> My electric fan ran down my Optima battery on my TR6. I have a battery
> charger than can trickle charge at 2 amps, quick charge at 35 amps or jump
> the car off at 200 amps. If I want to bring the battery up to full
> strength, how long do I charge? Is it ok to charge for an hour
> or two at 35
> amps?
1 hour @ 35 amps would probably be safe for a deeply discharged battery, but
I wouldn't go any longer than that without checking the voltage. Optima
says to monitor the voltage and be sure it doesn't go over 15.6 volts when
doing a rapid recharge. 30 minutes @ 35 amps is safer and should be plenty
to start the car.
> How does one know how long to charge?
It's a complicated formula, to really get it right you have to measure the
battery voltage and temperature. Without specialized tools (like a smart
charger), IMO it's better to rapid charge only halfway or so, which is
enough to start and run the car, then either let the car finish charging it
or use a trickle charger overnight.
> I did look on the battery and did not see anything that mentioned amp
> capacity.
The actual capacity varies a great deal depending on (dis)charge rate. Lots
of info on their website at
http://www.optimabatteries.com
Depending on which Optima starting battery you have, the C/20 capacity is
advertised as either 44 or 50 amp-hours. "C/20" means it's measured at the
discharge rate that makes the battery last 20 hours, so that's 2.2 amps or
2.5 amps respectively. But the "reserve capacity" is only 90 or 110,
meaning that at a constant 25 amps, the batteries only deliver 37.5 or 46
amp-hours. (RC is time in minutes at 25 amps.)
In spite of all the hype around electric cars, batteries are only efficient
compared to hugely inefficient internal combustion engines. Unlike a fuel
tank, you never get back all of what you put into a battery. And the worse
you need it, the less you get <g>
Kind of like a loan at the bank.
Randall
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