Thursday, August 23, 2012

USB Charger for Bicycle Dynamo or Generator Hub

I made some efforts to make a bicycle (hub generator) USB charger. Unfortunately I learned that the available 6 Volt and 3 watts were insufficient to charge smart phones such as my Galaxy S2 and S3. Therefore I've abandoned the project.

The first prototype used a supercapacitor, bridge rectifier and a low power 7805. This did not work well and supercapacitors are rather expensive ($6-$10). I wanted the charger to be inexpensive to build so I'd be able to turn it into a viable product.

The second version, built on a prototype board, used a voltage doubling circuit and regular capacitors.
To make it sturdy I potted it in epoxy.

I wrote a small Android app for my phone to track the charging state and the speed with the phone plugged in to the USB port on the charger prototype while I go for a ride on my bicycle. You can see that on the Youtube video here.

This worked much better than the first prototype, but it was not able to supply sufficient power to reliably charge the phone. For lower power demands it should work fine though.


  1. There are existing systems. For instance by Busch & Mueller:

    This is expensive though.

  2. I have a Gazelle with inbuilt front wheel generator at 6 volts, been looking around for a unit to buy to charge phone etc, wondered if there is any latest news on your 'gadget'?

    1. I've abandoned it. With a hub dynamo that produces at most 6V 500 mA AC, it's a challenge to produce 500mA 5V DC. Modern smart phones like charging rates over 1 A.