Is 12.7 volts while the car running okay?
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From: Lithia FL
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Is 12.7 volts while the car running okay?
I never realized what normal is. My C4 is around 14 volts when the car is running but my C5 is reading 12.7 when the car is running :confused:
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Joined: Feb 2000
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From: Carrollton Texas
Re: Is 12.7 volts while the car running okay? (REDGAR)
A fully charged battery will put out 2.2 volts per cell or 13.2 volts. While the car is running the alternator should put out in eccess of that number of volts. Anything less is unacceptable and requires repair. Hope this answers your question.
Melting Slicks
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From: Central NJ
Re: Is 12.7 volts while the car running okay? (REDGAR)
Edgar, put a meter across the battery w/ the engine running. You should have at least 13.8 volts, if not further diagnosis will be required. If you're going to be around tomorrow night(Friday) I could bring over some test equipment and tell ya what's wrong...
Artie
Artie
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Re: Is 12.7 volts while the car running okay? (NJVetteGuy)
I agree. It takes at least 13.8 v to charge the battery, below that you add nothing. With an indicated 12.7 you will ultimately end up with a dead battery after a few starts.
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Re: Is 12.7 volts while the car running okay? (REDGAR)
REdgar,
In the late 80's/early 90's I owned a generator shop, a rule of thumb is 13.6-14.2 volts at idle, sounds like a blown diode in the alternator.
In the late 80's/early 90's I owned a generator shop, a rule of thumb is 13.6-14.2 volts at idle, sounds like a blown diode in the alternator.
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Re: Is 12.7 volts while the car running okay? (NJVetteGuy)
Hey Artie thanks for the offer.
Here is an update. This morning before starting, the DIC read 10.8.
Then after starting it read 13.4
After 10 minute drive to work running it read 13.0
I was late for a meeting so I did not check what it read with he car off.
I may be taking the to the Vette Doctors for something else this weekend. I will let them test the alternator.
Thanks
Here is an update. This morning before starting, the DIC read 10.8.
Then after starting it read 13.4
After 10 minute drive to work running it read 13.0
I was late for a meeting so I did not check what it read with he car off.
I may be taking the to the Vette Doctors for something else this weekend. I will let them test the alternator.
Thanks
Melting Slicks
Joined: Sep 2000
Posts: 2,756
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From: Satellite Beach, FL, USA
Re: Is 12.7 volts while the car running okay? (REDGAR)
The GM alternator has a partial failure mode where it will not put out full power. It has happened in my C2500 twice so far. Many times the voltage will read >13.5 volts, but the engine and accessories will hog all the current that the alternator can supply and thus the battery gets starved for charging current.
Many dealer techs cannot tell the difference between a weak alternator and bad battery. Mine used a standard electronic test tool that diagnosed my battery being bad, when I knew it was the alterator. It took a lot of arguing to get my alternator replaced instaed of my battery. Ther only way to truly test an alternator is with a voltmeter AND an ammeter .
Many dealer techs cannot tell the difference between a weak alternator and bad battery. Mine used a standard electronic test tool that diagnosed my battery being bad, when I knew it was the alterator. It took a lot of arguing to get my alternator replaced instaed of my battery. Ther only way to truly test an alternator is with a voltmeter AND an ammeter .
Melting Slicks
Joined: Oct 2001
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From: Central NJ
Re: Is 12.7 volts while the car running okay? (REDGAR)
Here is an update. This morning before starting, the DIC read 10.8.
Then after starting it read 13.4
After 10 minute drive to work running it read 13.0
I was late for a meeting so I did not check what it read with he car off.
Thanks
Then after starting it read 13.4
After 10 minute drive to work running it read 13.0
I was late for a meeting so I did not check what it read with he car off.
Thanks
Artie
Melting Slicks
Joined: Sep 2000
Posts: 2,756
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From: Satellite Beach, FL, USA
Re: Is 12.7 volts while the car running okay? (NJVetteGuy)
Sounds like your battery is bad, if the DIC is correct. At 50 degrees ambient you should have read more voltage than the DIC displayed. Verify the DIC is correct, if so I'd start with a battery. The bad battery may have also caused your alternator to try and put out too much current to charge the battery, and put the alt. into partial failure mode. Looks like it could be an expensive weekend...
Artie
Artie
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From: Austin TX
Re: Is 12.7 volts while the car running okay? (99HT)
> This morning before starting, the DIC read 10.8.
> Then after starting it read 13.4
I agree with the others.....sound like a weak sister battery to me. I have been round and round with my dealer on the AGM battery. They did replace an alternater and that helped but the battery was about 11.2 or 11.3 volts in the morning before starting the car. GM will not authroize battery replacement until it fall below 10.5 volts. Your is right on the edge. BTW, when you fire up the engine it should show 14.1 or 14.2 volts then fall back to 13 point something.
I begain to suspect a battery problem when the head light and DIC would dim under loads like the brake pedel or pushing the UP button on the windows.
As part of having my engine replaced I told them to install a fresh brand new battery. It will be interesting to see if the lights still dim. It was either a weak sister battery or a bad ground connection. God only know what will happed with the ground connections during the engine transplant in process this week.
> Then after starting it read 13.4
I agree with the others.....sound like a weak sister battery to me. I have been round and round with my dealer on the AGM battery. They did replace an alternater and that helped but the battery was about 11.2 or 11.3 volts in the morning before starting the car. GM will not authroize battery replacement until it fall below 10.5 volts. Your is right on the edge. BTW, when you fire up the engine it should show 14.1 or 14.2 volts then fall back to 13 point something.
I begain to suspect a battery problem when the head light and DIC would dim under loads like the brake pedel or pushing the UP button on the windows.
As part of having my engine replaced I told them to install a fresh brand new battery. It will be interesting to see if the lights still dim. It was either a weak sister battery or a bad ground connection. God only know what will happed with the ground connections during the engine transplant in process this week.
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From: Lithia FL
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Re: Is 12.7 volts while the car running okay? (Dick Kriss)
> I begain to suspect a battery problem when the head light and DIC would dim under loads like the brake pedel or pushing the UP button on the windows.
Thanks all
