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RV-7 wireing questions

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jul 10, 2014 12:47 pm Post subject: RV-7 wireing questions

At 01:17 PM 7/10/2014, you wrote:

Hey Bob, I have your book Aeroelectric Connection 2005 and I am 

building an RV-7.  Great book by the way (I am a super beginner). I 

am going to use your figure Z-11 generic light aircraft electrical 

system diagram for pretty much all of my system but have a few questions.

I want a master switch and an avionics switch on my panel so I can 

start my engine before I power up my avionics



    Okay, why do you want to do this? No such feature is

    suggested on any of the Z-figures . . . the value

    for an avionics master switch was poorly perceived

    when it was birthed (about 1968). Today, rudimentary

    design skills make virtually every appliance

    immune to what ever the system might throw at it . . .

    including the cranking of engines.



    Some readers have proffered the idea that turning

    avionics loads off will enhance cranking performance. . .

    an idea without foundation in physics for an airplane

    with a properly maintained battery. If you're willing

    to go flying with a battery that might not get the

    engine started if it were presented with a few amps

    additional load, then I suggest there's value in

    a review of your design goals as they drive risks.



    Don't get me wrong, if you WANT any switch in the

    airplane for ANY purpose, fine by me. I suggest

    there is value in understanding the exactly what

    the switch will (or will not) do for you . . .

    and how it figures into your assessment of risks.

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Fri Jul 11, 2014 7:24 am Post subject: Re: RV-7 wireing questions

Z-11 is a good choice.  An avionics switch is not recommended because if it fails, all of the avionics stop working.  And any switch will eventually fail.  I would question the qualifications of anyone who warns about damaging voltage spikes during engine start.  Have they written a book on aircraft wiring?  Dynon states in their Pilots User Guide for both the D-180 and SkyView that it is OK to have their units powered on during engine start.

  The real problem during engine cranking is not voltage spikes, but rather voltage slump, aka brownout.  That is an annoyance, not a danger to avionics.

Joe

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_________________
Joe Gores

kleh(at)dialupatcost.ca
Guest

Posted: Fri Jul 11, 2014 7:58 am Post subject: RV-7 wireing questions

About once every 50 engine starts my Gemini ADI (glass stand alone ADI) 

will freeze up. The only indication of that before takeoff is that the 

gps heading does not change during taxi. For aircraft without brown out 

protection, it might be convenient to have a switch of some kind, or an 

accessible circuit breaker, to reboot any devices that don't have their 

own on-off switch.

Sure the battery master will also do it but I choose not to test the 

load dump capability of my internally regulated alternator, or my PM 

alternator, by deliberately cycling the master with a running engine. My 

John Deer PM regulator does not like load dumps.

Ken



On 11/07/2014 11:24 AM, user9253 wrote:

 	  Quote: 	
		   

 <fransew(at)gmail.com>



 Z-11 is a good choice.  An avionics switch is not recommended because

 if it fails, all of the avionics stop working.  And any switch will

 eventually fail.  I would question the qualifications of anyone who

 warns about damaging voltage spikes during engine start.  Have they

 written a book on aircraft wiring?  Dynon states in their Pilots User

 Guide for both the D-180 and SkyView that it is OK to have their

 units powered on during engine start. The real problem during engine

 cranking is not voltage spikes, but rather voltage slump, aka

 brownout.  That is an annoyance, not a danger to avionics. Joe



 -------- Joe Gores

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jul 11, 2014 12:17 pm Post subject: RV-7 wireing questions

At 10:58 AM 7/11/2014, you wrote:

 	  Quote: 	
		  



About once every 50 engine starts my Gemini ADI (glass stand alone 

ADI) will freeze up. The only indication of that before takeoff is 

that the gps heading does not change during taxi. For aircraft 

without brown out protection, it might be convenient to have a 

switch of some kind, or an accessible circuit breaker, to reboot any 

devices that don't have their own on-off switch.


	


    The Gemini ADI installation manual does speak

    to an ADI Master Switch downstream of a 1A

    breaker. This is a very low power consumption

    device!



    How a bout a miniature, normally closed push button

    next to the instrument in series with the power

    input that would allow you to do a 'hard' reset?



 	  Quote: 	
		  Sure the battery master will also do it but I choose not to test the 

load dump capability of my internally regulated alternator, or my PM 

alternator, by deliberately cycling the master with a running 

engine. My John Deer PM regulator does not like load dumps.

Ken


	


   Don't you have positive alternator control?

   For a PM alternator, a set of relay contacts

   in series with the AC output winding will

   offer a way to shut it off without undue

   stress.

   Bob . . .

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