4amp draw- high pitched whine from engine compartment- ignition off

[gluaisrothaii]

All,
Issued resolved- seems like a problem with the new alternator. DMCH replacement was sent and installed; all is good. Great service from DMCH! No more whining from the alternator with the ignition off.

Best,
Ken

I spoke too soon. The ignition-off whine is back, and battery has gone dead twice on me with the new alternator. Same symptoms as before. I had to revert to disconnecting the battery at night.

[Bitsyncmaster]

I spoke too soon. The ignition-off whine is back, and battery has gone dead twice on me with the new alternator. Same symptoms as before. I had to revert to disconnecting the battery at night.

Maybe you have a sticking relay. Try unplugging them until the whine goes away.

[gluaisrothaii]

Maybe you have a sticking relay. Try unplugging them until the whine goes away.

The implication being some stray voltage passing through the L line and activating the alternator? I have checked and seen 0v there with IG off, but that doesn't mean there's occasionally something there....

No...the only draw is through the alternator main feed. That is not on a relay, it's direct to the battery. If the main or aux relays were sticking I would see power draw with the alternator isolated- and I don't.


Others have reported a similar issue with the DMCH alternator in this thread, so there must be something odd about the interaction of the vehicle's wiring and the regulator in this alternator..but of course there's nothing magical with the control circuit. I might try a forward biased diode on the L line. The breakdown voltage would have a high enough threshold to cut off stray voltage that might be holding the regulator on with IG off. Either that or a high value resistor to ground in parallel with the L line to zero out the line once the ignition is off.

[David T]

Pull the alternator and have it bench tested. Recheck the wiring to the alternator. As a stop-gap alternative you can install a battery master switch.

[Michael]

A lot of rebuilders take short cuts. They may look for broken coating on the windings, pry apart what they can see and just re coat what it visible instead of actually rewinding the rotor.

A good rebuild will be with fresh windings.

[Ron]

I was following this when it seemed to be resolved. Food for thought:

Pulled fuses to troubleshoot-either 4, 10 or 16 eliminated the issue (or just coincidental timing) but the load was gone when I plugged the fuses back in.

...

Though it is not documented by DMCH, it seems to be optional to use the brown as a voltage sense line so that the VR drives to 14.8V at the battery rather than just at the B+ post of the alternator.

With the original alternators, the Brown wire is normally connected to AUX #2 Relay. Using the same terminal, it also feeds the BATT light via a Green wire through Fuse #5.
(! not 4, 6, 10 ???)

I'm suspecting PO mods e.g a radio's Always Hot Power/Memory wiring for the radip etc crossed up....Something feeding the regulator on a common circuit... Maybe see what happens if fuse #5 only is pulled.

(I'd jump the sense wire to the Main Alternator post, if not using the Brown wire even though all of the alternators I've seen so far with the feature have it virtually connected internally....)

FWIW-
Make sure the BATT bulb is correct. The wrong incandescent or a LED causes problems.

When you hear the sound, look VERY carefully at the BATT light for a faint glow.
If it does, the little diode trio/regulator in the alternator may be getting zapped...or defective Alternator #2.

[Ron]

A lot of rebuilders take short cuts. They may look for broken coating on the windings, pry apart what they can see and just re coat what it visible instead of actually rewinding the rotor.

A good rebuild will be with fresh windings.

+1
But, although the stator windings are replaced a lot, rotors and their windings rarely are in any rebuild shop. If the rear bearing surface is ok, the slip rings are trued up or replaced ant it's back on the street.
FWIW- Shops will have an excess of rotor and starter field windings but have a shortage of starter armatures and alternator field windings.
Big difference in their spin tests and load tests!

[iflights]

Had both of these symptoms. High pitched whine with engine off that only my son could hear (too much time for me as a roady), and a dead battery every 2 days.

Resorted to using my battery cut off switch for a year while I checked and/or replaced everything else...relays...fuses...door switches...glove box switches...hood switch...engine cover switch...replacement battery...everything.

Finally, for the price of a new alternator and simple installation my world changed and problem was solved. Purchased Alternator from PJ Grady.

[Patrick C]

Had both of these symptoms. High pitched whine with engine off that only my son could hear (too much time for me as a roady), and a dead battery every 2 days.

Resorted to using my battery cut off switch for a year while I checked and/or replaced everything else...relays...fuses...door switches...glove box switches...hood switch...engine cover switch...replacement battery...everything.

Finally, for the price of a new alternator and simple installation my world changed and problem was solved. Purchased Alternator from PJ Grady.

Good to know! If my whine reappears in the spring I will go this route as well.

[gluaisrothaii]

Pull the alternator and have it bench tested. Recheck the wiring to the alternator. As a stop-gap alternative you can install a battery master switch.

The alternator works perfectly- i.e. generates appropriate levels of smooth DC when running, and most of the time it shuts down when the ignition is turned off. A bench test will show it has zero issues. The problem is that it occasionally turns itself on, not every time.....DMCH already replaced it for me once. I'm sure they'll do it again.