Re: Supposedly alternator, but symptoms seem unusual - Saab 900 Bulletin Board - Saabnet.com
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Re: Supposedly alternator, but symptoms seem unusual
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Posted by Eric Law [Email] (more from Eric Law) on Thu, 7 Mar 2002 08:22:02 Share Post by Email
In Reply to: Supposedly alternator, but symptoms seem unusual, KT, Thu, 7 Mar 2002 00:40:00
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KT,
You need to get your multimeter back! That's going to give you your definitive answer.

First thing to do is charge the battery fully. With no load, a fully charged battery will usually produce about 13 volts. Now switch on the headlights. If the battery is strong, you'll still have 12 volts or more.

Now switch off the lights and other bit electrical loads like rear defroster, heater fan, etc. and start the car. You should have no less than 13.5 volts at the battery. If not, either the alternator is bad or the power it's producing isn't making it to the battery - check the grounds, etc.

Last, switch on the headlights, rear defroster, and the heater fan on high (car still running). The voltage at the battery will probably drop a bit to perhaps 12-12.5 volts. Revving the engine up just a bit (2000 rpm) should bring the voltage at the batt. back up to 13.5-14. If not, the alternator may be weak (bad diode, worn brushes), or there could be a voltage drop somewhere - again could be grounds and such.

Easy way to check grounds is to run the engine and load the alternator by turning on the headlights. Use your multimeter and measure 2 voltages: from the alternator housing to the engine block, and from the block to the battery negative terminal. If either exceeds 0.15 volts, you've got a bad connection in the respective circuit.

Eric Law

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