High pitched noise from alternator

Last night I heard a weird noise that seemed to be coming from the alternator. It was about 15 minutes after I'd turned the car off. Keys were still in the ignition but the noise continued after I took them out. It was a high-pitched whine, sounded kind of like tinnitus or the electrical field noise you hear behind a CRT tv that's on mute.

I noticed this same noise last year when I was having the issue with the throttle sticking and thought it might have had something to do with the engine revving at 5000+ rpm, but this was after a normal drive home from work that never went much above 3000. I can't say with 100% certainty that it hasn't been happening the whole time because I'm not usually in the garage with the door closed at night after shutdown. When it happened last year I asked a mechanic friend about it and he didn't think there was any way the alternator could be making noise with the engine off but it definitely sounded like that's where it was coming from (I didn't hear it at all inside the car). Last time it went away when I switched the battery cutoff off.

Has anybody ever heard of anything like this?

This is the alternator: Attachment 63902 Attachment 63903Attachment 63904

The guy who sold me the car swears it's a 200 amp that came from DPI but they don't currently sell one with that rating and I can't find any DeLorean vendor who does. (It was installed around 2016.) Another mechanic friend of my neighbor looked at it and said it looked like a Chevy alternator. Does anyone recognize it?

I had taken the car to Autozone to get it tested when all this happened last year and they said it had a bad voltage regulator but the car has been starting and running fine this whole time (volt meter stays around 13). How likely is it that that's actually the case? If it actually is a 200 amp, is that too much for this system? I'm not running any insane aftermarket electrical stuff.

I've had that same issue with the GM alternators (2 of them); like a tube TV high frequency noise. The noise came with a parasitic drain on both alternators so you may want to check for that.

Definitely not one of ours. All of our units have black powder-coated finished fans, billet bracket, billet pulley, and 5/16 bolt instead of the 10mm. This is Hervey's unit for sure.

Thanks, guys. It does kind of look like the ones Hervey had on his site back in the day. https://web.archive.org/web/20160326...ternators.html

I've got a DuraLast from Autozone that I bought just in case, might swap it out and take the current one to a rebuild shop and see what they say.

dmcnc - when you say there was a parasitic drain, what symptoms were you having? Low voltage, battery drain?

Check the charge rate. I would not be surprised to hear it's burnt up.

Battery drain. BTW - you could purchase something like this and just swap the front case (the aluminum shell facing the pulley), making it a direct fit.

https://www.amazon.com/DB-Electrical.../dp/B007XUI4MG
https://www.ebay.com/itm/200-AMP-811...Make%3APontiac

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Originally Posted by DaraSue

when you say there was a parasitic drain, what symptoms were you having? Low voltage, battery drain?

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My DMC alternator has the whine and parasitic drain. Replaced it and the second DMC unit does the same. Not every time, and what I have found is that if I turn the ignition back on for a couple seconds after shutting down, the whine stops and there is no parasitic drain. Can’t really figure out why that works but it does

If the charging light lights up when you start the motor and then goes out once the motor is running, the problem is internal to the alternator. That whine is not good and you are draining the battery. I could go into a technical explanation but the bottom line is you should not hear that whine with the motor off and the key off. You don't hear the whine when the motor is running because of the noise of the motor.

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Originally Posted by David T

If the charging light lights up when you start the motor and then goes out once the motor is running, the problem is internal to the alternator. That whine is not good and you are draining the battery. I could go into a technical explanation but the bottom line is you should not hear that whine with the motor off and the key off. You don't hear the whine when the motor is running because of the noise of the motor.

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David- I know the alternator controller is keeping the field active and the whine is from the PWM field current controller. What I don't know is why the alternator controller in the DMC alternator decides to keep the field turned on when I switch off the motor after a drive, and why it consistently turns off when I cycle the ignition. Second DMC alternator with identical issues.

The problem can be caused by incorrect wiring to the alternator keeping the voltage regulator "excited" or it can be a problem internal to the alternator/voltage regulator. Once you can be sure when the key is off there is no voltage to the voltage regulator on the N/Y (Brown/Yellow) wire, if the alternator continues to whine, the problem is the voltage regulator. I have seen where the wrong bulb is used and the bulb is very dimly lit sending some voltage to the voltage regulator. Can also be leakage in the ignition switch through the bulb. The next time you hear the whine, check for any voltage on the N/Y wire. Then pull the wire off the alternator and check again, the voltage regulator could be backfeeding some voltage into the N/Y wire. Once you can verify the circuit in the car is OK the problem is in the alternator's voltage regulator. Because you are having problems with the charging circuit I would also verify you have the correct bulb. That can only be done by removing the binnacle and actually looking at the number on the bulb. Because of all of the work involved in doing that, it makes sense to just replace ALL of the bulbs in the binnacle. It is rare but I have seen voltage regulators "self excite" like this by backfeeding power from the battery terminal. The fix is to replace the voltage regulator. More often shops just replace the alternator, not wanting to take things apart and try fixing it. They make more money and get a warranty that way. Besides, the brushes are probably worn and the bearings are tired too. Because it seems to be the alternators from DMC I suggest you try an alternator form a different source. I recall they had some issues in the past, the charging light would blink.

DaraSue,
I'd try disconnecting the alternator and see it it stops.
Pull the alternator and get it load tested, as suggested. If it shows a short, you've probably found the problem.
200 amps is double what you need...
(See below.)

Gluaisrothaii, I noticed several D's do that when connected to a trickle charger (then turn the key off). At first, I thought it was the cheap charger introducing AC somehow, but later noticed they also acted exactly as you describe w/o it connected. I never could find exactly where the sound was coming from. They are all still working without any other issues...of course the battery will run down if you don't hear it and cycle the switch.

David, using the "wrong" bulb will not send voltage to the voltage regulator -- With the key off, the bulb has no voltage to send. If the bulb barely glows with the key off, it's usually one of the smaller three diodes connecting the regulator to the 3 stator-rectifier terminals (if used). Otherwise, at least one of the rectifier diodes are leaking.

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Originally Posted by Ron

David, using the "wrong" bulb will not send voltage to the voltage regulator -- With the key off, the bulb has no voltage to send. If the bulb barely glows with the key off, it's usually one of the smaller three diodes connecting the regulator to the 3 stator-rectifier terminals (if used). Otherwise, at least one of the rectifier diodes are leaking.

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Key words, with the key off. I have seen cars wired up where that bulb is always powered or there could be a problem with the ignition switch. If you look really closely you can see the bulb dimly lit. Rare but worth checking.

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Originally Posted by David T

Key words, with the key off. I have seen cars wired up where that bulb is always powered or there could be a problem with the ignition switch. If you look really closely you can see the bulb dimly lit. Rare but worth checking.

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Agreed, but my point was that a wrong bulb doesn't fit the issue.
If the bulb is always powered, the regulator will ground it and the bulb will burn until you start the engine or the battery runs out of power. And if it is always powered by a problem with the switch, the key is not really off.

A wrong charge light bulb can: have too much resistance, causing the bulb to not burn correctly and/or not excite the regulator; have a low wattage rate, causing it to blow like a fuse; be an LED, which will not pass current in both directions as required. Look elsewhere.

I took it to a rebuild shop yesterday and they got it done that afternoon. They said the voltage regulator was fine, but the brush holder had melted. They said that could have had any number of causes but it was possible the battery cable corrosion had contributed to it. The cable was starting to corrode again so I ordered a new AGM battery too.

Also, it was 85 amps, not 200. :facepalm: The replacement I got from Autozone is 96 but I guess I've been doing just fine with 85 so I'm just going to put the old one back in since it's plug and play.

Remember that time you stopped by and your starter was held in by 1 7mm bolt when it is normally held in by 3 8mm ones? The amount of stress on the electrical system had long term side effects.

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Originally Posted by Delorean Industries

Remember that time you stopped by and your starter was held in by 1 7mm bolt when it is normally held in by 3 8mm ones? The amount of stress on the electrical system had long term side effects.

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When I'd intermittently turn the key and nothing would happen? And it was just waiting to strand me in the middle of Nebraska? Oh yeah, that was a fun time, LOL. Always an adventure with this car...

Yeah, I wouldn't discount the hardship the electronics went through during that period. Like most things in life, only so much abuse can be taken before a hard failure.

Well, I installed my freshly rebuilt alternator and took it for a test drive and it was still making the noise afterwards. :swear1: Guessing I need to look elsewhere in the system? It did go away when turned the key on and off like Gluaisrothaii's did.

The weird thing is, if it's been doing it this whole time, it doesn't seem to be draining the battery? I've never had it not start since last summer when I had the corroded battery cable.

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Originally Posted by DaraSue

Well, I installed my freshly rebuilt alternator and took it for a test drive and it was still making the noise afterwards. :swear1: Guessing I need to look elsewhere in the system? It did go away when turned the key on and off like Gluaisrothaii's did.

The weird thing is, if it's been doing it this whole time, it doesn't seem to be draining the battery? I've never had it not start since last summer when I had the corroded battery cable.

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Before I figured out that cycling the ignition stopped the whine, I did some testing to see what voltage the regulator needs to see on the wire coming through the alternator idiot light to turn on the field current. I was able to turn on the regulator with as little as 0.3V, which was the lowest controlled voltage I could create. My suspicion is that the DMCH alternator has a hair trigger to turn it on, and that something in the DMC electrical system- possibly some capacitors- creates a lagging voltage in the ignition circuit that holds the circuit active.

Not sure why it would not eventually turn off as the capacitors bleed down, but thinking about how the regulator operates the idiot light it makes sense that it stops grounding the bulb once the alternator field is active (that's why the bulb goes out) so if there's a capacitor floating the circuit with the ignition off it might take quite some time to bleed down.

Anyway one thought was to put a 1k resistor to ground in parallel with the ignition light circuit to see if that helps drain off any lagging voltage on that line.

Now I'm ready to be flamed by the EEs on the board :)

You can try the 1K ohm resistor but I doubt it will fix the problem. DMCH had a run of alternators with problems, I don't know if the current issue is any better. Specifically they would blink the alternator light. Either get a Battery Master switch or try a different alternator. The resistor will light the alternator bulb dimly when the ignition is on but should make it go out with the key off. A diode may be what you need.

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Originally Posted by DaraSue

Well, I installed my freshly rebuilt alternator and took it for a test drive and it was still making the noise afterwards. :swear1: Guessing I need to look elsewhere in the system? It did go away when turned the key on and off like Gluaisrothaii's did.

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Did you try disconnecting the alternator?
Try the field wire first then the main. If still no luck, pull the fuses one at a time (there nay be more than one...)

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Originally Posted by Ron

Did you try disconnecting the alternator?
Try the field wire first then the main. If still no luck, pull the fuses one at a time (there nay be more than one...)

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I wonder if the voltage monitoring connection is connected to the battery if that would stop the problem. My DMCH alternator is connected that way to stop the voltage dipping and the error code flashing so maybe it would also stop the high pitched noise.

If you put a diode in one direction, when you turn the key on, current will not flow through the bulb or get to the regulator as it should. If you put it in the other direction, when the key is off, a leak in the rectifier (or diode trio, if used) will not reach the bulb as it should. (Note the switch grounds the bulb's feed side when off on most vehicles.)

I agree a resistor will dim the bulb (and probably prevent the tell tail glow when the key is off).

I'm not sure, but I thought the DMCH alternators flashing was because the newer generation of regulators sent codes??
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I'm not surprised that 0.3 V turns the regulator on. You might find it interesting that, after a rotor has been used a while, the shaft can become a weak permanent magnet. Most of them are strong enough to get the alternator to kick in even if the field circuit (bulb's) is disconnected.

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Originally Posted by Bitsyncmaster

I wonder if the voltage monitoring connection is connected to the battery if that would stop the problem. My DMCH alternator is connected that way to stop the voltage dipping and the error code flashing so maybe it would also stop the high pitched noise.

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lol... Now I remember it was your's that sent codes.

Good idea!
But we're not sure the noise is coming from the alternator yet, are we??
I wanted to chase this down on the last D I mentioned before, but I had it doing head work and the owner said it never gave him a problem (and hasn't since).
What's been bugging me is that my battery charger would start the noise off. It would continue after removing it and I had to cycle the switch...

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Originally Posted by Ron

lol... Now I remember it was your's that sent codes.
But we're not sure the noise is coming from the alternator yet, are we??
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I'm 100% sure it's from the alternator. I can trigger it by sending an independent voltage to the field when everything else is turned off.

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Originally Posted by gluaisrothaii

I'm 100% sure it's from the alternator. I can trigger it by sending an independent voltage to the field when everything else is turned off.

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Got ya...Are you applying it to the field wire (connected) or the field terminal only?

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Originally Posted by Ron

Got ya...Are you applying it to the field wire (connected) or the field terminal only?

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Directly to the field terminal, nothing feeding back to the chassis wiring.

Interestingly here's another member with the same issue just posted with a DMCH alternator. I get a 4amp draw associated with the regulator being active also.

http://dmctalk.org/showthread.php?18...w-with-key-off

My first thread on the alternator issue

http://dmctalk.org/showthread.php?17...t-ignition-off

Has a conversation with Stephen from DMCH this morning on this. We're going to troubleshoot with some information from my car....

Best
Ken

I was going to ask if the noise went away when you disconnect the field wire, but I gather it does from the link above.

With the field wire disconnected, does turning the key off send it to good ground or open.

A few drives had gone by without hearing it, but it did it again last night. It went away when I pulled the #4 fuse. On the schematic it looks like the shortest path between that fuse and the alternator is the white wire that connects to the cluster by the auxiliary relay (which also connects to the ignition). IIRC that relay was making a weird squealing noise last summer after the ignition accidentally got left on overnight when I had the car towed home due to the electrical failure. I have a spare one of those relays so I'm going to try changing it and see what happens.

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Originally Posted by DaraSue

A few drives had gone by without hearing it, but it did it again last night. It went away when I pulled the #4 fuse. On the schematic it looks like the shortest path between that fuse and the alternator is the white wire that connects to the cluster by the auxiliary relay (which also connects to the ignition). IIRC that relay was making a weird squealing noise last summer after the ignition accidentally got left on overnight when I had the car towed home due to the electrical failure. I have a spare one of those relays so I'm going to try changing it and see what happens.

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In addition to fuse 4, the auxiliary relay switches power to fuses 3 and 5. It also provides power to the coil via the ignition resistors. If it were failed completely, the car shouldn't run.

Just looking at this and considering that it went away with fuse 4, is it possible that the hazard switch is back-feeding a small amount of current to the aux relay contact then on to the alternator? The hazard switch is powered by fuse 6 which is always live. As a test, the next time it happens, pull fuse 6 (with fuse 4 still in) and see if it stops. If it does, that would implicate the hazard switch.

Ron

Could there be something amiss in the new DMCH alternators? I had never drawn down my battery before, but then I changed my alternator to the new DMCH one because I could sense that the bearings were going bad. Well, it charges, does not make any noises when the key is out, and the light works as it should. (My door lock module is disconnected and the radio has no memory current draw, BTW.) With a brand new battery, in 2 days the battery was dead while the car was sitting with the key off and out of the car. I am going through the fuses and seeing if I can find a culprit. But I never had a problem with my original stock alternator, so it makes my wonder. The install is so easy and straightforward that I see no way that there is a wiring error. Of course the alternator could be to spec but just under some unusual condition of my car, there is a current draw.

It hasn't made the noise since my last post but last Saturday I saw a pretty massive voltage drop at idle with the lights and a/c on. (It was down by the lower unmarked red line.) Testing it in the garage with a meter, it would drop to 9 or below with lights and fans on. When I started cleaning the grounds and connections in the engine bay I found that the stud in the alternator had broken loose so I took it back to the shop and they fixed it and replaced the regulator just in case. We'll see what happens...

An alternator and/or battery are among the most mis-diagnosed parts in a car. Both they and the wiring all work together to make the electrical system work and something wrong with one part can damage the others, and some symptoms may look like one part when, in fact, it is another. The best way to eliminate the alternator as a possibility is to remove it and have it bench tested. While the battery can be tested, there is no test that is 100% definitive because batteries can fail intermittently and you can't always catch that in a single test. Same problem with wiring. Knowing the history can help to diagnose the problem too. Generally, if the battery is over 5 years old, and you are having electrical problems, replace the battery. If the car has a lot of non-factory wiring modifications or damage, they are ALL suspect. You must approach electrical system problems considering the WHOLE system, not individual parts. Sometimes you see unusual (weird) symptoms like when you use one thing something else does something. This can be caused by a backfeed because of bad grounds and the current is trying to get back to the battery through another circuit backwards. Sometimes you see things work intermittently because of bad connections. A lot of things can be attributed to an older electrical system that was marginal when it was new and now it is approaching 30 years! Getting back to the battery, don't use AGM type batteries. The car was not designed to use them. They fail in unusual ways. They are very expensive and don't offer any significant benefits over lead-acid plate type batteries in this application. Taking the latest technology and plunking it into an older design is not always a good thing. To help reduce the load on the alternator, use a Battery Tender once a month if you are not using the car and use it the day before you plan on using the car to have the battery as charged as you can so the alternator doesn't have to work so hard. I do not leave mine plugged in constantly. I use it for 1 day a month for only 1 day. I also have a battery master switch that I turn off to reduce the drain. Because of the pandemic most of us are not using our cars much now so you have to keep the battery charged. Allowing the battery to go flat is VERY bad for it. It shortens the battery's life significantly. Batteries are not like sponges, you can't empty them completely and then expect them to be refilled and act like nothing happened. Kind of like cats. You don't know when all of the 9 lives are gone till you are on the last one!

Road tested it today with a drive to Costco, voltage stayed around 13 or a little above even with the a/c on full blast. Continued the road test with a drive to the move theater across town to see BTTF. So far, so good. :headbang:

With the key out, I see +13 VDC at fuses 6,7,17, and 18, and the speed 3,4 breaker. Looking at the schematics this seems to be correct. I then removed each fuse to look for current across the fuse slots, and not even 1 mA showed up on any of them. Then checked current drain from the whole system to the battery and saw 1-2 mA at most, which is probably at the limit of accuracy for the meter. Essentially nothing. I then ran it, turned the key off, checked it all again, turned key on and off, etc. No change in the readings. Well, I will see if it happens again. I have never had a battery darin problem with this car before. If I can just remember to use my battery cut-off switch, that would be helpful. But still wonder why, now, that this problem cropped up. Oh well it will show itself, if it is even reproducible.

Oh, something else that may be relevant... Most of the times I've driven it lately, I've had the a/c on and the fans run for a few seconds after I shut the engine off (I have Dave M's fan relay). I wonder if that's a factor in why I'm not hearing the noise, if it's bleeding off the residual current or something.

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Originally Posted by DaraSue

Road tested it today with a drive to Costco, voltage stayed around 13 or a little above even with the a/c on full blast. Continued the road test with a drive to the move theater across town to see BTTF. So far, so good. :headbang:

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You purchased something at Costco that fit in the DeLorean?:shock::)

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Originally Posted by CFI

You purchased something at Costco that fit in the DeLorean?:shock::)

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LOL, it's easy when you're only shopping for one person and 3-1/2 cats. :p

I've driven it a few more times since then and no recurrence of the issue. Wonder if it was related to the voltage regulator after all.

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Originally Posted by DaraSue

LOL, it's easy when you're only shopping for one person and 3-1/2 cats. [emoji14]

I've driven it a few more times since then and no recurrence of the issue. Wonder if it was related to the voltage regulator after all.

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Where do the 3.5 cats fit in the DeLorean? And what's 1/2 cat?

Sent from my Pixel 3 using Tapatalk

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Originally Posted by MrChocky

Where do the 3.5 cats fit in the DeLorean? And what's 1/2 cat?

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I've never had all of them in the car at once but I've had two of them in the big carrier and they fit in the front seat just fine. I marveled at how much easier it was to get it in and out of this car than a normal one.

The 1/2 cat is the outside one, I figure she only counts as the front half, haha.

(Unless I actually own SCP-529. I can neither confirm nor deny...)