Chuck wrote: >> I'm not understanding why a warmer (Pb-acid) battery takes more >> current to produce a given voltage under charge than a cooler >> battery. Seems that lead-acid batteries are supposed to be more >> efficient (less internal resistance) when warm than cold. So I >> would expect the opposite of what occurs. Any explanation?
Pau G wrote: > No, this is exactly what you would expect. The warm battery has less > resistance and is charging more efficiently. If you put one amp for > one hour in a battery then you can get an amp hour out. If you have > to put it into a cold battery at 2.4vpc your still only gonna get it > out of that battery at 2.0vpc. If you put that charge into the > battery when it was warm you may have been able to get it in at 2.3vpc > - thats more efficient. I hesitate to jump into this topic because it is so complicated. Lots and lots of things are happening when you change a battery's temperature: hot cold temperature --- ---- ----------- - + voltage, open-circuit + - voltage, under load - + voltage, while charging - + voltage, gassing threshold + - amphour capacity - + internal resistance + - self-discharge current - + life For example, if your charger is not temperature compensated, it applies the same charging voltage no matter what the temperature. A hot battery has a lower voltage, and so draws more current for a longer period of time. It starts gassing sooner, and goes into overcharge sooner. So the charger puts too muchg energy in; it overcharges the battery. The overcharging generates excess waste heat; thus charging is less efficient. The waste heat causes the battery to get hotter still, which can lead to thermal runaway (destruction of the battery from overheating). Or, if you fully charge it when cold, and then heat it up, it's no longer fully charged because the capacity has increased. Thus, figuring out state of charge when the battery temperature is changing becomes very difficult. -- Lee A. Hart Ring the bells that still can ring 814 8th Ave. N. Forget your perfect offering Sartell, MN 56377 USA There is a crack in everything leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen
