Captain Caffeine <sfisher@wsl.dec.com> laments over his dyslexic disability
with automobile electrical systems (or, to be Politically Correct, should I
say "Electrically Challenged?" :^)
> I brought a car back to life this weekend.
Jolly good of you.
> [...]
>
> But having British cars has made me slightly dyslexic when it comes
> to batteries, polarity, and ground/hot cables. I carefully looked
> over the new battery (realizing after I returned home with the new
> one that I'd forgotten to note the orientation of the old one before
> removing it), repeated the Britcar-owner's mantra ("positive earth?
> Negative earth? Damn") and quickly wired it up backwards. This led
> to the most interesting sizzling noises when I tried to touch the
> "ground" strap to the positive terminal after carefully wiring the
> "hot" strap to the negative pole first.
>
> [...interesting starting pyrotechnics deleted...]
>
> But the ammeter was quite interesting. One of the nice things about
> the Super Sport package is that it has gauges, while the base model
> only has idiot lights. Of course, this being a (gasp) domestic auto,
> the gauges have no calibrations; well, the oil pressure gauge has 0
> and 60, the temperature gauge has C and H, the gas gauge has E and F
> and the ammeter has D and C. On starting, the ammeter drops into
> the D range, as is expected; and at idle, it sits at the marked
> center of the gauge, where it's supposed to be.
>
> But at any speed above idle, the system charges like Imelda Marcos at a
> 9 West factory discount sale.
Great analogy. I like it.
> At freeway speeds, the needle is pegged up at the C end of the range.
I notice that you have been suspiciously thrifty with the description of this
tow vehicle. sfisher wouldn't be ASHAMED of this car would he ... Nah!
Lesse, ... Lister-Corvette, ... Quadra Jet, ... SS package, ... old enough
to be worth too little to have in running condition for more than a few
racing seasons, ... got to be a mid '60s Chevelle, 327 hi-po, and if he's
really lucky, the 4-speed Muncie gearbox.
I also recall this from Robb Pryor's amalgamation of the "Brit-Cars-Owned-
List:"
1965 Chevrolet Chevelle Super Sport
Condition: 5
Owner: sfisher@Pa.dec.com
Or was it the '77 Catalina?
> Is it your experience that the problem could be caused by reversing
> the polarity? Could I have blown the alternator diode?
Make that diodeS. Almost guaranteed. With that vintage of car, the diode
stack in the alternator is always connected across the battery (in series
with the stator windings), and are normally back-biased when the engine is
not running. With your fumble-fisted frolicks, you forward biased them
and put about a gazillion amps through them (okay, I exaggerated: HALF a
gazillion amps). On the brighter side - I think that the regulator in
that car is mercifully electro-mechanical (as opposed to electronic),
so I don't think that you toasted its brains. At any rate, (ugh!) it
appears from your description that the regulator is trying to charge the
battery.
> If so, would that cause the system to charge at such an excessive rate?
Um, whatever the effect is you're seeing on your ammeter, it's not charging.
A shorted alternator diode will cause the AC output of the particular stator
winding to go into the battery, and batteries don't do AC. The battery will
get very upset, hot, and begin to *boil* its electrolyte away! (I have
personally seen this happen due to a shorted diode - not for long mind you!)
(I had an e-mail exchange where someone - Jerry Kaidor, I think - claimed that
if all three diodes in the alternator are (equally) shorted, that the output
of the alternator would be effectively shorted, and the battery would see
nothing. This may be true, but *I* think that it will still see a reduced
AC current, only it will be at 3 times the frequency. Go figure.)
I seem to remember that a typical ammeter movement has a diode across it
that is normally intended to protect the movement from excessive voltage.
This could explain what you're seeing on your ammeter - the diode could be
rectifying the output of the alternator to look like the battery is being
charged. Of course, my brain has long since turned to peanut butter, and
what do I know anyway. X-)
> And what
> will it do to my battery -- I'm guessing that it will at the very
> least cause it to overheat, to evaporate its contents early (I had
> that problem on an MG once many years ago) and might actually cause
> it to explode?
And you thought the starting noises were fun...
Oh - by the way: if you do have (a) shorted diode(s), it (they) will
discharge the battery if you leave it connected, even with the key off.
You DID disconnect the battery cables, didn't you??!? Oh-oh...
Pat Vilbrandt John Fluke Mfg. Co., Inc. Everett, Washington USA
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