15.5+ Volts - normal/acceptable?
Thread Starter
Race Director
Joined: Oct 2000
Posts: 11,891
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From: Kansas City, MO ...I'd like to go fishing and catch a fishstick. That'd be convenient. - Mitch Hedberg
15.5+ Volts - normal/acceptable?
I just replaced my alternator with one from Advanced Auto Parts. The alternator was putting out 15.81V according to my multimeter. I didn't like that so I had them get another one. The parts guy tested the new one at the store and the output was 15.5V. Then he tested the one I was returning at 15.5V. He told me that 13-16V is normal operating range. I didn't like the voltage being that high. I know the system is designed to run at 14.4V and that's what I expected from the new alternators. I returned it and drove to O'Reilly's and ordered a new one from them. I will have it on Thursday. (rear defrost=oddball alternator)
Was I wrong to return it? Is 15.5V acceptable?
Was I wrong to return it? Is 15.5V acceptable?
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
In my limited experience 15+V is too high and will cook a battery in no time at all.
Have them test the new alt at Oreilly and see what voltage it puts out under load.
What brand was the one you bought and returned twice?
Have them test the new alt at Oreilly and see what voltage it puts out under load.
What brand was the one you bought and returned twice?
Burning Brakes
Joined: May 2007
Posts: 945
Likes: 0
From: Ventura California
15.5 is high. However, the regulator will function when connected to the battery.. Many of the testers that are used place no load on the alternator and just see simple voltage output. I'd be willing to bet the 15.5 alternator would put out less than that when connected to your battery. If the regulator sees no resistance to amps (such as on a bench test), it will put out a bunch. Living on a sailboat with 4 200 pound lead acid batteries has taught me a bit. If you DO get 15.5 going to the battery when connected, just know you've got a problem. That will "gas" the batteries. The electrolite will boil and it will be done.
Melting Slicks
Joined: May 2007
Posts: 3,246
Likes: 4
From: Bay Area CA
15.5 is high. However, the regulator will function when connected to the battery.. Many of the testers that are used place no load on the alternator and just see simple voltage output. I'd be willing to bet the 15.5 alternator would put out less than that when connected to your battery. If the regulator sees no resistance to amps (such as on a bench test), it will put out a bunch. Living on a sailboat with 4 200 pound lead acid batteries has taught me a bit. If you DO get 15.5 going to the battery when connected, just know you've got a problem. That will "gas" the batteries. The electrolite will boil and it will be done.
I just replaced my alternator with one from Advanced Auto Parts. The alternator was putting out 15.81V according to my multimeter.
13.8 is what cars are speced to run at. 15.5, you could claim dammages if something fried. looked at my pioneers voltage specs, it says 14.4 nominal, 15.1 MAX.
Last edited by RunningMan373; Sep 26, 2007 at 03:37 AM.
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Brett Foote
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
The very most you should ever get under any circumstances is 14.7 volts, and if the bat is good, that will last all of maybe 15 seconds, and drop back to under 14 volts, then down to the 13.3-13.5 running voltage.....anything else is messed up....
Advanced
Joined: May 2006
Posts: 89
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From: Derby Kansas
If you are using a digital meter, which I think you are since you say 15.81V, beware. I recently replaced my alternator and was showing over 15.7 volts with the digitial meter, but when I checked the voltage with my 30 plus year old meter, it showed right at 14.5. Ended up the digital meter was no good.
-Jim
-Jim
Team Owner
Joined: Aug 2006
Posts: 24,125
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From: Columbia Missouri
If you are using a digital meter, which I think you are since you say 15.81V, beware. I recently replaced my alternator and was showing over 15.7 volts with the digitial meter, but when I checked the voltage with my 30 plus year old meter, it showed right at 14.5. Ended up the digital meter was no good.
-Jim
-Jim
He said the parts store tested the same alternator and even they tested it with 15+V.
Race Director
Joined: Nov 1999
Posts: 10,643
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From: Foxfield CO 1970 Convertible
I'm going to side with the "that's too high" crowd on this one... 
I didn't know pioneers had batteries... 
Melting Slicks
Joined: May 2007
Posts: 3,246
Likes: 4
From: Bay Area CA
the only thing that's going to be affected in a car this old is the modern electronics and matbe the HEI if he has one. Still can't figure out what you find so funny about the comment though, what standard are you using, or are you just kinda figur'in?
Last edited by RunningMan373; Sep 27, 2007 at 04:51 PM.
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
13.6-14.4 volts is normal to prevent the lights from blowing out or any thing that is 12 volt rated including your radio. The alternator is charging correctly but the regulator is not functioning to limit the alt to 14.4. Early C3`s have a external regulator and later has the internal regulated system. Ither way the regulator is bad and allowing the alt to max out at the 15+ volts your registering. Diagnosis is to replace the regulator....
Thread Starter
Race Director
Joined: Oct 2000
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From: Kansas City, MO ...I'd like to go fishing and catch a fishstick. That'd be convenient. - Mitch Hedberg
I'm not replacing the regulator in a brand new part. That's why I purchased another from a different store. I'm picking up the new one tonight on my way home from work. Hopefully it will work fine and I'll be able to drive my car to work.
Drifting
Joined: Apr 2007
Posts: 1,970
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From: Cameron Park CA
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
GM alternators were externally regulated until 1973. 1973 was the first year for the internal regulated alternators. Also 1972 was the first style of case changes to a ribbed rear case, but still externally regulated although it had the same appearance as only the plug was different appearance wise.,,,,,.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
GM alternators were externally regulated until 1973. 1973 was the first year for the internal regulated alternators. Also 1972 was the first style of case changes to a ribbed rear case, but still externally regulated although it had the same appearance as only the plug was different appearance wise.,,,,,.
Pete