G1000 C172 w/ a constant standby battery discharge

Ajax

Ajax

¯\_(ツ)_/¯
I'll preface this with the fact that I'm not a mechanic but just a curious CFI.

We would typically get a small discharge from the standby battery, -0.3 amps while the system remains at a constant 28.0 volts. The S amps is either level at 0.0 or -0.3, no more or less(aside from a slight recharge after test and PFD initialization).

We thought it might be the standby battery, and it showed some signs of corrosion. Brand new one this morning, still the same song. It was 0.0 until just after wheels up, and then hung at a discharge for the majority of the flight--at all power settings.

I don't know what would cause it, and perhaps it's just pure coincidence but I have noticed that moving flaps, switching on/off air conditioning, and lights sometimes but rarely cause a change.

Is it a possible indication problem, or is there the possibility of something constantly drawing from it?
 
I'm not sure...
I would talk to Garmin/Cessna.
Usually something like that is not component failure (battery etc) but bad/loose/corroded connections or wiring. That is my general observation from troubleshooting and tracking down lots of electronics/EFIS gremlins.
 
It was on a different efis system but similar problem with a standby battery and it was a bad one way diode on the positive wire that allowed the battery to be charged but kept it isolated to prevent it from putting power back into the main bus.
 
On our G1000 equipped Cessna 172s we sometimes get faulty readings. One plane likes to show a 1 amp discharge the entire flight while the system remains at 28 volts. MX cleans the connections, and it works just fine again.
 
Thanks guys, I think we were over thinking the issue. They cleaned it up a bit and it seemed to be doing well tonight. Only a few discharges after wheels up
 
The G1000 172's bus logic is ingenious when it all works right, but I could see how cooky things can happen, especially like this, if something isn't. Basically it seems like the Standby Battery is powering the essential bus when it shouldn't. Everything connected to the ESSENTIAL BUS is also connected to another bus. The PFD is also connected to AVIONICS BUS 1, as well as ADC/AHRS and NAV 1 ENG CBs. COMM 1 is only CB'd to the ESSENTIAL BUS, as well as STBY IND LGTS, as well as, obviously, the STBY BATT CB.

Now, the G1000 logic is a little, shall we say, unique. Navigation, Communication, and a whole slough of other computery-processory-thingies are sort of all crammed into one unit, the Garmin Integrated Avionics unit, of which the G1000 has two installed, which do not directly cross-talk. the GIAs have their own NAV/COMM, Their own GPS, and depending on your model, the WAAS receiver as well. My question is why does one GIA unit need two separate circuit breakers? Additionally, the Engine Indicating System is a completely separate LRU, but shares its CBs with the NAV1 CB.

Now, what could be happening in your case, is start with simple:
1- Corroded or otherwise problematic connection from of the two main busses to the essential bus. If the items on the Ess bus arent receiving enough power from the main battery, they will draw it from the standby battery.
2- The G1000 electrical system and avionics system has a few back doors, if the POH/G1000 guide is to be followed. The GIA 1 is on on two circuit breakers, connected to two separate busses, as is the PFD, the ADC/AHRS, and Engine Indicating System. If the problem persists after checking the connections, you may need to check out the electrical connections in each of those LRU's as well.

**I am not a Mechanic, but I spent well over a year writing training material on C172 Aircraft systems for the flight school I instruct at. Also, I stayed in a Holiday Inn Express last night.
 
The G1000 172's bus logic is ingenious when it all works right, but I could see how cooky things can happen, especially like this, if something isn't. Basically it seems like the Standby Battery is powering the essential bus when it shouldn't. Everything connected to the ESSENTIAL BUS is also connected to another bus. The PFD is also connected to AVIONICS BUS 1, as well as ADC/AHRS and NAV 1 ENG CBs. COMM 1 is only CB'd to the ESSENTIAL BUS, as well as STBY IND LGTS, as well as, obviously, the STBY BATT CB.

Now, the G1000 logic is a little, shall we say, unique. Navigation, Communication, and a whole slough of other computery-processory-thingies are sort of all crammed into one unit, the Garmin Integrated Avionics unit, of which the G1000 has two installed, which do not directly cross-talk. the GIAs have their own NAV/COMM, Their own GPS, and depending on your model, the WAAS receiver as well. My question is why does one GIA unit need two separate circuit breakers? Additionally, the Engine Indicating System is a completely separate LRU, but shares its CBs with the NAV1 CB.

Now, what could be happening in your case, is start with simple:
1- Corroded or otherwise problematic connection from of the two main busses to the essential bus. If the items on the Ess bus arent receiving enough power from the main battery, they will draw it from the standby battery.
2- The G1000 electrical system and avionics system has a few back doors, if the POH/G1000 guide is to be followed. The GIA 1 is on on two circuit breakers, connected to two separate busses, as is the PFD, the ADC/AHRS, and Engine Indicating System. If the problem persists after checking the connections, you may need to check out the electrical connections in each of those LRU's as well.

**I am not a Mechanic, but I spent well over a year writing training material on C172 Aircraft systems for the flight school I instruct at. Also, I stayed in a Holiday Inn Express last night.
 
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