Multiple Alternator Failures

[Peter Orban]

Hi Vittorio,

The capacitor is there for interference suppression, it is connected to the same B+ line where the power comes out of the alternator, just at a different, smaller terminal.
If the capacitor is leaky, it could drain the battery when the engine is off. The capacitor can be left out, probably the radio in your car would not notice the difference. 

You can check the capacitor with an Ohm meter when removed, it should read infinite resistance.
Alternator regulators come in different voltages, usually nominal 14V at room temperature.
Looks like you just had two bum alternators.
If you put in a used one, at least check if the brushes are still adequate.

Good luck, Peter



________________________________

Message: 1
Date: Sun, 6 Jan 2013 23:12:51 +0000
From: "Bares, Vittorio" <Vittorio.Bares at nuance.com>
To: "quattro at audifans.com" <quattro at audifans.com>
Subject: Multiple Alternator Failures
Message-ID:
    <A78B9842431FBB4BA3F53EDED195564232A7D35B at SOM-EXCH01.nuance.com>
Content-Type: text/plain; charset="us-ascii"

Subject: Audi 90 with AAN conversion

Symptoms: Battery drains while running

Analysis:

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 -