another alternator question
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Joined: Jun 2004
Posts: 73
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From: Hatfield PA
another alternator question
Hey guys-n-gals,
I tried the search, but its hard to search for my specific problem. It goes like this:
When i start the car voltage is always at 12.0 or 12.1 It will sit there for 10-15min and then jump to 14.7 and sit there. It will usually stay at 14.7 the rest of the way to work (another 15min) but sometimes it will drop again to 12v
back and forth. Lowest i've seen is 11.8v but thats only happened a couple times.
problem seems rather random as to when the alt decides to start charging. Doesn't seem to be temp or time or vehicle-speed related.
Should i order a regulator or an alt or a battery from the parts store?
thanks!!
-Mike
I tried the search, but its hard to search for my specific problem. It goes like this:
When i start the car voltage is always at 12.0 or 12.1 It will sit there for 10-15min and then jump to 14.7 and sit there. It will usually stay at 14.7 the rest of the way to work (another 15min) but sometimes it will drop again to 12v
back and forth. Lowest i've seen is 11.8v but thats only happened a couple times.
problem seems rather random as to when the alt decides to start charging. Doesn't seem to be temp or time or vehicle-speed related.
Should i order a regulator or an alt or a battery from the parts store?
thanks!!
-Mike
Melting Slicks
Joined: Dec 2004
Posts: 2,954
Likes: 2
From: Obama=death for America
You should always do the cheapest things first when trying to fix a problem. The first thing I'd check and obviously the cheapest, is to check your battery cable connections. Make sure all the cables are good and tight. Make sure you check the cable that's attached to the starter.
After that, you can test the battery with a battery tester. If you don't have one, you can bring your battery to Autozone or somewhere that checks batteries and they can tell you if it's fully charged, etc. If not, that's your problem. The regulator is internal, so forget that. If the battery checks out, I'd suspect the alternator has gone bad.
12.0 V is a bit low. Anything under 12 V is definitely low. 14.7 V is a bit high. The best numbers that you'd want to see are approximately 13.8 V to 14.2 V. That's the perfect situation, but it depends a lot on what you're running. If you have your A/C, lights, radio, wipers, etc. on, your reading is expected to be a bit low due to the demand, but that's what the alternator is for. I suspect from what you're describing that your regulator went or is going and your alternator needs to be replaced.
After that, you can test the battery with a battery tester. If you don't have one, you can bring your battery to Autozone or somewhere that checks batteries and they can tell you if it's fully charged, etc. If not, that's your problem. The regulator is internal, so forget that. If the battery checks out, I'd suspect the alternator has gone bad.
12.0 V is a bit low. Anything under 12 V is definitely low. 14.7 V is a bit high. The best numbers that you'd want to see are approximately 13.8 V to 14.2 V. That's the perfect situation, but it depends a lot on what you're running. If you have your A/C, lights, radio, wipers, etc. on, your reading is expected to be a bit low due to the demand, but that's what the alternator is for. I suspect from what you're describing that your regulator went or is going and your alternator needs to be replaced.
Melting Slicks
Joined: Feb 2001
Posts: 2,512
Likes: 5
From: ZR1 Gathering '04, '05 Northlake Texas
What I would do, after having the battery checked, is take the alternator out and get it tested. They should be able to tell you in 5 minutes if your alternator is defective. And from what you say, I bet its the alternator.
Race Director
Joined: Jul 2004
Posts: 16,795
Likes: 62
From: Lake Havasu City, AZ
Hmmm, sounds just like my problem.
I took ot to Autozone and they hooked up a Baer charging system diagnostic device. Had to run at 2000 rpm for a minute or so then let it idel. they confirmed the battery was good, but the alternator had a bad diode pattern.
Now I'm planning to rebuild it.
I took ot to Autozone and they hooked up a Baer charging system diagnostic device. Had to run at 2000 rpm for a minute or so then let it idel. they confirmed the battery was good, but the alternator had a bad diode pattern.
Now I'm planning to rebuild it.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
Have you compaired the readings from the onboard gauge to a voltmeter?
Mine reads a coupla tenths low.
Take note that the alternator powers the car's systems and the excess is used to top off the battery. WHen the power demands of the car go up, the alternator is compensating to deliver that power requirement.
Are the fans kicking on? A/C, lights, radio on?
Try sitting in the driveway and cycle all these items and check to see what items make the changes. Also if you have underdrive pulleys this can cause issues when there is lots of idling time.
Mine reads a coupla tenths low.
Take note that the alternator powers the car's systems and the excess is used to top off the battery. WHen the power demands of the car go up, the alternator is compensating to deliver that power requirement.
Are the fans kicking on? A/C, lights, radio on?
Try sitting in the driveway and cycle all these items and check to see what items make the changes. Also if you have underdrive pulleys this can cause issues when there is lots of idling time.
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