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Date: Fri, 27 May 2005 13:50:01 -0400
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From: "Gary Casey" <glcasey@adelphia.net>
Subject: Re: [LML] B&C BC-100 Battery
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> First came the hand prop, the engine started but the battery was so
> dead that it couldn't put out enough current to start the alternator.
> After about 20 minutes of flying the current into the battery went
> from 20 to 30 to 40 to 50 amps before the alternator circuit breaker
> (CB) blew.

I won't comment about whether to take off with a dead battery, but the
characteristic after that is understandable.  Batteries have an internal
resistance that drops as the temperature goes up.  If the internal
resistance is low to start with, and I think the B&C is one of those, the
charging current can be expected to gradually rise as the battery is charged
since charging will heat the battery.  I've watched this happen many times
charging batteries on the bench.  A small aircraft battery will probably not
take very long to accept a full charge and the current will then drop back
down, probably within 15 minutes with a 50-amp charge rate.  The thing that
puzzles me is why the CB blew during the charging.  The CB should have a
current rating equal to or higher than the rated output of the alternator
and therefore should not blow even if the alternator is charging at the
maximum rate.  I doubt very much if there is anything wrong with the battery
at all as a deep discharge shouldn't cause any big problem with the battery
even though it will shorten the life slightly.  With the correct CB rating I
suspect the flight should have gone off with no problem at all.

But would I take off into IMC conditions with my only battery dead?  The
short answer is no.

Gary Casey