Need 12V+behind Avionics Master

[NicoN]

I am dreaming of LEMO-connectors for my Bose A20 Headset.

For this, +12V is needed to feed the Headset circuits. Without, I have no advantage from the LEMO-connector.

I would like to have it powered from/with the Avionics Master(aka Radio Master)

These days I had to remove the turn coordinator and - voila - the clamps of the Radio master CB are right behind, waiting for me . That's what I thought.

Astonishingly, that CB works not as expected.

WIth Master switch off, the clamp block which is screwed on the bottom pole of Avionics Master, Low boost and High boost has no power.

With Master ON, there is 12V on thes CB. BUT - the other clamp of avionics master has +12V in OFF-position and no power when switched ON.

I guess, the CB drives a solenoid.

Nevertheless, where is the best place to get access to +12V switched via Avionics Master?

Ideal candicate would be the Audio-Panel C/B, but for this, I need to remove the C/B-panel, right? Are the cables long enough to survive a removal ?

All is intended for a 1980 M20K

[bob865]

It really needs to be connected to the ouput of a circuit breaker that is powered by the avionics bus otherwise you only have the protection of the upper bus circuit breaker.  If you have an unused breaker you can tie into that and relabel it.

[tony]

Isn't an M20K a 28 volt system?  If so, I think its not as simple as you think.  You'll need a DC to DC converter.  

Edited September 25, 2018 by tony

[jrwilson]

I think one of the changes from 231 to 252 is a change to the 28v system.  Most 231s I see are 12v.  My 84 is at least

[N201MKTurbo]

Avionics buses are normally powered from a normally on relay. I think this is so any failure of the switch or wiring will leave you with the radios on. 

[Yetti]

Show us a pic of your CB panel.  may need a step down circuit.

[thinwing]

3 hours ago, tony said:

Isn't an M20K a 28 volt system?  If so, I think its not as simple as you think.  You'll need a DC to DC converter.  

 It doesn't matter..if he is installing a lemos to power a headset ,both Bose or Lightstream headsets can accept 24/12 v as I recall

[Steve W]

Yea, I found that tidbit out(normally closed relay) when I was testing some work I'm doing on ground power, on my M20J that relay is on the Aux bus, so when I had the breaker pulled, turned on the master and my Stormscope came on... Anyway, best place will be to make it like the factory, add a new breaker to the CB panel and pick up power there, may even have one already on an Avionics bus bar you can use.

On my M20J you can pull the CB panel a few inches forward without disconnecting any wires(I did have to take the MP gauge out, the hose wasn't long enough), enough to get to the breakers and swap one out, the factory wiring should be fine, any aftermarket stuff may not have left enough service loops though. Other option is to unscrew the front of every breaker and any instruments in that panel and just pull the face off, but that sucks and still may not give enough access. 

[NicoN]

Here are some pictures of the cB panel.

Is there a dedicated instruction available how to remove it or at least move it, so I can reach the clamps for the Audio-Panel CB.

This one seems to be the most suited CB. I do not have a unused CB (AFAIK)

[Steve W]

Pull the entire panel forward, unscrew the front of the 3 breakers in the COM row, push them and their associated bus-bar back far enough to slide a new breaker in at NAV 2, attach to bus bar, attach wire for new outlet, reattach front nuts to all 4 breakers, route wires(with service loops) re-attach panel. Probably only a couple minutes longer than attaching another wire to the Audio panel breaker. Remember to drop the associated screws at least 20 times. 'Easy'... Why yes, I did just do this for my JPI, except I re-used an old Fuel-Flow breaker slot and the already routed wire instead.

[jetdriven]

The  keep alive 12V wire goes to the overhead lights. It’s contained in a bundle that goes up the left side of the windshield post