Multiple Alternator Failures

Bares, Vittorio Vittorio.Bares at
Sun Jan 6 15:12:51 PST 2013

Subject: Audi 90 with AAN conversion

Symptoms: Battery drains while running


n  Checked the voltage at alternator (power post to chassis ground) only showing battery or power pack voltage

n  Had the alternator tested, testers indicated "stator circuit is bad"

n  Replace the alternator with one that actually was supposed to go to an Alpha Romeo - but had the same size and was 115AMP and all mounting points the same - only, the capacitor (??) on the back was switched from the old to the new (I don't know what that is or what it does)...

n  Put the new one in, measure voltage at the alternator, 14+ volts - seems like all is well.

n  Run it  a day or so, then it starts making a noise (luckily in the driveway), and soon after stops producing voltage.

n  2nd (same part no.) alternator is installed, capacitor (??) or whatever it is , is switched from one to the other and re-installed.

o   Now on this one, I can't be sure if it was good or not, it measured over 13Volts - but I can't recall if the battery pack was on it or not...

o   In any case - it's now dead as well.

n  I've checked to make sure the blue wire is working

o   Ignition on, batt light is on

o   Motor running, batt light is off

o   I also took a bulb and put it across from the battery post on the alternator to the blue wire post (b+?) and it also worked in the same manner.

n  I've check the grounds. We cleaned up the grounds to the motor from the chassis.

o   Also, checked voltage from different grounds - all the same.

Does anyone know what that capacitor (??) wire is on the back and if it could effectively kill the alternator in anyway?

I think our next step is to just get an  S6 alternator - but interested to see if there is anything else that may be killing these alternators...or maybe, just dumb luck that we got 2 bad ones in a row?

Vittorio -

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