Has anyone out there ever seen an avionics master relay installed for C-180 /185?

not common to have a actual relay installed, but I'm sure it can be done. If there is an avionics bus installed it's typically a on a switch (with a circuit breaker type switch) you don't really need a relay with such a simple bus system.

54C

Relay - NO
Why would anyone want to cut a perfectly good wire to stick in a fallible gadget to control ALL avionics?
If the Master dies ALL the Slaves go out with it.

If you really mean the "SPLIT" Master Switch then yes.
I also put a separate pull - push circuit breaker in for each of the avionics.

Chris C

I agree NO relay, just another failure point.

What I have on my 185, that I had not seen before I bought it, is two avionics switches mounted next to each other. They are simply wired in parallel in case one fails. Simple and cheap.

T

My 1977 A185F has a factory installed avionics bus relay that opens when the starter is energised to protect the radios from low voltage during the start if they were left powered up. This particular airframe was sold from the factory with no radios and had a King stack installed immediately after delivery according to the logbook. At some time in the future when I decide what I'm going to do for an upgrade, I was planning on wiring the relay up to a switch to manualy control it.(avionicsmaster) I was led to believe by an avioncs tech that it would be considered to be a minor alteration to add the switch, but to remove the relay would be a major alteration of the electrical system? I believe that Cessna started to get more creative and sophisticated with their avionics installations towards the later years of production. Don't know if this info is any help, but maybe more insight.

I've never cared for avionics masters. In fact I've removed a couple from previous airplanes but I left the one alone in my 180. It made sense when someone explained to me that it might save a lot of wear and tear on the little (and expensive) on/off switches on the radio & transponder. Plus, it is kinda nice to just throw one switch after start-up and have radio txp intercom and now my electronic horizon all come on together.

Mine is a standard Cessna pull switch wired off the buss, and wired to separate circuit breakers for com txp gps & horizon.

a3holerman wrote:I agree NO relay, just another failure point.

What I have on my 185, that I had not seen before I bought it, is two avionics switches mounted next to each other. They are simply wired in parallel in case one fails. Simple and cheap.

T

I like this, seems like great insurance for an IFR bird. Do you alternate their usage? Or just leave one off all the time?

Having an avionics master can be very valuable. Being able to shut down the entire radio stack can help in a possible emergency situation i.e. Radios stack fire/short.

And if you don't want to install a switch, at least make sure you replace old circuit breakers with ones you can actually pull to turn stuff off.

i have an avionics master, but I don't think its tied to a relay. I'll look under there next time I'm at the hangar, but I only remember seeing a master relay and a starter relay.

hotrod180 wrote:I've never cared for avionics masters. In fact I've removed a couple from previous airplanes but I left the one alone in my 180. It made sense when someone explained to me that it might save a lot of wear and tear on the little (and expensive) on/off switches on the radio & transponder. Plus, it is kinda nice to just throw one switch after start-up and have radio txp intercom and now my electronic horizon all come on together.

Mine is a standard Cessna pull switch wired off the buss, and wired to separate circuit breakers for com txp gps & horizon.

Actually, the main reason for a separate avionics bus is to protect the sensitive innards of your expensive radios. If all your radios are on during engine start the voltage spike on the shared bus can be very strong. Cutting down on wear and tear for your individual radio on/off switches is just an added benefit.

Additionally, on high end avionics installations an isolated ground may be desired to help control radio noise.