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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!



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?



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!

Hemon from Motueka, New Zealand



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



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.




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!


Mike S.



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



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




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/ .




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:




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.





Congratulations, I love this project.
Just one thing,I think inertia would be interesting, here you are an example for an increased inertia pedal machine

kris de decker


@ Mike S

Thanks for your advice. Our spindle is indeed wearing out pretty quickly, because the material is too soft. But if we take power directly from the chain, as you suggest, how do we achieve the gear ratio that we need? Also, if we remove the wheel, where do we get the inertia we need?

@ Rudi

Thanks. We did not test the efficiency of the buck and boost converters, but it's something to consider.

Concerning the charging of lead-acid batteries. Indeed the idea is to rely on the wind charge controller, and let it adjust the voltage as required. Otherwise we would need to fine tune the voltage constantly.

We don't need to switch all the switches on just to get 5V output, so I guess our diagram is a bit confusing.

Schottky diode: I think you are right and we may just leave it out. We were probably a bit too careful here, the wind charge controller should take care of that.

@ Mathew

I have no idea what is inside the flywheel that makes it so heavy. Sand or water seem unlikely. Could it be concrete? Although it looks like a normal tire from a distance, it surely is not when you take a closer look. It has a very hard surface.

A direct chain drive is surely more efficient, but in that case how do we get sufficient gear ratio and inertia (see also my reply to Mike)?

@ Jonathan

Great advice on the cycling shoes and pedals! That is something we may try out. The aerodynamic wheel cover is also worth a try.

@ Stefan

Pressing the generator down onto the flywheel: I don't think that would make any difference, and it would be more complicated to build well. The arrangement we have now very easy to make and works very good.


Finally, more comments at hackernews: https://news.ycombinator.com/item?id=30589638




The idea is to replace the flywheel’s hub with one that has sprockets on both sides. You would drive the sprocket on one side of the flywheel (set to a good drive ratio) and pull power from the sprocket on the other side (set to a good generation ratio). These sort of double-sided bicycle wheel hubs are sold as “flip flops.”

Of course, swapping the flywheel’s hub requires either disassembling the existing flywheel or building a new one. It sounds like the heavy, solid tire used for mass may not be removable, and so building up a new flywheel may be required.



Dear Kris De Decker and Marie Verdeil,

Thank you for your research and divulgation.

In your post you talk about the advantages of a flywheel to provide inertia that will give comfort for the rider and constant speed to the generator. Completely agree but I haven't seen any mention about the importance of the freewheel sprocket as a necessary complement to achieve this comfort and speed smoothness. Some stationary bikes* use a flywheel as a surface to apply friction and a rubber belt for a silent transmission but they don't have a freewheel sprocket. In consequence, when the rider tries to stop pedalling, the flywheel tries to keep spinning and comfort and efficiency disappears. I suppose your BH stationary bike is equipped with a freewheel sprocket but I think the design I mention can be quite common in the second hand market and probably it would be helpful to provide this detail in the post to avoid some frustrating outcomes.


* As you can see in the provided images

PS 1: the images of the stationary bike are from a similar model to this one: https://es.wallapop.com/item/bicicleta-estatica-antigua-727668727
PS 2: another model than probably have the same design without freewheel sprocket: https://es.wallapop.com/item/bicicleta-estatica-708590359



Hi, Kris. I’m glad to see you warming up to pedal generators. How you source your build materials makes the difference between being sustainable or not.

As you probably know, eliminating the friction drive is the single largest improvement you can make for energy and material efficiency. I’ve built several of these over the years (all from stuff laying around the house), and by far the most efficient one is my latest. It’s actually just an eBike on a trainer stand, but it is a rare one in that it uses a 36-volt hub motor with regenerative braking (regenerative braking is what enables its use as a generator).

I removed the 36-volt battery and connected the bike’s battery terminals to a 12-volt capacitor, which then feeds my GoalZero Sherpa 100AC. A little bit of searching to find the right gear, but once I do, I can rather easily generate around 40 Watts at 15 volts. My older builds all used some form of friction drive (either wheel-to-wheel or belt), and the best any of them could do was 30 Watts output while working me harder than my latest build does.

Each iteration of friction drive I used had either a belt or tire that would wear. The generators I used also had brushes that would wear out over time. My latest generator has none of that, as it uses a 3-phase AC motor. I don’t need a rectifier, as the bike’s controller passively rectifies the 3-phase motor output to DC.

The GoalZero pack allows me to store 100 Wh, and it can power AC loads up to 100 Watts, USB-A loads, and USB-C loads, including my laptop. A 10-minute ride this morning was enough to charge up my iPhone for the day. Since the chain directly turns the motor/generator, there is no friction drive to wear out or rob power. A combination of the rear wheel and the capacitor smooth the power delivery, allowing the Sherpa’s MPPT input to accurately track the power curve. Pre-existing bicycle maintenance infrastructure will keep the generator going for years to come.


rob a


Been really excited about this post and doing more research to try to build one myself. Came across Robert Murray-Smith's video series on youtube. Have you watched any of his videos? Shows how to make a quick easy flywheel, also DIY Kinetic Energy Recovery System and more.

Think you will like them if you haven't seen them already.

Solrac Z


Excellent article and effort. I have built a bicycle generator that uses my existing bike mounted in a basic bike trainer. I removed the tire from the rear rim used a belt around the rim to turn the generator spindle. I get to use my existing bike with its gears and familiar comfort, I can add weights to the spokes to create a flywheel effect and smooth out the pedal strokes, and with a few minutes effort, can be riding my bike outside.

The most major difference in my generator system is that I used a 15v ultracapacitor to "digest" and regurgitate all of the power that I generate. No need for a regulator as the ultracapacitor takes in unregulated power and discharges it as needed to the powered appliances. The ultracapacitor acts as a sort of "bottomless battery" that spits out power as needed. I am not doing a very good job of explaining how it works, but it takes all of the finicky regulators out of the equation. Here's a link to David Butcher's youTube walk through of his power board:


I have found this system to be far easier to build and understand than using boost and buck items.

Cavan Mejias


Thanks for the inspiring write-up, I think you guys have taken care of the 99% perspiration for the rest of us.

This YouTube video https://youtu.be/BQt35C5dSCA?t=190 goes over pedal power and invites viewers to take a look at your stationary bike generator.

Keep up the good work and best regards.

J. R. 'Bob' Dobbs


Hi Kris,

Really enjoy your magazine; I think of it as a spiritual successor to the sustainability journal "Whole Earth Catalog" published in the 1970s.

Do you have a tips/submission address for article ideas? I've just seen an article on low-tech heat storage at https://www.abc.net.au/news/science/2022-07-19/sand-battery-debuts-in-finland-world-first-heat-thermal-storage/101235514 that looks interesting, particularly if it would be practical at the scale of a typical household or farmstead.

Pamela Murray


There are bicycle dynamo hubs that produce power so you wouldn't need the do the spindle, friction, etc. I have the Kasai SPV8 which produces power for my front and rear lights. Why wouldn't you use that and then you can use your bike as is?



Hello :::
First of all, thank you for this wonderful article. I set my head into building one of those and I hope you don't mind if I ask, why not just go with a car adapter inverter and then have all the appliances running over this.
Instead of having different circuits. for me the pro would be that I had space to implement a desk.
My Laptop requires an input of 20 V and 3.25 A. The way I read your manual, I could only achieve this with the car adapter and 220 V inverter, cause otherwise I wount be able to pedal for 20 V.
Why can I not use a AC Generator and go 220 V strait for the laptop
I would love to hear your opinion on that.

Bests and thanks again for this great share :::



Very nice. This article would be even more interesting if it included another curiosity: An economical evaluation of conversion of additional food energy required to produce such amount of electrical energy. It would be very interesting to see charts of conversion from potato or rice to kilowatt-hours of usable electric. Moreover, how about calculating the ratio of potato energy to boil that exact amount of potatoes? "Potato EROEI"...



there is a smaller version of the exercise bike to obtain 3000 RPM, see here : https://veloma.org/2022/09/03/generateur-a-pedaleavec-alternateur/
with permanent magnet alternator and belt you can get good results and put it next to comfortable sofa...



Good idea.
Role division:
- wife - bicycle and power generator
- me - reading a book

Dan S.


In a first place, please excuse the potential english errors that may occure, I am not a native english speaker.
Now, because you are measuring the output parameters, maybe you could make an estimation about how much energy (Watts-hour, or hundreds of Wh) could produce a mature man in a day (I dont know, maybe 2 to 3 hours of pedaling the bike discontinuously in my case...). There is already more then 6 months since I'm thiking to build something similar, beginning with the generator (the neodymium N50...N55 magnets are still pretty expensive), but I don't know exacly how much power a man can provide through the pedals. I know a proffesional bicicle racer can provide about 400W of power for long term (hours), but a average person I think is far away from this value. Anyway, the output power I would like to store it into a powerbank with lithium accumulator cells. Do you think a 200W generator would be to much...? Should I limit to 100W generator? I mean, the output power could be electronicaly adjusted at will (I could build some electronic controllers for this purpose), but I would like to have some kind of starting point, or „landmark” from someone with experience in this field.
At the same time I want to loose some weight, in fact I must to do that (I've already riched about 220 lbs. from 165, since I got sick).
Thank you very much for your time.

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