Shortcuts With Battery Management

A project log for Bicycle Regenerative Braking System

Turn excess kinetic energy into electrical energy rather than waste all it as heat. Built from commonly available and recycled parts.

recyclojunkrecyclojunk 09/01/2014 at 08:080 Comments

With less than two weeks until the planned date for the trip, I really have to hurry up and get this done, so I can start packing and organising the other stuff.

So I've decided to take a shortcut. Instead of charging 16 removable batteries separately, I'm going to build a non-removable 15V pack (4x4 series-parallel). I'm not going to bother with balancing, but I'll ensure the cells are matched so there won't be as much need for balancing anyway. I will most likely implement the proper charging circuitry later on after this trip however (or if I get time before it).

The new dynamo seems to put out a lot less voltage than the last one, even when in low gear. 1.1V and 0.34V per km/h for low and high gears respectively (with 0.3Ω internal resistance). So I might as well just use an ordinary boost converter for the charging. I'll run the controller directly from the battery so it will work even at very low speeds/input-voltages. 

Ready for a quick test. Works well, but I'll have to modify the controller as currently the duty cycle won't go above 50% (Vout = Vin / (1 - Dcycle) )

(I did briefly consider using a 12V 7Ah lead-acid battery in the last post but at 2kg and only 85Wh I'd be better off simply (ab)using some laptop batteries in an unbalanced pack.)