Eric's alternator question

[graham.hilder@domain.elided (Graham Hilder)]

Eric wrote :
"When driving at night I've noticed a (very) faint red glow of the idiot =
light.  Additionally, the voltmeter indicates around 11 volts.=20
If I crank up the radio volume and hit the high beams I get a
brighter glow from the idiot light.  At high RPM I see a slight drop in =
voltage and at idle I have a higher voltage. I'm assuming the drop in =
voltage at high RPM is caused by the ignition system placing more of a =
load on the alternator than at idle but this is just my guess.    It seems =
to me that the instruments are indicating a "real" alternator problem". =
=20

I think there are two issues here.....=20
Firstly, I think there is a genuine problem in that the low voltmeter =
readings indicate that the alternator really is not producing what it =
should be.  As others have mentioned, first check for good connections to =
battery, alternator and the relevant grounds, in case it's something =
simple like that; and failing that, suspect brushes, regulator or =
diodes.=20

Secondly, I think there is a false problem, which is the faint red glow of =
your charge warning light which varies with conditions but is always =
rather faint. This is most likely a well-known false alarm from Alfa =
charging systems, due to the layout they typically use for the charge lamp =
circuit, which is also the alternator field circuit. This circuit has a =
particular fuse in it (the fuse number will vary from model to tmodel), =
and there are several other loads also off this fuse (these also vary, but =
are often the wipers and blower and other sundry items). If this particular=
 fuse or its holder gets just a little bit dirty (and don't they all?), =
then the extra resistance can cause a small voltage drop which causes a =
faint lamp glow, even if your alternator is working perfectly well (not =
that yours is though!).   This small voltage drop occurs when you draw =
more current through that fuse, by turning on the wipers or blower or some =
other item using that fuse, or maybe when you turn on heavy loads off  =
OTHER fuses, such as headlamps, which means more field current in the =
dirty circuit.

So if your alternator's faulty  and you have it repaired, you may still =
see the faint charge lamp glow under some conditions unless that particular=
 path is really clean. But at least your voltmeter should read correctly =
again.

Re your note "At high RPM I see a slight drop in voltage and at idle I =
have a higher voltage. I'm assuming the drop in voltage at high RPM is =
caused by the ignition system placing more of a load on the alternator =
than at idle but this is just my guess". =20

Noooo, this shouldn't happen. When all is well, the regulator will =
maintain the voltage prety well constant at all RPM above a fast idle or =
thereabouts.  If anything, the voltage may rise a little at high revs, but =
shouldn't fall. =20

Oh, and just as an aside, the ignition system isn't a very big load on the =
system as far as I know, at any RPM. =20

Regards,
Graham H,
New Zealand.
(Alfasud, GTV, Alfetta....
 all with identical charge lamp cct.....
  and all have had the above symptom exactly).

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End of alfa-digest V7 #688
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