Voltage Question
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AutoX
Joined: May 2001
Posts: 10
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From: CHICAGO
Voltage Question
I realize this is the 911 forum and I own an 86 911 turbo but I get quicker responses from here.Nothing against the turbo forum. I was told when I did my ppi that I would need an alternator and that it was only charging at 12.5V. Since I have gotten the car,I have replaced the battery with a new one. Now it's charging at 13.97V. Is this normal voltage or am I going to have to RR the alternator? Thanks for any info. Terry Also the old battery was 4 yrs old and would not hold a charge.
AutoX
Joined: Apr 2002
Posts: 12
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From: London, England
4 years old is plenty for a lead acid car battery. I've found they tend to start giving up after about 3 years with problems like not starting or turning the engine over slowly in cold mornings. Its difficult to say if a battery is absolutely ok just with a voltmeter unless you can put the battery under load at the same time as measuring the voltage like they can do at battery retailers - but these are some general rules:
12.5v is low but 13.97 is spot on when the engine is running at idle. If you increase the engine rpm to 2000 plus you shouldn't see (much) more than 14.5 volts. With the readings you have all appears ok now.
When the engine is not running expect some voltage above 12 at the battery terminals, probably in the 12.2 to 13v range. 12v and below indicates a flat battery including a tired one like you had.
Hope that helps and if there is going to be a problem you'll find out the next time you try to start it in the morning!
Viv
911 Carrera 3.2
12.5v is low but 13.97 is spot on when the engine is running at idle. If you increase the engine rpm to 2000 plus you shouldn't see (much) more than 14.5 volts. With the readings you have all appears ok now.
When the engine is not running expect some voltage above 12 at the battery terminals, probably in the 12.2 to 13v range. 12v and below indicates a flat battery including a tired one like you had.
Hope that helps and if there is going to be a problem you'll find out the next time you try to start it in the morning!
Viv
911 Carrera 3.2
Intermediate
Joined: Apr 2002
Posts: 34
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From: Orlando
I agree that it sounds like your alternator is good. I'll bet that your old battery had a nearly shorted cell in it that was "dragging down" the alternator. BTW, did you get an Optima gel battery? Those are awesome and you should keep one in mind for your next replacement if you don't have one already.
