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Dead Battery Fix
Posted by ED HABERERN - http://saabnet.com/tsn/forms/e.php3? (more from ED HABERERN - http://saabnet.com/tsn/forms/e.php3?) on Mon, 1 Sep 2003 11:48:27
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

I have a 89 Saab 900 Turbo whichÊad chronic battery failure problems over
the last 6 years.  The battery would fail as the car was driven on hot summer
days with A/C cranked up.  The car would shut down and the battery would be
so dead that the starter would not even click.  The 'experts' diagnosed over
and over that the battery simply failed and that the charging system was
fine.  My last break down 2 weeks ago prompted me to look at the wiring
system closer.ÊI changed the alternator and battery in May of 2003 to
prevent this same problem.  I found that the positive charging wire from the
alternator is fed to the starter solenoid.  There the charge line shares the
main cableÊo the positive battery wire.  When I took a resistance test with
my Ohmmeter, I found that I had 3.2 Ohms of resistance from the alternator
post to the positive post on the battery.( I had the negative terminal
disconnected during this test)  I disconnected each connection in the circuit
and cleaned each terminal.  This helped as my battery voltage under high
amperage load was higher but but I still had a reading of 1.8 Ohms
resistance.  I changed the positiveÊattery cable and thisÊeems to have
solved my problem.  Resistance is now down to .1 Ohms.  TheÊtarter spins
faster and the operating voltage is higher.Ê(I installed a voltmeter in the
compartment under the radio to keep an eye on the system.  I tapped the power
off of theÊpower sunroof switch (Brown Positive/Black Negative) directly
below the console.)  The battery cable that I purchased at an aftermarket
retailer was 72' long.  The factory cable has a plastic shield for the cable
that runs over the tranny.  I had to cut off the terminal of the new cable
which connects to the starter to feed it through the plastic shield and
re-crimp a new connection onto it which I purchased atÊardware store.
 
I think the problem is at the battery terminal post which is where corrosion
usually occurs.  Another solution I considered was to bypass the main battery
cable and wire the alternator directly to the battery.  You would need to
disconnect the wire that runs from the alternator to the starter in this
application.
 
You might also get away with changing the battery post connection on the
cable if the cable are long enough.
 
This resistance reading may seem small but if you consider the voltage drop
equation of
 Voltage Drop= Current x Resistance in a 80 amp circuit, it really slows down
the charging circuit.
 
Good luck.
 
Ed
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