Loose Ground on Battery makes CHT and OT do funny things

[AllThumbs]

We have been seeing CHTs and O/T doing funny things on the Dynon for a few weeks (after having done some work that affected the battery connections). Since all other ground-related functions were fine and there were no tell-tale problems with the radio or other senders we suspected a dynon internal problem.

After way too much thinking and analysis it all turned out to be slightly loose connections to the battery ground and from battery to the first ship's ground near the battery.

We found this by turning on all the avionics and measuring the voltage between battery GROUND (-) and the dynon cage ground. It was about 6 millivolts (mV). That doesn't sound like much but it indicated there was a faulty ground path to the panel. After tightening things up properly we were down to 1.2 mV. The CHT/OT spiking and strange excursions went away.

NOTE: the dynon does some input smoothing to the sensor data so we saw rapid, but not always drastic, changes. This fooled us for a bit.

Hope this helps someone avoid tearing all their hair out.

-Neil

 

[Mike S]

Thanks for the info

Good info to know, thanks for posting it.

This type of gremlin can be a real pain to chase down.

 

[ScottSchmidt]

I'll follow up on that.

There was an RV-10 flyer that has had the same issue for a few months now. His EGT, CHT, RPM, OIL Pressure...EVERYTHING was all over the place and he had spent a couple thousand dollars on A&P's trying to trouble shoot it.
A computer technician looked at the data and immediately knew it was noise most likely from the alternator. He looked at the plane and told them to replace the connectors on the ALT Field wire. So this past weekend he found that one of the wires had broke in the connector where it is crimped and the insulation was the only thing holding the wire on.
It fixed everything. A 6 cent part was causing all those problems, he was soooooo relieved.

By checking resistivity on wires may have helped trouble shoot this issue.
Just more knowledge to transfer to all of us.

 

[erich weaver]

Measuring small differnces in resistivity can be difficult to impossible with standard multimeters. Better to measure differences in voltages. Learned that from 'lectric Bob.

erich