Date: Thu, 13 Oct 1994 08:05:57 -0700 (PDT)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Wes Neuenschwander <wesn@eskimo.com>
Subject: Re: Battery Drain
On Wed, 12 Oct 1994, Tim Smith wrote:
> Date: Wed, 12 Oct 94 15:51:20 CDT
> From: Tim Smith <smitht@jupiter.sun.csd.unb.ca>
> To: Multiple recipients of list <vanagon@lenti.med.umn.edu>
> Subject: Re: Battery Drain
>
> I've always had a slight drain on my battery, due to clock/LCD display in
> the stereo which I measured around 90 milli-amps, tiny. When my battery got
> old/weak and I didn't drive for a week or so I had starting problems. I was
>
>
The 90 milli-amp draw of a car radio/cassette/CD/clock may be "tiny" but
don't discount it entirely, especially with older batteries. 90
milli-amps (0.090 amps) amounts to a draw of 2.16 amp-hours (AH) per day
or 15 AH per week. In addition, there may be other small loads such as
the built in clock, security/alarm systems, etc. If the vehicle isn't
driven frequently, and/or driven on short 'errand' type trips, it is
indeed possible to run the battery down. I found this out the hard way
($300 for diagnostics, new battery isolator, voltage regulator, etc.) on
my '82 camper. Battery had "tested" (that is accepted a charge" OK.
Since the alternator had tested good, the battery became the next thing
to replace (industry standard pin-head logic - I've never met a mechanic
yet who had an inkling of the laws of physics - or had even heard of
Ohm's Law). Problem solved! Mystified, I dragged out the amp meter and
calculator and realized that I was sucking out about 40 AH (vehicle was
only being used every couple of weeks) from a 4 year old battery that was
originally rated at 50 AH. When I went back to the so-called "auto
electric specialists" they didn't even want to hear about it (when I
started to do the "math", ie multiplying 0.100 x 24 hrs x 7 days, the
"mechanic" grimaced like he was having severe indigestion!). I wasn't
even griping; just wanted them to know that 'tiny' loads could indeed
run down a reasonably healthy battery. The other day in an auto stereo
shop, saw the same thing. Lady, who's car these folks had loaded down
with stereo, ultra high-tech alarm and portable cellular phone (with
re-charger left plugged into lighter socket), was being sold a new
battery (which interestingly enough they stock!), because "everything
else checked out". Fortunately, these guys could multiply and quickly
figured out that with a couple of false alarms per day (proximity sensors
of course!), even a new battery could go dead in a week with this setup.
I noticed they still sell new batteries, but hopefully not as many now.
--------------------------------------------
Wes Neuenschwander
Seattle, WA
(wesn@eskimo.com)
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