Setting fuel pressure on Garmin G3X

Uri,
Thanks for providing the information from Garmin, but I’m not sure if I agree with setting volt meter 1 to FADEC A Volts, and volt meter 2 to FADEC B Volts. Why not use one of them to monitor the engine (FADEC) volts and the other monitor the airframe bus volts.  

I may be wrong, but this what I’m thinking...

Under normal operation alternator A is supplying voltage to both ECU Lanes A and B.  So if you set the voltage meters to read FADEC A/B, it would seem like both meters would be reading the same voltage source, which is generator A.  During normal operations alternator B is suppling voltage to the airframe components, so by setting one of the two to read  “Bus 1 volts”  you can monitor alternator B as well.  If alternator A fails, then alternator B is automatically directed to provide ECU power and is disconnected from the airframe, so you would expect to see the FADEC voltage stay normal and Bus 1 voltage begin to fall.  

Hi Jeff,

What you are saying makes sense, however, the Rotax Owner Manual does describe a fault of 

4.15) EMS voltage supply below the minimum required level

I did not find (yet) in the manual if EMS voltage must be displayed and monitored by the pilot, but if so, then it also makes sense to monitor each EMS voltage separately and get the indication for the battery from the Current or GP voltage input

I guess one more question is if FADEC A Voltage is the voltage supplied by Alt A or the Voltage that is supplied by Alt A or B to the FADEC A?

(though I'm pretty certain it is the Voltage to the FADEC) 

Maybe someone in the forum can share more info on the correct setup (I can open a new thread if needed)

2 things I do notice in my plane:

1. During Lane and Ignition check, when I switch ECU A off - FADEC A Voltage is blanked, and when switching to ECU  B off - FADEC B Voltage is blanked, however I do not know if its the alternator is not supplying voltage or the ECU not presenting the voltage to the G3X...

2. On the Amp meter, I see the switch from Alt A to Alt B when RPM is set to above 2500 RPM and battery start getting charge (indicated by negative current) (from Operational Manual: Increase engine speed above 2500 rpm and hold for 5 seconds (Generator B shifts to Generator A).)

Let me challenge Garmin Support with what you wrote

Uri,

I have volt meter 1 set to “Bus 1 volts” and volt meter 2 set to “FADEC Lane B volts”.  When I turn off Lane A there is no change to either volt meter.  When I turn off Lane B volt meter 2 goes off (X) and volt meter 1 stays normal. Next time I’m out there I’ll put EFIS 1 on it’s backup battery and turn off the master switch, I would expect volt meter 1 to go to zero.   

Hello Jeff,

Pasting here the reply from Garmin to your input ("Why not to use one of the voltage indicators to monitor the engine (FADEC) volts and the other monitor the airframe bus volts...  "):

" I think your reasoning is correct, but when you are using the FADEC interface, you are limited in your options to what FADEC is providing over the CAN Bus. I'm not sure how exactly is Rotax'es FADEC system monitoring power supply too lane A/B. I think that Rotax Support would be better equipped to answer that question.

 Having said that, I do not see a reason why you cannot use one of the General Purpose inputs to monitor voltage on the Alternator B if you wish to do that."

I totally agree with this solution. Moreover, if you remove GEN B Fuse I did it (inside fuse box) ECU A Volts and ECU B volts continue showing the same values on the G3X. So it would be more practical to monitor ECU A/B Volts together and BAT Volts on another GEA 24 input. Most of the time when engine is running ECU A/B will be supplied by Generator A and BAT Volts by Generator B. 

Regards,

Maximo.