High pitched noise from alternator

[SBL]

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.

[DaraSue]

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...

[David T]

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!

[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.

[SBL]

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.

[DaraSue]

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.

[CFI]

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.

You purchased something at Costco that fit in the DeLorean?

[DaraSue]

You purchased something at Costco that fit in the DeLorean?

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

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.

[MrChocky]

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

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.

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

Sent from my Pixel 3 using Tapatalk

[DaraSue]

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

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...)