A USB Charger for Your Bike
As you ride your bicycle from one place to another, whether to save money on gas, for exercise, or as some combination, there’s a good chance you’ll be using a phone or other electronics on the way. Such devices need power to operate, and as it just so happens you can harvest a fraction of your personal energy input into the bike via a dynamo for electrical power.
While this dynamo is a neat way to produce power, the challenge is that it’s highly variable, based on how fast the bike is going. To help provide useful charging power, creator Vulcaman came up with the Fahrradlader V3.1, German for Bicycle Charger V3.1. This open source design features a rectifier arrangement of four diodes for converting the raw AC input into DC, a DC-DC converter, and circuitry for USB charge optimization.
Perhaps the most interesting feature, however, is that it has four 3F supercapacitors, which are charged up by wheel movement to keep it supplying a device for 20 seconds or so when stopped. A relay and MOSFET are used to regulate charging, which allows for disconnection of the dynamo input. This means that excess charging can be averted without having to shed extra energy via heat.
To test this setup, Vulcaman attached a Shimano DH-3N30 dynamo hub up to a lathe to successfully simulate operation at 100km/h. Whether or not the dynamo and your bike is up to these kind of speeds in the real world is a bit of an open question, but at least your phone will work!