Batt Amps flashing -1 on RV-12iS G3X

[CTCole]

I have a 912iS Sport installed in a RV-12iS (16 hrs TT) with a Garmin G3X MFD. Starting about 2 hrs ago, the MFD shows the Batt Amps flashing -1. That value will go lower (-2, -3) when I turn on strobes, landing lights, etc. When I turn them off, the amps rise back up to 0 and the flashing stops, but after several seconds it will drop again to -1. The voltage remains at 14.0 or drops to 13.9 when the flap motor runs, but then goes back to 14.0. Alt Amps varies between 5 and about 12, depending on how much equipment is turned on. This behavior doesn't seem to depend on engine rpm -- it will continue in flight (ca. 5000 rpm) as well as during ground running (2500 rpm).


What might cause this? My knowledge of aircraft charging/electrical systems stops in about 1967. To me this seems like a faulty voltage regulator. What diagnostic tests might identify the problem?

 

[Mich48041]

According to schematic WH-00134-2.pdf, there are two shunts, one for the generator and one for the battery. I suggest that you check the battery shunt. If like most shunts, it should have 4 wires connected: two large ones (battery cable) and two small sensor wires. Make sure those terminals are clean and tight. There should be a 1amp fuse connected to each of the shunt small terminals. Make sure those 1 amp fuses are not blown. If the shunt signal wires were reversed, that would cause a negative battery current indication. That scenario seems unlikely if everything worked fine for the first 14 hours. But just to make sure, check if the battery current indication is negative with the engine shut off.
The charging system is definitely working OK if the voltage is 13.9 or 14 volts. If the charging system was not working, then the electrical system voltage would be less than 13.5 volts, more likely 13.3 or less which is the fully charged voltage of an EarthX battery.

 

[CTCole]

Thanks, Joe, I'll look into that.

 

[penguin]

Or remove the indication from the display, bus voltage is a much better indicator of charging system health...

 

[mburch]

You might want to take a look at the bus current calibration settings in section 30.4.32.15.1 of the current G3X installation manual (revision AW), particularly the "Zero Deadband" setting.

 

[CTCole]

I tried to check the 1-amp fuses mentioned by Joe. I removed the AV-60000 Power Module and found the shunts, but could not find the 1-amp fuses he mentions (they are shown on the wiring diagram). I did test for continuity between the Battery and Generator lugs on one end, and the D-sub connector pins corresponding to those 4 fuses on the other end, and all 4 showed continuity, so I believe they are intact.

I looked at the calibration settings Matt describes -- interesting, a bunch of "fudge factors"-- and yes, I'll try the Zero Deadband setting. But I still nags me wondering why this problem has appeared, and if there is something bogus going on that I'd be papering over by setting the deadband to ignore it.

 

[Burndout11]

I tried to check the 1-amp fuses mentioned by Joe. I removed the AV-60000 Power Module and found the shunts, but could not find the 1-amp fuses he mentions (they are shown on the wiring diagram). I did test for continuity between the Battery and Generator lugs on one end, and the D-sub connector pins corresponding to those 4 fuses on the other end, and all 4 showed continuity, so I believe they are intact.

I looked at the calibration settings Matt describes -- interesting, a bunch of "fudge factors"-- and yes, I'll try the Zero Deadband setting. But I still nags me wondering why this problem has appeared, and if there is something bogus going on that I'd be papering over by setting the deadband to ignore it.

I had the same issue, but mine would only go -1 when I had the landing lights on. I consulted with some on VAF, one of which pointed out that his would do the same and return to 0 after about 15-30 seconds. After paying closer attention, mine went back to 0 after about 30 seconds. I decided to not worry about it and just monitor the issue.

 

[unladenswallow]

AFAIR the 1A fuses are small red boxes soldered on to the circuit board and secured in place using what I think is either silicone or hot-melt glue.

 

[CTCole]

The Batt Amps will stay flashing at -1 indefinitely. If I turn a load off, the Batt Amps will go to 0 briefly and then return to flashing -1. I reset the zero deadband to +/- 0.8 Amps, and then tried 1.0 Amps, but that did not stop the behavior (although at -1 A it may be inhibited longer at high RPMs).

Since the battery remains steady at 13.8 V, and the Alt Amps rises and falls as loads are turned on and off, I think the voltage regulator is doing its job properly. Poring over the wiring diagrams doesn't shed any light (for me) on how the circuit produces an amperage reading: maybe that happens in the GEA 34 black box, or in the MFD itself...??

I didn't see those small red fuses on the AV-60000 when I took it out, but I was down in the footwell and perhaps need to fully remove the unit and disassemble it.

Still a mystery.