Alt Circuit Breaker Popped Twice Yesterday

[Neal]

I assume you have a GMA 245R over the rear seat? There is a USB port on the front of it. Do you have anything plugged into that?

I had the FLD breaker pop once and it's the only time I ever used that USB port to try and power a GoPro.

 

[Cactus Charlie]

Here is the FX-3 CB group. You can see the reason for the confusion caused by describing the field CB as the alternator CB.

 

[Neal]

Hard to believe there is no ALT breaker but then again you have a larger ALT than us. I’m curious, what breakers are on the front of your seat base?

 

[Cactus Charlie]

The schematic shows an alternator fuse not a CB.

 

[lrobichaux]

Schematic attached. Pic of panel attached.

 

[lrobichaux]

There is a USB port on the front of it. Do you have anything plugged into that?

Remote audio panel is located in the aft avionics bay (which the FX-3 does not have). Nothing plugged into the USB power outlet.

 

[Cactus Charlie]

As suggested in my email - start your visual inspection at the shunt.

If no problem found there you will have to inspect all the wiring between the shunt and the battery as well as the start and main solenoid connections.

 

[lrobichaux]

Actually, there is one CB not on the main instrument panel. The left ignition CB. See attached.

 

[lrobichaux]

If no problem found there you will have to inspect all the wiring between the shunt and the battery as well as the start and main solenoid connections.

I’ll update everyone what the avionics shop finds . This is outside of my attention span and most likely skill level too.

 

[Neal]

I’ll update everyone what the avionics shop finds . This is outside of my attention span and most likely skill level too.

Good call. I'm out of ideas and my skill level of suggestions. These are too complicated and I'm no A&P by a long shot. The planes have quite a bit of variance at least from the breaker setup. I hope someone finds it and you can regain peace of mind.

 

[Cactus Charlie]

Also, the X/NX schematics I have seen do not match the charging system of the aircraft under investigation. If it was my aircraft I'd be asking for the applicable revision of the DC power schematic.

I'll retract that but I'm unable to delete it. It was based on the incorrect assumption that the aircraft under investigation had an ALT CB not the fuse shown in the schematic.

 

[ve6yeq]

Schematic attached.

Now that I can see the schematic, it is interesting to see that they attempted to "simplify things" by switching to an external alternator regulator with built-in overvoltage protection rather than the SS/EX/FX, which has an alternator with a built-in voltage regulator and an external overvoltage protection system. I have several concerns about how they wired the external regulator in, but that is really for another time.

From the technical overview of the external regulator, it is clear that the voltage regulator became unstable, and that triggered the overvoltage protection to trip the field breaker. The regulator claims to be a "linear voltage regulator" design that should prioritize stability over efficiency, so either the regulator internally failed in some way, or more likely had external noise injected from a poor connection. I would carefully inspect all wire terminations to and from the regulator and alternator, as one or more appear to be loose and/or corroded.

 

[Cactus Charlie]

From the technical overview of the external regulator, it is clear that the voltage regulator became unstable, and that triggered the overvoltage protection to trip the field breaker.

Did you look at the flight log for the "normal" flight with no CB trip? It shows a 37 A alternator current spike and numerous lower amplitude spikes. The zoomed in view of that spike shows the voltage dropped rather than increased.

The log for the CB trip does not show an alternator current spike before the trip. That is likely because Garmin heavily lags displayed and recorded data.

It was the "normal" flight data that I think points to an intermittent short of the alternator output, not a regulator fault.

 

[Cactus Charlie]

From the technical overview of the external regulator, it is clear that the voltage regulator became unstable, and that triggered the overvoltage protection to trip the field breaker.

The documentation for the regulator is here - https://bandc.com/wp-content/uploads/2018/05/lr3c_technical_manual_revC.pdf

It confirms that this regulator is designed to trip the field circuit breaker for over-voltage protection. This does not necessarily mean OV protect is the only reason for field CB trip.

Interesting problem and I'm glad it's not mine.

Very surprising to me that CubCrafters did not provide any alerting for alternator failure. It would be a trivial change to the ALT AMPS scale definition.