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Old 01-25-2011, 08:50 PM   #1
Mr Pops
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Is 12.2 volts normal at idle with ALL loads on?

Ok, so I know a fully charged battery is 12.66 volts, so I realize that I'm draining my battery if my alternator charges at any less than that. What I'm wondering is if it's normal for my voltage to drop down to 12.2 with the truck in drive, at idle, with headlights on, (highbeams and fog lights) heater fan on high and wipers on? This is on my 1990 Chevy crewcab, thanks for any comments.
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Old 01-25-2011, 09:09 PM   #2
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Re: Is 12.2 volts normal at idle with ALL loads on?

Where are you getting that voltage at? Directly at the alternator or on the battery? You should be close to 14v at the alternator.
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Old 01-25-2011, 09:12 PM   #3
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Re: Is 12.2 volts normal at idle with ALL loads on?

Quote:
Originally Posted by N2TRUX View Post
Where are you getting that voltage at? Directly at the alternator or on the battery? You should be close to 14v at the alternator.
Voltmeter on the battery terminals. It charges fine while I'm driving, just not at a stop in gear with EVERYTHING on..
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Last edited by Mr Pops; 01-25-2011 at 09:14 PM.
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Old 01-25-2011, 10:15 PM   #4
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Re: Is 12.2 volts normal at idle with ALL loads on?

Sounds like the low side of your alternator might be out or weak. I would check it at the output of the alternator. If you don't have more than 13v you should consider getting the alternator load tested.
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Old 01-25-2011, 10:19 PM   #5
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Re: Is 12.2 volts normal at idle with ALL loads on?

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Originally Posted by N2TRUX View Post
Sounds like the low side of your alternator might be out or weak. I would check it at the output of the alternator. If you don't have more than 13v you should consider getting the alternator load tested.
Hmm.. might be a good time to upgrade to a higher output one anyway, since I want to add some work lights, driving lights and a better stereo. I got a guy who will build me a 100amp alternator for $100.
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Old 01-25-2011, 10:28 PM   #6
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Re: Is 12.2 volts normal at idle with ALL loads on?

That's not a bad idea, but I would confirm that your Alt is bad first. I don't want to suggest that's the problem and its another issue. Thats not a bad price for a 100amp.
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Old 01-26-2011, 12:10 AM   #7
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Re: Is 12.2 volts normal at idle with ALL loads on?

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That's not a bad idea, but I would confirm that your Alt is bad first. I don't want to suggest that's the problem and its another issue. Thats not a bad price for a 100amp.
Yeah, I think I'll get it bench tested like you said, or test it at the alternator instead of at the battery to see if i got a bad cable..
As far as a new one goes, I was told that you can't really go bigger than 100amp without going to a bigger core. I put a 100amp alternator in my Blazer to help keep up with the 12v air compressors, and that seemed to help a bit. I'm actually thinking of having on board air on my crewcab too so I can have a mobile air tank for fixing tires while out in the boonies, I also have an air horn thats waiting to be installed..
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Old 01-26-2011, 11:27 PM   #8
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Re: Is 12.2 volts normal at idle with ALL loads on?

The short answer is NO.
12.2 volts is too low. Should be in the range between 13.5 and 14.6 volts.
The stock alternator in that vehicle IS rated 100 amps, and is easily capable
of 70 amps output at IDLE speed.
The most likely failure for the CS130 alternator is an open diode. they will make partial output for awhile, before complete failure.
Look in the yellow pages, under auto electric, probably a shop nearby that can load test (free of charge, generally) and will repair or rebuild your alternator.
Don't bother uprating that particular alternator, 100 amps is plenty for heater and headlights.

Last edited by Fullpower; 01-26-2011 at 11:28 PM.
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Old 01-27-2011, 12:07 AM   #9
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Re: Is 12.2 volts normal at idle with ALL loads on?

Quote:
Originally Posted by Fullpower View Post
The short answer is NO.
12.2 volts is too low. Should be in the range between 13.5 and 14.6 volts.
The stock alternator in that vehicle IS rated 100 amps, and is easily capable
of 70 amps output at IDLE speed.
The most likely failure for the CS130 alternator is an open diode. they will make partial output for awhile, before complete failure.
Look in the yellow pages, under auto electric, probably a shop nearby that can load test (free of charge, generally) and will repair or rebuild your alternator.
Don't bother uprating that particular alternator, 100 amps is plenty for heater and headlights.
Thanks for the info, it was very helpful guys.
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