Alt Circuit Breaker Popped Twice Yesterday

[lrobichaux]

It shows a 37 A alternator current spike and numerous lower amplitude spikes.

That short alt current spike was me turning on the pitot heat momentarily.

Did you look at the flight log for the "normal" flight with no CB trip

This was the flight immediately prior to the FIELD breaker pop. In looking at various other previous flights with nearly NO variation in voltage output, it's clear that the loss of regulator control started on this flight, although no CB pop.

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

Again, that spike was not an un-commanded spike. It was me turning on, and then off, the pitot heat.

 

[Cactus Charlie]

What heated pitot is fitted to your aircraft? The Garmin GAP probes appear to have a maximum current of 12 A when cold. This current spike was about 24 A.

 

[Cactus Charlie]

This is what a heater test looks like for my GAP 26-10 probe:

 

[lrobichaux]

What heated pitot is fitted to your aircraft?

It's a big ass pitot tube. It's not the standard Garmin probe on the FX-3s. Sadly, this is also why the X/NXCubs do not have AOA connected on the G3X. I've considered having a Garmin pitot tube installed just for the AOA.

 

[Cactus Charlie]

It's a big ass pitot tube. It's not the standard Garmin probe on the FX-3s. Sadly, this is also why the X/NXCubs do not have AOA connected on the G3X. I've considered having a Garmin pitot tube installed just for the AOA.

If it has a part number marked on it I'd be curious what it is. I can't find any heated pitot probes that draw near 24 A and the CB is only rated at 20 A.

 

[ve6yeq]

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.

In this case, the voltage drop is simply the load limit of the alternator not being able to keep full voltage when loaded to almost maximum rated current. This is clear from how the voltage returned to normal as the current dropped.

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

If it was a short on the alternator output side, then it would have also shorted the main battery to ground which would have caused more issues. I don't agree with how the external regulator was added to the system for reasons such as this.

I'd like to know why regulator BUS VOLTAGE SENSE is wired to the START CB. Isn't the alternator required to work with the START CB pulled?

Another of the external regulator integration issues. If I had an XCub, then I would be planning to revisit the alternator integration sooner rather than later.