Eric Fitchett

A few years ago I found out about a set of bicycle lights that were powered by a small generator. Being interested in renewable energy, I decided to see if I could use the generator to charge small household batteries.

This was one of my earlier electronics projects, and I didn't really know what I was doing - making it much more difficult for me than it should have been.
Turns out this is a very easy project (as long as you don't care about the possibility of overcharge). An optimal project would include some form of charge controller - my version did not.

The generator is rated for 6 volts, 3 watts. In my testing, it put out AC voltage in the range of roughly 1 to 17 volts.

My first task was to convert that voltage to DC. This was easy - just use a bridge rectifier. Not having one on hand, I made one out of diodes.

At this point, I could have tried to create some sort of voltage regulator/charge controller, but instead (since that would have been way over my head), I just hooked up what I had to two dead AA batteries (positive to positive, and ground to ground - just like jumping a car) and rode around for a few miles. When I got back home, the batteries were mostly charged.