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Test alternator on car?

 
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  #1 (permalink)  
Old 04 Jan 2020, 12:40 am
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Default Test alternator on car?

'10 PT Cruiser NA
Can anyone point me at how to test the alternator ON the car (since it's so much work to remove it)?
I've been to the FLAPS & had them test the charging system & battery (battery replaced under warranty). Tests fine, charges fine. No key in the ignition, I threw a test light across the battery post & cable end, and it lit up brightly. That means I have a drain, right? I've pulled every fuse & the light continued.
I was wondering if the problem could be that the alternator itself it causing the drain. (I had this happen with an alternator fresh from the FLAPS 20 years ago) Bad diode? Rectifier? Is that the right diagnosis I am thinking of? If so, how do I prove it? I am tempted to go to the local UPULL lot & snag an alternator, but again, it's so hard to R&R the alternator, I figured I would ask first.

John in Albuquerque
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Old 04 Jan 2020, 08:13 am
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Default Re: Test alternator on car?

I'm not sure I understand what you're doing, John. If you're running a test light from the ground cable to the positive cable on the battery, it's going to light up because you've completed the circuit. Do you have a volt meter? If so, with the car running, take the positive lead and place it on the battery positive post and the black/ground lead and put it on the battery ground post and read the voltage. It SHOULD be somewhere around 14.5 volts. That would mean the alternator IS working. To test the alternator output, take the positive/red lead from your volt meter and put it against the hot wire post on the back of the alternator and the black lead to any bolt you can find to ground it on and read the volt meter. It should ALSO be in the 14.5 volt vicinity. If it's much less than that, you should probably consider another one. If it's close, then clean your battery posts and clamps and recheck. As long as the voltage off the alternator and at the battery with the car running is close, you will be okay. I just replaced a neighbors alternator on his 2001 Ford F-250 Super Duty diesel. One of the easiest ones I've ever done. It was only putting out .07 volts.
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Old 04 Jan 2020, 10:58 am
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Default Re: Test alternator on car?

Quote:
Originally Posted by chuzz View Post
I'm not sure I understand what you're doing, John. If you're running a test light from the ground cable to the positive cable on the battery, it's going to light up because you've completed the circuit. Do you have a volt meter? If so, with the car running, take the positive lead and place it on the battery positive post and the black/ground lead and put it on the battery ground post and read the voltage. It SHOULD be somewhere around 14.5 volts. That would mean the alternator IS working. To test the alternator output, take the positive/red lead from your volt meter and put it against the hot wire post on the back of the alternator and the black lead to any bolt you can find to ground it on and read the volt meter. It should ALSO be in the 14.5 volt vicinity. If it's much less than that, you should probably consider another one. If it's close, then clean your battery posts and clamps and recheck. As long as the voltage off the alternator and at the battery with the car running is close, you will be okay. I just replaced a neighbors alternator on his 2001 Ford F-250 Super Duty diesel. One of the easiest ones I've ever done. It was only putting out .07 volts.
Chuzz he says the generator (alternator) is charging okay.
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Old 04 Jan 2020, 03:16 pm
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Default Re: Test alternator on car?

I'm guessing you saying you have a drain on battery which in turn need jumped or charged before starting.
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Old 04 Jan 2020, 03:40 pm
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Default Re: Test alternator on car?

Obviously, I don't understand the situation. I'm out. On a side note, to just continue my distrust of Autozone electrical parts, the alternator I swapped out for John is only putting out 13.3 volts. I called the Autozone Tech Support line and dude told me that's not enough. The variances are SUPPOSED to be 13.8 on the low end and 15.7 at the top. He told me to return the alternator because that one obviously has something wrong with it. I took the NAPA one back to a local NAPA and they swapped it for a new one, no questions asked. When it stops raining tomorrow or Monday, I'll try that one and tell him to take that Durajunk one back to the Zone for a refund.
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Last edited by chuzz; 04 Jan 2020 at 03:44 pm.
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Old 04 Jan 2020, 04:36 pm
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Default Re: Test alternator on car?

Not about alternator but I've been going through NAPA batteries a year at a time.. Going to switch brands next time.
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65 Dodge Coronet 6 cyl 2dr Post
66 Ply Satellite with 273 engine swap to 69 340 4spd
70 340 4spd Dart Swinger "Those were the days my friend"
73 Charger SE
Had a few Vetts on the way 69, 85
Several Neons some flips
01 Sebring flip
Cruiser's 01, 220K Gone to a new home
Cruiser 03 133K Gone to a new home
Cruiser 06 110K Project Gone to new Home
Cruiser 05 Ltd 120,809 bought with broken belt Oct2015
May 16 Resurrected to once again roam the streets.

20 Miles South Of Pittsburgh
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Old 04 Jan 2020, 07:26 pm
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Default Re: Test alternator on car?

FLllll
Quote:
Originally Posted by chuzz View Post
Obviously, I don't understand the situation. I'm out. On a side note, to just continue my distrust of Autozone electrical parts, the alternator I swapped out for John is only putting out 13.3 volts. I called the Autozone Tech Support line and dude told me that's not enough. The variances are SUPPOSED to be 13.8 on the low end and 15.7 at the top. He told me to return the alternator because that one obviously has treesomething wrong with it. I took the NAPA one back to a local NAPA and they swapped it for a new one, no questions asked. When it stops raining tomorrow or Monday, I'll try that one and tell him to take that Durajunk one back to the Zone for a refund.
Chuzz he is asking if it has a battery drain problem is causing the alternator voltage to go down.

He needs to ask the right question.

The question he should e asking is hjow do I check te alternator witjhout replacing it.

My cell phone is going �� LOL
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Last edited by ptcruisersteve; 04 Jan 2020 at 07:42 pm.
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Old 05 Jan 2020, 07:33 am
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Default Re: Test alternator on car?

He's got a little over 400,000 kilometers on this truck and said he's on his 6th alternator. He's got Morotcraft batteries with a CCA rating of 800. IDK how old they are, but they don't look too old to me. I'll try to find a date on them after church today. Checking the output from the alternator lug to the closest ground. No matter where you ground it, it reads 13.3. Same voltage readings off both batteries. Didn't mean to hijack this thread, so will drop the subject of the BLUE OVAL. He's got money and if the new NAPA alternator doesn't read any better, I'll guess he has a wiring problem somewhere. Not my circus, not my monkey after that. Sorry about that ABQJohn. I hope you find the answer YOU need here. I can't help you with that.
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Old 05 Jan 2020, 08:03 am
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Default Re: Test alternator on car?

Quote:
Originally Posted by chuzz View Post
He's got a little over 400,000 kilometers on this truck and said he's on his 6th alternator. He's got Morotcraft batteries with a CCA rating of 800. IDK how old they are, but they don't look too old to me. I'll try to find a date on them after church today. Checking the output from the alternator lug to the closest ground. No matter where you ground it, it reads 13.3. Same voltage readings off both batteries. Didn't mean to hijack this thread, so will drop the subject of the BLUE OVAL. He's got money and if the new NAPA alternator doesn't read any better, I'll guess he has a wiring problem somewhere. Not my circus, not my monkey after that. Sorry about that ABQJohn. I hope you find the answer YOU need here. I can't help you with that.
Hi Chuzz,
There is an answer to this question but it has been a long time since I remember the answer. I know some members who know the answer since they are certified mechanics or tree mechanics who work on cars every day.
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Old 05 Jan 2020, 08:05 am
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Default Re: Test alternator on car?

Quote:
Originally Posted by ptcruisersteve View Post
Hi Chuzz,
There is an answer to this question but it has been a long time since I remember the answer. I know some members who know the answer since they are certified mechanics or tree mechanics who work on cars every day on this forum.
&jkkkkjkkjj
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