More efficient bike charger for USB devices?

I' been inspired by these bike lights from reelight.com. I have a set of these for my bicycle for reliable and very effective lighting. It's stated they are powered by "pure induction".

There's got to be a way to harness the energy from both wheels to charge a USB device (5 volt) in the same manner. Instead of using a friction generation mechanism bike charger or bike generator.

Any thoughts?

wobbler8 years ago
Because there are no mechanical friction losses compared to a bottle dynamo, it will only take out of the wheel the energy it is feeding into the circuit and therefore will have a much higher efficiency in terms of losses. The difficulty is in getting the power as the coil is not in the magnetic field most of the time, hence the use of leds in the lights. Hub dynamos work similarly and have much less drag on the wheel as anyone who's use one will tell you. Unfortunately they are much more expensive than a cheap bottle dynamo and usually heavier too.
frollard8 years ago
"pure induction' is just because the magnets are mounted on the wheel, and the coil is in the light. It works the exact same as any other generator, just doesnt involve EXTRA mechanical parts, so is theoretically more efficient - but any energy you pull from it is still gonna be pulled from the energy in your forward velocity.

That said - building one would be a breeze. Wind a coil wound and mounted on the fork, and toss some high-power magnets on the rim (balanced opposite one another), then a simple charge controller circuit, a small battery pack, then a dc-dc buck puck to put out the voltage you need.

https://www.instructables.com/id/How-to-Charge-Any-USB-Device-by-Riding-Your-Bike/
has done exactly what you want (the charger part), you'd just need to make a passive generator like is used on your 'reelight'.
110100101108 years ago
maybe connecting the outputs in paralel is all you need maybe you have to connect the inner generator ac lines though the standard generator has all parts tight together so maybe it actually outputs more electricity (though less efficiently) than the frictionless generator any generator works on pure induction. in standard generator the friction is attribute of the mechanics and not how it makes electricity