Originally Posted by
Aznman
Thank you for the well wishes. I do want to create some charging systems (using the dynamo to re-charge the batteries instead of inefficient capacitors) so that my bicycle can be "entirely" indepedent, but I just don't have the knowledge, tools or the time right now.
I keep hearing contradictory information about the safety of re-chargeable Ni-CAD batteries being charged while in use.
Regarding efficiency, I would say that capacitors are at least as efficient as batteries. There is less power lost when charging capacitors than batteries. If you are actually referring to the ability to store power, then batteries have a higher energy capacity for a given package size.
I've designed my own dynamo headlights with good standlights, using both a AA nicad cell and a 100F super-capacitor to drive the same standlight circuit. The AA nicad will power the standlight for 30 minutes, while the 100F super cap will power it for 10 minutes. Both are more than enough. The 100F super cap is more expensive and bigger than the AA nicad, but the AA nicad is cheaper and heavier.
The only risk of using nicads is that they will vent a small amount of hydrogen if severely overcharged. In general, they are about the safest type of rechargeable battery. It's pretty easy to design a charging circuit that won't overcharge a nicad pack, even while using it.
Steve in Peoria