EarthX signal wire to GRT HX -- draining the battery

[AMillin]

I installed two ETX680C batteries. I have dual GRT HX units.

I ran without the signals connected to the EFIS for six weeks. They crank like monsters. The normal top-off draw after start takes a minute or two. Everything is good, time to hook the signal wire into my GRT EFIS.

I connected the EarthX signal wires to my HX analog inputs. I configured per the EarthX instructions. I tested the warning by grounding the GRT Analog input wire. It worked as expected.

I came back four days later and the voltage on the batteries was down. The signal wire connection was the only change made to the aircraft. When the master switches are off the batteries are disconnected completely with contactors. Under normal circumstances, there was no way for the batteries to discharge.

I spoke with Reg at EarthX. He said the signal wire will float around 2 volts. I confirmed this with a meter. With everything off, there was 2 volts flowing. Reg said the signal wire can provide up to 100ma.

OK, how do use the signal wire without having my batteries discharge?

Thanks,

Andy

[BobTurner]

First, ask Reg for a real schematic. The one shown cannot supply any current or voltage when the EFIS is not powered.
Now, guessing what?s really inside: put 3 ordinary diodes (or an LED) in series with the signal line. That should stop any discharge when power is off.

[AMillin]

Thanks Bob,

Yes, I was thinking of adding a diode. However, I'm not sure if that would defeat any warning signal. It is a good idea and I'll keep it in mind.

I spoke with Mark at GRT shortly after I made this post. Mark said the impedance resistors in the EFIS should not allow enough current to go through to drain the batteries. This is exactly what Reg thought. On an academic level, agree! However ... it IS draining the battery.

Mark really wants me to get a reading on current. I just picked up a meter that will work and I'll try it tonight.

Andy