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From: ken@hertz.njit.edu (ken ng cccc)
Newsgroups: sci.electronics
Subject: Re: When is the battery fully charged?
Message-ID: <1991May7.205639.27130@njitgw.njit.edu>
Date: 7 May 91 20:56:39 GMT
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In article <1900@eastman.UUCP> levi@kodak.com (Ilia Levi) writes:
:How can you tell when a lead-acid (car) battery is fully charged?
:I want to build a charger for the backup sump pump system in the
:basement, and don't want to overcharge the battery (heard it was bad).
:How much voltage should a charger put across the terminals?
:While we are at it, what about the Ni-Cads?

Well, I'm not sure if this is the RIGHT way of seeing if batteries are
charged, but I've noticed over the years that if they get warm they are
either charged or your frying them :-).  I usually try to charge at about
1/10 the rated capability and leave it on for about overnight or until
they get warm.

Speculation on why they may get warm when charged: while the battery is
being charged, the energy goes into moving chemical ions back and forth
to the various plates and electrolyte.  When the battery is charged, the
energy has no where to go, so it is disappiated as heat.

People who know better are free (and encouraged) to post corrections.

Kenneth Ng
"No problem, this is how you make it" -- R. Barclay, ST: TNG