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Avionics Master

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 03, 2016 7:58 am Post subject: Avionics Master

 	  Quote: 	
		  Comments/Questions: Bob ... I took our seminar many years ago and you suggested not to use an Avionics Master .. that you can just turn on each component etc.  So that's what i did .. and it's worked just fine.  However, I'm now redesigning my panel with remote mount avionics .. COMM, TRANSPONDER, AUDIO PANEL etc.  Now I'm curious how I should protect these during start up?  Should I now plan for a MASTER or do I have to use individual switches for each component?  



 Thank you for your expertise!  



 Regards,



 Dave

 	




  

 The avionics master switch was borne of an idea not

 grounded in physics. I was at Cessna in the 60's when,

 for reasons we didn't understand, radios were being

 killed in brand new airplanes by the dozens. Adding

 the AV Master did indeed 'help' but for reasons we

 did not know.



 Check out the writings on my website concerning

 the AV Master.



  http://tinyurl.com/mr2jk8g



 If you ever get to OSH, it would be interesting

 to stop by the booths of the manufacturer of ANY

 solid state device be it radio, instrument, system

 controller, etc. and inquire as to their recommendations

 for 'protecting their product from the effects of

 engine cranking'.



 If any one of them says that an AV Master is recommended,

 I'd like to hear about it. Since the universal adoption

 of DO-160 protocols about 50 years ago, risks to electronics

 from startup transients (or other any well understood

 transients) has gone to zero.



 Turns out that the 'radio killer' in the 1960's Cessnas

 was soggy batteries combined with poor design rules

 for the radio's newly minted solid state power supplies.

 That combination of shortfalls was easily and has been

 eliminated.



 

 

   Bob . . .

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Dec 06, 2016 5:47 am Post subject: Re: Avionics Master

Not to poke a sleeping bear...



I've got an avionics master not because I'm worried out spikes.  My concern is with the opposite.  Sags.



I also have remote avionics (no power switches on the devices) with a VPX power distribution system.  When I'm starting up the EFIS will reboot if the voltage gets too low (I'd have to check the doc's but I think it gets unhappy below 18 or maybe 20v). The radios are a bit more tolerant as they will handle much lower voltages.  Not sure about the GPS or audio panel.  



The greater issue is that when the EFIS power sags, sometimes it won't reboot and just goes into limbo.  Then I have to go in to the VPX, shut off the breaker, wait, and then reactivate the breaker to get the EFIS back up.



The EFIS doesn't reboot on every start.  But if I've been fighting a stubborn hot start then the battery can get a little tired.  For the primary EFIS, I have a small backup battery that powers the EFIS that during engine starts. 



I could have put in a second backup battery for the other EFIS, or a switch for the second EFIS.  But it seems like the simplest solution is an avionics master.  This also allows me to power up the electrical system if I want to work on the gear retract system, lights, etc., without powering up the avionics. 



Just my .02

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Dec 06, 2016 8:25 am Post subject: Avionics Master

At 07:47 AM 12/6/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com>



 Not to poke a sleeping bear...



 I've got an avionics master not because I'm worried out spikes.  My concern is with the opposite.  Sags.



 I also have remote avionics (no power switches on the devices) with a VPX power distribution system.  When I'm starting up the EFIS will reboot if the voltage gets too low (I'd have to check the doc's but I think it gets unhappy below 18 or maybe 20v). The radios are a bit more tolerant as they will handle much lower voltages.  Not sure about the GPS or audio panel. 	


   Low voltage is generally not a stress to be

   'handled' beyond the ability to make a graceful

   recovery after the brown-out event. This

   shortcoming is generally limited to devices

   with micro-controllers that are not fitted

   with brown-out protection features . . . 



   Failure to design such features into a modern

   appliance is something akin to forgetting

   to include a filler-spout on a fuel tank.

   Pretty elementary.



   In 50+ years of designing and fabricating

   electro-whizzies for aircraft from Hawker

   4000 to ultra-lights,  I've never been

   challenged by the notion that brown-outs of

   any magnitude, rate and duration are a

   special force to be wrestled with.



  	  Quote: 	
		   



 The greater issue is that when the EFIS power sags, sometimes it won't reboot and just goes into limbo.  Then I have to go in to the VPX, shut off the breaker, wait, and then reactivate the breaker to get the EFIS back up.



 The EFIS doesn't reboot on every start.  But if I've been fighting a stubborn hot start then the battery can get a little tired.  For the primary EFIS, I have a small backup battery that powers the EFIS that during engine starts. 



 I could have put in a second backup battery for the other EFIS, or a switch for the second EFIS.  But it seems like the simplest solution is an avionics master.  This also allows me to power up the electrical system if I want to work on the gear retract system, lights, etc., without powering up the avionics. 



 Just my .02 	


   Unfortunately, there are numerous products offered

   to the aviation markets that are not designed to the

   spirit and intent of legacy rules-of-the-road for

   aviation appliances. 



   Brownout mitigation has been discussed numerous

   times over the years here on the List with a

   variety solutions offered. They all have the

   disadvantage of increased weight, system

   complexity and potential electro-magnetic

   compatibility issues (radio noise).



   Do these affected systems not have their

   own power switches? If not, then you're

   not really adding an avionics master but

   simply a power control switch to a device

   that does not already have one. In such cases,

   it seems prudent to have a separate switch

   for each device . . . this gets

   around the issue of generating single points

   of failure for multiple appliances.



   Cost of ownership for adding switches will

   be lower than for adding more batteries

   that need to be maintained throughout

   the life of the aircraft . . . but only

   serve a useful purpose for a few tens of

   milliseconds every flight cycle.



 

 

   Bob . . .

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Dec 06, 2016 10:38 am Post subject: Re: Avionics Master

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 07:47 AM 12/6/2016, you wrote:

 Do these affected systems not have their own power switches? 	


Nope.  These devices have no external controls.



 	  Quote: 	
		  If not, then you're not really adding an avionics master but simply a power control switch to a device that does not already have one. In such cases, it seems prudent to have a separate switch for each device . . . this gets around the issue of generating single points of failure for multiple appliances. 	


I thought about doing that.  But I felt the additional wiring and switches to be an added complication.  Besides, each device can be powered on or off through the VPX so that is my "individual device" switch. And my "Avionics Master" switch can be bypassed from the VPX as well (should it fail). 



So to me, that seems like a win-win.

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cluros(at)gmail.com
Guest

Posted: Tue Dec 06, 2016 10:54 am Post subject: Avionics Master

All the Beech products I flew had a NC relay opened by turning the avionics master switch off. If the switch failed and the avionics went dark, you just pulled the breaker for the switch and the avionics came back on.

Seems like a simple solution to me. 

Sebastien

 	  Quote: 	
		   On Dec 6, 2016, at 10:38, donjohnston <don(at)velocity-xl.com> wrote:

 nuckolls.bob(at)aeroelect wrote:

> At 07:47 AM 12/6/2016, you wrote:

> Do these affected systems not have their own power switches?

 Nope.  These devices have no external controls.

> If not, then you're not really adding an avionics master but simply a power control switch to a device that does not already have one. In such cases, it seems prudent to have a separate switch for each device . . . this gets around the issue of generating single points of failure for multiple appliances.

 I thought about doing that.  But I felt the additional wiring and switches to be an added complication.  Besides, each device can be powered on or off through the VPX so that is my "individual device" switch. And my "Avionics Master" switch can be bypassed from the VPX as well (should it fail). 

 So to me, that seems like a win-win. 

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=463754#463754

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