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Thread: Alternator Question . . .

  1. #1
    Registered User
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    Alternator Question . . .

    I searched the forum and have not found the thread. My 1993 R100RT has a new rotor and new brushes. Rotor rebuilt and checked out with multimeter. After putting everything back together I get a red discharge light and a voltmeter reading about 11.8 v when running. What order should the three heavier wires mounted close and parallel to each other. Green, b/w, red? Top to bottom?
    Any other ideas? Brushes are riding on the copper part of the rotor.
    Thanks,
    Campbell J Tellman II

  2. #2
    Registered User mneblett's Avatar
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    Rather than re-write the good info out there, here's link to a diagnostic guide:

    http://bmwmotorcycletech.info/trbleshootALT.htm

    More thorough background material is here (articles 14A % 15 in particular). The answer to your specific wiring Q will be in there.

    http://bmwmotorcycletech.info/techni...icles-list.htm
    Mark Neblett
    Fairfax, VA
    #32806

  3. #3
    Alps Adventurer GlobalRider's Avatar
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    Quote Originally Posted by CTellman View Post
    Brushes are riding on the copper part of the rotor.
    But is there anything making out to the brushes.

    Have you tried by-passing the voltage regulator?

  4. #4
    Administrator 20774's Avatar
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    The three wires from the alternator carry each one of the three phases to the diode board for rectification. Their order doesn't make any difference.

    What resistance did you get when you checked out the rotor?
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    Rally Rat
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    People often mix up the insulating washers for the positive brush. They also occasionally mix the wires on the brushes. Or, if they solder in the brushes, they occasioanally extend the wire into the stator frame. Any of these errors cause the generator light to stay lit.

  6. #6
    MonoRT MonoRT's Avatar
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    I'm assuming that you did not have to pull the diode board - that you just disconnected all of the wires at the stator housing. If that was the case, another sort-of easy mistake is to reverse the wires from the voltage regulator to the brushes. If you get those reversed, the D+ current that is supposed to flow through the rotor just dumps straight to ground and the alternator doesn't.

    Once, I was messing about under the front cover and somehow loosened or failed to properly reconnect the big red plus output wire from the diode board to the starter relay. The connector popped off the diode board lug and I got the same symptoms that you just described - plus a very sheepish look when I pulled the front cover and saw the end of the positive output write dangling near the diode board.

  7. #7
    R100GS, '89 Guenther's Avatar
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    has a new rotor and new brushes
    Why was this done? Because of any charging problems?

    If so it could be the small diodes on the diode board are bad. Thes diodes "feed" the voltage regulator AND the charging light bulb.

    Or, the D+ wire (from the small diodes) does not connect correctly to the voltage regulator (hence the 11.8V).

    The D+ is the thin blue wire plugged into the back of the diode board (leaving one spade unconnected between the thick wires and the D+ spade).

    /Guenther

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