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**[email protected]** · May 21st 07, 11:01 PM posted to rec.aviation.owning,rec.aviation.homebuilt

In rec.aviation.owning wrote:
Intermittent problem with an Aerospace Logic VA-100 Volt & Amp
indicator.
Volt side works at all times and is accurate, amp side works properly
occasionally but more often than not displays -0.0 amps. When it does
work it indicates charges and discharges properly.

I'd guess an open in one of the twisted pair wires to the shunt. With
the given wiring, it has to be reading the system voltage between one
of the twisted pair wires and ground, so both wires in the pair probably
aren't open.

If the shunt itself was intermittently open, you'd probably see the
displayed voltage rise quite a bit (alternator working without the load
of the battery) or fall quite a bit (battery not being charged by the
alternator) depending on which side of the shunt the voltage is read
from. Shunts are usually pretty stout mechanically, anyway.

For diagnostic purposes, you could disconnect the twisted pair at the
indicator and connect the pair to a multimeter. If the multimeter
sometimes indicates 0 mV even when you know there should be a charge or
discharge, check the twisted pair wire and the shunt. If the multimeter
always indicates correctly, then there may be a problem inside the
VA-100 indicator.

Matt Roberds

Disclaimer: This is based on experience with ground vehicles. I don't
have an A&P; I don't even have a TG&Y. Some of this may not be
allowable owner maintenance. Your mileage may vary.