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MFleming

Joined: 31 Oct 2017
Posts: 17

Posted: Mon May 25, 2020 11:44 am Post subject: Questions about Architecture Design

I hope these questions are not too rudimentary or repetitive.



I'm moving in on finalizing the wiring design for my RV-7. A few question have nagged me for a while and I'm eager to better understand the rules or rationals for these conundrums.



I'm basically speaking to Z101.



(1) The 6AWG wire from the battery contactor to the main bus is unprotected and not length limited. My calculations show I can use a smaller wire. Is the 6AWG permitted to be downsized or is it integral to safety?



(2) Since I don't have an electrically dependent engine (one p-mag) I'm planning the Clearance Delivery bus be secondarily fed from the main bus through a diode. Should I fuse the wire (18AWG) or come directly off the bus? Also, I have no need for a battery bus. My plan is to feed the clearance delivery relay (Relay needed? 3.8amps max) from the battery side of the battery contactor...is this acceptable?



(3) I am going to have an avionics bus (sorry, I just don't want all that stuff running when I start), so the same question. Do I fuse the 18AWG wire to the avionics bus? I see that most endurance busses are not fused...not sure why not?



(4) Fuselinks depicted in a lot of the Z drawings. How do I size them and where do I get them?



(5) Relay vs switch. Is there a rule of thumb for when to add a relay instead of using a beefy switch?



Thanks in advance.



Michael Fleming

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_________________
Michael Fleming

nuckolls.bob(at)aeroelect
Guest

Posted: Mon May 25, 2020 4:56 pm Post subject: Questions about Architecture Design

At 02:44 PM 5/25/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "MFleming" <sagriver(at)icloud.com>



 I hope these questions are not too rudimentary or repetitive.



 I'm moving in on finalizing the wiring design for my RV-7. A few question have nagged me for a while and I'm eager to better understand the rules or rationals for these conundrums.



 I'm basically speaking to Z101.



 (1) The 6AWG wire from the battery contactor to the main bus is unprotected and not length limited. My calculations show I can use a smaller wire. Is the 6AWG permitted to be downsized or is it integral to safety? 	


   It would be better for this to be 'robust'. I.e.

   take it's place in the constellation of power

   distribution feeders . . . I wouldn't go smaller

   than 8AWG but unless you already have some 8 and

   don't need to buy some 6, I'd use the 6. Here's

   one source of many . . .



  https://tinyurl.com/ya4756q6



   You'll like working with this 'fat' wire.



  	  Quote: 	
		  (2) Since I don't have an electrically dependent engine (one p-mag) I'm planning the Clearance Delivery bus be secondarily fed from the main bus through a diode. 	


   Yup, that's what Z101 shows.



  	  Quote: 	
		  Should I fuse the wire (18AWG) or come directly off the bus? 	


   How many devices on your clearance delivery

   bus?



  	  Quote: 	
		  Also, I have no need for a battery bus. My plan is to feed the clearance delivery relay

 (Relay needed? 3.8amps max) from the battery side of the battery contactor...is this acceptable? 	


   Sure . . . your 'battery bus' is the hot side terminal . . .

   It just has one feeder departing the 'bus'. I recommend

   10A local in-line fuse and 18AWG wire to your CD switch.



  	  Quote: 	
		  (3) I am going to have an avionics bus (sorry, I just don't want all that stuff running

 when I start) . . . 	


    What is the 'down side' for having 'all that stuff

    running' during start? Z101 as depicted supports all

    auxiliary busses with independent feed paths. What

    are your plans for an avionics bus?



  	  Quote: 	
		   so the same question. Do I fuse the 18AWG wire to the avionics bus?

 I see that most endurance busses are not fused...not sure why not? 	


   They are fused at the battery source for alternate feed.

   Not fused in normal feed from the main bus because

   wires are short(*).



  	  Quote: 	
		  (4) Fuselinks depicted in a lot of the Z drawings. How do I size them and where do I get them? 	


   You make them from fuse link wire. Where do you

   plan to incorporate them?



 

  	  Quote: 	
		  (5) Relay vs switch. Is there a rule of thumb for when to add a relay instead of using a beefy switch? 	


   Depends on how much wire you want to run

   the 'high current' through. Which switch(es) are

   you talking about? If you're switching 7A or

   less, you could consider eliminating relays.



 

   Bob . . .

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user9253

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

Posted: Mon May 25, 2020 6:41 pm Post subject: Re: Questions about Architecture Design

The main power bus is one of the most reliable things on an airplane.  It is 

connected to 2 power sources, a battery and an alternator.  There are no 

fuses to blow in the main power feeder.  An avionics bus has a switch that

can fail.  And if it is protected by a fuse, that is one more unnecessary 

failure point.  It is a bad idea to have two fuses in series.  If a load fuse 

blows, the bus fuse could also blow and disable all avionics.  Eliminate the 

avionics bus.  Yeah, I know you are concerned about voltage spikes during 

engine start.  But there is no such thing.  Who are you going to believe, 

flight instructors and mechanics who do not even own an oscilloscope and 

base their advice on 1950 technology, or an electrical engineer (Bob) who 

has worked for major aircraft companies and has tested starter motors in 

a laboratory and proved that there are no voltage spikes?  I do not have 

an avionics bus.  My airplane has been started hundreds of times with all 

avionics turned on.  No avionics have failed.  Yes, some do reboot from 

voltage sag which is annoying.  Brownout protection can be installed if 

desired.  Give me the name of a modern avionics manual and page

number that states that their product must be powered off during engine 

start. There are none.  Make your airplane safer, and less complicated by 

not having an avionics bus.

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_________________
Joe Gores

MFleming

Joined: 31 Oct 2017
Posts: 17

Posted: Mon May 25, 2020 8:40 pm Post subject: Re: Questions about Architecture Design

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 02:44 PM 5/25/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "MFleming" <sagriver>



 I hope these questions are not too rudimentary or repetitive.



 I'm moving in on finalizing the wiring design for my RV-7. A few question have nagged me for a while and I'm eager to better understand the rules or rationals for these conundrums.



 I'm basically speaking to Z101.



 (1) The 6AWG wire from the battery contactor to the main bus is unprotected and not length limited. My calculations show I can use a smaller wire. Is the 6AWG permitted to be downsized or is it integral to safety? 	


   It would be better for this to be 'robust'. I.e.

   take it's place in the constellation of power

   distribution feeders . . . I wouldn't go smaller

   than 8AWG but unless you already have some 8 and

   don't need to buy some 6, I'd use the 6. Here's

   one source of many . . .



  https://tinyurl.com/ya4756q6



   You'll like working with this 'fat' wire.



  	  Quote: 	
		  (2) Since I don't have an electrically dependent engine (one p-mag) I'm planning the Clearance Delivery bus be secondarily fed from the main bus through a diode. 	


   Yup, that's what Z101 shows.



  	  Quote: 	
		  Should I fuse the wire (18AWG) or come directly off the bus? 	


   How many devices on your clearance delivery

   bus?



  	  Quote: 	
		  Also, I have no need for a battery bus. My plan is to feed the clearance delivery relay

 (Relay needed? 3.8amps max) from the battery side of the battery contactor...is this acceptable? 	


   Sure . . . your 'battery bus' is the hot side terminal . . .

   It just has one feeder departing the 'bus'. I recommend

   10A local in-line fuse and 18AWG wire to your CD switch.



  	  Quote: 	
		  (3) I am going to have an avionics bus (sorry, I just don't want all that stuff running

 when I start) . . . 	


    What is the 'down side' for having 'all that stuff

    running' during start? Z101 as depicted supports all

    auxiliary busses with independent feed paths. What

    are your plans for an avionics bus?



  	  Quote: 	
		   so the same question. Do I fuse the 18AWG wire to the avionics bus?

 I see that most endurance busses are not fused...not sure why not? 	


   They are fused at the battery source for alternate feed.

   Not fused in normal feed from the main bus because

   wires are short(*).



  	  Quote: 	
		  (4) Fuselinks depicted in a lot of the Z drawings. How do I size them and where do I get them? 	


   You make them from fuse link wire. Where do you

   plan to incorporate them?



 

  	  Quote: 	
		  (5) Relay vs switch. Is there a rule of thumb for when to add a relay instead of using a beefy switch? 	


   Depends on how much wire you want to run

   the 'high current' through. Which switch(es) are

   you talking about? If you're switching 7A or

   less, you could consider eliminating relays.



 

   Bob . . . 	




"How many devices on your clearance delivery 

bus?"



Four, Primary EFIS, GPS, Comm and strobes so I don't forget to turn off the clearance delivery switch.



"Sure . . . your 'battery bus' is the hot side terminal . . . 

It just has one feeder departing the 'bus'. I recommend 

10A local in-line fuse and 18AWG wire to your CD switch."



Got it.



"What is the 'down side' for having 'all that stuff 

running' during start? Z101 as depicted supports all 

auxiliary busses with independent feed paths. What 

are your plans for an avionics bus?"



OK, I gave my avionics wiring diagram a hard look. If I eliminate the avionics bus and move those devices to the main bus, I only have two items that might reboot during start, they are the Garmin GMC-507 auto pilot head and the #2 MFD. The rest are on the TCW IBBS 6ah back-up battery.



The autopilot head I'm not concerned about. Currently the second power pin on the #2 MFD (GDU-470) is not being used. I could run a Keep Alive wire from the Garmin GAD-27 which conditions the line voltage during engine start and prevents any annoying reboots from the #2MFD.



This sound simple and appealing. I'll give it s good look tomorrow.



"You make them from fuse link wire. Where do you 

plan to incorporate them?"



I currently show a 16awg fuselink on the ALT 'B' line just before the starter solenoid.



"Depends on how much wire you want to run 

the 'high current' through. Which switch(es) are 

you talking about? If you're switching 7A or 

less, you could consider eliminating relays."



The clearance delivery switch would be a candidate to eliminate the relay. 3.8A on the clearance delivery bus. 



-M

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_________________
Michael Fleming

nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 26, 2020 9:41 am Post subject: Questions about Architecture Design

 	  Quote: 	
		  

 How many devices on your clearance delivery 

 bus? 



 Four, Primary EFIS, GPS, Comm and strobes so I don't forget to turn off the clearance delivery switch. 	


    Do your strobes have their own power

    switch? If there is risk that the

    CD switch is inadvertently left on

    at shutdown, how is there less risk

    that the strobes are not independently

    shut off and the CD switch is now

    un-monitored?



    Checklists are a time honored, legacy

    proven hedge against human weakness

    of the gray matter. The FARS require

    a single-stroke feature for making the

    aircraft electrically 'cold' . . . in

    the case of multiple, dual-feed buses

    it's easily managed with a 'crash bar'

    over the row of switches.



    Sorry if I seem 'fussy'. I cannot help

    being extra attentive to things done to

    mitigate 'forgetfulness'. Airplanes

    are not SAFE. They are exceedingly

    unforgiving as demonstrated in countless

    NTSB incident/accident narratives . . .

    the vast majority of which have foundation

    in over confidence/forgetfulness.     



  	  Quote: 	
		  What is the 'down side' for having 'all that stuff 

 running' during start? Z101 as depicted supports all 

 auxiliary busses with independent feed paths. What 

 are your plans for an avionics bus? 



 OK, I gave my avionics wiring diagram a hard look. If I eliminate the avionics bus and move those devices to the main bus, I only have two items that might reboot during start, they are the Garmin GMC-507 auto pilot head and the #2 MFD. The rest are on the TCW IBBS 6ah back-up battery. 	


   With Z101 you have probably the most failure

   tolerant architecture flying . . . and you've

   still got a back-up battery?



  	  Quote: 	
		  You make them from fuse link wire. Where do you 

 plan to incorporate them?



 I currently show a 16awg fuselink on the ALT 'B' line just before the starter solenoid. 	


   Trying to accurately describe an architecture

   with words leaves much to be desired. If

   you're basing your plans on Z101, then

   exactly how do you plan to modify that

   drawing?



   Those remote relays for alternate feed

   paths allow clustering major components

   together on short (*) leads making

   fault protection easier. There are several

   instances of fuse-link wire illustrated

   on Z101.



 

   Bob . . .

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Zoom2136

Joined: 03 Oct 2018
Posts: 7
Location: Montreal

Posted: Sun May 31, 2020 5:41 am Post subject: Questions about Architecture Design

Hi all,

I'm new here trying to post on the forum, but cannot. I've lost my password and cannot get the system to send me a new one. It does tell me that an email was sent to my email address, but nothing. I've checked my spam folder but nothing either. 

Also tried sending my electric diagram for my Cozy directly to aeroelectric-list(at)matronics.com for your comments, but that email also did not go through.



Hope this one does. As I would greatly appreciate your help in building a safe airplane.

Thanks

Eric D

MontrÃ©al, Canada

                  

                                                                    On Tuesday, May 26, 2020, 05:35:00 a.m. EDT, user9253 <fransew(at)gmail.com> wrote:                 

                 



                 



                 --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>



The main power bus is one of the most reliable things on an airplane.  It is 



connected to 2 power sources, a battery and an alternator.  There are no 



fuses to blow in the main power feeder.  An avionics bus has a switch that



can fail.  And if it is protected by a fuse, that is one more unnecessary 



failure point.  It is a bad idea to have two fuses in series.  If a load fuse 



blows, the bus fuse could also blow and disable all avionics.  Eliminate the 



avionics bus.  Yeah, I know you are concerned about voltage spikes during 



engine start.  But there is no such thing.  Who are you going to believe, 



flight instructors and mechanics who do not even own an oscilloscope and 



base their advice on 1950 technology, or an electrical engineer (Bob) who 



has worked for major aircraft companies and has tested starter motors in 



a laboratory and proved that there are no voltage spikes?  I do not have 



an avionics bus.  My airplane has been started hundreds of times with all 



avionics turned on.  No avionics have failed.  Yes, some do reboot from 



voltage sag which is annoying.  Brownout protection can be installed if 



desired.  Give me the name of a modern avionics manual and page



number that states that their product must be powered off during engine 



start. There are none.  Make your airplane safer, and less complicated by 



not having an avionics bus.



--------



Joe Gores



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http://forums.matronics.com/viewtopic.php?p=496516#496516



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_________________
Eric D
Cozy IIIx C-GEDZ

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