The Penny Drops

[Fisher, Scott]

Huw answers Tommy Tow from Fairfield, California:

> The alternator is a device for turning motion into electrical current.
> it does this by spinning an electromagnet <---

The key word here being "electromagnet" -- meaning, I assume, that if you
stop applying current to the electromagnet, it stops turning motion into
electrical current.  Yes?

Two weeks ago I was headed home from my San Francisco trip in the '83 Coupe.
It was Saturday of Labor Day weekend, just around 100 degrees, and it had
taken me over an hour to make the roughly five-mile stretch from the bridge
to highway 80 eastbound.  Needless to say, I had the A/C on full, adding to
the underhood heat load.

The traffic finally made it to I-80 and I started zooming up to speed.
Suddenly at high RPMs the engine cut out.  I dropped the revs and continued,
thinking something had gotten fouled or gummed in the heat/stop-and-go.
Tried again, more cutout (where "cutout" means "the whole car shook and
shuddered as though being hit by automatic 20mm cannon fire").  I managed to
limp to a Shell station, let the car cool off, and looked into it.

Once at rest, turning on the key provided nothing -- no click, no turn of
the starter.  Oh, THAT.  I had exactly the same symptoms 15 years ago in my
first British sports car, a 1974 M.G. Midget.  The problem then was that the
alternator had failed in such a way that it was pumping out 18V, which
boiled all the water out of my fairly new battery and burned the ground
strap inside it.  I turned the key again and sure enough, the voltmeter on
the dash shows about 6-8V -- not enough to throw the solenoid, much less
turn the starter.

I called for a tow truck (mainly to see if jump-starting solved my problem;
if it did, I was across the parking lot from a Sears, suggesting an easy
remedy) and Tommy Tow shows up in decent time.  He hooked up one of the
neatest toys I've seen in a long time: a little lunchbox-sized jump-starter.
I gotta get one.  The Coupe roared to life, but when Tommy disconnected the
jump-starter it started to die again.

"Y'oughta get your alternator looked at," sez Tommy.  "Car oughta run if you
take the battery OUT once it starts."

I thought that, while this is certainly true on my 356 with its generator,
it's demonstrably NOT true on the Audi, nor was it true on my '74 M.G. those
many years before, but I made polite noises while signing the auto club
paperwork.

Before he left, I borrowed Tommy's crescent wrench to disconnect the old
battery and hoofed it over toward the Sears.  About a third of the way there
I realized the building I was walking past was a Firestone auto center;
since it had cooled off to a balmy 95 degrees and I was carrying a big-ass
Group 41 battery, I walked into the building.  They had precisely one Group
41 battery in the store, and were happy to give me the Special Price (where
"special" means "you're six hundred miles from home, sucker, obviously
hand-carrying your battery, and the Sears looks like it's half a mile away
in this heat").  I carried the new battery back to the car  (noticing that,
unlike the old battery, this one made a sloshing sound as I walked),
installed it with the pliers attachment on my Swiss army knife, and made
record time home to Portland -- eleven hours door to door (eight of 'em
after dark), with a one-hour traffic delay and a one-hour repair delay, on
what is usually a ten-hour trip.  Frank Biela got nothin' on THIS
Audi-drivin' boy (well, except I don't think Frank had to change his own
transmission en route to the winner's circle :-).

Not long after returning home I did a Proper installation of the new
battery: removed it, cleaned out the battery tray, tightened the hold-down
clamp properly, greased the terminals and used my nice 10mm wrench on the
cables so I could get them tight enough without fear of rounding off the
nuts with my Swiss army pliers.  Turning on the key gives about 13V, idling
gives about 13.5, idling with the brights on about 12.5.  Life appears to be
good.  It's about time for new belts, though, and I've got a gallon of the
Spezial Audi Uberkoolant ready to winterize the car.

But as long as I'm telling the story -- what are the chances that Tommy Tow
was right, and that there's some alternator fault that's going to catch me
up again?  Got any home diagnostics to verify correct alternator functioning
(apart from the fact that it happily produces 13V or more while idling)?  Or
should I just go look at Huw's alternator page to see what it says there?

--Scott Fisher
  Tualatin, Oregon