Re: 89 Turbo (driven?) Alternator

[Heather & Jeff <hjr@buffnet.net>]

Igor,

Sorry for your alternator plight.  I'm not very familiar with Bosch
alternators or their connections, but let me clear up a couple of
items.  

1. The filter capacitor has no bearing on your problem. If it goes open,
you stand a chance of increased noise on the radio & stuff.  If it goes
short, well, it won't be that way for long because it will blow like a
firecracker.

2.  I doubt that your stator windings and diodes are bad.  An alternator
is a three phase device; three sets of windings and three sets of
diodes.  Usually if a diodes opens or shorts you lose one phase, and one
third the output.  (Unless of course you have a catastrophic failure of
the entire diode bridge assembly; but this usually happens after a high
heat/output situation, not after starting the car after it sits.

3. The rotor resistance seems about normal.  (most 5" alternators draw
3-5 amps on the field coil (rotor))

4. I don't remember whether Bosch alternators of that vintage have a
diode trio rotor power up scheme or not.  If they do, this is likely
your problem.  (Diode trio is a small pack of three diodes across each
of the three phases to provide power to the rotor; kind of an archaic
way of turning the alternator on)

4. Are you sure that the Fox actually is charging with the Audi reg?  If
yours is not a trio-type alternator, then it really sounds to me like
you have a regulator/brush/field excitation problem.

Sorry, I don't have any good suggestions on replacement.

Good Luck!

Jeff

'88 80q