"TimPerry" bravely wrote to "All" (15 Feb 05 02:11:34)
--- on the heady topic of " battery charging"

Ti From: "TimPerry"
Ti Xref: aeinews sci.electronics.repair:10570

Ti Maybe... the supply voltage needs to be far enough above battery
Ti voltage to allow it to fully charge.

Ti The supply must be able to provide sufficint current to charge in a
Ti reasonable amount of time (say 10 to 12 houres).

Ti The supply must be current limited so as not to destroy itself or
Ti catch on fire when shorted out (as in charging a depleted battery.


Do I need to
be concerned about current ratings vs. ampere hours of battery?

Ti You need to be concerned about max charging current. too much causes
Ti excessive heating which might lead to more serious issues.

Lately stores have been selling portable car battery backup systems in
various sizes. One such model claims 500ccA from a 12V 18aH sealed
battery. I suppose it might work however the charging time is spec'd
at between 36 to 72hrs. Reading the manual a little more closely I
finally found that the charging current from the AC line is but a mere
0.5A. No wonder it takes so long to charge up! 18aH/0.5A=36hrs but
IIRC a lead-acid battery requires 10 to 20% more time to achieve full
capacity.

The manual also hints that the 12V power socket can be used for
charging directly from the car's lighter socket however it warns not
to exceed 4hrs. The current is thermally limited to 10A at the 12V
socket but the connecting cable seems a little flimsy.

Anyways I'm wondering if increasing the AC charging current a little
say to 1 or 2 amperes would be safe for the sealed battery?

BTW I've never seen a car with a dead battery actually start with one
of these gadgets. So far it stands at 3 for 3 no go...

Comments?

A*s*i*m*o*v

.... Electrical engineers deal with current events.