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Old July 16th 04, 04:28 PM
John P
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Chris,
I think what John_F said is great!
The clues a
It's happened since new
It's a PA24-250
All grounds cleaned and "checked"
Any big load trips the OVP ( except gear up which is less)

I still thinks it's a ground loop. I believe it's the battery cable to
the frame(?) I forget how this
attaches on the PA24. Measure the voltage drop on the battery from minus
terminal of battery to the frame
and with a long "wire" to the bolt on the starter ground while someone
"cranks". How much voltage?
I thinks it's a ground resistance problem! Et all, does this make sense?
A ground problem would raise
the voltage seen to the OVP artificially, trip it.... The alternator seems
to keep the battery up, lower current
will not trip OVP, only higher current...
I know on our Cherokees I always took the battery cables off the belly
and cleaned em.....often..
and every low resistance high current connection also.
Did I miss a clue here that blows this out of the water? I looked at
this that the alternator is working fine!

John N3DR

wrote in message
om...
We had a similar problem in our 172M. The over voltage detector was
firing at too low a voltage, and we would get multiple dropouts.

To simplify diagnosics we used a handheld electric motor and Vee belt
to drive the alternator and then an adjustable power supply or fat
resistor load while looking at the 14 V lead with an oscilloscope. It
is a lot better than working around a spinning propeller. Found the
problem right away.

I noticed that the original overvoltage wiring "blob" had a small
tweekpot adjustment screw showing on one end. I suppose we could have
adjusted the trip voltage a little higher with that, but we already
had purchased a new one. Pipers may not be the same.

BTW - when measuring voltage drops, be sure to measure across as many
faying (joint)surfaces as possible. Your resistances sounded kinda
high.