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Thread: High pitched noise from alternator

  1. #21
    Administrator Ron's Avatar
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    Quote Originally Posted by DaraSue View Post
    Well, I installed my freshly rebuilt alternator and took it for a test drive and it was still making the noise afterwards. Guessing I need to look elsewhere in the system? It did go away when turned the key on and off like Gluaisrothaii's did.
    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...)

  2. #22
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Ron View Post
    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...)
    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.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #23
    Administrator Ron's Avatar
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    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??
    ======

    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.

  4. #24
    Administrator Ron's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    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.
    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...

  5. #25
    Member gluaisrothaii's Avatar
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    Quote Originally Posted by Ron View Post
    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??
    .
    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.
    1981 DMC 12- Black
    VIN 46**
    Alameda CA

  6. #26
    Administrator Ron's Avatar
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    Quote Originally Posted by gluaisrothaii View Post
    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.
    Got ya...Are you applying it to the field wire (connected) or the field terminal only?

  7. #27
    Member gluaisrothaii's Avatar
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    Quote Originally Posted by Ron View Post
    Got ya...Are you applying it to the field wire (connected) or the field terminal only?
    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
    1981 DMC 12- Black
    VIN 46**
    Alameda CA

  8. #28
    Administrator Ron's Avatar
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    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.

  9. #29
    Stupid Newbie DaraSue's Avatar
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    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.

  10. #30
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    Quote Originally Posted by DaraSue View Post
    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.
    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

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