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Battery Drain & 14.56volts at the Alternator

2K views 8 replies 6 participants last post by  twistedshadows 
#1 ·
my 1997 T9000 CS has a battery drain. It starts and runs fine. let it sit over night for 2 days (with alarm activated and doors locked) and the battery will be completely drained. Followed procedure in my book to measure alternator output to the battery while car is running and we got 14.56 volts (I think normal is more like 13.0 - 13.5). I suspect something at the alternator is out of whack (maybe voltage regulator has stopped regulating)?

I wanted to solicit an opinnion before my buddy and I go thru the work of pulling out the alternator and replacing.

Any thoughts would be appreciated.
 
#2 ·
On my 97 Aero the temperature gauge/radiator fan switching program in a ECU in the instrument panel failed. This caused the cooling fan to switch on at random moments whether the engine was running or not. Because no one was present when the cooling fan went on the resulting flat battery was a mystery. Even the mechanics were stumped.


The bad news is the failed part is very expensive. So, my mechanic bypassed the cooling fan circuit and hooked it up as for previous models so the cooling fan cannot run if the ignition is off.

One symptom was a temperature gauge that fails to read properly, the needle jumps around from "off" to normal temperature. The other symptom was the voltage display was inaccurate.

You seem to have excessive voltage at the battery so this my not be relevant to you. If the voltage at the alternator is too high then the diodes are going in the internal voltage regulator.
 
#3 ·
BATT DRAW..disconnect the neg. batt. terminal, put a test light between the neg. batt. post and the neg batt terminal, pull your fuses one at a time to find the guilty circuit then trace from there (don't forget the fuses inside the car)...it may be over charging trying to bring the batt back to life (13.5-14.8v is a general spec--anything over 15v would be a cause for alarm but 14.5 is fine)..remember the car is an AC system (alternating current so it will change)
 
#4 ·
no the car is a direct voltage system.
the alternator creates ac current then converts it to dc current before it leaves the alternator.
so only inside the alternator is there ac voltage.
u may want to get ur battery tested.
bad batterys may hold voltage for a few hours but slowly drain down to a lower voltage. (keeps happening on my moms toyota camery her car kills batterys on a yearly basis and we cant figure out why so we just gave up on it and just shell out the money every year to replace it)
like superaero said 14.5 volts is normal, but as the battery charges it should drop down to about 12.5-13.5 so the battery may be bad.
also superaeros idea to pull all the fuses and install 1 at a time to figure out what may be cause the battery to drain is a good idea.
but there are a few systems in the car which are always on so they will draw voltage no matter what.
like the alarm and radio.
hope this helps
joe
 
#5 ·
Above poster has a good start point. have the batt- when fully charged load tested to see if it is at fault and not holding charge. Hook and watch your multimeter #'s when turning electricals on and of to see the performance of the alternator.
 
#6 · (Edited)
I've tried 2 different batteries and the car has completely drained them both in 2 days of sitting. It's possible that I had 2 bad batteries, but unlikely (since the other one's sitting in my old car and running pretty normal now).

Can someone give me the drainage test procedure again (S...L...O...W...L...Y)

(1) Disconnet neg. battery terminanal
(2) Set multimeter to.......(volts? Ohms?) and place inbetween Neg cable & neg
terminal. (Question: what should the reading be normally?)
(3) then pull each fuse/relay? and look for significant drops?

Is this correct?
 
#7 ·
if ur are using a multimeter set it to volts.
remove all of the fuses from the car (under the hood and in the glove box).
place the multimeter between the negative terminal and connection.
start installing the hood fuses till u see one that causes the multimeter to read some voltage (ull will see anywhere between 5v and 12v depending on the system)
write down what system is drawing power.
then remove that 1 fuse (if any) and leave the rest in the hood fuse box and start installing fuses 1 at a time in the glove box untill u get a reading.
once again write down what system its a part of.
then post up ur results so we can help u trace down the problem.
joe
 
#8 ·
Surely placing a multimeter set to volts in line with the circuit (negative cable to negative terminal) will blow the multimeter when you put a fuse in as it will take all the current for that circuit. I would have set it measure current, you can only measure voltage drop across a device (in parallel to it) rather than in series with a cabel in a circuit.

If you're measuring amps, you will get a reading of how much energy that circuit is drawing which will tell you which circuit is draining the battery when the ignition is off.
 
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