I was wondering if it is possible to to use a magnetic trainer as a dynamo.

While riding on trainers, at a gym, or at home, I always think to myself, "I wish I could capture all this energy and put it to good use".

Has anyone ever turned a trainer into a dynamo? If so, I'd like to know what modifications are needed and what tools and parts are necessary, plans, etc.

Moreover, I'd like to know if it is then possible to use this dynamo to supplement power to ones' home, as opposed to just storing it. While discussing it with a friend, the main challenge that came to mind was converting the current to A/C and synchronizing the phase, voltage, frequency, etc. with the power coming into the house. Probably a bit overkill if you're not an experienced electrician (which I'm not) but maybe I'm wrong.

If hooking one up to the home is not realistic, is there any simple configuration that one could use to provide useful energy and store it?

  • A trained cyclist can put out about 400W for a hour, an average person maybe 100-150W. Accounting for loses, an average person could contribute around 100W to the house hold power, probably 0.5 kWh/week. Can it be done, yes, it has been. One 'experiment' I once read about was to power the play station and TV form the bike. Kids could get about 1 hour of play time for every hour of exercise.
    – mattnz
    Jan 7, 2017 at 1:21
  • If you watched the newest The Grand Tour episode on amazon (came out yesterday in the US), you'd have seen James May did this.
    – Batman
    Jan 7, 2017 at 2:08
  • 2
    Or a magazine article. Looks like it was intended for school children.
    – Batman
    Jan 7, 2017 at 3:30
  • 2
    This answer on sustainability.se might help: sustainability.stackexchange.com/questions/4924/…
    – Móż
    Jan 7, 2017 at 6:51
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    In this video they're probably not directly powering the toaster with the bike, but it gives a good idea of how much power you aren't putting out. youtube.com/watch?v=S4O5voOCqAQ
    – alex
    Jan 7, 2017 at 19:54

3 Answers 3


You could. If you were a hobbyist, it'd be simple enough to hook a DC motor to act as a generator, smooth the output, boost-buck it to the right voltage, and use it to charge a deep-discharge lead-acid battery.

From there, you could either use it to charge your USB equipment or get an inverter to run some lights. I would not hook it into your mains, the equipment to do so safely is expensive.

I'd estimate the setup would cost just around $200-1000 depending on what parts you already have lying around.


That said, let's say you already had most of the parts so it only cost you $200.

You could most probably output 100-400 watts an hour. Let's say, you're in very, very, very good health and can do 250 watts for 2 hours a day. That's 500 watt-hours. Over a month, training 20 days that'd be 10,000 watt-hours or 10 kWh.

In my region, electricity is 20 cents a kWh, so you would be generating $2 a month.

So you would amortize your equipment cost of $200 over 100 months or 8 years. That's if you're in excellent health.

Note 0: Values chosen for ease of calculation rather than strict adherence to reality. However, I believe they are within an order of magnitude correct.

Note 1: your energy expenditure will be such that your increased food consumption will likely exceed $2/mo.

Note 2: if you break or wear out anything, you'd be back to square zero. Even deep discharge batteries have a limited life span.

Note 3: This model doesn't include charge/discharge/inverter inefficiencies. You should most probably multiply everything by 70-80%.

Note 4: this exact scenario was used in an episode of Black Mirror, season 1.

  • If you got 12V (ish) out of it as you imply with the lead-acid battery you could run lighting designed for caravan use. For charging USB, it might be more feasible to rig (even multiple) bottle dynamos (with rectifiers etc.)
    – Chris H
    Jan 7, 2017 at 19:45
  • Yes, you could skip the 120/240vac inverter and just power 12V lights off the battery. Bottle dynamos are horrible in so many ways. Extremely inefficient. Noisy. And they shred tire sidewalls.
    – RoboKaren
    Jan 7, 2017 at 19:49
  • With a custom frame you could run a bottle dynamo on the tread rather than the sidewall, but anyway that would only ever get you a few Watts while your more difficult approach would get a up to a few hundred so different applications.
    – Chris H
    Jan 7, 2017 at 19:51
  • Bottle dynamos are just horrible. They have lifespans in the 10s of hours. Have you felt one while in operation? They get extremely hot (especially the contact-wheel), which indicate just how inefficiently they are running. And to make things worse, they output a low AC voltage, which would have to get rectified, smoothed, and stepped-up to be any use.
    – RoboKaren
    Jan 7, 2017 at 19:54
  • Sounds like you've been using very bad bottle dynamos. I had one that worked for years until hub dynamos became available. The noise was annoying, but otherwise it just worked. The problem with dynamos is that the output varies a lot, voltage can be anything from 2 to 25 V depending on what was connected to it. The halogen bulbs could tolerate a lot, but still tended to blow out fast. I wouldn't connect anything more sensitive or expensive to a dynamo.
    – ojs
    Jan 7, 2017 at 20:23

Another option I’m thinking about trying would be to use an e-bike with regenerative braking and USB power output, like the RadCity, and put it in a bike trainer stand without connecting the wheel to the resistance element. Then just set the e-bike max speed to some low value (the Rad bikes go as low as 12kph) and start pedaling. The regenerative braking will kick in, storing the excess energy. If necessary, you can also lightly pull on the brakes to engage full regenerative braking, which if the display is correct is over 200W.

The Rad bikes’ battery is about 650Wh. It can only put out 5W on the USB port, but you can leave that plugged into a USB battery bank to get 50Wh of charge overnight. There are even have some USB-C charged battery banks with a built in 120V AC outlet that would let you use the stored energy to run higher-power devices. The 5W USB would mean you could generate and use up to ~100Wh/day, enough to fully recharge a tablet and three large phones each day with about a half hour of pedaling.

And if you don’t want to buy/use a bike stand, you could ride the bike around outside to recharge the battery. I haven’t yet tested the efficiency of either approach. Riding outside would be less efficient, but the evaporative cooling might allow you to achieve higher power output and recharge faster.

  • Note that the question was most interested in feeding the energy into their household electrical system, not just storing it. Do you have any thoughts on that?
    – DavidW
    Mar 1, 2021 at 16:19
  • As others have said: it's not worth it. At the very least, you'd need either a grid-tied inverter (if you wanted to make pennies selling your power back to the grid) or a generator circuit to isolate your house's system from the grid (if you wanted to under-power appliances during an outage). Better to do a stand-alone system to use the pedal power to recharge a battery and power some electronics directly off that. That best accomplishes the OP's desire for a "simple configuration that one could use to provide useful energy and store it". Mar 2, 2021 at 21:56

You want to buy a Grid Tied Wind Inverter.

These are pure sine-wave inverters that are designed to synchronize with a power grid and feed directly into you home's power distribution system.

However, you should note, that these devices typically require permits to run; as a poorly maintained/designed system has a very high potential to electrocute power company engineers (they expect that the power line will be safe after they isolate it from the grid, not expecting you to own a small generator at home).

Once you receive all your permits required, you can just hook up your bike to a small DC motor/generator and the inverter. Everything should work very simply.

You should be able to get one of these inverters for about USD150 these days.


  • If you add the cost of the permit, the inspection, and the licensed electrician to hook everything up, you're running more than several hundred dollars. It makes sense if you want to tie in your $2000-10,000 backup generator for your house, but not for your bicycle dynamo.
    – RoboKaren
    Jan 9, 2017 at 16:05
  • @RoboKaren YES. The permit, inspection and licensed electrician.... Anywho, grid tied inverters are useless with a backup generator. All legal grid tied inverters will shut down during a power outage (so as to not electrocute electricians). As for electrician, a small micro inverter wouldn't require an electrician to wire up. Permits are usual free in the EU.
    – Aron
    Jan 9, 2017 at 17:06
  • This isn't really an answer but I think it's pertinent to the question none the less. Thanks Aron.
    – ebrohman
    Jan 12, 2017 at 19:13

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