Matronics Email Lists :: View topic

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Z11 revision needed?

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

ceengland7(at)gmail.com
Guest

Posted: Wed Jan 22, 2020 4:59 pm Post subject: Z11 revision needed?

Hi,



I'm in-process, updating my purchased RV6 electrical system. It was 

loosely based on the AEC Z figures, but needs updating for several 

reasons. This is a relatively simple, 1 battery/1 alternator system with 

1 mag & 1 Lightspeed ignition, and Bendix style injection.



While consulting the Z figures to rearrange loads to various buses, I 

noticed the boost pump feed on the Endurance bus is shown as 3A. No 

doubt Z11 was created when 'simple' planes had fueled delivered by 

carbs, but Bendix style injection has become quite common on RVs & other 

Lyc powered homebuilts.



The issue I'm raising is that virtually all the commonly used 'boost' 

pumps (actually *backup* pumps) in use with Bendix style fuel injection 

these days have at their core, an automotive fuel injection pump which 

draws a minimum of roughly 6A continuous, with no doubt, considerably 

higher startup inrush current. With only a 7A fuse (and 16 Ga wire) 

feeding the Endurance bus, This seems quite marginal. Even if we assume 

minimal actual loads from the other active devices on this bus, the need 

to activate the backup fuel pump could result in getting 'close to the 

edge' of voltage drop ratings for 16 Ga wire, and if we are already 

operating in Endurance mode, could easily take out the 7A fuse supplying 

the endurance feed to the bus.



Should wire sizes and fusing be increased on this drawing, as has been 

done on some of the other drawings where the backup pump load is shown 

as 10A?



I should note that several other Z figures also show 7A protection and 

16 Ga wire to the Endurance bus, but most of the others don't define any 

loads on that bus. Assuming that a high pressure pump is needed in the 

a/c, it would need to be on the Endurance bus and, it seems to me, the 

bus would need a more robust supply.



Even with everything (including the alternator) on line, having to add 

the backup fuel pump load to the other loads on that bus will push 

voltage drop on the feed wire past the typical 10% limit.



Thanks,



Charlie

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 23, 2020 8:14 am Post subject: Z11 revision needed?

At 06:56 PM 1/22/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com>



 Hi,



 I'm in-process, updating my purchased RV6 electrical system. It was loosely based on the AEC Z figures, but needs updating for several reasons. This is a relatively simple, 1 battery/1 alternator system with 1 mag & 1 Lightspeed ignition, and Bendix style injection.



 While consulting the Z figures to rearrange loads to various buses, I noticed the boost pump feed on the Endurance bus is shown as 3A. No doubt Z11 was created when 'simple' planes had fueled delivered by carbs, but Bendix style injection has become quite common on RVs & other Lyc powered homebuilts. 	


   The z-figures are ARCHITECTURE EXAMPLES to

   aid in fabrication of a power distribution

   appropriate to YOUR project.



  	  Quote: 	
		  The issue I'm raising is that virtually all the commonly used 'boost' pumps (actually *backup* pumps) in use with Bendix style fuel injection these days have at their core, an automotive fuel injection pump which draws a minimum of roughly 6A continuous, with no doubt, considerably higher startup inrush current. With only a 7A fuse (and 16 Ga wire) feeding the Endurance bus, This seems quite marginal. Even if we assume minimal actual loads from the other active devices on this bus, the need to activate the backup fuel pump could result in getting 'close to the edge' of voltage drop ratings for 16 Ga wire, and if we are already operating in Endurance mode, could easily take out the 7A fuse supplying the endurance feed to the bus. 	


   This is what the LOAD ANALYSIS is for . . . it

   should be the very first document you craft in

   the planning for your airplane. This document

   provides the foundation for ADAPTING a z-figure

   to your specific needs.



 

  	  Quote: 	
		  Should wire sizes and fusing be increased on this drawing, as has been done on some of the other drawings where the backup pump load is shown as 10A?



 I should note that several other Z figures also show 7A protection and 16 Ga wire to the Endurance bus, but most of the others don't define any loads on that bus. Assuming that a high pressure pump is needed in the a/c, it would need to be on the Endurance bus and, it seems to me, the bus would need a more robust supply.



 Even with everything (including the alternator) on line, having to add the backup fuel pump load to the other loads on that bus will push voltage drop on the feed wire past the typical 10% limit. 	


   Size ALL circuit protection to the anticipated

   loads along with considerations for the use

   of fuses that need 25 percent headroom for

   steady loads . . . EXTRA for loads with inrush

   currents. Fuses can be 'hammered' to failure

   by seemingly ordinary circumstances.



   Fuses are first sized to wire then upsized to

   grunt transients. This consideration is above an

   beyond any decisions about architecture. What

   your involved in now is the first phase

   of failure mode effects analysis based on a

   knowledge of system components.



   Good on you my friend.



 

   Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum