires simplify this part.

Image: How to wire the on-off switches.

Schottky Diode

A Schottky diode ensures that the current can only flow in one direction through a cable. This tiny part is essential when there are batteries attached to your system. Without a diode, the battery could power the generator (and turn the pedals) instead of the other way around. We put a Schottky diode right after the generator to prevent this. It needs to be rated for the correct amperage: above your expected power production. Our maximum power production is 8-9A, the Schottky diode takes 10A.

Dashboard Instruments

The control panel includes several displays that show the voltage and current in different electric circuits. The analog volt- and amp meter on top is the most important one. It shows how much power the generator is producing (V×A=W). The voltmeter tells you how fast you are pedaling, the amp meter how hard you are pedaling.

Analog V&A meters are most precise in the middle of their range, so we choose a voltmeter that goes up to 30V and an amp meter that goes to 15A. A digital V&A meter is more compact, but analog meters display variations better. Above the meter, there is a USB circuit to plug in a small LED light. That allows you to keep an eye on the V&A meter when dark. It’s also handy to quickly check if the system is working.

Image: How to wire the analog voltmeter and ammeter.

Below the V&A meter are three voltage meters for every buck and boost converter. These show the voltage output for each of the circuits. The voltage output should be 12.0V for the 12V and 220V electric circuits and 14.4V for the 14.4V circuit. The first two may fall below that value if you don’t pedal fast enough, while the last one may go above that value if you pedal too quickly — the wind charge controller will also make this clear to you. There is also a voltage and current meter on the 5V circuit. That helps to maximize power production by adding as many USB devices as possible (up to 2A).

Two more instruments are not on the dashboard itself: the voltage meter of the lead-acid battery and the temperature meters of the electric kettle and the Peltier refrigerator. None of these are essential. However, they can motivate the power cyclist. On the road, your efforts result in distance covered. Stationary cycling can be boring — you are not going anywhere. The instruments help you to set goals. For example: let’s get the refrigerator temperature down by 2 degrees C before you take a shower.

Dashboard Panel and Fixation

We attached the control panel to the handlebars and added a luggage rack in front that holds extra parts such as an inverter, a wind charge controller, and a lead-acid battery. On top of the box are the power outputs for each circuit and a USB distribution hub. The box has an open lid and holes for the dashboard’s cables to pass through (they first go inside the handlebar).

We used a laser cutter at a maker space (MADE Barcelona) to produce the panel. All components are fitted in or sandwiched between two layers of 4mm MDF. You can easily remove the front panel if something needs to be changed or repaired. A transparent acrylic plate protects the buck and boost converters. You can take it off to adjust the output voltage. We attached the dashboard to the bike handle with rubber pipe clamps, M8 cap nuts, and bolts.

How to Wire the Dashboard?

Complete Control Panel:

1: Schottky diode. 2: Fuse. 3: Cables. 4: Analog ammeter and voltmeter. 5: On/Off switches. 6: Wire connectors. 7: USB Led Light.

5V circuit:

8: USB Buck converter. 9: USB Voltmeter & Ammeter. 10: USB Multi-plug and cable.

12V circuit:

11: Buck Converter. 12: Dimmer.

14.4V circuit:

13: Boost converter. 14: Wind turbine charge controller. 15: Lead-acid battery. 16: Battery electronic voltmeter.

220V circuit:

17: Buck Converter. 18: Inverter.

Manual: Components List

Generator

Motor (x1). Ampflow P40 - 250W Pancake DC Brushed Motor 24-12V.
Shaft arbor (x1). Threaded Shaft Arbor conversion from 8mm to M10
Wheel (x1).

Dashboard

Schottky diode (x1). BOJACK Diode Schottky 10SQ045 (10A 45V)
Fuse (x1).
Analog ammeter (x1). Analog Ammeter DH-670 0-5A Class 2.0 & Analog voltmeter (x1) — Analog Voltmeter DH-670 DC 0-30V Class 2.0
On/Off LED Switch (x8) — KR1-5 Series Rocker ON/OFF Switch 12V 20A 3 pins with LED
Wire Connector (≈16 of different formats)
5V USB Led Light. Any USB flexible arm LED light will do.
5V Buck converter (x2). Buck Converter MH KC24 DC-DC 24-12V Charging Step Down to 5V USB with Fast Charging Protocol.
5V USB Voltmeter & Ammeter.
5V USB Multi-plug.
12 V 5A Buck Converter (x2). Buck Converter DC-DC Adjustable 12-24-36V 5A
Dimmer & 12V DC Socket (x1). RUIZHI DC 12V waterproof Female Car Cigarette Lighter Socket.
Boost Converter (x1).
Wind turbine charge controller (x1) — Asixx Waterproof Wind Charge Controller 24-12V 300/600W.
Battery Electronic Voltmeter.
12V 15A Buck Converter — Buck Converter 200W 15A DC 3-60V to 1-36V step-down adjustable voltage regulator synchronous rectifier module.
Inverter (x1) — 300W or less Inverter DC 12V to AC 220-240V
Cable (+10m). 0.52mm2 10M conductor parallel silicon wires 20AWG 11A (10M of each)

Hardware

M3 Bolts. They fit with the electronic components to secure them to the dashboard.
M6 Bolts. To attach the motor to the wooden board.
M8 Bolts. To attach the two parts of the dashboard.
Big door hinge. To attach the motor at an angle.
Metal mounting brackets (all sizes and shapes). To strengthen the structure.
Rubber metal clamps. To attach the dashboard to the bike handle.
Wood glue, screws (all sizes), bolts, washers and nuts (normal, lock, rounded, wing-shaped), wooden cleats and boards, black acrylic paint, etc.

The Costs

We only include the components we effectively used:

Generator

Vintage exercise bike (second hand): 60 euro
Generator: 60 euro
Arbor shaft: 10 euro
Spindle: 3 euro
Total: 133 euro

Dashboard (all circuits)

Wires: 17 euro
Connectors: 25 euro
Analog volt meter: 9 euro
Analog ampmeter: 9 euro
On-off buttons: 20 euro
Diode: 1 euro
Fuse: 1 euro
Total: 82 euro

5V circuit

5V USB buck converter (2x): 8 euro
5V USB V&A meter: 8.50 euro
USB distribution hub: 30 euro
Total: 46.5 euro

12V circuit

12V 5A buck converter (2x): 24 euro
12V 5A boost converter: 8 euro
12V 15A buck converter: 25 euro (extra circuit we added later)
Dimmer: 7.50 euro
Total: 64.5 euro

14.4V circuit

Inverter: 50 euro
Battery (14Ah): 31 euro
Wind charge controller: 34 euro
Total: 115 euro

Hardware

To fix the dashboard and the generator: +/-30 euro

Total cost

Grand total: 471 euro

Max amperage of all components (circuit limitation):

All components used must sustain the power that goes through it. The voltage is usually not a problem, but you have to watch the amperage. Power production was limited to 60 watts (12V, 5A) — but that was before we thoroughly cleaned and oiled the bike drive train. After cleaning, we discovered the bike could produce almost double that power (12V, 8-9A). That required us to make some updates.

Components get more expensive as their maximum rated amperage increases. For the 12V, 220V, and 14.4V, we stuck to a limit of 5A. Although the bike generator can produce more power, we usually combine several circuits — each limited to 5A. We added an extra 12V circuit with a 15A buck converter and thicker wires to run a more powerful appliance. This circuit bypasses the dashboard entirely. We plan to move this to the unregulated electric circuit on the dashboard (and upgrade the wiring).

Cables: 11A, 18A for the extra circuit
USB buck converters: 2A
2x Buck converters: 5A
1x Buck converter: 15A
Boost converter: 5A
On-off switches: 20A
Diode: 10A
Fuse: 12A
Connectors: 20A

Tools you need

Wire cutter
Tiny screwdriver (to adjust voltage output on buck and boost converters)
Calculator, multimeter, tachometer
Soldering iron. We soldered the on/off switches and the two USB buck converters. However, this can be avoided. Switches can be bought prewired and there are alternative options for the USB converters.
Wood saw: to make the luggage rack
Metal saw: to cut custom threaded rods
Drill: to mount the luggage rack and the dashboard
Wrench socket set: very handy when working on a bike.

The First Prototype

The control panel can take different forms and use other tools and materials. We built a proof of concept with scrap wood and Meccano then strapped it to the handlebars with iron wire and some wooden blocks.

Initially, we screwed the generator on a large wooden board and put the bike on top. We made holes in the board for the four legs so that the bike was always right where it had to be. This set-up worked and was handy to try out different spindle sizes, but it takes much more floor space than our final configuration.

Kris De Decker, Marie Verdeil.

Special thanks to Adriana Parra, Eris Belil, Gabriel Verdeil, and Manvel Arzumanyan.

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Comments

We welcome technical feedback concerning further improvements. To make a comment, please send an e-mail to solar (at) lowtechmagazine (dot) com. Your e-mail address is not used for other purposes, and is deleted after the comment is published. If you don’t want your real name to be published, sign the e-mail with the name you want to appear. Your comment may also appear on paper.

paul

Interesting proof of concept. I’d like to see this with a belt or chain direct drive (Priority Bikes makes belt drive bikes, as did IKEA at one time, and direct drive bike trainers are growing in popularity) for greater efficiency as you mention at the beginning.

John A Saavedra

Cool! Thanks!

Tony

From that other linked article (“Bike generators are not sustainable”), I got the impression this was thought to be a project not worth doing. Did I read it wrong, or has technology changed sufficiently in the last decade to make it worth doing?

Hemon from Motueka, New Zealand

Nice article thanks for putting the time into researching this. I know it may be counter to your original aims (of making this setup cheap and easy to build), however using an older discarded e-bike would have a brushless electric motor of the right size and kv (speed to voltage) ratings already. If then you spend some time finding a motor controller that was able to do variable regenerative braking (I think the BionX controllers did something like this), this would more easily act as a variable load to the user, and would be very efficient as it would also be able to interface directly with a LiIon battery, which most e-bikes are based on these days.

A drawback to this is the expense and more technologically complex. However the other benefit is that you can use a standard bike and make a frame for it in-side to elevate the rear wheel, so you can still use the bike for transportation and exercise, and energy generation (into the battery) at the same time - increasing its utilisation. The drawback here is that it may not fit nicely in the lounge and may be dirtier, and less practical to have inside.

I think the main aim of a project like this is to manage generation and storage energy efficiencies because of the nature of the limited input power source, ie. the user. Putting more effort into making efficiency gains could dramatically improve the power and energy outputs, enabling the bike to do more with less input effort. The PbA (lead acid) battery that you are using will likely only be at best 60-80% efficient, and the friction drive is great at sucking up energy too. However, it is a great effort and I look forward to your future articles!

Stefan

what fun! a thought…rather than have it below could you hinge the generator/alternator so its weight presses it down onto the flywheel? possibly assisted by a door or gate closing spring?

kris de decker

Tony,

Technology certainly improved, but that earlier article also raised several issues that this bike generator has solved. It has a flywheel and it can power several types of devices directly, without needing a battery. I don’t think that the bike generator is conceptually flawed. It needs more innovation. It’s not a technology that has received much attention.

Quincy

Howdy,

In the diagram labeled “Complete Control Panel”, I believe labels 3 and 4 are switched.

Thank you very much for another excellent essay, and for exhibiting the true nature of what it means to be human: to share in the experience!

Warmly, Quincy

Mike S.

Greetings!

I’ve been pedaling my bike for thousands of miles with a generator attached. After much research, I’ve learned a few things that could improve your stationary setup.

Imagine yourself with a budget for power losses. Every loss, measured in Watts, is power that your legs must produce, but you do not get to consume as useful electricity.

By way of mechanical losses, you should consider putting an old cog on your generator shaft, and taking power from the chain instead of the tire. Your current setup will require you to replace the tire every few hundred kilowatt-hours of production! By taking power from the chain, the wear is minimal, and you can power greater loads without slippage. You could also remove the wheel (and its aerodynamic losses) entirely.

Since you’re using a brushed DC generator, the brushes “cost” power in commutation loss as well as friction loss. You would experience greater efficiency with an AC generator (or “alternator”). While automotive alternators are better suited to larger loads, they are often available for free, and would make an interesting experiment.

A “gotcha” of using an AC generator, however, is that an inductive load (like a motor) must be balanced with capacitors for good efficiency. Such a balancing circuit has been designed long ago, and goes under the name “forumslader” (En: Forum Charger) since the design is available for free on a German cycling forum.

I look forward to seeing your future work!

Mike S., USA

JohnD

Very nice! And LOL to the dot matrix printer : )

Rudi

I’m a fan of the magazine, discovered it from the solar powered website article, and have been reading it since.

I do software engineering as my job, but I do have a degree in electronics engineering, so I have some insights that might help.

Buck and boost converters:

You mention in the article to go for either buck or boost, but not a buck/boost as it does not keep the output voltage after power cycle. There’s nothing inherent in a buck converter that it would remember the output voltage, and nothing inherent in a buck/boost converter that it would forget it. Maybe most commercial devices operate that way for some reason, but you could definitely have a buck or boost converter that doesn’t remember the voltage after a power cycle, or a buck/boost converter that does.

I also saw something mentioned in the parts list, but not in the article. One of the buck converters are listed as synchronous, but the rest don’t specify. I would definitely suggest using only synchronous switching converters, it takes the efficiency from ~80% to ~90%. Synchronous converters use two switches (usually MOSFETs or something similar), while a basic converter uses a Schottky diode and a switch, and there’s a significant power loss through the Schottky diode. They will be more expensive though, due to the additional switch and complexity.

Charging lead acid batteries:

This is a bit more complicated than what was mentioned in the article. There are two ways to charge a lead acid, float charge, where you’re charging at ~13.5V over a long period of time, and a fast charge, which is a 3-stage charge of constant current, constant voltage, and float. I think the article kind of describes a fast charge, but it’s not doing the constant current part of it (stopping when the current drops low enough). But relying on the wind charge controller should solve the battery charging, but I’m not very familiar with them.

Schottky diode:

It’s correct that you’ll need one to avoid voltage feeding back to the motor, but I’m not 100% sure that its placement is best. By placing it after the generator, you’re sacrificing efficiency. You only really need it for charging the battery, so perhaps better to connect it to the battery so you only have the power loss when charging it, and not when powering the other devices. But in that case, I would expect the wind charge controller to handle that, but I’m not too familiar with them so I can’t say for sure.

Complete control panel wiring diagram:

It looks to me that all the switches in this diagram are wired in series. That seems a bit odd to me, you wouldn’t want to have to switch all the switches on just to get 5V output. It would probably be better to have these in parallel.

Thank you for researching, building, and writing up this guide. I find it very insightful. The use of an old exercise bicycle is very clever, and the insight of just how much power it uses to make a cup of tea is very well illustrated in having to cycle for an hour to heat the water. I never knew about the 12V appliances before, but they make a lot of sense. I used to run the router on a UPS, which is a lead acid battery with an inverter, to be able to have internet during power outages. I’ve recently switched to a li-ion based UPS, that instead has a 12V output to directly power the router, and it’s a lot smaller, quieter, and more efficient (and hence cooler), because it doesn’t need to go from 12V battery to 220V AC, back to 12V for the router. I’m not sure if you have similar products locally, but they do take 12-25V solar input, so they could be a smaller and cheaper alternative to a lead acid battery + wind charge controller: https://sinetechstore.co.za/shop/solar-kits/backup-power-kits/ratel-430s-micro-dc-ups/ .

Regards, Rudi

Mathew

Kris, I love seeing your articles about integrating low-power and low-tech systems into your everyday life!

The flywheel appears to be a standard-sized bicycle free wheel (with a tire filled with water? Sand?) that can be replaced. The friction system can therefore be easily swapped for a direct chain drive. There is a type of hub, called a flipflop in the US, that is aimed at fixed gear bicyclists and that features a freewheel on one side and a fixed gear on the other. Such a hub can be driven on the freewheel side and have power taken off of the fixed gear side. It sounds like this could net you nearly 15% improved efficiency.

Joseph Shupac

Very cool you built this!

I was inspired by past articles you wrote on this topic to try to come up with an idea for a low-tech bicycle that would generate and retain heat (if not from a pedal powered pump, then at least body heat), to allow people to exercise and socialize outside in cold (covid-era) weather.

I wrote a short article about it, maybe you’ll like it:

https://future-economics.com/2022/03/10/the-warmly-behatted-bike-in-a-box-for-winter-outdoors/

Jonathan

I’m glad to see a comprehensive look into building a bike generator alongside its power management system.

I have a few suggestions to make on the bike side of things. These have a range of feasibility and potential gains, so I will try to order them by decreasing utility.

1) I had the same thought as Mathew regarding a flip flop hub. It could be an elegant, out-of-the-box solution to connecting two chains to the flywheel, directly driving the DC generator. Depending on the hub, it might even be easy to change the included sprockets, if other gear ratios are desired. This would also not be subject to wearing down the tire and slipping off the generator, two issues Mike S. pointed out. These can be bought as a standalone component or as part of a pre-built wheel.

2) Cycling shoes and pedals. Stiff-soled cycling shoes transfer more power from a rider’s legs into the pedals of a bike over any other kind of footwear. Using them in conjunction with clipless pedals (which you counter-intuitively clip into) allows a rider to effortlessly maintain their foothold on a bike. Clipless pedals also help a rider maintain a better form while pedalling and crucially, allow for a rider to pedal on the upstroke, not just on the downstroke. Caged pedals are a simpler and cheaper way to accomplish the last two benefits and can work with any (or no) shoes, but have a less secure footing and don’t have the greater power transfer that cycling shoes offer.

I would like to emphasise how this reduces fatigue. Even if other benefits didn’t matter, I can personally attest to how freeing this change is. Without cages or clipless pedals, the rider needs to always apply a little bit of downward force on the upstroke in order to keep the foot on the pedal. In other words, the rider must always be pedalling against themselves in order to keep their feet in place.

3) I had something here about the seat height before reading the footnotes. Definitely a comfort & fatigue improvement once that part arrives.

4) This exercise bike is nearing 70 year old, it might be time for a tune-up! As demonstrated with the chain, cleaning load-bearing components could further reduce losses and improve power output of this system. A local bike shop could assess the condition of the bottom bracket, wheel hubs, sprockets (a dirty chain can grind down the teeth), and chain (even with it clean now).

5) Swapping to bladed spokes. This has contested value on a bike in the “real world” where cross-winds are unpredictable. However, in a controlled indoor environment, the aerodynamic gains in the wheel are consistent and guaranteed, albeit minimal at low RPM. A more effective approach would be to use an aerodynamic wheel cover to entirely encase the rim as is done in velodrome racing.

Unfortunately, as with electronic components, performance is correlated to cost. I hope some of these ideas may be helpful as this project progresses.

Jonathan

One exception, though. We had to remove the friction roller and screw that adjusts the resistance on the pedals of the exercise bicycle. We cut this part with a small metal saw. ↩
It’s important that your saddle is at the correct height to maximize power production. The saddle on our bike is too low. We need to find a longer seat post. ↩
The resistance on the pedals depends on the device that you are powering. If you are charging a smartphone, then you will only be able to produce a few watts – as much as the smartphone needs. Therefore, to find out the maximum power output of a bike generator you need an appliance or multimeter that is more powerful than yourself. We did the test with an electric air compressor. ↩
To calculate the RPM at the pedals cycle for 15 seconds and count the number of complete pedal turns (the left or right pedal takes a complete turn). Multiply this number by four. ↩
There are many other types of USB connectors but those require a steady 12V input. ↩

The Revenge of the Hot Water Bottle

2022-01-20T00:00:00+01:00

Hot water bottles could save a great deal of energy and money without sacrificing thermal comfort. They work both indoors and outdoors. Illustration: Marie Verdeil.

A hot water bottle is a sealable container filled with hot water, often enclosed in a textile cover, which is directly placed against a part of the body for thermal comfort. The hot water bottle is still a common household item in some places – such as the UK and Japan – but it is largely forgotten or disregarded in most of the industrialised world. If people know of it, they usually associate it with pain relief rather than thermal comfort, or they consider its use an outdated practice for the poor and the elderly.

Nevertheless, when I sent two dozen hot water bottles to friends and family as a Christmas present, the reactions were almost unanimously enthusiastic. People show themselves very much surprised that such a humble object can provide so much comfort. Because I don’t have the time nor the budget to send hot water bottles to everyone, I have written this article. It’s largely based on my personal experience – I have been using hot water bottles for many years and they are the only heat source in my apartment.

The history of the hot water bottle

Croat inventor Eduard Penkala patented the rubber hot water bottle – which he dubbed the “Termofor” – in 1903. However, it did not come out of nowhere. In fact, the history of the hot water bottle goes back thousands of years, albeit in different guises.

Rubber hot water bottle, made in Germany (1925-35). Source: Museum Rotterdam.

The first “hot water bottles” – quite literally – were other people and animals. Since time immemorial, people have warmed themselves by huddling together. For example, it was common for the whole family to sleep together in the same bed – and this included potential visitors. ¹ People also took advantage of the heat from animals – “hot water bottles” with a standard fur cover.

They snuggled up against cows and pigs, which were either sharing the living space or lived in the stables below it. In the eighteenth century, wealthy women kept specially bred “hand dogs” – toy poodles – around to keep their lap and hands warm. ² Personal heating devices also took the form of objects – stones, bricks, potatoes – that were heated in or near the fire, wrapped in cloth or paper, and kept in people’s laps, in pockets, or in the bed.

As early as the 1500s, people started to use all kinds of portable containers filled with hot coals from the fire. These were used as foot warmers, hand warmers, and bed warmers. ³ Most were made of metal, either brass or copper, and placed inside wooden or ceramic enclosures to prevent skin burns. Over time, hot coals were replaced by hot water, which is a cleaner and safer heat storage medium.

Initially, these first “real” hot water bottles were made from hard materials such as glass, metal, or stoneware. It was only with the invention of vulcanised rubber in the nineteenth century that more comfortable lightweight and flexible hot water bottles became an option. Spanish friends told me that hot water bottles used to be made from animal skins, but I could not verify this. It may well be true, because all over the world there’s a long tradition of using “water skins” for storing liquids.

An example of a hot water bottle in common use in households in the mid 20th century before the use of rubber ones (1940s, Melbourne, Australia). Source: Victorian Collections. https://victoriancollections.net.au/items/5a2622e921ea6a17dcba0799.

A foment can is filled with hot water and used very much like a hot-water bottle to apply warmth to the body. Fomentation actually means “to apply warm liquids to treat the skin.” This oval-shaped can is curved to fit the body. Maker: Kenworthy Son and Company. Place made: Southport, Sefton, Merseyside, England, United Kingdom. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/gf42542b.

Hexagonal hot-water bottle, Austria, 1791-1798. This hexagonal hot-water bottle is made of pewter and is engraved with a forest scene. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/b452vwjm.

This foot warmer (made in 1927) was used to give warmth and comfort to patients who were resting in the hospital wards. Made from tinned iron, the warmer would have been filled with hot water and secured with a cork. Place made: Glasgow, Scotland, United Kingdom. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/mfjujndv

French foot warmer, date unknown. Source: Musée Départemental Albert Demard

Hot water bottles today

The classical hot water bottle for sale today is either made from rubber or PVC plastic. The latter material has few advantages. It’s often a bit cheaper and can be made transparant, but unlike rubber it contains toxic chemicals (which make the plastic flexible). A third option – a bit harder to find – are plastic hot water bottles without chemical softeners, which are rigid instead of flexible.

The distinctly shaped Japanese hot water bottle – the “yutampo” – is usually of that type. Its use dates back to the fifteenth century when it was made from metal or stoneware. Of course any sealable container can function as a hot water bottle. I have successfully used metal drinking bottles and even plastic PET-bottles – more about those later.

In spite of its dull image, the hot water bottle has seen some interesting innovations lately.

The typical hot water bottle has a rectangular shape and holds up to two litres of water. However, in spite of its dull image, the hot water bottle has seen some interesting innovations lately. A first novelty are much smaller rectangular bottles, which hold between 0.2 and 0.8 litres of water. Judging by their covers, these are mostly aimed at children, but they can be just as useful for adults who can carry them in pockets or put them inside clothing.

There are now also larger hot water bottles available, which hold up to three litres of water or more. Finally, the most successful novelty has the form of a hot dog: it’s a hot water bottle 80 centimetres long. It can be tied around the waist but is just as practical as a companion on the couch or in the bed. It can easily be shared by two people and its shape makes it luxuriously comfortable. It holds up to two litres of water.

Rubber and PVC hot water bottles. Image by Marie Verdeil.

Rubber hot water bottles. Image by Marie Verdeil.

A Japanese hot water bottle, or yutampo, made of hard plastic. Source: All About Japan. https://allabout-japan.com/en/article/6244/

The Japanese yutampo is still available in metal. Source: Maruka.

How to use hot water bottles?

People who know hot water bottles usually think of them as bed companions. However, they can keep you warm wherever you are, throughout the day. This includes the sofa, of course, but you can also surround yourself with one or more hot water bottles when seated at a desk or a table.

I use one, two, or exceptionally three hot water bottles simultaneously, depending on the indoor temperature. They usually end up in my lap, behind my lower back, and/or under my feet. Although only some body parts are directly heated, the warmth from the bottle(s) is distributed throughout the body by skin blood flow.

Hot water bottles can be combined with a blanket, which further increases thermal comfort. If I put a blanket over the lower part of my body when seated at my desk, it traps the heat from the bottles and keeps them warm for longer.

Even better is a blanket with a hole in the middle to stick your head through – a basic poncho – or a blanket with sleeves. If it’s large enough, it creates a tent-like structure that puts your whole body in the warm microclimate created by the water bottles. Draping long clothes over a personal heat source was a common comfort strategy in earlier times.

A blanket traps the heat of hot water bottles. Illustration by Marie Verdeil.

You can go one more step further and put a large blanket over the desk or table and then put your legs underneath it. Such heating arrangements have been used in different parts of the world, usually with hot coals as the heat storage medium. Examples are the Japanese “kotatsu”, the Middle-Eastern “korsi”, and the Spanish “brasero de picon”.

The first two are rather low to the ground – people sit on the floor – while the latter fits the common seat height in the Western world. It’s easy to build such a heating arrangement – and a few hot water bottles are the ultimate heat source for it.

Hot water bottles outdoors & on the move

The arrangements described above only work for people who stay in one place. The need for an external heat source decreases when we move around and are physically active, because our body produces more heat.

Nevertheless, hot water bottles can also keep you warm when you are standing up doing things or when you are moving through a space or a building. They can be worn underneath clothing or even put in specially designed pockets or backpacks. A small backpack holding a hot water bottle – positioned between the shoulder blades – also works great while sitting on a chair.

Hot water bottles provide thermal comfort with all the windows open. Illustration by Marie Verdeil.

Hot water bottles work both indoors and outdoors – provided that the body is protected from wind and rain – or indoors with the all the windows open. Modern central heating systems provide thermal comfort mainly by heating the air in a space, an approach that obviously won’t work well outdoors or in a well-ventilated indoor space. In contrast, hot water bottles transfer heat directly to people through physical contact (a heat transfer method called “conduction”). They heat people, not spaces.

This makes hot water bottles a safe and sustainable alternative for terrace heaters in bars and restaurants. The investment is minimal: a collection of hot water bottles and a kettle – the water can be re-used over and over again. Alternatively, everyone could bring their own hot water bottle and fill it up on the terrace.

Hot water bottles are a safe and sustainable alternative for terrace heaters in bars and restaurants.

One could take this idea even further and envision a public infrastructure for refilling hot water bottles, not just on bar terraces but in multiple locations such as schools, offices, and public buildings. ⁴ People could gather around the hot water dispenser just like they gather around the water cooler.

Historically, hot water bottles – and their predecessors using hot coals – were also taken out of the house. Their use was common in coaches and trains, as well as in churches, which were unheated. Smaller hot water containers with carrying strings and fabric covers were put into fur muffs or pockets. Nowadays, you could also store hot water in a vacuum flask and then pour it into a hot water bottle hours later.

Stoneware Queens Muff Warmer. Source: Antiques Atlas. https://www.antiques-atlas.com.

Curved rectangular hot-water bottle, France, 1751-1810. Made of pewter, an alloy of tin and lead, this hot-water bottle is engraved with birds and plants and has a curved shape to fit close against the body. Source: Science Museum, London. (CC BY 4.0). https://wellcomecollection.org/works/g5ufhayn.

900 hot water bottles per day: energy savings

Unsurprisingly, there’s little – or actually no – academic research into the energy savings potential of hot water bottles. Instead, in recent years scientists have investigated more sophisticated personal heating devices such as electrically heated desks and seats, radiant heat bulbs, or battery-powered heat pillows. ⁵⁶⁷

These alternatives look needlessly complex in comparison to the hot water bottle. Water can be heated in many ways both high-tech and low-tech, and containers can be made from locally available materials.

Nevertheless, these studies show that personal heating sources with similar effects as hot water bottles could save a great deal of energy while maintaining and often even improving thermal comfort. For example, one study revealed that lowering the air temperature in an office from 20.5°C to 18.8°C (69°F to 66°F) and giving employees a heated chair to compensate for the discomfort leads to 35% less energy use and consistently higher scores for thermal comfort.

There are few interventions in the building envelope that can achieve such large energy savings for such a small investment, and yet the decrease in air temperature was far from radical in this experiment. If personal heating devices would be combined with a change in clothing insulation and/or blankets the energy savings could become much larger still.

Another way to investigate the energy savings potential of the hot water bottle is to calculate how much energy it takes to prepare one and compare that to the energy use of a central heating system. Because rubber or PVC bottles can only be filled up to two-thirds for safe and comfortable use, I assume a somewhat larger model – 3 L – which can hold two litres of water in practice.

This makes the calculation also valid for containers that can be filled completely, such as the Japanese yutampo. It takes 4,200 joule to raise the temperature of 1 litre of water by 1°C, meaning that heating two litres of water from 10°C to 60°C (50°F to 140°F) requires 420 kilojoule or 116.7 watt-hours.

Advertisement for Westbrook & Thompson Ltd’s ‘Cosimax’ hot water bottles, made with Dunlop rubber. 1938. Science Museum / Science & Society Picture Library. Source: https://www.ssplprints.com/image/95677/sleep-well-hot-water-bottle-august-1938.

In comparison, the average household energy use for gas heating in Belgium – which has a moderate climate – is 20,000 kWh per year. Assuming that the average Belgian heating system is used for six months per year, daily energy use corresponds to 109.6 kWh per day. This energy could heat roughly 900 water bottles per day – enough to keep the whole neighbourhood comfortable.

Imagine that four household members each use two hot water bottles simultaneously and reheat them every two hours throughout their waking hours (16 hours). Total energy use is then below 4 kilowatt-hours, almost 30 times less than the heating energy consumed by the average Belgian household.

This is not to suggest that hot water bottles need to replace a central heating system. The rather short and mild winters here in Barcelona allow me to use hot water bottles as the only heating system because it rarely gets colder than 12°C (54°F) in my unheated apartment.

In less hospitable climates, hot water bottles can be combined with a central heating system. The hot water bottles create islands of thermal comfort for low metabolism activities while the rest of the indoor space is comfortable to move through or be physically active in.

Safety

Hot water is a safer heat storage medium than hot coals, but it is not without its risks and hot water bottles need to be used carefully. They carry the instruction not to use boiling water, which is very sound advice, but hot water doesn’t need to boil to be dangerous. Water above a temperature of 60°C (140°F) can scald you and lead to very serious injuries.

Therefore, it’s recommended to use only hot tap water, or any other hot water source below 60°C. This temperature is sufficiently high to make you comfortable and the only advantage of using hotter water is that you need to reheat it less often.

Too hot water can hurt you in several ways. First, there’s always a chance you spill water on your hands while filling the bottle. Second, a rubber or plastic hot water bottle can start leaking, either through the cap or through the seams.

Third, and this is the worst-case scenario, a hot water bottle can burst and release two liters of hot water on your body. Such accidents are rare, because nowadays hot water bottles are made according to quality standards. However, they do occur, usually because the bottle has worn out.

The Jayne Mansfield Hot Water Bottle hit the market in 1957. The Mansfield figure—in a pin-up pose with hands behind her neck and wearing a painted-on black bikini—is made of “blushing” pink–colored plastic with a screw-on “hat” cap and measures close to two feet head-to-foot. Source: https://vintagenewsdaily.com/at-the-height-of-her-career-in-the-1950s-jayne-mansfield-even-modeled-for-this-awesome-hot-water-bottle/.

To safely use rubber or PVC hot water bottles at higher water temperatures, it’s important to replace them after a few years of use, and to store them properly. If you really want to use higher water temperatures, metal hot water bottles – inside a cover to prevent skin burns – are the safest option.

However, if you keep the temperature below 60°C (140°F), the worst-case scenario is just getting wet. If you use PET-bottles, you should surely stick to this maximum temperature, because at higher temperatures they could melt. Furthermore, a PET-bottle should not be used for drinking after it has been used for heating, because the higher temperatures may release chemicals in the water.

Water use & infrastructure

Hot water bottles also require a source of water. It’s possible to reheat the same water over and over again, thus limiting the water use to a few litres during the lifetime of the bottle. However, that’s not always the most practical solution. In modern households, hot water can be sourced from an electric kettle, a pot on the cooking stove, or the hot water tap.

Although hot tap water is the safest source of water for a hot water bottle, once the water has cooled down there’s no way to get it back into the pipes for reheating. Furthermore, it takes time before the water comes up to temperature, meaning that more than two litres of water will be consumed.

Even a slightly lower shower frequency easily provides you with the water and energy for continuous hot water bottle use.

Using an electric kettle – or a pot on the cookstove – makes it easy to reuse the same water over and over again, but it faces some problems too. First, if your electric kettle does not come with a programmable water temperature, you need to make sure the water does not get too hot. I solve this by dipping the probe of a digital thermometer in the kettle while warming the water.

Second, if you reheat the water from rubber bottles, the kettle (or pot) can no longer be used to heat water for human consumption because it will taste bad. So, either you use a separate kettle for use with hot water bottles, or you warm the water in the only household kettle and discard it after use.

Even if the water is not reused for other purposes (such as watering the plants) the waste is quite limited. The average shower consumes enough water to fill 37 hot water bottles. Likewise, the energy use of the average shower corresponds to the energy use for heating 17 hot water bottles (which use water with a higher temperature than a shower). Consequently, even a slightly lower shower frequency easily provides you with the water and energy for continuous hot water bottle use.

Stoneware hot water bottle (1901-1910). Source: Auckland War Memorial Museum

The Japanese offered guests a small roundish ceramic pot with fuel inside, called a “te-aburi”. Copper or bronze box-shaped hand warmers a few inches across, often with perforations and carrying handles, were called “shou lu” in China. Image in the public domain. Read more: https://homethingspast.com/2011/11/26/hand-warmers-muff-warmer/.

Cold water bottles

Hot water bottles can be used for cooling as well. In this case, they are filled with cold water or put in the freezer. Cooling people is much more energy efficient than cooling spaces. I don’t have air conditioning and rely entirely on fans and cold water bottles in summer, when temperatures are usually above 30°C. I use “cold water bottles” in a similar fashion to hot water bottles – they go into the bed, under my feet, or behind my back.

For cooling I use plastic PET-bottles and metal drinking containers, not rubber water bottles as they get hard and brittle. Keep in mind not to fill the bottle completely – water expands when it’s frozen – and to put the bottle inside a protective cover to prevent iceburn. Also keep in mind that they will get a bit wet on the outside as the ice melts – although this effect only enhances the cooling. Like hot water bottles, cold water bottles work outdoors as well as indoors.

Kris De Decker

Proofread by Alice Essam

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Will K

How long does a typical rubber or pvc stay long for, if filled with 60c water?

Michael Lipkin

awesome. if you boil a 2/3 full kettle and top up with cold water before filling the bottle you get about the right temp. No need for thermometer

Tim

I live in a very (!) old family house house in north-east France, near the belgian border, and even though the house has been partially equiped with a central heating system, heating the place as you would heat a modern house simply isn’t an option (unless you don’t mind burning A LOT of heating fuel). As a consequence of that, HWB have always been the house standard when it comes to thermal confort during night time when a thick sweater and a scarf usually fixes it during the day. I did find a new interesting use for HWB, though : I’ve recentlly started homebrewing and my fermentation chamber (aka: the closet) lacked a couple of °C during the night, when the central heating system is turned off. I was afraid that this might screwup my fermentation process so I quiet naturally thought of wrapping the 5L fermenter into a couple of blanckets with a HWB stuck next to it and wrapped itself in cloth to allow a slow night long heat transfer and avoid overheating. Did the job perfectly!”

Thanks. Great article.

Kris De Decker

@ Will K

That depends on the environment, but in my case they stay warm for roughly two hours. Under a blanket they stay warm for longer.

Loads of comments on hackernews: https://news.ycombinator.com/item?id=30023681

Tjitske

Hi Kris, thanks for the insightful article. What’s your opinion on heat pillows? Like cherry stone or rice pillows? If my calculations are correct, heating one in the microwave is even more efficient than heating the water for a water bottle. Heating in the oven is probably pretty inefficient although I can imagine tossing the pillow in after cooking and not heating for the pillow specifically would help. Additionally, heat pillows don’t wear as much as pvc/rubber bottles and there’s no waste associated with their use. They can be produced from scrap fabric and food waste (cherry stones) or other organic materials, limiting waste potential in the production chain. I’m curious to hear your thoughts.

Hugh R

In New Zealand, at least until the 1950s, some hotels would put hot water bottles in guests’ beds while they dined. A well understood local custom when central heating was not common. My parents, staying at one hotel, were startled as they returned to their room to hear very loud noises, beating, and shouts coming from a nearby room. The reason? An American guest, returning from dinner, and seeing a suspicious lump in the bed, believed it was a snake and was attacking it with a golf club. The bottle burst and he now of course had an amused audience and a soaking wet bed.

A Kalkman

Very funny piece of info. I am 71 years old and use the hwb already for 50 years. I bound one on my back once when I was working as an upholsterer and had a backache. It brought me through the day. I use a very old rubber waterbottle allredy more than 20 years old. I will google and try and find the Japanese one. Thanks again very much for this interesting piece of information. From Holland with love, Ans Kalkman

Wim

With the Boy-Scouts we used to heat bricks in the camp-fire and then carefully roll them in newspapers and blankets; kept us warm even during camping at -5C or worse.

My mother had a few copper hot water bottles made from old WWII canon-bullets. I still use 1 or 2 plastic hot water bottles in Portugal during the cold season, typically 3 months… Enough to avoid heating the whole house. Together with thick blankets it keeps the costs of winter to a minimum.

Etienne

One alternative to the hot water bottle which is often used in Switzerland is the “Cherry Pits Pillows”/”Cherry Pits Bags”. Cherry pits, which you can easily gather with a cherry pitter when making preserves, (and I assume previously mainly from distillery waste as each farm was distilling all kinds of fruits) are cleaned and dried. Then, you sew them in a bag, and put them into an oven. There was a space for backing and heating up stuff in each farm kitchen when people cooked with wood, but the modern electric oven or even microwave work as well. Then you use them as the hot water bottles you mentioned. There are commercially available ones, you can find them with the word “Kirschensteinkissen” or “Chriesisteisäckli”.

Will Lisak

I think you neglect here the real original hot water bottle, - the hot stone. The hot stone has been used doubtles for the same purpose since the domestication of fire, but has survived in cultural memory because it does not leave behind a discernible artifact, (a stone looks like a stone) except in the case of the ubiquitous shaped marble and soapstone warmers. Here in Vermont they were placed on or around the stove during the day and taken to bed at night and others were used to put under your feet driving a sleigh or cart or even to stand on if you had a cold outdoor job to do in one place. I use them (the soapstone pieces) and they are truly remarkable in their heat retention.

I’ve seen old timers around here with soapstone blocks stacked up all over and around their woodstoves, increasing the heat mass and slowing and regulating the heat dispursursion. as an aside, I was asking last year for advice on an efficient wood stove, thinking I might get one of the soapstone wood stoves that are so lauded in the us, and a russian friend said to just stack stones all around my current old iron stove and it would yield the same benefits. I’m not sure of soapstone vs water but the manufacturing and opportunity costs are surely much lower and it’s less messy and prone to catastrophic failure.

Matt

I was using a 2l plastic fizzy drink bottle filled from the hot water tap and stuffed in my jacket for the frosty drive to work, my car’s heater would take ages to warm up and this bottle of hot water made all the difference,

on arrival at work the guy who usually unlocked the gate would often be parked outside because the padlock was frozen, my bottle of water poured over the padlock thawed it in moments,

I also never bought any windscreen de-icer, I’d just have a second bottle of hot tap water and pour it in a line across the top of the windscreen and rear window,

the tap water from a modern domestic hot water system is regulated to a temperature not high enough to cause scalding and in my experience not hot enough to cause frozen windscreens to shatter, the plastic fizzy pop bottle is of course free!

Rolf Bauche

Hallo,

mal wieder ein sehr interessanter Artikel!

Zwei kleine Anmerkungen:

In Frankreich werden bis heute “Wärme-Keramiken” aus glasierter Keramik in Ziegelsteinform hergestellt. Eine interessante Alternative, die kein warmes Wasser benötigt und im Kachelofen aufgeheizt werden können.

Siehe: https://koerper-waermespender.de/pages/waermespender.php

Das Bild “Foot warmers on the floor of a railway carriage (1929). Source: The History Trust of South Australia. ” zeigt meiner Meinung nach Spucknäpfe und keine Fußheizungen. Typisch für Spucknäpfe sind die trichterförmigen Oberteile.

Mit freundlichen Grüßen

Rolf Bauche

Tjeerd

Dear Kris,

I’ve been experimenting with similar heat-the-person-methods. I use 17 Watt grow-matts for young plants. They are flat, very comfortable and cheap. I typically use one under my feet (plus blanket) and one behind my back in an office that is kept at 13 degrees.

So I use 34 Watts. This compares with you calculation: every two hour re-heating water from 30 to 60 C requires about 60 Wh and I use 34*2 = 68 Wh of electrical power. However if one heats cold water to 60 C one would use twice as much energy.

The savings in terms energy are indeed immense, and comfort is indeed higher than heating the whole room when I just sit behind the desk.

The great advantage of warm water is that they are more portable, so I will start using these as well.

Best,

Tjeerd

Sue Rine

I was fascinated to read your article about the history and use of hot water bottles. For 4 years our family lived in a cabin with no power. In Winter hot water bottles were a feature of daily life. even with the fire going there were times when the temperature was below 10deg C all day and lower at night. Each family member had two hot water bottles which we mainly used in bed, but there were also many times when we had one tucked up our jumpers during the day. We’ve graduated to a passive solar house and the hot water bottles are now a memory. 😀

Romain Lange

Bonjour,

Do we know if hunter-gatherer societies, or the Inuits, use the hot bottle technique ?

I see in this documentary about paleolithic techniques, with bladders used as water bottles. Could they be used as hot water for cold nights ? https://youtu.be/Wnv5WVB4j34?t=2203

kris de decker

@ Will Lisak @ Rolf Bauche Indeed it seems that I missed part of the story: the hot stone. Great to see this, thanks!

@ Tjitske Heat pillows are an alternative but hot water bottles can hold more heat.

@ Romain Lange Could be but maybe stones were more practical.

jillene

I love this! I use my 40 year old daughters little pink baby hot water bottle since… 37 years. It’s Swiss quality and still totally intact. I always struggle with cold feet and this little treasure goes to bed with me at my feet 9 months a year. I fill it all the way up with quite hot water and it works fine. I also take it on airplanes to keep my feet warm and the hostesses fill it up for me. And yes I can sleep in a much cooler room thanks to this!

jillene

PS THANXXX for posting this

Carlos E.R.

There are electrically heated “bricks”. They are connected for 5 minutes to the mains (a thermostat automatically impedes overheating), then unplugged and put inside the bed. I assume they are a ceramic body with a resistance inside, put in a metal casing and a wool cover.

Heat last for hours. I much prefer these to the water bottle, which eventually will burst and wet the bed, ruining the night and more.

OcracokeIsland

Try a large cherry pit pillow, cherry pit foot warmers

We use a Water Heated Mattress Pad, basically a small water heater unit, under mattress pad has medical grade tubing running up and down in a pattern. We have an additional fluffy pad on top of the hot water one,to reduce any lumpy feel,works great.

Search for “Navien Mate EQM 350, Queen – EMF-Free Water Heated Mattress Pad – Dual Tempera”, the premium $$$,from there you can find cheaper brands,what we have for $135 and up, prices fluctuates,Google “MERRY HOME Water Heated Mattress Pad Topper”.

Also something like a Whitby Hand warmer,uses catalytic head burner, no real flame, but it gets very hot, you have to put it in a small pouch, you don’t want to sleep with it because of the heat output and it uses oxygen. Will heat 8 hours.

As with anything use common sense, and at your own risk.

Ocracoke

“I’d just have a second bottle of hot tap water and pour it in a line across the top of the windscreen and rear window”, probably never happened to you, but excellent way to crack glass,in my neck of the woods,I use cold water.

Shane Wilson

Kris,

I’m surprised you didn’t mention the largest hot water bottle of all — a water bed! I slept on these for years in cold climates and crawling into bed was ALWAYS a pleasure. But, they seem to have fallen out of favor.

Steve Bohne

Yeah…great…until the stupid cap comes off and fills your bed with tepid water. No thanks.

Teri

Fill a tube sock with rice, tie a knot on top, microwave it for two minutes, stay warm all night. Reuse for years.

vyasamoorthy

Thanks for wonderful story on hot water bottles. I once wrote about Human bed warming Services offered in a Hotel. See link: https://vyasa-kaaranam-ketkadey.blogspot.com/2010/01/human-bed-warming-services-offered-by.html This was in 2010 - don’t know if this continues now!

Wendy E Powell

I was raised using hot water bottles to stay warm. Sixty years later and I still heat my bed and feet with a hot water bottle. I put hot tap water in it for 15 minutes before half emptying and topping up with boiled water. My bottle is tepid temperature when I wake up the next morning (7 hours of sleep). I’ve gifted water bottles to family and friends and they all love them.

candace

GREAT to see an article about hot/cold water bottles!!! Brilliant!

I use them myself any time I get a bit too chilly but don’t want to make a fire… to save time mostly and gain comfort. My house is wood heated. Making and tending the fire (not to mention gathering the wood and all that entails) is a very time consuming process!

Fortunately the house has solar power. So often I simply heat water and fill a hot water bottle rather than make a fire…IF my hands are not too cold to function. That is the line for me. I love to do art and my hands must be able to move.If the hot water bottle does the trick that is all I need.

The challenge with the hot water bottle for me is being able to walk around with my hands free to function rather than holding onto the bottle. With the bottle tucked between layers of my warm clothes, and moving around, how to keep the bottle from falling out is the question. I have tried wearing a belt over the clothes just below the bottle level. That sort of works. I have tried a soft rope that went through a hole in the lip of the hot water bottle tied around my neck. This sort of works too. But neither is very comfortable. Suggestions?

candace

Oh, I forgot to add to my first comment, my grandfather, who grew up in South Dakota in a SOD HOUSE (!)…must have been in the late 1800s…would go to school on a horse drawn sleigh in the wither. To stay warm they had a big round rock that had been heated in the fire then wrapped in a buffalo skin. The children huddled around it on the way to school.

On my wood fire stove I keep a pot to heat water for dishes or what ever. If that fire is going, rather than bother with the water bottle, I use 3 fire bricks that are always on that stove. I can take a brick for my feet or lap and rotate them to keep the warmth up. I put one at the base of my bed before going to sleep and take one with me for my arms. My sleeping room is never heated, so the bricks or water bottle do save energy and make the bed quite comfortable.

Pawan Kumar Gupta

Despite electricity operated tell bottles, the hot water bottle (water in a rubber bottle) is still very common in India. They offer much better thermal comfort to body in winters. Often used to sooth the painful joints or troubling veins in the legs.

Mark O’Connor

Years ago when I looked after an old farmhouse in Italy, the inside temperature at night in winter was often below freezing. I found that one hot-water bottle would be cold and useless before morning. But two bottles, placed back to back and wrapped in a double-bed sheet, were as good as another human in the bed—still warm in the morning. A tip worth knowing!

Tomislav Plechinger

Another great article!

Just a small typo that I noticed - not “Croation” but “Croat”.

Thank you for spreading the word about the little-known but very prolific inventor, the great Eduard Penkala.

Jenny Matthews

Kris you should head up a climate change conference because we’re going to need all the help we can if the targets are going to be met - which they’re not at the moment, and time is running out. We were invited to a garden supper in Mallorca in January - zero temperature - the table had a massive blanket over it, big enough for 6 people to tuck around their hips, and with the 1 bar electric heater under the table, we were very toasty nearly up to our waists - thermal tops etc. kept our top halves warm, and we enjoyed a great supper very comfortably. I guess hot stones would have done the job equally well.

Erik

I guess that today a microwave oven will be convenient for reheating the bottle.

Sweden does not have a strong tradition of hot water bottles. In upper class homes coal heaters were probably used in the 18-hundreds. Warm water bottles would often be insufficient here and houses should be properly insulated and heated. There are stories of people in the country side sometimes keeping it real warm (25-30 degrees perhaps more) inside in the winter time in areas where firewood was one of the few commodities available in ample supply.

In the last couple of decades pillows filled with wheat that should be heated in the microwave oven have been marketed as warmers. Perhaps more against aching body parts than for sleeping. The heat capacity would clearly be lower than for hot water.

Erik

Tom

Many African safari camps place hot water bottles wrapped in towels in your bed at night (nights can be cold!). On her first safari my partner crawled into bed and pushed her feet up against the hot water bottle. She shrieked and jumped up, thinking some African critter had crawled into her bed. We now use hot water bottles in bed in the winter so we can keep the room cool but our feet warm.

Dale

All through my childhood, we used a red rubber HWB. It never burst, over a period of some 20 years, and there was never any talk of its needing to be replaced because of fear that it might burst. The first HWB I bought after returning to the US following a decades-long stay abroad burst and flooded the sofa on which I was using it. What a shock!

Why are there no long-lasting rubber HWBs on the market today? Experience tells me they should be possible. I suspect that companies find it in their interest to force people—on pain of burns or flooded beds—to buy new ones every 2 years or so, and how I resent that!

Erin

My father grew up in Montana in the 40’s and his parents were ranch hands (employees on a large ranch). He had a long walk to his one-room schoolhouse down the snowy roads and he said in winter his mother would give him two hot baked potatoes for his pockets to keep his hands warm, and then that would be his lunch.

Ulrich H

In northern Germany hot water bottles are a common household item. I’d expect roughly 10-20 of the population, mainly women, to use them regularly, during their period, for stomach-aches, or for being cold. Also, sacks filled with cherry pits, heated in the microwave with a glass of water, are used for a tight neck or back, or also to add some heat during cold nights if the blanket is too cold.

Interesting, that apparently in other places they are not that common at all.

zifro

There is one other thing, you can do with hot water:

Make Tea.

If you have an infrastucture of Samowars, the uttility would greatly increase, if you could use that hot water to make tea.

Public Samowars filled with potable water, have the advantage that you do not need to bother with recycling the water if the people can drink it.

Of course the problem of providing the people with clean drinking containers would come up.

But Hydration is one of the major concerns for the homeless.

So even a public fountain with cold, potable water would improve their situation.

Vanda

I live in Melbourne, Australia. I have always been very fond of hot water bottles, and far prefer them to electric blankets which I find quite uncomfortable. Another use for them that I worked out a few years ago is to fill them with water and place them in the freezer in summer. They are great to put in your bed on a really hot night. They cool the sheets down beautifully.

I lived for some years right in the city, and there were many homeless people. Melbourne’s winter temperature can be quite low, and many nights are under 5C. The wind chill factor makes the temperature lower. In the really cold weeks of winter, I would take out filled hot water bottles at night for people sleeping on the street. I had an agreement with some of the local 24 hour convenience stores that they would allow people to refill them. As you could imagine, the bottles were very much appreciated. I sometimes tucked them in with people who were already asleep, making certain that they weren’t touching bare skin of course. I hope it helped them feel as if someone cared.

I have sustained burns from hot water bottles when sleeping with them when drunk! It’s amazing how much damage they can do. I tend not to do that nowadays, and I also prefer bottles with covers as they are more comfortable to use and stay hotter longer. I have a couple which have amazing covers and actually stay warm all night and well into the next day, which is great if you are in bed with a cold or something.

When I first set up my facebook page and I was asked during set up what I liked, I didn’t know that it meant I could like pages. It was winter, so I just said hot water bottles. Nothing happened, presumably because there were no hot water bottle appreciation pages. Maybe there are now!

Maggie

You are wonderful. For decades, nearly impossible to find rubber hot water bottles unless one wanted to douche. I think they are still nearly impossible to find. I treat mine better than I do myself. All praise to you. Maggie

John Cliff

While serving in the army during a German winter a great way of keeping warm while traveling on a 432 APC was to sit above the engine cooling louvers. It was wisest to rope yourself on, just in case of falling asleap. The hot airblowing out of the louvers would blow the snow away no matter how heavy it was comming down.

John

Good article. However, a word of caution. Just before Christmas my partner burned her left ankle, badly, when her HWB burst. She is still having the burns treated.

The HWB had worn through on the shoulder and finally gave out, not on the seam or neck. We only realised how worn it was when we removed the fabric cover- it was her favourite Teddy Bear one- nothing was showing on the cover. Please, occasionally, take the cover off and check the actual bottle for wear.

Chris

I own (and frequently use) a metal Japanese hot water bottles as well as a pair of rubber bottles. While both styles do an excellent job of keeping me and my bed warm, I prefer the Japanese one over the rubber version.

Despite being rigid, meaning it can feel uncomfortable depending on where you put it, the metal version retains heat noticeably longer than the rubber version. I sometimes heat water on the stove to about 150 F, put it into the metal bottle, stick it in my bed anywhere from 30 to 60 minutes before bedtime. In the morning, the water is still quite warm if not hot to the touch. (I haven’t checked it with a thermometer, but an educated guess would be around 110 F, no more than 120 F.)

Last comment: As someone else mentioned, cloth covers are mandatory, especially| with metal hot water bottles.

Aynsley Brown

For at least the past 30 years, I have been heating our HWBs in our microwave. Heating on full power for 5 minutes works perfectly. Just make sure that the bottle can freely rotate in the oven and heat up evenly. HWBs that have brass screw threads in the neck funnel should be avoided. Rubber bottles are to be preferred, they seem totally unaffected by the microwaves. Some plastic-material bottles can develop hot spots in the wall of the bottle and locally melt. This is probably because some plastics seem not to be as ‘transparent’ to microwaves and can get heated in local spots, to the deterioration of the bottle. The great advantage of heating the bottle in this way is that the same water can be used over and over again.

Sandra

I love my HWB - great article, thank you and warm wishes to all users

Deborah Lindley

I started making hot water bottle carriers last year to keep people warm working from home and meeting friends outside in winter lockdown www.deborahlindley.com I barely take mine off.

Clare

A friend mentioned a great use for hot water bottles. She used to have to spend a lot of time waiting in her car while her children played football, etc. Instead of freezing or leaving the car running, a hot water bottle kept her toasty and she read away happily while she waited!

Mark

Thanks for this excellent article. I grew up reading Walter Hottle Bottle stories https://www.lookandlearn.com/characters/character.php?c=walterhottlebottle and still use one every night x

Benoît Gingras

I’m a newcomer to this site, it’s absolutely great. Special mention to the illustrator and her illustrations for this article, my girlfriend and like them a lot! They are funny and the lines are beautifully drawn.

Thanks for suggesting the use of hot water bottles. My flatmate told me about this very article. We live in east of province of Quebec (Canada) in countryside and I am eager of giving a try to this idea. I would like to try using hot water bottles under the low table in the living room covered by a cloth or blanket. The idea of cold bottles in the summer might be a good idea for me too. I am really weak under high temperature.

Benoît

www.bazaroccidental.org

Benoît Gingras

PS. I forgot to mention that this article reminded me of friends hearing a man in Yukon saying that he boils eggs and then keep them hot (in their shells of course!) in his pockets while going outside. It provides some heat to your hands and minimal heat to your body and you have a healthy and useful snack on your way!

Benoît

Robert

Interesting article.

I think you should have a look at Camelbaks. They’re basically hot water bottles worn as a backpack, and they have a tube to drink from them. This solves the issue of reusing the water.

They’re quite popular for people skiing or doing other kinds of outdoor sports, keeping you warm and hydrated at the same time.

Tuck

I have been using small NATO ammo cans (metal boxes with sealed lids) 1/3 to 1/2 filled with tealight candle wax as a hot water bottle substitute. I place them on low heat on an electric stove until all the wax is liquified, which is when heat can be felt from the top of the boxes. The heat output is better than a HWB, as it is more evenly distributed through the night. Caution must be used however, as overheated, they will probably cause a fiery explosion.

John Hackett

Dear Kris,

I loved your recent article on hot water bottles. It inspired me to buy a ceramic yutanpo and it is incredible. I’ve been looking at your picture from the article, of the desk surrounded by blankets to trap the heat, and wondered if you’d seen the kotatsu people have in Japan? See this article:

https://www.japan.travel/en/uk/inspiration/kotatsu/

I’m considering one as a maybe slightly more elegant solution than nailing some blankets to my desk :)

Thought you might be interested, apologies if I’m preaching to the converted!

Thanks for reading, John Hackett

PS, the site is amazing, never stop!

Kris De Decker

John,

Thanks. The kotatsu is mentioned in the article. But the link you sent had some surprises for me. Most notably: a railway carriage full of kotatsu’s !

Dorothy

bloody marvellous ! Use mine often for an old ladies comfort

GDR!

In an on-grid scenario, a typical western home has a microwave oven which heats quickly and efficiently. For such scenarios, there are termofors made of fabric, filled with cherry seeds.

I have one of these (bought for ~€5) and it keeps warm for about 45-60 minutes after heating it in a microwave for 90 seconds. According to advertising, it works great for cooling too. Haven’t tried.

And, of course, it would be easy to make one yourself.

David Veale

We’ve been using antique footwarmers made from soapstone, and found the thermal inertia to be absolutely amazing — roughly 2.5cm thick, and 25cm square, they’re warmed atop our wood stove and then wrapped in a towel and brought to a cooler room. The significant heat stored lasts for over 4 hours!

Ben Hunkins

Thank you for your article. Our family lives in an off grid cabin in northern New York State. We fill two liter soda bottles (very common in the US) with hot water from the wood stove and then cover them with repurposed sweater sleeves. If we need the heat to be more form fitting then we have small pillow shaped bags (8 inches by 6 inches) filled with rice that we heat directly on the wood stove top. This is achieved by flipping the bag every 5 seconds or so until it’s warm enough for the person using it. We also have a few cats :)

This custom was accompanied by strict rules. For example, male visitors ended up sleeping on one side of the bed, while the family’s daughters were on the other side. Source: Ekirch, A. Roger. At day’s close: night in times past. WW Norton & Company, 2006. ↩
https://www.encompassingdesigns.com/blog/hot-water-bottlesa-thing-of-the-past ↩
The “warming pan” or “bed warmer” was a metal container filled with hot coals and fitted with a long handle. It was slid between the bedsheets and then moved across the bed to warm all corners before someone got into it. Yet another solution to warm the bed was the so-called “bed wagon”: a wooden frame or sledge designed to hold a pot of hot coals, which was slid below the bed and covered with a metal sheet. Unlike a warming pan, the bed wagon provided warmth throughout the night. See: http://www.oldandinteresting.com/warming-the-bed.aspx ↩
Some cities had public hot water supply systems. For example, in the first half of the twentieth century, the Dutch city of Rotterdam counted hundreds of “water distilleries” where people came to fill buckets with hot water for domestic use. China has a long and continuing tradition of providing its citizens with hot water everywhere they go – mainly for drinking. By the 1830s, hot water stores – known as “laohuzao” or “tiger stoves” – popped up in major cities all over the Yangtze river delta. Today, almost every government body, business and school administrative office in China has hot water dispensers – even high speed trains have them. Read more: https://www.sixthtone.com/news/1000919/the-history-behind-chinas-obsession-with-hot-water. ↩
Verhaart, Jacob, Michal Veselý, and Wim Zeiler. “Personal heating: effectiveness and energy use.” Building Research & Information 43.3 (2015): 346-354. https://www.tandfonline.com/doi/abs/10.1080/09613218.2015.1001606 ↩
Deng, Qihong, et al. “Human thermal sensation and comfort in a non-uniform environment with personalized heating.” Science of the total environment 578 (2017): 242-248. ↩
Mishra, A. K., M. G. L. C. Loomans, and Jan LM Hensen. “Thermal comfort of heterogeneous and dynamic indoor conditions—An overview.” Building and Environment 109 (2016): 82-100. https://www.sciencedirect.com/science/article/pii/S0360132316303560 ↩

The Printed Website: Volume III & The Comments

2021-12-02T00:00:00+01:00

Image: The Printed Website.

Low-tech Magazine Volume III

The newest Low-tech Magazine book collects 18 articles published between 2018 and 2021. At 368 pages it’s a thin book compared to earlier volumes. When we started the book series, the challenge was to unlock an archive of almost 12 years. It made sense to pack this content into as few volumes as possible.

However, looking ahead, we will publish more often, once every one to three years, depending on the number of articles written. From now on, the articles will be arranged chronologically, from oldest to newest, and no longer the other way around. This volume contains 184 images in black and white.

Low-tech Magazine: The Comments

We also launched a book which collects almost 3,000 comments on the roughly 100 articles which are published in the three other books. This volume has 688 pages and no images. We included all feedback up to November 7, 2021. Read more about the comments book here.

Over the years, readers have often stated that the comments on the website are (at least) as interesting as the articles themselves. We agree. Low-tech Magazine would not have been even half what it is now without the comments. You can even take this literally, because this is one of the thickest books we have published so far, despite the extra small font we use.

New Edition

Finally, we have published a second edition of the first book we published in 2019. This new edition has almost twice as many images and follows the same design as the other volumes. In contrast to the first edition, the images are not “dithered” and of higher quality. We use a smaller font to pack more content on fewer pages. This second edition also fixes some errors in the articles and the references.

Image: Low-tech Magazine: The Comments (2008-2021).

Image: Low-tech Magazine Volume III (2018-2021).

Contents Volume III

How Circular is the Circular Economy?
Keeping Some of the Lights On: Redefining Energy Security
Heat your House with a Mechanical Windmill
Reinventing the Small Wind Turbine
How to Make Wind Power Sustainable Again
Mist Showers: Sustainable Decadence?
Too Much Combustion, Too Little Fire
How Sustainable is a Solar Powered Website?
Fruit Trenches: Cultivating Subtropical Plants in Freezing Temperatures
Thermoelectric Stoves: Ditch the Solar Panels?
How to Make Biomass Energy Sustainable Again
How and Why I Stopped Buying New Laptops
Vertical Farming Does not Save Space
How Sustainable is High-tech Health Care?
Urban Fish Ponds: Low-tech Sewage Treatment for Towns and Cities
How to Design a Sailing Ship for the 21st Century?
How to Build a Low-tech Solar Panel?
Fascine Mattresses: Basketry Gone Wild

Print on Demand

The books are printed on demand, meaning that there are no unsold copies (and no large upfront investment costs). Our US publisher Lulu.com works with printers all over the world, so that most copies are produced locally and travel relatively short distances. Note that it takes 3 to 5 work days to print the book.

Low-tech Magazine Volume I (2007-2012).

Low-tech Magazine Volume II (2012-2018).

Low-tech Magazine Volume III (2018-2021).

Low-tech Magazine: The Comments (2008-2021).

Comments

To make a comment on this article, please send an e-mail to solar (at) lowtechmagazine (dot) com. Your e-mail address is not used for other purposes, and will be deleted after the comment is published. If you don’t want your real name to be published, sign the e-mail with the name you want to appear.

Tom Karches

Are paginated digital versions available?

kris de decker

The third volume will appear as an e-book in a few weeks — if that is what you mean?

Cliff Bates

I retired 16 years ago from the utility electrical generation after 35 years. I have experience in all forms of electrical generation, except solar and wind machines. I was also a load dispatcher, which was the worst job I have ever had. Let me assure you that when I retired I built a new home, packed to the gills with insulation in its 8” thick walls. floors, and ceilings. It also has solar panels, and a 16 KW propane fueled generator, with a 150 gallon tank. I also have a fair sized wood stove. (I should of made a stone stove after reading the book.) Due to my knowledge of the utility industry during my experience, I believe, and have for some time, that the “good old days” of reliable power is in a declining phase. Not because most of the utilities are negligent, but because the natural sources of energy have been exploited long ago. Wind machines are the new rage, but they have a problem that is not discussed publicly of changing the local weather. You do not suck thousands of horsepower out of low altitude winds without affecting their flow. Wind energy is NOT FREE ! Hydro generation also has its problems. But on the whole, it does prevent floods, supplies irrigation water, creates recreation areas. and has a large power output without the CO2 outfall. Nuclear power is a joke. It uses low pressure steam, and therefore is extremely inefficient due to the fact that the reactors heat has to heat the water into steam through a heat exchanger. To make the heat exchanger walls thin enough to transfer the heat efficiently through the heat exchanger walls requires that its working pressure be less than 1000 psi. The lower the steam pressure, the more thermal energy required to change it from water to steam. Nuclear energy is only practical due to the governments subsidizing the cost of the nuclear fuel to make it so for the rate payers. This of course is totally disregarding the handling of the nuclear waste produced for thousands of years. This cost factor isn’t discussed, and again is stored at government expense. Surprisingly, gas, oil, and coal fired steam plants are capable of steam pressures of up into 3200 psi range, and are one of the most efficient large power sources known. However,they require HUGE volumes of fossil fuel to do so. I once worked at a large coal fired steam plant. It produced at full load, (its most efficient mode), 1600 megawatts of power. It had its own coal strip mine, and coal processing plant. It used, 20,000 tons of coal in 24 hours at full load. 10,000,000 pounds of air were required to burn that much coal an hour to generate 10.000.000 lbs of steam and hour at 3200 psi. And at the plant site we had to maintain by government regulations, a coal supply reserve of one million tons of coal in storage, which we lost a third of per year due to spontaneous combustion. The plant was amazingly complicated. I can recall many times staring at the plant as it did its thing with amazing reliability, wondering how after mining and processing the coal, the boiler of each unit contained 88 miles of 2 1/2 inch stainless steel tubing, seam welded together. The boiler was 13 stories tall. The amount of heat released into the boiler to make the steam was so intense, that if the boiler wasn’t cooled by the water being changed to 3200 psi steam, it would of melted that 88 miles of steel tubing in one and a half minutes ! It was amazing to me, that after running all the accessory equipment to make it work, that it could even light a 100 watt light bulb ! Natural gas, and oil boilers use just as much energy as a coal fired plant, but are slightly less complicated. But only from their fuel processing taking place off site. Solar is about as undamaging to the environment as you can get. Unfortunately the Sun must reach the ground in order for them to do their thing. Plus, solar cells currently are extremely inefficient, while occupying huge tracks of land, and are expensive to build. I haven’t mentioned diesel engines, or using jet engines, and geothermal power, as they can’t be built to a large enough scale to contribute with any practical effect to the needs. And yet now electric cars and trucks are becoming practical. However, no thought is given as to how we are going to generate the power to supply their electrical charging needs, when we are hanging by our fingernails just supplying our “personal needs”. Currently storing electrical power for later use isn’t practical. Batteries in the size and volume required are way-way to expensive. Plus high efficient batteries are made of extremely rare minerals, which the U.S. has only one small producer of the required minerals that I am aware of, and that comes as a very small waste product from other mining operations. What I foresee in the future is the evolving of small neighborhood power plants. Say 5 to 10 square miles in size to a power plant. This would increase future reliability, lessen storm damage, and lessen transmission line losses. Besides allowing tuning of the power plants energy needs, to that areas resources and needs requirements. However, the utilities are highly against any such proposals.

Yet this idea would also isolate a little known threat, very seldom discussed publicly. And that threat is the effect of an electromagnetic pulse (EMP). This threat is being taken seriously in Europe, but not very seriously in the States. This threat is a REAL possibility that could throw our Country back into the late 1800’s in an instant, and kill literally millions and millions, from starvation and lack of water. Unfortunately it can be generated either by a simple high altitude nuclear explosion, or by a large Sun solar flare. It is a simple effect, with devastating consequences, and has happened several times naturally already on a small scale around the world. As well as by nuclear testing in space in 1963. (Those two nuke tests scared the Hell out of the scientist at the effects created, and they have never been repeated in space again.)

I mention all this, because where electrical power comes from is not really a considered thought by most people. It is just there, like gravity, at least most of the time. And now, in one hundred years, our lives and economy are totally dependent on it. Take it away and your water stops flowing out of a tap. Gas pumps don’t work. Grocery stores can’t order their stock. The internet ceases. Your cell phone doesn’t work. And, depending on the model of your car, it might not work either.

I started reading the book, “Low Tech Magazine 2007-2012”. mostly out of curiosity. I can honestly say I was stunned at how wise some of these old time engineers were in coming up with a means of transporting power over several miles by mechanical means. True, these ideas in the book will not solve our National electrical energy problems. But locally, or applied to your home, it could well be extremely practical for you to adapt, or at least consider some of them seriously that could apply to you. I am 79 years old. I consider that if Climate Change worsens, (and it will a bunch), and the U.S. as a Country continues declining, that I have lived in the U.S. at it’s peak in history. Like the Roman Empire. If something occurs that forces this issue to happen during the rest of my limited life time, then if I and my wife can last 3 months, I will consider that I won the game. Why just months ? Because by then, the pills I require will be gone. One of the most positive aspects of this book is the authors approach to employing some of these aspects to your lifestyle. He pulls no punches on the practically in their use and application. He gives a very honest assessment of the practical applications both pro and con. However on a small scale, many are more efficient than present day methods, The idea’s, and their need in an emergency situation may cause you to change your view of having some of these ideas available. Or maybe even as a method to entertaining the Grand Kids in doing something totally different in pedaling away to create dinner. They have a lot of energy to burn off anyway, and give them something to talk about in school.

I commented to my wife that I was considering making some kitchen appliances that were pedal operated. She scoffed at me and said, “You’ll have to pedal them, not me !” When I next came in she said, “I’ve thought over what you said, and I think you should try making one with attachments. I pedal an excerise bike to stay fit, and do nothing worth while burning the calories. Might be kind of fun to do some food preparation while I burn up the calories doing something useful.

Aud

The past few years, I’ve loved popping into your website to explore random articles every now and then whenever I’ve had down time, but I’ve finally started sitting down with your books, reading them cover to cover — and I love this website even more in that format. I’m very excited that there’s a third volume! Publishing smaller volumes more frequently is an idea that makes me very happy. Thank you for creating such an amazing website with such beautiful content! Your articles are quietly life-changing.

h.f.

i hope to read a french version of all of this soon!

kdd

The first French volume will be out in about one month !

Alvaro

Will there also be a Spanish volume?

kdd

Sí, pero probablemente no será para este año.