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  #1  
Old 12-29-2007, 03:43 PM
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Bad Alternator?

Has anyone had a bad alternator, even if it passed a bench test?
I still have the dash lights coming on, this time it comes and goes continuously (lights come on, voltage drops)(Light go out, voltage goes up).
I had the alternator checked at Auto Zone, A&A, and an Alternator shop, it checks out fine.
I removed the remote start, alarm, alternator wire upgrade, starter bypass mode, and I checked all the wiring and connections under the dash and engine compartment.
I also cleaned the battery posts and the ground wire.
I'm losing this battle, I'm ready to give up, help!
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  #2  
Old 12-29-2007, 03:50 PM
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How is the alternator being bench tested? If it's being removed from the car and tested on a stand, they might be missing one very important factor: Heat. My alternator worked fine, until it got good and hot, then it would die. It might be that an isolated bench test doesn't subject the alternator to enough heat to bring out the problem.
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  #3  
Old 12-29-2007, 04:03 PM
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You could have a good alternator an bad wires to it.
Check the wireing going to the hot terminal on the top, and the plug and connectors that connect on the side.
Even if you have to remve the black plastic wireing cover to get to them.
Tom
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  #4  
Old 12-29-2007, 05:45 PM
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If what you report is exactly correct, the alternator has a faulty diode or rectifier component, but this is intermittent.

The output must be checked under load and with an oscilloscope or a bar graph multi meter as the second choice, and for a period with mechanical stress to show up anything loose. As mentioned earlier here, heat is also a very relevant factor.

I doubt very much that an auto electrical facility would carry out this sort of test for AC voltage, and if for free with due diligence.
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  #5  
Old 12-29-2007, 08:02 PM
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Thanks for the replies. Heat is something to consider because it always happens after I drive the car for awhile. I don't believe I have a loose wire because the symptoms happen even while idling, with no movement (after a short drive of course). This is a rebuilt Alternator I installed recently. I still have the core and will have that one rebuilt to see if it does the same. If it is heat related, what is the solution? Will this happen to every alternator I install?
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Old 12-29-2007, 08:39 PM
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Quote:
Originally Posted by dannmarr View Post
Thanks for the replies. Heat is something to consider because it always happens after I drive the car for awhile. I don't believe I have a loose wire because the symptoms happen even while idling, with no movement (after a short drive of course). This is a rebuilt Alternator I installed recently. I still have the core and will have that one rebuilt to see if it does the same. If it is heat related, what is the solution? Will this happen to every alternator I install?
A good alternator should not be affected by normal engine related temperature.

Now a special important request ------

I have previously requested someone do an experimental test which could be of real benefit to members if successful. However the thread involved became a mess and the request was sidelined.

Do you have or can you procure a multimeter with AC voltage ranges? Is so switch the meter to an AC voltage range which will cover 12 volts AC. With the engine not running, connect the meter across the battery and see if you obtain a steady reading.

There may be an short indication immediately on connection. No steady reading will prove that the meter has full wave rectification and is OK. The meter may take 20 - 30 seconds to settle, due to internal capacitance.

Next run the engine at say 2,000 RPM to ensure the alternator is charging and again apply the meter as before. A steady reading after an interval, will indicate the presence of an alternating current and an AC voltage imposed on the supply line. It is this reverse voltage which bypasses diodes blocking a sneak circuit in the warning light circuitry and causes them to illuminate.

If there is no reading and AC is not detected, switch to a lower voltage range as a further test. All is suggested as an experiment which has every chance of working, but requires proving. If you can do so all will be indebted to you. It will be appreciated that experiment can only carried out with a faulty alternator on hand and the opportunity is not common. Please note carefully what is required as well as results.
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  #7  
Old 12-30-2007, 04:38 AM
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Quote:
Originally Posted by dannmarr View Post
I don't believe I have a loose wire because the symptoms happen even while idling, with no movement (after a short drive of course).
What I was suggesting was a BAD wire.
Internal corrosion, intermittant break in the wire, occasional grounding, arcing,
that sort of thing.
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  #8  
Old 12-30-2007, 01:15 PM
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VAC Test Findings

Trevor,
I have done the tests and these are the results:

AC READINGS without any dash lights on

Battery terminals with engine OFF = 0 VAC
Battery terminals with engine ON = .042 VAC


AC READINGS with the dash lights ON

Battery terminals with engine ON = .018 VAC

I have checked all the readings over and over and these are the accurate numbers.
I’ve also noticed one wire out of three (seen through the alternator slots) that had the insulation cracked open and exposing the bare wire. Could this have anything to do with it?
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  #9  
Old 12-30-2007, 02:34 PM
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Quote:
Originally Posted by dannmarr View Post
Trevor,
I have done the tests and these are the results:

AC READINGS without any dash lights on

Battery terminals with engine OFF = 0 VAC
Battery terminals with engine ON = .042 VAC


AC READINGS with the dash lights ON

Battery terminals with engine ON = .018 VAC

I have checked all the readings over and over and these are the accurate numbers.
I’ve also noticed one wire out of three (seen through the alternator slots) that had the insulation cracked open and exposing the bare wire. Could this have anything to do with it?
Dan, (?) Good stuff and special thanks.

I had hoped for a more substantial reading of the AC voltage but the result is still indicative, particularly as turning on the dash lights on causes a reduction. There is little doubt that the alternator rectifier circuit is faulty.

Would you please advise exactly which dash lights you are referring to and exactly how they are affected, i.e. come on when they should not be and steady or flashing?

The wire exposed would appear to have an enamel covering intact and it is difficult to see if it is making contact with the frame. Can you see if there is evidence of actual contact?

Whatever, it does not indicate good workmanship in respect of the rebuild and could comprise a fault. As it is one wire of a bundle of three, this could indicate a fault in a single phase in the alternator output.
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  #10  
Old 12-31-2007, 03:13 AM
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Subsequent to our exchange of PM's it has come to mind that possibly the lock nut is missing, which would account for the confusion regarding the adjustment procedure, as well as the loose adjustment screw/bolt.

Please ignore this post which does not belong in this thread, Refer later apology.
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Last edited by Trevor; 12-31-2007 at 01:35 PM.
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  #11  
Old 12-31-2007, 05:27 AM
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Lock nut, screw bolt?????????
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  #12  
Old 12-31-2007, 01:31 PM
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Quote:
Originally Posted by dannmarr View Post
Lock nut, screw bolt?????????
Sorry and sorry again, Stupid and stupidly I got threads mixed up and the post belongs elsewhere. at self.
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