Alternator Question

[Huw Powell]

> Huw,
>
> I have been helping Sean troubleshoot.  A few questions/comments below
> preceeded by --

I created this (partially finished?) diagram while we were discussing
this:

http://www.humanspeakers.com/audi/altpix.htm  (second image)

I left out the way the other warning lamps are tied into the oil
pressure relay for testing.

> -- it is interesting that we seem to have several bad alternators that came
> out of working cars, and in fact one rebuilt, and all tested good by local
> shop - I can't say how good the shop's testing methods are as they are not
> specialists.  My understaning is they "load tested"  the alts which showed
> good.

You're judging them "bad" by their lack of function in this one car?
Seems a bit precarious.

> -- Is the exciter wire supposed to connect to ground(-), or positive.  We
> looked at the circuit diagram, and as best as we can tell, the working
> operation is a circuit is completed through the activation of the oil
> pressure switch (engine on), and that completes the exciter wire circuit to
> ground (via relays, etc.), but diagram does not show sufficient detail to
> be sure exactly how this works.

12 volts - switched, as you note, by the oil press. unit.  it is
grounded when there is no pressure, and this is what causes the 3.5
light test display when the key is on with the engine off.

> -- Sean just by passed the oil switch stuff and went directly to ground for
> the exiter wire.

which won't work, of course.  no idea what sort of weirdness or even bad
things might ensue there...

> - seems all of the alternators exhibited these characteristics to a degree.

In one car?  I'd look more closely at the car.  it'll run with an alt,
and you can test the output of the exciter wire (off, and running), with
it *hooked up right* to see what is going on.  Those '84's have pretty
nasty electrical wiring still (got a lot better in 85, 87, 88...), and
all kinds of things might not be working right.

> - The upshot of Sean's testing is that the alternators appear to have a
> current draw when not operating.  The testing was to rule out other
> comjponents in the car.  The test is just a simple circuit:  Battery (+) to
> Alt (+) terminal  and Alt. chassis to Battery (-)/Ground.  Exciter wire
> could be hooked to gound or not.  Irregardless, it appears that there is
> current draw through all of the alternators we tested, and even the rebuild
> had current draw.
>
> -- Sean can clarify on my comments, as I was not checking over his shoulder
> on every step.  These results are certainly a mystery to me.

It should not be possible to run current against the diodes (output wire
to ground).  But it is also hard to perform useful diagnostics on a
device when its operation is not fully understood.  I struggled mightily
(and failed I am sure) to explain how these things work on my alternator
file.  But they are actually quite simple.

PS, there are unfused circuits running off the fusebox, btw...

--
Huw Powell

http://www.humanspeakers.com/

http://www.humanthoughts.org/