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Old 01-11-2005, 09:48 PM   #1
Scooby Specialist
Member#: 27136
Join Date: Oct 2002
Have a Nice Day? Relationship between alternator whine, voltage, and alternator health

Hey. I've recently did a little search on alternators and stuff associated with it's failure. I gathered some knowledge that some alternators died very early on some cars, many are apparently still fine on most cars. A few of the problems I read about included a very loud whirring noise just before the alternator was about to die, extreme voltage drops, car not starting because battery was not charged fully, etc.

My question dealt with the fact that recently, through my curious and observant self, I noticed that I have a constant very high pitched whine that sounds non-mechnical, leaning towards electrical noise. The noise is so high pitched that it can barely still be described as a whine, but not exactly as low pitched as a buzz. Before, I did notice that at idle I would hear this same whine with a fairly long duty cycle if you will. If the noise were to be visually illustrated as a line, it would look like this. _________ ___________ ______________________ ____ _____ _______________

^ The solid line being when you hear the whine. Now, as my car approaches the 30,000 mark (29,80xx) the whine is basically constant when at idle. It disappears when the engine is revved and comes back just after being at idle for a little while. The sound would be illustrated as this now ... __________________________________________________ ___________

I have read another thread about this weird "whine" that others also seem to have, but cannot pinpoint. For me, it seems to be an electrical whine but personally, all I can think of is the alternator.

My curiosity guiding me, I measured my voltage at idle via a multimeter at the battery terminals, and noticed that it has dropped a little from before. About, say 2,000 to 3,000 miles before, the voltage would read a steady 14.2-14.3v. Now, the voltage seems to have dropped to 13.8-13.9v. I don't really know what the voltage drop is related to. I can imagine that it could either be the voltage regulator in the alternator, or a low battery? I am trying to disreguard the voltage regulator in my battery because as the regulator fails, wouldn't the voltage usually be excessive? Or, in the case of my battery; it has not been really drained fully, the electrolyte level is fine, and it seems healthy as far as I can tell.

I could be paranoid, and the voltage drop / weird noises could also be normal, perfectly fine noises of an engine that has been around the block a few times, and is aging normally.

I do not have the tools/equipment required to perform the various industry standard "tests" to see if my alternator is bad, nor can do a load test on my battery. If required, i'll see if I can get it checked out though.

So, all in all, my alternator SEEMS to make funny noises, and the voltage dropped a few hundred millivolts over time. Should I be worried, what can I check, and is this something I can fix / make better by myself?

Thanks, I have a tendency to type long posts, but I try to explain my problems and concerns as well as I can.

Any help would greatly be appreciated.
Thanks in advance.

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Old 01-13-2005, 03:21 AM   #2
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Old 01-16-2005, 06:15 AM   #3
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Chapter/Region: MWSOC
Location: Illinois
1980 VWRabbit Diesel
w/AAZ Swap


I think you have the right idea, the alternator. I had a 400watt amp powering one 12" kicker compvr, no capacitor (my mistake)

I think the sub drawing the amount of power it did killed my alternator and it sounded kind of like a supercharger and it got louder as the rpms went up. that was at 44000 miles. I now have 78000miles on the car.

What I am getting to is I noticed the voltage drop from the output of the alternator. healthy alternator 14.4v and up. When I replaced my alternator the new one was putting out around 14.8volts -- which was impressive since I got it used from Axis-Racing, for a mere 55 shipped. Anyways, From what I read your alternator is dropping output voltage. My suggestion is to look into replacing it before it possibly dies. It may make different noises as different parts of the alternator go, I am not sure what made mine sound the way it did. If it were the bushings, or bearings I have no clue what. But for me I knew obviously what I had done, because of the huge draw I placed on the electrical system with the subwoofer.

Note: I haven't gone to tech school yet, but I start at the end of the month. Right now all I can do is speculate and give my 2 cents.


Last edited by erice1984; 01-16-2005 at 06:25 AM.
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