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  #14  
Old January 24th 05, 08:33 AM
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Peter wrote:
> Am I right on this:
> When a battery being recharged is nearing full
> charge, it would accept less and less current,
> say around 1A or less, as indicated by ammeter
> on the charger (if there's one).
> So that means you can hook a charger (say 6A) up
> to a battery and leave it, since the battery
> won't overcharge. No matter how high the
> charger capacity is, a near-fully charged battery
> will only take in <1A.


The final charging rate depends on both the condition of the battery
and the voltage applied to it by the charger. The battery's voltage
rises as it's charged, placing a lower load on the charger, which makes
a manual charger's voltage increase. This is no problem with a trickle
charger, but higher-amp chargers will never taper down below 1-3 amps,
which can damage the battery if not stopped, maybe in about 12 hours
with 2-3 amps, 1-2 days with 1A. Automatic chargers prevent
overcharging by regulating their voltage to limit it to about
13.6-14.5V even at full charge, usually resulting in a final charge
rate of .15-.5A., and .5A should be safe for several days, < .2A for a
month. These amp rates don't include the current draw by the car's
electronics, and any car equipped with an engine computer (almost all
since 1981), clock, or alarm system will draw .01-.70A, even while
parked. Also a battery with a bad cell or just generally worn out will
have a higher charge rate, whether attached to an automatic or manual
charger. The final charge rate with an automatic charger isn't a bad
indicator of battery condition.

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