Alternator Question

[Sean Shoemaker]

Richard,
  Thank you for the help.   I am on my way now to pick up the new alt.  As I
mentioned before I was concerned that there may be something in the car that
was hurting the alts.  Perhaps it was me, but at least you have given us
something to think about.  I will have to confer with Ben to totally grasp
the concept, but I think I am getting it.
-Sean

----- Original Message -----
From: "Ben Swann" <bswann at worldnet.att.net>
To: <rick-l at rocketmail.com>
Cc: <quattro at audifans.com>; "'Huw Powell'" <human747 at attbi.com>;
<shoemakersp at comcast.net>
Sent: Thursday, September 12, 2002 12:11 AM
Subject: RE: Alternator Question


> Richard,
>
> Thanks, that is helpful.  I am working off my recollection of the 4000 q
> wring diagram.  I happened to have the 5000 series one with me.  The 5000
> ones refer to the exciter wire as D+.  I did not see that on the '84 4000
q
> diagram.  That wire appeared to ultimately route to ground.  Of course
> current tracks were jumping across multiple pages, so it wasn't clear.  As
> best as I could tell, operation of the engine closes the oil pressure
> switch whereby the exciter wire gets enable to ground.  Perhaps we read
the
> diagram wrong - three engineers misinterpreting the diagram.  Anyway,  I
> recheck,  Perhaps Sean's testing was killing the alternators.
>
> Thanks again for the reply as it helped my understanding enough to go back
> and recheck the diagram and perhaps I'll be able to tell how the
> exciter/feild wire is supposed to be actuated.  I'll advise Sean to double
> check before trying the new alt.
>
> Are there perhaps two variations on the feild wire one that goes - and
> others that are +.   ??  Or perhaps I /we misinterpreted the diagram and
> they are always go to + when engine running.  I think Huw mentioned that
it
> goes to ground per oil switch when the engine is off - in which case we
had
> things bass-ackwards.
>
> Ben
>
> [From: Richard J Lebens <rick-l at rocketmail.com>
> Subject: RE: Alternator Question
> To: quattro at audifans.com
>
> I came into this discussion late but, go to
> http://www.john-joyce.co.uk/electron/altoreg/
> for a typical picture.  Grounding what you call the field wire or the
> wire to the left of the charge warning lamp in the referenced schematic
> would do bad things to your field rectifier diodes if the car was
> running.  Probably let the magic smoke out.  That wire provides current
> through the warning lamp to the regulator to energize the field winding
> from the battery before the alternator starts to output current.  No
> field current -> no magnetic field -> no output.  The lamp also serves
> as a resistor to limit the current.  note: if you disconect the wire
> your alternator may still work for a while because of the residual
> magnetism in the rotor.  The lamp goes out because when the alternator
> is passing current through the diodes both sides of the lamp are at
> battery potential and no current flows.
>
> The field rectifier diodes serve two functions.  They rectify the
> output of the alternator to provide a DC current to the field to create
> a mechanically spinning magnetic field.  Also the diode voltage drop
> across them is about equal to the rectifier diodes so the output of the
> field rectifier presented to the regulator is pretty close to what the
> battery voltage is.  As mentioned above, before the alternator is
> spinning converting mechanical energy into electrical, the field
> current has to be provided from the battery.
>
> --- Ben Swann <bswann at worldnet.att.net> wrote:
> > Huw,
> >
> > As it turns out, the new/rebuilt alternator was bad after all - Sean
> > will
> > be getting a new one from the local dealer for about the same cost.
> >
> > I am still interested in exactly how the exiter/feild current wire is
> > supposed to operate.  My understanding is that when it is hooked to
> > ground
> > (-) it enables the alternator to pass current.  Seems it's there to
> > prevent
> > the alt from passing current backward through the alternator when the
> > engine is not running, therefore acting as a switch.  The oil switch
> > is
>
>