Date:         Fri, 7 Apr 2000 18:08:34 -0400
Reply-To:     David Beierl <dbeierl@IBM.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@IBM.NET>
Subject:      Charging system strange symptom
Content-Type: text/plain; charset="us-ascii"; format=flowed

I was hanging about with Ken Wilford the other day, as he mentioned.   He
was showing off his marvelous little Digitool which I hooked up to my beast
and was watching do its tricks.  Well, it (the beast) has been acting a bit
cranky and getting mileage that was not exactly of the finest, so I was
more than just passively interested.

Anyway, I was using the external voltage probe (that Darrell so
thoughtfully provided in the design) to chase the grounds around, and I was
astonished to find that the alternator case was a third of a volt negative
to the rest of the engine.  That doesn't sound like much, but it
is.  There's too much drop in the main charging circuit anyway, which the
alternator doesn't see b/c the voltage regulator monitors right at the
alternator instead of at the battery.

So I had to remove the alternator and shine up the inside of the bracket
and the mounting bosses on the alternator case.  Voltage drop went down to
25 millivolts instead of 350, and of course it charges better than before
(I had noticed that the battery was a bit feeble, but hadn't started
tracking it down).  I could be dreaming, but I think the motor runs better,
too.  It certainly got better mileage on the way back from New Jersey --
not great but a definite difference.

Anyway, something to check when looking at the charging circuit.  I've
always measured charging voltage to the alternator case, since it's handy
to clip the meter lead onto one of the protruding screws.  Never occurred
to me that there might be a high-resistance joint (somewhere around 0.005
to 0.01 ohm) between the alternator and engine.

david

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"