Is there a built in regulator in that 20B alternator?
If so it could, in theory, run your battery down faster than if you
had an external regulator with separate field winding.
I think the failure mode that causes this is a shorted field.
It helps if you can disconect a shorted field from the battery.
That way the EFI/IGN can run longer. Something along these
lines as I recall.

Paul Lamar

Ed Anderson wrote:

Paul,
    I fly with the Mazda alternator with internal regulator.  I placed a

5

amp circuit breaker in my field coil circuit to pull and disable the
alternator should it malfunction.  So far no malfunctions, but pulling

the

CB does disable the alternator output.

Ed Anderson

So it is not a true one wire alternator with the field fed internally?
What year is that Ed?

Paul Lamar

Ed Anderson wrote:

Correct, Paul.

    There is a wire that feeds the field coil (CB in this one), one that is
used for the idiot light, and the large one for the Output voltage, so three
altogether.  Mine is a Bosch alternator  remanufactured  for the Mazda RX-7
1986 vintage. Thus far it has stood up well.

Ed Anderson

 This is exactly what I have on my LE, using a NipponDenso alt from an
85ish Honda Civic.  I feed it 12v for the field via my "ALT" half of my
master switch (Cessna type) thru a 2 amp fuse.  I, too, have verified that
I can shut off the alt in flight.  Also have a 60 amp CB in the output line,
and am using the idiot light connection for an idiot light (what else?).

Bill Freeman

 
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