Huge amp drop on G3X

[sea2jet]

I have been having an intermittent amp drop with spikes to -680 amps then back to zero amps and then another drop. It did it as well about 6 hours ago but has been fine until today. Here is a link to the flight with engine parameters
https://www.flysto.net/logs/goctlqw2...&check=125uaqp
‘voltage 1 stays steady at 14.3 and voltage 2 at 14.1, but the spikes don’t last long before going back up. Usually I’m at +3 amps. Any idea what might be causing the extreme drop in amps? Shunt? Thanks.

[Andy]

Can you please post a link to the raw CSV log file. Private message if you prefer.

With the data you have provided I'd be checking the shunt sense connections. I think it's unlikely that the battery could source over 600 A without pulling down the voltage of MAIN bus.

[sea2jet]

Here you go Andy, Thanks for the reply. Pete at Cub Crafters had the same suggestion. I’m wondering if the problem is in the 1 amp fuse holders?

https://www.dropbox.com/scl/fi/d2c03...f3gid6nv6&dl=0

[sea2jet]

I’ll follow that procedure in the future. That is good information to know. Thanks Andy. I’ll update the thread once I remove the G3X to access the shunt and see what the issue might be.

[Andy]

I think it's unlikely that the battery could source over 600 A without pulling down the voltage of MAIN bus.

There is a 40 A fuse between the master solenoid and wire PO3A10BK which conects to one side of the shunt. The other side of the shunt goes to MAIN via P09A10BK. The battery could not source 600 A through the shunt as the fuse would blow. The battery could perhaps source 600 A very briefly but not through the shunt circuit.

[Andy]

The fuses and the poorly protected terminals all go away if a Hall effect sensor is used. I used an Amploc KEY100 sensor when I added alternator current monitoring to my FX-3. I expect to replace the battery current shunt with a KEY100 at some time.

[Andy]

Unrelated to the current issue but I notice that your log does not start until after engine start and stops before engine has completely shut down. That means you are not recording data that may be useful in some future investigation.

Quite a long time ago I ran some tests in the hangar and was upset when I got home to find I had no data recorded. I asked Garmin for the conditions that had to exist for the data log to run. I was told:

The data log begins when at least one of the below criteria are met:
Have a valid GPS fix
Engine running
System is in the air
Autopilot is engaged

I power IBBS, and usually have a GPs fix, before engine start and only power off IBBS after I have logged times after engine stop. I'm curious to know your power up, start, stop, power down sequence.

[Andy]

Thanks.

I had a quick look at the CSV log and I see no correlation between the Battery Amps anomaly and any other parameter. I did find it interesting that the AMPS parameter appears to go out of range and become invalid but the GDU does not alert for that condition. Was battery current red X at this time?

I still think careful inspection of the shunt sense connections is the next step. I'd want to experiment with intentional open circuit of each sense lead (pull the fuse) to see what indicated currrent is shown if no obvious fault is found.

It may be worth asking Garmin experimental support what GEA 24 currrent reading would be expected for an open circuit in each shunt sense lead.

[sea2jet]

Nope, no Red X during the event.

[Andy]

Nope, no Red X during the event.

Interesting. What was the indicated current for the approx 30 second period for which the data log shows no current data and no CAS alert (13:18:43 to 13:19:12 local)?