cordless drill...charger voltage?

[ve6pg]

  hi from tim...i have 18v batteries for cordless drills...nickel metal types...i cant seem to find the wall wart chargers...so, my question is, what is the dc voltage to charge these things?..

..thanks..

..sk..

[Pete, WA2CWA]

Who makes the battery and/or the drill?

[WD5JKO]

Tim,

  The NIMH batteries prefer a smart charger for optimum performance and lifetime. Most commercial stuff we buy doesn't do that however. You could charge at a constant current until the voltage across each cell is ~ 1.4 - 1.5v. So you might have 12 or 14 cells depending how they rate the batteries. These batteries under load put out about 1.25 volts per cell.

  When to stop charging is always a question, and economics kick in also. Sometimes we monitor the battery temperature, sometimes we have a timer, and sometimes we have a dumb charger at low current. I might pick one of the small 100 ma 3 terminal regulators and set the output voltage for 1.5V / cell. When starting a charge cycle the regulator will limit to 100ma, and when the voltage rises above 1.4 v / cell the current should drop to a trickle rate.

Jim
WD5JKO