dead battery, Charging amps and time question

[SmellyCat]

Hello again, Here is the question. I have a dead battery, 550 amp battery, how long would I leave it on a 10 amp charger. Safely. Thx sc

[mort]

Originally Posted by SmellyCat

Hello again, Here is the question. I have a dead battery, 550 amp battery, how long would I leave it on a 10 amp charger. Safely. Thx sc

hi SmellyCat,
Very roughly - assuming that 550 is CCA, the number of amps the cold battery can deliver for 30 seconds before the voltage drops so low that the engine won't start (7.2 volts) - so 550/10 is 55 and 55 X 30 seconds is about 27 minutes.
But this all depends on the charger. If it truly delivers 10 amps regardless of battery condition, figure about a half hour. If it delivers a maximum of 10 amps and tapers off as the battery charges, then figure an hour. If the charger tapers off to below 2 amps, you can leave it charging all day and not hurt anything.

-mort

[SmellyCat]

Thx Mort. It seems like 27 minutes on a 10 amp charger will not charge up a dead battery. I do like how you explained the math behind charging time. if I,have zero amps in the battery, like I left the key in the ignition for a week. Don't I have to get a bunch of amps back in the battery. doesn't a ten amp charge stuff 10 amps in a battery per hour? Sc

[2000mc]

Like you left the key on... But was anything on? Check for anything on with the charger hooked up? Have a voltage meter?

[SmellyCat]

Ok I had it on 10amp charger fo 3.5 hrs. The voltage is 12.3. Seems like. That is. 80%charge or so. How much longer should I charge it. Sc

[2000mc]

12.66 is a full charge w/o any surface charge. But 12.4 is actually more like a 50% charge, that being said, 12.3 on a good battery may be enough to start, I would want to have the meter on to watch voltage while cranking as I suspect a bad battery given the recent heat, unless you know why your battery is discharged

[SmellyCat]

Alright, Ya I left the key on for 5 days. That drained it dead. This is all great info since I,m running the Volvo with the alt off

[TheEnemy]

CCA (cold cranking amps) and Ah (Amp hours) are two different measuremets for two different purposes. For charging you would want the Ah rating which is typically 45 or more. So your looking at 4.5 hours to charge give or take.

[Ryland]

Your 10amp charger doesn't really put out ten amps unless the battery is dead, or you have a modern solid state charger that charges at a constant amp rate, so as it reaches full it will taper off, so you are really charging at closer to 5 to 6 amps, so I would leave it on over night and check the voltage, if you ran it all the way dead you want to equalize it, 13.8 or so while on the charger 13v while at rest after taking it off the charger and waiting at least a few minutes, the voltage should be the same after 3 hours to get an accurate reading.

[vskid3]

If I were you, I would leave your alternator hooked up until you get charging figured out. With as many times as you've run your battery dry in the last few weeks, you'll be replacing it more often than your oil and your fuel savings won't offset it. Lead acid, especially starting batteries, hate being completely drained.