Posted by David Sherman on Friday, June 20, 2003 at 7:14PM :
In Reply to: OT-Combo batt charger? posted by Kevin on Friday, June 20, 2003 at 5:30PM :
If you know a little bit about electricity and you don't need huge amounts of current, you can probably pick up an old variable voltage bench power supply at an electronics flea market, ham fair, etc cheap. Typical bench power supplies are adjustable from 0 to 15 or 20 volts and are protected against damage from short circuits.
Ideally, you'd find one with both current and voltage meters on it. The really fancy ones have current limit adjustments, but you don't need that unless you find a real monster that could charge your vehicle battery too fast. Lead-acid batteries can be safely charged with a constant voltage of about 2.3 volts/cell. If you need to charge it faster, you can turn the voltage up until you get your desired amount of amps or as much as the unit will put out, and then come back and turn it down to a "float" level when it gets pretty well charged. 2.4 volts/cell is pretty much the upper limit for charging. A fully-charged battery that's set for a day or so without current going in or out will measure about 2.1 volts/cell.