Alternator voltage
#1
Alternator voltage
I'm wondering if my alternator/voltage regulator is going bad. My '88s4 has 106K miles on it with, I believe the original alternator. Normally the gauge shows a maximum of 12 volts, never charges any higher than that, but I noticed that with the A/C on at idle it drops to 10volts - or below that if I turn anything else on. It does go back up to 12 when driving and everything seems to work fine but it seems odd that the voltage would drop that low. I've had other cars that will charge the battery at 13 or 14 when the battery is low or there is a heavy electrical load. Is the 10-12 volt range normal?
#2
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Dear Andy,
You have to measure across the battery with a multimeter. Do not take any real notice of battery indicators. You may find the voltage readings are confirmed which means you need a new alternator.
After 2 mins after start, giving battery a chance to recover, the voltage across the alternator should be a minimum of 13.8VDC to say 14.4VDC (too much for me but I have seen them this high).
If you have less than 13.8VDC then you will have troubles. 12.4VDC and the like can only mean one of two things. Alternator/Regulator is the battery has shorted cells and will not take a charge.
You have to check across the battery terminals though. The internal battery indicator should also show 13.8VDC if it is correct unde rnormal driving conditions. With Everything burning and turning around 13.2VDC is normal. However I mean everything is powered up, lights, aircon everything,
Ciao,
Adrian
911C4
944
You have to measure across the battery with a multimeter. Do not take any real notice of battery indicators. You may find the voltage readings are confirmed which means you need a new alternator.
After 2 mins after start, giving battery a chance to recover, the voltage across the alternator should be a minimum of 13.8VDC to say 14.4VDC (too much for me but I have seen them this high).
If you have less than 13.8VDC then you will have troubles. 12.4VDC and the like can only mean one of two things. Alternator/Regulator is the battery has shorted cells and will not take a charge.
You have to check across the battery terminals though. The internal battery indicator should also show 13.8VDC if it is correct unde rnormal driving conditions. With Everything burning and turning around 13.2VDC is normal. However I mean everything is powered up, lights, aircon everything,
Ciao,
Adrian
911C4
944
#4
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As others have mentioned, the real test of alternator output is to measure at the battery or at the alternator output.
The voltage guage on 928s are notorious for giving low readings - usually due to increased resistance from aging of the wiring harness, instrument pod circuit board connection and within the guage itself.
The voltage guage on 928s are notorious for giving low readings - usually due to increased resistance from aging of the wiring harness, instrument pod circuit board connection and within the guage itself.