Alt Circuit Breaker Popped Twice Yesterday

[lrobichaux]

On flight yesterday, temps were 40 degrees F on the ground. My alternator circuit breaker popped twice during about two hours of flight. Once a couple of minutes after start-up while still on the ground, and again on approach at the end of the flight. There were no other unusual indications. I was not using pitot heat either time when the CB popped, although I turned it on during flight, let the alt load stabilize, and there were no problems. Any suggestions on where to start looking? Might it be related to the cold temps (although that would be troubling in and of itself if true)? I've got a 60 amp alt., plane is less than one year old.

 

[Neal]

You may want to review the logs and see what the amp draw pattern is. Feel free to attach the flight (csv) if you want or you could use FlySto if you haven't tried that yet.

 

[Neal]

I would also send the log off to Pete for review. Per our discussions of late any ALT issues are very concerning.

I would expect you'll be told to inspect wiring and areas around the alternator. I've heard of some grounding issues in the past from builders and having to grind off the painted surface. @Cactus Charlie may know more. Not sure if it's a faulty breaker but that could be a something to consider.

I've flown in crazy cold here in VA and no issues related.

 

[Cactus Charlie]

Events like this make me glad I added alternator current monitoring and recording to my FX-3. Battery current and Main bus volts may provide some clues. Plot both for the flight. Send me the CSV log if you need help with that.

I very much doubt you could have a normal 60 A load. A intermittent short after the alternator breaker seems more likely.

 

[Neal]

@lrobichaux if it were me I'd consider the plane grounded for now.

 

[lrobichaux]

You may want to review the logs and see what the amp draw pattern is. Feel free to attach the flight (csv) if you want or you could use FlySto if you haven't tried that yet.

Great suggestion ... will do. Will attach the data here and send to Pete.

Events like this make me glad I added alternator current monitoring and recording to my FX-3.

I seem to recall that you described this in a prior post. Can you remind me where this was discussed?

 

[Cactus Charlie]

C

Post in thread 'Carbon Cub EX-3 Engine Failure (N40DT)'

Oct 17, 2025

You don't need a shunt to add alternator current monitoring. Simply disconnect the alternator wire at the circuit breaker, slip a Hall effect sensor over the wire, re-connect the wire to the circuit breaker. That part is a 5 minute job.

What takes the time is fitting the sensor wires to the GEA 24 connector and configuring the custom GP input definition.

Some would argue that Battery Amps tells you if the alternator is working. Battery Amps will go negative immediately if the alternator fails. I prefer to have battery and alternator current displayed and recorded.

I used the Amploc...

• Cactus Charlie

• 

 

[lrobichaux]

Thank you!

 

[lrobichaux]

Well, well, well. Lookie here. Clearly there was some kind of irregularities in the alt field for approximately 18 minutes before the breaker popped. Resetting the breaker seemed to resolve the problem for the short remainder of the flight. Graph is of Volt1 and Amp1. Any ideas?

 

[Neal]

Loose connection at the starter battery?

 

[Cactus Charlie]

Any ideas?

If you want my input send me the entire CSV file. Alt field current is not instrumented or recorded on a standard CC aircraft.

 

[lrobichaux]

You bet. Will email you in the morning. Thx!

 

[Cubonaut875]

You may want to review the logs and see what the amp draw pattern is. Feel free to attach the flight (csv) if you want or you could use FlySto if you haven't tried that yet.

You may have address this in a previous post and this may be better in a different thread, tell me more about the Fly Sto app and how you use it.

 

[lrobichaux]

@Cactus Charlie see link below. I’m working to download the actual data file and will post that up too.

SavvyAviation

apps.savvyaviation.com

 

[Neal]

You may have address this in a previous post and this may be better in a different thread, tell me more about the Fly Sto app and how you use it.

Thread 'A look at FlySto.net - amazing tool for flight analytics'

Apr 6, 2025

FlySto — Flying stories you can trust

FlySto — innovative avionics log and flight data analysis software

flysto.net

• Neal
• Replies: 13
• Forum: Articles of interest (or videos)

 

[lrobichaux]

I’m working to download the actual data file and will post that up too.

Will load up CSV files later this afternoon.

 

[Cubonaut875]

Thread 'A look at FlySto.net - amazing tool for flight analytics'

Apr 6, 2025

FlySto — Flying stories you can trust

FlySto — innovative avionics log and flight data analysis software

flysto.net

• Neal
• Replies: 13
• Forum: Articles of interest (or videos)

That's it - thanks!

 

[lrobichaux]

Three files attached. The file dated 12/15 ending with "KDTO" is the first flight of the day with no abnormal electrical indications. The file dated 12/15 ending in "KRPH" is the last flight of the day during which the ALT circuit breaker popped. Abnormal indications can be seen for approx. 18 minutes with VOLT1 at which time the CB popped. CB was reset which resolved the abnormal voltage indications for the few minutes left in the flight.

Lastly, the file dated today ending in "30F" reflects a lengthy run-up this morning after inspecting the alternator connection, battery connections and connections at the firewall terminal block (all were normal). This morning, I did as good of a visual inspection as possible - no abnormalities were noted. Note that I pulled the ALT CB during this run-up today just to observe the VOT1 indication with the breaker pulled. All appeared normal.

Any ideas would be much appreciated.

 

[Neal]

The files didn't attach, please try again.

Bummer when you can't find the "smoking gun."

 

[lrobichaux]

Had to change file name extension. See attached.

 

[Neal]

What was the original file extension and I'll see if I can fix up the forum'ware for future uploads.

 

[lrobichaux]

Yes, the website does not accept CSV files. I converted to Excel and it accepted the files.

 

[Neal]

CSV is allowed now.

 

[Neal]

Had to change file name extension. See attached.

Hopefully @Cactus Charlie can take a look at the files you posted in this post when he has time.

 

[Cubonaut875]

I'm just taking a wild stab at this- Neal you remember when your ignition was about to fail that there were weird electrical things that happened? Same with me, I had weird fuel flow readings that caused me to take the whole cowling off and test fuel pressure, tested just fine and then an ignition coil failed. Replaced the coil and suddenly the fuel flow was fine. Remember - I'm a mostly retired orthodontist with zero engineering experience.

 

[Neal]

Yes, I had all kinds of issues with the coil packs failing but never an ALT breaker popping. I did have a FLD (field) breaker pop once when I tried using the USB port to power a GoPro from the GMA 245R. Wouldn't rule it out but sure seems like either a bad alternator or suspect wiring/connection. Reminder I'm no A&P or orthodontist and I'm just a mutt and relatively new aircraft owner trying to learn the ropes and keep safe

 

[Neal]

@lrobichaux has Pete provided any insight? Is a warranty replacement of the Alternator an option? I don't know if they can cause this or just completely fail. I hear they are robust. But hate to see whatever is causing your ALT breaker to pop.

 

[Cubonaut875]

Yeah - they said the coil packs were robust and almost never fail

 

[Neal]

Yeah - they said the coil packs were robust and almost never fail

LOL - good point

 

[lrobichaux]

Good morning, all. Pete suggested I take the steps outlined in Service Bulletin XK-SB004 focused on improper hardware installed at the factory to attach the alternator wire at the alternator "B" terminal. Yesterday morning, I removed the cowling and did just that. Everything was tight, correct with zero signs of interference, arcing or any sort of abnormality. I traced the charging wire back to the firewall and all was normal. I checked connections to the main battery and starter relay which are located in the aft avionics bay. All connections were tight and normal. Buttoned everything up and did an extended ground run, which was normal.

The CC393 does not use the same EIS as the CC363. I believe my engine has the Lycoming EIS which does not have external coil packs.

@Cactus Charlie is still looking at the data files and may have additional thoughts. Unless he finds something to investigate, my plan is to take it to my avionics shop to install the Hall effect sensor that that @Cactus Charlie mentioned and also have the shop see if they can find anything. If nothing turns up, I'm going to fly it locally until the problem repeats. Recall that I upgraded my right ignition IBBS to a 6AH battery, so I'm confident I will be able to safely return to an appropriate maintenance shop in the event the breaker pops again.

Appreciate the input.