Jan 06, 2002, 03:27 PM
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USA, FL, Apopka
Joined Dec 2000
4,072 Posts
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I learned this from a post on chargers by Rkane
"The rough formula for calculating DC power supply current rating is: (Vpeak*Achargerate)/Vsupply, where Vpeak is the voltage of the battery pack just before peak, Achargerate is the maximum charge current you expect to use, and Vsupply is the voltage of your power supply.
The voltage on my 8 cell packs will go over 14 volts before peaking. If I charge at a 3 amp rate, the power delivered to the pack is 42 watts (14v*3A) just before peak. The charger will have to draw that amount of power from the supply, plus some additional to make up for it's own internal losses. Assuming a 12v DC supply, the current into the charger will be 42watts/12v=3.5 amps, plus a little to keep the charger warm. A 10 cell pack would require nearly 18 volts to maintain a 3 amp charge rate, so it would draw (18v*3A)/12v=4.5A. A charge rate of 3A into a 24 cell pack would draw 10+ amps from the 12v DC source. "
So with two 12 cell packs in series you had 24 cells or a Vpeak of around 43 Volts, if you wanted a 8 amp charge rate from a 12 V power supply you would actually draw 28.66 amps at peak. The charger was just trying to do what you asked it.
Brad
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