RV-12iS / G3X Bat Amps question

[CTCole]

Today when I turned on the landing light (everything else was on), the engine monitor screen BAT AMPS display started blinking red. The ALT AMPS remained about 9, and the system voltage was 13.9. The BAT AMPS would blink whether the engine was idling on the ground or at cruise power in the air, when I turned on the landing light.

At 12 hrs I'm still learning the systems. I'm very old-school, steam-gauge, etc. -- accustomed to a single ammeter on an aircraft, showing whether current is going into or out of the battery.

What is the BAT AMPS measuring? Is this discharge from the battery? And if so, why would there be a discharge? Where is this sensed? What kind of fault could be producing this display? What tests should I make? What can I do to correct this?

 

[jcl777]

I had a similar issue several years ago. Mine was caused by one of the plugs not being fully seated into the HIC module. It reoccurred sometime after that but was resolved with the newer HIC module. Also check that all the pins are fully inserted into each of those plugs.

The main issue was observed when I had the landing lights on steady. On pulse things were OK.

 

[CTCole]

I had a similar issue several years ago. Mine was caused by one of the plugs not being fully seated into the HIC module. It reoccurred sometime after that but was resolved with the newer HIC module. Also check that all the pins are fully inserted into each of those plugs.

The main issue was observed when I had the landing lights on steady. On pulse things were OK.

Thanks, John. Following your reply I checked to make sure the HIC module connectors (which are the new type) are fully secure & wires are fixed in place. All good, so I'm still scratching my head.

 

[rcarsey]

I think this is "normal" and it happens to me all the time. When turning on the landing lights (or any high amp load), you'll see the battery discharge -1 or -2 A. After < 30 seconds, you'll see it come back down to 0A.

The explanation (in my mind anyway), is that under a certain load, the alternator can put out 14.1v. When that load is increased (e.g. landing lights on), it can't continue to output 14.1, but instead will maybe come down to 14.0. Now, the alternator and avionics bus has 14.0; while the battery has 14.1. The battery will discharge so that it's at the same level as everything else its connected to. As the battery comes down to 14.0, it is discharging and showing negative amps on the display. Once the battery is back in equilibrium, you should be seeing 0 amps.

The real question is why does the bus voltage go down slightly when you turn on the landing lights. 3 possibilities.. 1. The voltage regulator (on top of the fusebox) isn't doing a perfect job and is allowing the voltage to dip as the load gets higher. 2. The wire from the fusebox to Power Module [the alternator wire supplying the main bus] (K7124) is sized too small and is losing some voltage at high loads. 3. The traces on the back of the Power Module are sized too small and is losing some voltage at high loads.

My personal vote is #2. According to our wiring diagram, wire K7124 is 10 AWG wire and 60 inches (5 feet). This calculator shows a drop of 0.18v with 10 AWG copper wire, 13.9v DC, 5 foot length, and 15A (which is my total load with landing lights ON). That'll bring my voltage down to 13.72v. In real life, my G3X records show a drop of 0.1v after the lights turn on (rounding errors).

In reality, I'm sure this sort of thing has been happening all the time, but with analog ammeters, its really hard to notice it. Perhaps the real solution is to only generate a Warning CAS message immediately if the amps are more than -2 amps -OR- if its -1 or -2 for more than 1 minute. I think this logic can be programmed into the G3x with the latest rev.

 

[CTCole]

I think this is "normal" and it happens to me all the time. When turning on the landing lights (or any high amp load), you'll see the battery discharge -1 or -2 A. After < 30 seconds, you'll see it come back down to 0A.

The explanation (in my mind anyway), is that under a certain load, the alternator can put out 14.1v. When that load is increased (e.g. landing lights on), it can't continue to output 14.1, but instead will maybe come down to 14.0. Now, the alternator and avionics bus has 14.0; while the battery has 14.1. The battery will discharge so that it's at the same level as everything else its connected to. As the battery comes down to 14.0, it is discharging and showing negative amps on the display. Once the battery is back in equilibrium, you should be seeing 0 amps.

The real question is why does the bus voltage go down slightly when you turn on the landing lights. 3 possibilities.. 1. The voltage regulator (on top of the fusebox) isn't doing a perfect job and is allowing the voltage to dip as the load gets higher. 2. The wire from the fusebox to Power Module [the alternator wire supplying the main bus] (K7124) is sized too small and is losing some voltage at high loads. 3. The traces on the back of the Power Module are sized too small and is losing some voltage at high loads.

My personal vote is #2. According to our wiring diagram, wire K7124 is 10 AWG wire and 60 inches (5 feet). This calculator shows a drop of 0.18v with 10 AWG copper wire, 13.9v DC, 5 foot length, and 15A (which is my total load with landing lights ON). That'll bring my voltage down to 13.72v. In real life, my G3X records show a drop of 0.1v after the lights turn on (rounding errors).

In reality, I'm sure this sort of thing has been happening all the time, but with analog ammeters, its really hard to notice it. Perhaps the real solution is to only generate a Warning CAS message immediately if the amps are more than -2 amps -OR- if its -1 or -2 for more than 1 minute. I think this logic can be programmed into the G3x with the latest rev.

Thanks for taking the time to work through this, Rob. I appreciate your analysis & looked through the wiring diagrams (again). I'll check next time and see if the warning shuts off in due time.

-Chris