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)