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Avionics Master Switch

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wroe1(at)dbtech.net
Guest

Posted: Wed Dec 02, 2009 11:44 am Post subject: Avionics Master Switch

I am planning the switches for the panel in my RV-7 and wanted to get some

opinions about the options.  The proposed electrical schematic closely

parallels AEC Z-13 (all electric on a budget).  The plane will be configured

for IFR flight (GNS-430w, SL-40, AFS 4500, etc...).  I have noticed that

many builders are incorporating avionics master switches in their planes

that are exclusive to the DC power master (off-batt-main alt).  Unless I'm

missing something, it would seem to be beneficial to be able to start the

engine then bring up the avionics by way of the "avionics master".  



Also, I'm trying to decide whether or not to use a designated EFIS (on-off)

master for the AFS 4500.



Thoughts and/or comments would be appreciated.



Thanks!



Wade Roe 



(RV-7 in progress)

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Dec 02, 2009 3:19 pm Post subject: Avionics Master Switch

At 01:38 PM 12/2/2009, you wrote:

 	  Quote: 	
		  



I am planning the switches for the panel in my RV-7 and wanted to get some

opinions about the options.  The proposed electrical schematic closely

parallels AEC Z-13 (all electric on a budget).  The plane will be configured

for IFR flight (GNS-430w, SL-40, AFS 4500, etc...).  I have noticed that

many builders are incorporating avionics master switches in their planes

that are exclusive to the DC power master (off-batt-main alt).  Unless I'm

missing something, it would seem to be beneficial to be able to start the

engine then bring up the avionics by way of the "avionics master".



Also, I'm trying to decide whether or not to use a designated EFIS (on-off)

master for the AFS 4500.



Thoughts and/or comments would be appreciated.


	




See:



http://www.aeroelectric.com/articles/avmaster.pdf



http://www.aeroelectric.com/articles/DO-160.pdf



I have written to and talked with dozens of avionics equipment

designers at big and little companies alike for over 25 years

to inquire as to the physics behind any recommendation for

an avionics master switch. Most letters/e-mails produced ZERO

response. Every conversation produced a somewhat mystified

response . . . "Gee, we build these things to stand everything

BUT and nuclear EMP and folks are STILL worrying about

starter motors?"  Interestingly enough, when hydraulic packs

with PM pump motors were installed for landing gear systems,

the AV Master Switch acolytes didn't insist on killing all the

radios before extending or retracting the gear. This in spite

of the fact that the PM motors put bigger chunks of trash on the

bus than did some starter motors!



Bottom line is that the AV Master is a convenience/feel-good

feature and has no modern function as a firewall against

bus-borne hazards to radios.

        Bob . . .

                    ////

                   (o o)

    ===========o00o=(_)=o00o=========

    < Go ahead, make my day . . .   >

    < show me where I'm wrong.      >

    =================================

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