Alternator Problems - Any Ideas?
08-16-2009, 03:42 PM
#1
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The alternator in my car wasn't charging the battery and had caused my car to die on me at a drive-through a couple days ago. I ran some voltage tests to confirm it was the alternator and not the battery that was faulty.
The voltage across the battery terminals was (after charging with a good battery) approx. 12.5v with the car off. Once I started the car and idled it for a bit, the voltage started to drop, then really started to fall off once i started turning on accesssories.
The voltage dropped as low as about 6 before the battery ran out of juice and the car shut off.
Yesterday I went and got a rebuilt alternator from a shop my family's trusted mechanic recommended. In hindsight I should have had it tested at PartSource on the way home with it but I figured if my mechanic had recommended him his work must be legit.
Now I've swapped out the old alternator and dropped in the rebuilt, but I'm still having charging issues. The battery will hold a charge after i boost it with another battery, but it's not being recharged by the alternator, as evidenced by the voltage dropping during idle.
I also tried disconnecting the negative battery terminal with the car on and it quit right away, so it looks like juice just isn't coming from the alternator.
Does anyone have any other ideas of what the problem might be? I'm heading out right now to get another multimeter (fried mine today in a moment of stupidity) and I plan on testing the voltage at the alternator rather than the battery. Anything else I could try?
I'm heading up to a cottage on Wednesday so if I can't get this sorted out by tomorrow I'm gonna cave and go get my pockets pilfered by a shop to fix this problem.
The voltage across the battery terminals was (after charging with a good battery) approx. 12.5v with the car off. Once I started the car and idled it for a bit, the voltage started to drop, then really started to fall off once i started turning on accesssories.
The voltage dropped as low as about 6 before the battery ran out of juice and the car shut off.
Yesterday I went and got a rebuilt alternator from a shop my family's trusted mechanic recommended. In hindsight I should have had it tested at PartSource on the way home with it but I figured if my mechanic had recommended him his work must be legit.
Now I've swapped out the old alternator and dropped in the rebuilt, but I'm still having charging issues. The battery will hold a charge after i boost it with another battery, but it's not being recharged by the alternator, as evidenced by the voltage dropping during idle.
I also tried disconnecting the negative battery terminal with the car on and it quit right away, so it looks like juice just isn't coming from the alternator.
Does anyone have any other ideas of what the problem might be? I'm heading out right now to get another multimeter (fried mine today in a moment of stupidity) and I plan on testing the voltage at the alternator rather than the battery. Anything else I could try?
I'm heading up to a cottage on Wednesday so if I can't get this sorted out by tomorrow I'm gonna cave and go get my pockets pilfered by a shop to fix this problem.
08-16-2009, 06:38 PM
#3
Super Moderator
A conventional lead-acid battery drawn down below 10V is pretty much toast, or at least severely damaged, even if it will still take a charge. Go to any major auto parts chain store and they should be able to test the charging system for you, free, right then & there.