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From: john@zygot.ati.com (John Higdon)
Newsgroups: sci.electronics
Subject: Re: battery back-up
Message-ID: <32113@zygot.ati.com>
Date: 19 May 91 05:18:46 GMT
References: <1991May14.154859.21874@arcturus.uucp>
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Reply-To: john@zygot.ati.com (John Higdon)
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In article <1991May14.154859.21874@arcturus.uucp> graham@arcturus.uucp (Graham;Thomas D.) writes:
>
> Got a question re using lead-acid, car battery, as power supply for
> house alarm system.  I'm using a Delco 40 month rated about 20 hrs (?).
> A typical auto 12v battery.  I keep it on a floating charge at about 
> 13v, from a cheap  little battery charger.  I wanted to check its
> power reserve/capacity, even though the little green ball indicated
> full charge, so I discharged it at 4 amps rate.  In a little over an
> hour the voltage had fell to 9 volts.

Maintenance-free batteries were designed for one purpose and one
purpose only: for automobiles owned by people who are too lazy to take
care of their cars. These batteries have a terrible discharge
characteristic in that they cannot tolerate deep discharge nor can they
deliver any decent service with a slow discharge. They will start your
car and then they want to see charging current at all other times.

I found that in my Blazer, leaving the cellular phone on for only a few
hours was enough to make the car unstartable. The standby current for
the phone is around one amp, but maintenance free batteries fall apart
during any amount of prolonged discharge, regardless of how slight. For
this reason, these batteries are useless for anything other than
automotive service in which the vehicle is regularly used. I have had
disappointing results using them on standby generator sets (they don't
seem to like constant trickle charging without nearly daily, momentary
discharge), terrible results on battery backup systems, and find that
they are not all that hot in cars either. Leave your domelight on all
night sometime, and see if you don't start having a hard time starting
your car from then on.

While regular, fillum-yourself batteries typically will last over five
years in a car, maintenance free types will max at about three years.

Use a gell-cell for your alarm, or a heavy duty, deep-cycle battery.
-- 
        John Higdon         |   P. O. Box 7648   |   +1 408 723 1395
    john@zygot.ati.com      | San Jose, CA 95150 |       M o o !