re: Spiders, A/C, and low voltage

[Jay Negrin <jmnegrin@domain.elided>]

Ray Manners writes:

<<Seems like I'm not alone with this...

Problem- I turn on the A/C and the voltage drops. Big time!
This is my second '87 Spider with exactly the same problem.
At idle- A/C off- voltmeter is normal- about 12.3V
Turn the A/C on- fan low- it reads about 11.0V
Fan medium- 10.0V / Fan high- almost off the scale on the low side!
Voltage is so low that the wipers won't complete cycles, stereo cuts
out- even the headlights dim.
I have a brand new battery- 4 days old.. the highest capacity that will
fit in the car.
I've lived with the problem for a long time, but I'll be moving south in
a couple of weeks and A/C is imperative!
This explains the problem well...>>

I am not a mechanic, nor do I play one on TV.  That said, I think I
would look at, TA DA, the alternator.  It may seem to put out OK
voltage, but is it really?  Is it possible that a set of diodes is not
working properly, which leaves you with less than adequate electricity
when you need it the most?

As a corollary question, "When other high current accessories are used,
do you see a similar drop in voltage?"  I am thinking of headlamps
and/or high beams.

What happens to the voltage when at a fast idle, say 1500 - 2000 rpm?

Remember that alternators make AC electricity.  If I remember right, it
is produced in three different phases.  Each one has the "bottom half"
"cut off" somehow (magic is used here, the diodes I think - I said I
wasn't a mechanic.  I ain't no 'lectrician either!)  The three phases of
the AC, all with the negative half gone, in VERY simplistic terms, can
approximate Direct Current, at slightly over 12 and half volts.  With
one set of diodes not working, one phase of the AC lets the "bottom
half" sneak in, countering the "top half" of another of the phases.
Substantial loss of electrisicals (a very technical term, there)
results.

Help me, someone.  I think I just made a big whopping fool of myself.
(But I think I must like it there occasionally  :)

Jay Negrin
ARO So Cal
76 Alfetta GT - Asking how much a decent, but not grand paint job should
cost, including patching some rust.  No body work is needed, I think.
NOW I've done it - tempting the fates.

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