Battery Monitoring

I ended up with two EarthX ETX900-VNT batteries in N5412K. To monitor the batteries, I have a couple of things going on. First off, I have the battery fault ground wire coming all the way up to my panel where there is a red led (79-2977-ND) on my panel right next to my Master and Aux bus switches. In the event that there is a failure with one or both of the batteries, this LED will flash with an error status.




The error codes for the battery are as follows:


The second monitoring system on the batteries is the Garmin G3X with a GEA24. I have the GEA24 configured to display the volts and current for both the MASTER and AUX bus. The Volts 1 and amps fields are fed from the VPX-Pro serial line to display the MASTER status. The AUX volts (volts2) is fed from the GEA24 Aircraft Power 2 line (which is connected to my AUX fuseblock). The AUX amps (amps2) is fed from a shunt I have on my AUX bus near the fuseblock.

The shunt has a 1A fuselink (F2313-ND) on each one of the lines. Hopefully these never blow, but I did install them in a format that allow them to be easily replaced. Yes this photo is taken before securing the wires.




The G3X / GEA24 is configured to have Red,Yellow, Green bands on the engine display page. Since this is a lithium battery, the settings are a little different than a lead acid. By the time a lithium (12v) gets to ~11.5v it is completely drained. The normal resting voltage is 13.3v. So I configured with the following settings:

• Red: 0-11.5v
• Yellow with Alert: 11.5-13.5v (alternator not charging)
• Green: 13.5-14.9v
• Red: 14.9-16.0v

The Main alternator is a AL12-EE70/B while the backup is a FS1-14B. Only one alternator will be live at any given point in time and the switch over between the two is a manual operation via a physical panel switch that controls the VPX ALT1 and ALT2 power pins. The alternators do come together at the firewall pass through, so the alternators only ever feed the MASTER bus. The AUX bus gets charged via the X-Feed contactor (via the MASTER bus). This makes the AMP alert settings a little more complex. 


The AUX bus consists or a battery, contactor, a 6 Ga wire coming forward to the mid-panel where a fuseblock distributes the AUX power to the backup power pins of the essential avionics. The 6 Ga wire is the limiting factor for this bus. Let's be super conservative and say that in our 10ft run we don't want to exceed 30As. I do not have 30As of avionics even hooked up to this... So for the AUX bus I have the following

Red: 0-2A 

Green: 2-20A

Yellow: 20-25A

Red: 25-30A 

The thought here is that we are watching how much power is getting sinked into the system, not the amount of current going into the system (alternator shunt). So if the plane is on, we should have at least 1A going out of the AUX bus (from what I have been watching I have a consistent 2A with the transponder off). Anywhere from 2-20A is normal. 20A is the sum of all the fuses I have in the AUX fuse block,  so if there is more than 20A indicating, then there is a short between the shunt and the fuseblock (6inches).

The MASTER bus Amp reading gets its data directly from the VPX-Pro via the serial line. The VPX page on the G3X has a pretty nice display for each one of the outputs themselves. I chose to set the color bars on the Master Amp gauge relative to what the main alternator can output. This is a little mis-leading. If I am functioning off of my main alternator, then I have 70As to work with. However, if I have switched over to my backup alternator for some reason, then I only have 30A to work with. So I know how much my VPX is outputting, but I did not put shunts on the alternator lines, so I do not know how much current is coming from the alternators.

Red: 0-4A 

Green: 4-60A

Yellow: 60-65A

Red: 65-70A 

I have to look into this a little later to see if there is anything smart I can do with the GEA24 discrete inputs. I do know that if I have switched over to the backup alternator (for other than just testing), that I am already looking at where and how to land. So I am not sure I care to deep dive too much into this case.