Avionics power/reset problem

[DesertNomad]

I have two avionics master switches: the main one which I use every time I fly and an aux switch which I believe is connected in parallel. I do nt use the aux switch as it is meant as a backup if the main one fails.

For the past couple months, when I turn on the avionics master, sometimes nothing happens and I have to turn it off and back on. Oddly, seems to be affected by altitude. It did not do it much (if any) on our trip to Cuba when we were east of Texas. Today it did it in Reno (4415') but not in Watsonville (163').

Something new happened today though:

After flying 2 hours back to Reno from Watsonville, I parked on the east side to get fuel. After fueling, I started. I had to flip the avionics switch twice since the first time it did not turn on (which as noted above has been happening). After it was on and the 530W booted, I called ground to taxi to my hangar on the west side.

As soon as I hit the transmit button, my avionics reset. By that I mean, they briefly turned off and back on. Could this be related to the switch? Perhaps the power draw, being higher when transmitting, was too much for it?

After everything rebooted, it was fine. We don't have an avionics shop here... I get mine done in Portland, Oregon, 400 miles away. There is a shop at Stead, 10 miles away but most people I know will not them touch their planes.

Any ideas on if this is a bad switch and if the power cycle when I transmitted could be related? Also, any idea on how this could be at all related to altitude?

 

[SkyDog58]

You really don't need an avionics shop, just a half decent A&P. Without looking at your wiring diagram, my guess would be that you might have a bad relay. I also believe that the aux switch may not be in parallel with the main switch which operates the relay. Instead, I believe it bypasses the relay and connects the avionics bus directly to the main bus. Take a look at your wiring diagrams. You could also fly with the main switch off and the aux on to see if the problem repeats. My guess is that it won't.

 

[DesertNomad]

What is the purpose of the relay in that case and is there any real disadvantage to bypassing it?

 

[wilkersk]

What is the purpose of the relay in that case and is there any real disadvantage to bypassing it?

I've seen avionics "master switches" that weren't really. They were light duty switches wired up to complete a relay. Its the relay that is connecting the avionics bus to the main DC bus. If the relay fails, you've got problems.

I agree with SkyDog, it sounds like a sticky relay. If you bypass it, make sure your jumper is heavy enough to handle the load, and is terminated properly. This is a temp fix at best. And for a certified a/c, a ferry permit would be a good idea to CYA.

A better set up is to replace it with a heavy-duty DC rated switch with no relay in between.