> Here is one for all the electrical specialists:
    > I have a alternator from '86-'88 RX7. The field is turned on by a
    > switch on the instr. panel. It works fine, except that when I turn
    > off the field while running, it does not stop the output of the
    > alternator. Looks like internally is wired to do that.
    > I don't like it not being able to cut the output. How can I fix it?
    > Thanks.
    > Buly
    >
   This concept has been exhaustively discussed on Bob N's Aeroelectric
   Connection newsgroup. I'm not an expert, but apparently an internal
   regulator can fail and short the field into the ON position. Normally,
   killing the field voltage should prevent the alternator from working.

   This is a potential problem, because in an overvoltage situation, even
   with a "crowbar" or switch to kill the field current, a shorted field
   will still allow the alternator to put out power when it should not.
   This is bad.

   Many builders argue for an external regulator to allow definitive
   control of the alternator.  Several sites show how to dissect and
   disable the internal regulator (I have the documents somewhere if
   needed).  However, an external regulator might also fail in the ON
   position.  Another solution is to place a battery contactor or other
   heavy/constant duty relay in the B-lead wire, which allows it to be
   completely disconnected either automatically with a crowbar or manually
   in the event of an internal regulator failure.

   Scott Gettings



While an external regulator may fail in the "on" state, you still have
direct access to the field wire.  Because of this you can put a switch
(switch breaker) in the field line.  If you ground the field, you stop
the output of the alternator..

Most (all?) internally regulated alternator do not provide any direct
means of interrupting the field current.


Regards,

Matt-



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