This site is marvelous, but I haven't been able to find a circuit diagram for a battery charger. Have I just missed it?

Low power, low voltage. The problem, or one of them, is that the source of charging voltage is variable. Ideally, it will ignore the supply voltage when it is too low to charge the battery, charge when it is high enough, and not apply too high a voltage when the supply voltage gets very high.

As a silly example, you have a weird hamster on a treadmill. He goes from very lazy to hyperactive. When he's lazy, ignore him. When he generates enough voltage to charge the battery, use it. If he gets hyper, don't allow him to fry the battery.

Any pointers would be much appreciated!

Bill

 

The voltage of the battery to be charged is extremely relevant.

 

Yes, the battery voltage is important as is the chemistry (NiCAD, NiMH, Lead Acid...)
The charging voltage, what is it's low and high? What sort of current can it produce? What is it? Is it a solar panel?

 

Funny, I just got through posting this for Lightfire...

The Battery University

 

What is the battery chemistry?

Without knowing that, I'd suggest a DC-DC Buck/Boost converter with enough capacity (voltage & current) to run a commercial off the shelf battery charger for the type of battery you are charging.