Homebrew Grid Tie Inverter

Annoyed with the friction band on my stationary bike and wanting to generate electrical power I decided to build a generator and grid-tie inverter to feed the power back into the electric grid. I realized that the amount of energy generated would be minimal but the exercise would be interesting. And I can always convert the circuit to a stand-alone power generator.

The system consists of three parts:

The bike is a cheapo Tunturi bike. I removed the friction belt from the flywheel to be able to drive the generator. Images are in the converter part. Any bike with an exposed flywheel will work.

The generator is a EBM Papst VD-3-54.32 three-phase motor bolted to a Zeitlauf Pgp 63.1 9:1 reducer. I found no data online for this unit, which I got from an online tat bazaar (not e-FUCKEN-bay but owned by it).

The GTI is a crude square wave semi-sine converter which drives a big toroidal transformer connected to mains power.

The PoC with an RC car wheel (that quickly got destroyed) was successful. Getting rid of the friction band added significantly more momentum to the flywheel which in turn maked the cycling much more enjoyable. It now is a nice road cycling like experience. I managed to generate about 40 W of electric power with a modest amount of effort. This would suggest that 100 W is feasible. This of course is a puny amount of power to feed back into the grid but as an illustration it's really cool. Of course, the crude inverter is not something my power company would appreciate...

The final result is amazing! It turns out that the transformer and inverter are perfectly matched. A modest amount of cycling generates about 50 W. This is about 60-65 RPM. Pedaling faster makes the load increase quickly so that the cadence doesn't increase all that much. Going all out I can generate over 100 W but a trained cyclist can do much better than that, certainly for a short time. Someone even managed to upset the controller, but fortunately nothing failed. Also the friction wheel starts to slip. In any case, 50 W is more than enough to watch a TV show. All in all not a very good way to get rich. If I cycle for 20 hours I have generated 1 kWh, earning me a grand total of 22 eurocents...

UPDATE: the GTI has been PIC-ified!

Last update: 14 August 2019