Run only COM board of GTN650?

sbalmos · #1 04-09-2016, 05:44 PM

This is probably an absurd idea, but since the COM board of the GTN650 is on a separate fuse according to its install manual, is it possible to run just the COM radio alone with the rest of the box unpowered? My GTN is my COM1, which is on essential power in case of a total failure of both primary and backup alternators (a really bad day). At the moment I'll wire the whole box to essential power. But what if I could wire just the COM board to essential, but the GPS/NAV portion to my VPX, which would be load shed on that really bad day.

Is this even a possible wiring scenario? For further reference, in that really bad day scenario, I'd continue to run off the GPS in the GDU display.

Just wondering...

Jesse · #2 04-09-2016, 06:03 PM

I think I've tried that and it didn't work. The Nav power powered the screen.

Carl Froehlich · #3 04-09-2016, 06:07 PM

What Jesse said.

Carl

sbalmos · #4 04-09-2016, 06:16 PM

That's what I figured, but thought I'd ask anyway. Even looked at the serial links, so you could remote tune with the display off, in theory. But the serial links are on the NAV board also. Oh well. Pipe dream, as I thought.

So is it just transmitter/noise isolation that the COM board is on a separate fuse?

Mark Dickens · #5 04-09-2016, 07:32 PM

As I recall, you have three power pins, main, com and nav. You would have to power at least main and com. Since nav is a receiver, it wouldn't draw much power anyway. Practically speaking, I think you would be better off powering all three. I know you can shut down the nav side independently

Auburntsts · #6 04-11-2016, 11:32 AM

Just go ahead and wire the whole thing per your plan. What I have found is the current requirements we typically load plan with are far higher than the actual loads turn out to be which I guess is a good thing since it forces a conservative approach to architecture. I have a VP-200 and early on I was trying figure a "load shed" scheme but ultimately ditched it as unnecessary.

sbalmos · #7 04-11-2016, 12:08 PM

Yeah, it really doesn't matter in the end. The GTN and GAD ARINC look to be pulling ~3A. My whole "essential" bus is maybe 18A as it is, the majority of that being ~11A for the EFII injection/ignition (e.g. stuff that keeps the big fan turning). The backup alternator is 30A, so I'm not worried there. Even if I'm down to batteries, that's dual EarthX 680s, so no problem there (for a while). Okay, back to burying myself in wiring tonight.