Using trainer as dynamo

Question

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?

RoboKaren · Accepted Answer

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.

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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.

Aron · Answer

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.

http://www.sungoldpower.com/-grid-tie-power-inverter-wind-grid-tie-inverter_c21.html

scottleibrand · Answer

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.

Using trainer as dynamo

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