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

[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)?

[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.

[sea2jet]

Unfortunately I was not watching it all the time as I was coming in for a landing. I figured I would figure it out once I was on the ground but it went away. I do remember seeing over -700 amp draw and thought that can’t be right. I ordered a couple of blade fuse holders and 1 amp fuses in case there are glass fuses installed. I read over on the RV forum that others have had the same erratic readings with swings into the -600-700 amp range when using glass fuses and after changing out to blade type fuses, the issue went away.

[Andy]

Unfortunately I was not watching it all the time as I was coming in for a landing.

Sounds reasonable but how can you be sure there was no red X?

[Andy]

I read over on the RV forum that others have had the same erratic readings with swings into the -600-700 amp range when using glass fuses and after changing out to blade type fuses, the issue went away.

My FX-3 uses blade fuses but I don't know what was provided for the EX kits. If I ever had a problem with mine I'd solder glass fuses in circuit and sleeve them in heatshrink.