In a message dated 10/16/99 12:26:00 PM Pacific Daylight Time, hoops@owt.com
writes:
> Connect the negative side of your DVM to the starter, and the positive side
> to the coil primary or the fuse block while the engine is running. The
> reading will return the potential difference, which I believe will be Zero,
> unless the system uses a ballast resistor to the coil primary.
>
> Regardless, has anybody fried a timing light due to the charging voltage of
> give or take 13.9 volts ?
Lonn,
The problem is not that the system runs at 13.5-14.5VDC the lights are set up
for that.
The problem is that a coil produces high voltage AC for the ignition system
and there is a self induction effect in the primary circuit. In simple
language the coil positive terminal runs at about 100 volts AC. Back when I
taught a scope class for Sun Electric I would ask a class what voltage could
be observed at the coil primary with the engine running. Answers would
always be in the 6-14V range Then we would hook up a scope to an engine and
prove that what I said was true.
If you doubt what I am saying is true I can give you a little experiment to
do. Start the engine on your LBC grab something that is grounded with one
hand. Place your inner wrist of the other hand on the coil + terminal. If
there is only 14VDC you won't feel a thing. If there is the 100V AC you will
feel a definate tickle. (one type of car that I used to work on had a coil
located where, when I would adjust the fuel injection my wrist had a tendency
to lay on the coil.!) I supposed you could use an AC voltmeter, but there is
no adventure in that. Usual disclaimers apply, Do not try this at home, we
are trained professonals, YMMV, Don't run with scissors, object in rear view
mirror are closer than they appear.
Rick
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