What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

GMC vs GSA28 power: dual bus system

S

stevenclin

I'm New Here
Okay, I'm not building a Vans - I'm building a Rans S-21, but this forum is full of good knowledge so I'm hoping you guys will share it!

I'm planning out the avionics / electrical system now. My plan is to have dual independent electrical buses (which is a whole other topic for debate that I don't want to get into in this thread!).

The question is: I notice the Garmin GMC A/P controllers all have dual power inputs, i.e. "AIRCRAFT POWER 1" and "AIRCRAFT POWER 2", diode connected like all Garmin dual-power avionics. Yet the GSA28 servos have just a single power input.

What is the thinking here? What good is it to allow the A/P controller to have redundant power inputs when the servos themselves have just a single power input?

Seems like you'd just want to connect the GMC to the same bus as the servos are connected to. Connecting it additionally to the other bus would just allow the GMC to light up, I guess, but without the servos having power, that seems pretty pointless.

I think I am missing something - can someone enlighten me?

Thanks!
Steve Lin
 
The GSA 28 likely simply doesn't have enough physical pins to support dual power inputs. If you are concerned about power supply redundancy for your autopilot, it's simple enough to supply the servos from a Nuckolls-style essential bus that's appropriately diode-fed from multiple sources.

The GMC has some additional value as a means to easily control the flight director, so can be used in conjunction with a working display and attitude data source even if the autopilot servos are unavailable.
 
Don't know the reasoning behind why the GSA 28 servos don't have dual power inputs but for the GMC 507 my guess is that it is useful to have the flight director even if the servos don't work and the GMC 507 draws hardly any power which is good for an emergency backup power situation.
 
Make sense, guys - I hadn't really thought about the FD functions of the GMCs being useful without the servos. Thanks!
 
Would you need a diode on each power input from different busses? So a diode from main bus and a diode from e-bus?
 
Suggest you don’t make things more complicated with added complexity for no good reason.
 
You must log in or register to reply here.
Back
Top