Charging system help.
Thread Starter
Heel & Toe
Joined: Jan 2011
Posts: 18
Likes: 0
From: Lombard Illinois
Charging system help.
I noticed last week that my battery gauge had been fluctuating up and down a bit. I had a new alternator installed about two weeks ago. When I sit idle for say 4-5 minutes, the volts start dropping fairly low, but not low enough for the low battery light to engage. For me, this doesn't seem normal, as I've been constantly looking at the gauge ever since I was stranded. So this doesn't seem like an alright thing, any help or suggestions? The battery is over a month old by now. Thanks.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
If the cluster is reading below 12volts when at idle - you got problems. It is very normal for the "voltage" shown on the cluster to drop off a bit once everything heats up but again if the cluster is reading below 12volts when at idle - you got problems.
Race Director
Joined: Aug 2002
Posts: 13,356
Likes: 0
From: tucson AZ
St. Jude Donor '04 & '05
have you changed your rpm any. mine if i have accessories on drops down at idle to around 11/12..started after i installed a pulley system and new 120 alternator...i just live with it...
Last edited by oldace84; Mar 18, 2011 at 07:29 PM.
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
mine never goes below 12.6-7 , a good place to look would be the small ground that goes from your - battery post to the frame, specially if you've just changed batt and alt. if every thing looks good run ground from your batt.- to the alt. mount. it doesnt have to be much of one , if your voltage improves , its a ground issue, replace the ground wire and clean the mounting surface, a crudded up ground wire will add major resistance. if it doesnt , its usually a voltage regulator issue. hope this helps.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
I guess it depends on how loaded (amps) the alternator is with all the accessories "on"....."super duper" stereo components or failing accessories with high amp draws don't help either.
If you had a real problem you'd have issues once you went to restart the car.
You could pull the alternator off and have the output tested at you local autoparts store(most will test for free off the car-some might test for free on the car though).
I run AC delco (new or remy) alternators as they seem to have a lower failure rate as compared to the other brands.
If you had a real problem you'd have issues once you went to restart the car.
You could pull the alternator off and have the output tested at you local autoparts store(most will test for free off the car-some might test for free on the car though).
I run AC delco (new or remy) alternators as they seem to have a lower failure rate as compared to the other brands.
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Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
Here is what is normal. Idle speed should not be lower than 700 rpm, if it is, it could be the reason why your alternator cannot keep constant output voltage. Engine cold and normal electrical load, the dash voltmeter should read about 14.3 volts. The alternator output voltgage drops as it warms up and at its operating temperature, your dash voltmeter should be about 13.7 volts and steady. Wandering voltage and below 13.0 volts and I would suspect the alternator, new or not!
