I actually get 14.7 at times
alternator output
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,146
Likes: 9
From: Troy Ohio
alternator output
What should i be reading at the battery when I measure voltage with the car running. I suspect my alternator is going south. It measures 13 - 13.5 volts when the car is running. Should it be closer to 14 volts? Everything went dim last night and blew the gauge fuse. This is the second time this has happened in a couple of months. Fuse blows, then I lose A/C, and torque converter lock up. But this time didnt seem to be charging right. 
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,146
Likes: 9
From: Troy Ohio
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
The voltage will depend on the state of the battery and how much current you are demanding. Anything over 13 is charging.
Turn the high beams on and the AC fan to hi and then tell us what the voltage is.
Turn the high beams on and the AC fan to hi and then tell us what the voltage is.
Last edited by MK 82; Jun 20, 2010 at 07:24 PM.
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,146
Likes: 9
From: Troy Ohio
Last night as I was pullin up to the house with high beams on a/c off cause fuse was blown I flipped on the dash gauge and it was at 8 volts. Wierd that it metered out at 13 today though.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
Check the alternator and battery terminals and make sure they are clean and tight. Charge the battery tonight. Check the voltage in the morning after warm up with and without accessory load.
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Melting Slicks
Joined: May 2010
Posts: 2,082
Likes: 3
From: Conowingo Maryland
A couple of things check the voltage at the out put terminal of the alt, then check it at the battery, and then what it is reading on the gauge there should not be a 1/2 a volt difference between the 3. Pull the positive term off the battery while the car is running and see what your voltage is then should be right around 13.5 to 14.5. But I do not think this is what is causing your fuse to blow. fuse are a safe guard for excessive amps. I think your fuse blowing must likely is lock up related or A/C related. lockup selonoids have had problems with shorting out. and A/C clutches are also know for high amp draw as the get older. Could also be a short in either of these areas.
Le Mans Master
Joined: Jul 2007
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From: No HOA, New Hampshire
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St. Jude Donor '09
I would never disconnect a battery or alternator while the engine is running. Invest in a new battery and an alternator ($200) for the peace of mind.
Keep that 35th on the road where it belongs.
Melting Slicks
Joined: May 2010
Posts: 2,082
Likes: 3
From: Conowingo Maryland
paksr I am lost you would throw 200 in parts with out even trying to dianose the problem and most likely have nothing to do with the blown fuse. checking the voltage at the 3 spots I suggested is just a fast way to look for voltage drops at a couple of major places. disconnecting the positive cable while running takes all the vehicle load off the alt giving you what the alt is putting out ie a bench test to the vehicle. I have been doing these tests for 33 years and never once caused a problem. They are also taught in basic automitive electronics and even in some form of questing on ase testing
Instructor
Joined: Aug 2009
Posts: 146
Likes: 0
From: Broadway Virginia
FWIW, I always get a direct battery reading which is .3 volts higher than what the dash gauge reads.
I also would NOT pull the Positive terminal with the engine running.....too much Voodoo.
I also would NOT pull the Positive terminal with the engine running.....too much Voodoo.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
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From: backwoods upstate ny
last week, local 'asse certified' hero said he needed to charge his boat batt and started his truck, pulled batt cables off truck batt to switch boat batt in, few seconds later with no batt in the truck quit, won't restart...hero thinks the ecm is toast, no idea why sudden death.
shirt-tail relative bought a gorgeous 02 caddy a couple months ago for stupid low price, MIL was on (failed state inspection), dash lights all wacky, started good but ran rough, and numerous other probs...PO was told by his mechanic that it needed $4000 repairs, maybe more...first repair we did was a new $95 (list price, not actual) batt, everything except a few dark bulbs went back to showroom condit.
your horse, you can put the saddle on facing front or rear as you choose.
shirt-tail relative bought a gorgeous 02 caddy a couple months ago for stupid low price, MIL was on (failed state inspection), dash lights all wacky, started good but ran rough, and numerous other probs...PO was told by his mechanic that it needed $4000 repairs, maybe more...first repair we did was a new $95 (list price, not actual) batt, everything except a few dark bulbs went back to showroom condit.
your horse, you can put the saddle on facing front or rear as you choose.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
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My in-car gauge is about .5 V different from actual, so don't trust the in-car gauge.
It should be about 14.0-14.5 when the car is cold, as it heats up it'll drop into the 13s.
It should be about 14.0-14.5 when the car is cold, as it heats up it'll drop into the 13s.
Melting Slicks
Joined: May 2010
Posts: 2,082
Likes: 3
From: Conowingo Maryland
Vader that is what I was talking about. When you say actual you are getting a reading from the batt or back of the alt. If you were seeing a volt or more and I was having problems that is when I was looking backwards.
I will stand by the testing of unhooking the post for testing and also that fact that it would not hurt a thing. There is no vooodoo no majic or stranges things going to happen it is a field test and a simple way to bench test an alt....
I will stand by the testing of unhooking the post for testing and also that fact that it would not hurt a thing. There is no vooodoo no majic or stranges things going to happen it is a field test and a simple way to bench test an alt....
