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Z-14 Question

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Rocketman1988

Joined: 21 Jun 2012
Posts: 63

Posted: Thu Jun 28, 2018 12:22 pm Post subject: Z-14 Question

All,



I am going to use the Z-14 layout for my RV-10.  The -10 has aft mounted batteries, so I will need to run the main buss wires from the back to the front, where all of the electronics are.



My question is:  Do these wires need to have individual current limiters on them?  The distance from the batteries to the battery buss location is about 8 1/2 feet.  I am planning on using #8 AWG wire to feed each respective battery buss.



Thoughts?

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 28, 2018 3:09 pm Post subject: Z-14 Question

At 03:22 PM 6/28/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>



 All,



 I am going to use the Z-14 layout for my RV-10.  The -10 has aft mounted batteries, so I will need to run the main buss wires from the back to the front, where all of the electronics are.



 My question is:  Do these wires need to have individual current limiters on them?  The distance from the batteries to the battery buss location is about 8 1/2 feet.  I am planning on using #8 AWG wire to feed each respective battery buss.



 Thoughts? 	


   put the crossfeed contactor on the firewall and use it as

   the grand-central-station for fat wires. Then all you

   need running back to the batteries is a pair

   of cranking feeders. 4AWG would be fine for these

   as you'll have the the pair in parallel for

   engine cranking.



 

   Bob . . .

user9253

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

Posted: Thu Jun 28, 2018 3:50 pm Post subject: Re: Z-14 Question

Current limiters should not be used in the start circuit because they will drop the voltage to the starter motor.

_________________
Joe Gores

Mauledriver(at)nc.rr.com
Guest

Posted: Thu Jun 28, 2018 4:10 pm Post subject: Z-14 Question

On 6/28/2018 7:08 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		         At 03:22 PM 6/28/2018, you wrote:

               	  Quote: 	
		  -->           AeroElectric-List message           posted by: "Rocketman1988"           <Rocketman(at)etczone.com> (Rocketman(at)etczone.com)

           

           All,

           

           I am going to use the Z-14 layout for my RV-10.  The -10 has           aft           mounted batteries, so I will need to run the main buss wires           from the           back to the front, where all of the electronics are.

           

           My question is:  Do these wires need to have individual           current           limiters on them?  The distance from the batteries to the           battery           buss location is about 8 1/2 feet.  I am planning on using #8           AWG           wire to feed each respective battery buss.

           

           Thoughts? 	
       

         put the crossfeed contactor on the firewall and use it as

         the grand-central-station for fat wires. Then all you

         need running back to the batteries is a pair

         of cranking feeders. 4AWG would be fine for these

         as you'll have the the pair in parallel for

         engine cranking.

       

                

             Bob . . .                	
     

I have a Z-14 in an RV10.  Bob's approach sounds great.  I like       the symmetry.    Not having asked the question 10 years ago when       laying my Z-14 out, I took a different approach.     

I have the Xfeed mounted with the other two contactors back on       the battery tray.  2 AWG links them all up.  Then I have a single       2AWG lead going to the starter Contactor.  The other side has an       8AWG link going forward to one fuse panel (bus) and an 8AWG link       going from the starter contactor to the other fuse panel (bus).       

The current limiters on mounted on the firewall and protect the       lines going from the 2 alternators to the 2 main bus feeds.     

I've attached a schematic with the locations of devices implied.     

Bill "I love my Z-14" Watson

            	 		 			 				 			 		 		 			

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Rocketman1988

Joined: 21 Jun 2012
Posts: 63

Posted: Thu Jun 28, 2018 5:30 pm Post subject: Re: Z-14 Question

Thanks!  That is pretty much what I am going to do...all three contractors near battery, one #2 to starter solenoid, two #8 battery buss feeders going forward...



I like Bob's idea you, however, the #2 cable was run long ago and I do not think it would be an easy task to remove it...

ceengland7(at)gmail.com
Guest

Posted: Thu Jun 28, 2018 5:57 pm Post subject: Z-14 Question

On 6/28/2018 7:01 PM, Bill Watson       wrote:

     

      	  Quote: 	
		                On 6/28/2018 7:08 PM, Robert L.         Nuckolls, III wrote:

       

        	  Quote: 	
		   At 03:22 PM 6/28/2018, you wrote:

                   	  Quote: 	
		  -->             AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com> (Rocketman(at)etczone.com)

             

             All,

             

             I am going to use the Z-14 layout for my RV-10.  The -10 has             aft mounted batteries, so I will need to run the main buss             wires from the back to the front, where all of the             electronics are.

             

             My question is:  Do these wires need to have individual             current limiters on them?  The distance from the batteries             to the battery buss location is about 8 1/2 feet.  I am             planning on using #8 AWG wire to feed each respective             battery buss.

             

             Thoughts? 	
         

           put the crossfeed contactor on the firewall and use it as

           the grand-central-station for fat wires. Then all you

           need running back to the batteries is a pair

           of cranking feeders. 4AWG would be fine for these

           as you'll have the the pair in parallel for

           engine cranking.

         

                    

   Bob . . .          	
       

I have a Z-14 in an RV10.  Bob's approach sounds great.  I like         the symmetry.    Not having asked the question 10 years ago when         laying my Z-14 out, I took a different approach.       

I have the Xfeed mounted with the other two contactors back on         the battery tray.  2 AWG links them all up.  Then I have a         single 2AWG lead going to the starter Contactor.  The other side         has an 8AWG link going forward to one fuse panel (bus) and an         8AWG link going from the starter contactor to the other fuse         panel (bus).         

The current limiters on mounted on the firewall and protect the         lines going from the 2 alternators to the 2 main bus feeds.       

I've attached a schematic with the locations of devices         implied.       

Bill "I love my Z-14" Watson

            	
     Bill,

     

     Your install is obviously working, but it should be noted that your     alternator B lead protection should be on the other end. If there's     a fault in that wire, it should be big enough to handle everything     the alternator can throw at it, but it'll never be big enough to     handle everything the battery(s) can throw at it.

     

     FWIW,

     

     Charlie

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Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Thu Jun 28, 2018 6:20 pm Post subject: Z-14 Question

Having a flying IFR RV-10 myself I question the benefits of dual 

batteries along with dual alternators, etc. Almost all EFIS panels these 

days offer a backup battery, good for 1 hour or more. I have one for 

each of my EFIS screens. Most ship's batteries these days are good for 

an hour or more of minimized current. An Ipad can provide hours of 

moving map and GPS, and with some extras a nearly full EFIS screen.

I can see if you choose to have dual electronic ignition systems that 

then you are vulnerable to lack of electrons for at least one. It seems 

to me that the SD-20 alternator for a backup source of power, with a 

small, Odessey 680 or less mounted on the firewall should handle any of 

those needs. You only need one good sized battery, such as the Odessey 

925 mounted in stock rear location, for starter operation.s Or just keep 

one magneto for the backup, and eliminate need for dual electric power 

sources. You get 85% of the electronic ignition by replacing one mag.

Just my opinion, but I would strive to keep the design as simple as 

possible, and avoid having totally dual everything just because you can.

Just thinking your goals might be achieved with a simpler system.

Kelly

On 6/28/2018 6:56 PM, Charlie England wrote:

 	  Quote: 	
		  >>

> I have a Z-14 in an RV10.  Bob's approach sounds great.  I like the 

> symmetry.    Not having asked the question 10 years ago when laying my 

> Z-14 out, I took a different approach.

>

> I have the Xfeed mounted with the other two contactors back on the 

> battery tray.  2 AWG links them all up.  Then I have a single 2AWG 

> lead going to the starter Contactor.  The other side has an 8AWG link 

> going forward to one fuse panel (bus) and an 8AWG link going from the 

> starter contactor to the other fuse panel (bus).

>

> The current limiters on mounted on the firewall and protect the lines 

> going from the 2 alternators to the 2 main bus feeds.

>

> I've attached a schematic with the locations of devices implied.

>

> Bill "I love my Z-14" Watson

>

 Bill,

 Your install is obviously working, but it should be noted that your 

 alternator B lead protection should be on the other end. If there's a 

 fault in that wire, it should be big enough to handle everything the 

 alternator can throw at it, but it'll never be big enough to handle 

 everything the battery(s) can throw at it.

 FWIW,

 Charlie

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

Rocketman1988

Joined: 21 Jun 2012
Posts: 63

Posted: Fri Jun 29, 2018 5:46 am Post subject: Re: Z-14 Question

Kelly,



Thanks for your opinion. I hesitate posting on these forums due to the â€œnay sayersâ€ when anything other than the simplest tech from the 50â€™s is suggested. I have chosen to use a full EFII system and fully accept the additional complexities. I do appreciate your insight on things...



As for the previous post about the B lead current limiters, I would disagree with putting the fuse at the other end as that would place it between the battery and starter.

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Fri Jun 29, 2018 6:06 am Post subject: Z-14 Question

As I said, it is all about the builder's choices. I have too many years 

working on type certified airplanes as well as homebuilts, fixing self 

induced errors, etc. to be very enamored of new-fangled EFII. My 

experience in automotive arena tells me that the incremental 

improvements from continuous flow fuel injection that arrived in the 

late '50s to single cylinder electronic fuel injection of all but the 

latest cars is fairly small..while the current direct injection into the 

cylinder has had a much bigger improvement than anything since the 

switch from carburetors to fuel injection.

I applaud your willingness to take on the challenge of EFII. When it all 

works as advertised, it certainly will make starting easier and may also 

help reduce maintenance.

However, I don't believe it justifies having two separate systems of 

equal capacity. Still, your choice.

Kelly



On 6/29/2018 6:46 AM, Rocketman1988 wrote:

 	  Quote: 	
		   

 

 Kelly,

 

 Thanks for your opinion. I hesitate posting on these forums due to the Ã¢â‚¬Å“nay sayersÃ¢â‚¬Â when anything other than the simplest tech from the 50Ã¢â‚¬â„¢s is suggested. I have chosen to use a full EFII system and fully accept the additional complexities. I do appreciate your insight on things...

 

 As for the previous post about the B lead current limiters, I would disagree with putting the fuse at the other end as that would place it between the battery and starter.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=481273#481273

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

Mauledriver(at)nc.rr.com
Guest

Posted: Fri Jun 29, 2018 6:59 am Post subject: Z-14 Question

Help me here Charlie, I'm not quite       following you.  The B-lead protection (current limiters) are       installed between the Alternator B-lead terminal and main bus       line.  The battery is not 'behind' the protection  and the bus.        Rather the battery has no protection between it and the bus fuse       block(s).

       

       What am I missing?

       

       Bill

       

       On 6/28/2018 9:56 PM, Charlie England wrote:

     

      	  Quote: 	
		                Bill,

       

       Your install is obviously working, but it should be noted that       your alternator B lead protection should be on the other end. If       there's a fault in that wire, it should be big enough to handle       everything the alternator can throw at it, but it'll never be big       enough to handle everything the battery(s) can throw at it.

       

       FWIW,

       

       Charlie

       

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ceengland7(at)gmail.com
Guest

Posted: Fri Jun 29, 2018 7:08 am Post subject: Z-14 Question

On 6/29/2018 8:46 AM, Rocketman1988 wrote:

 	  Quote: 	
		   



 Kelly,



 Thanks for your opinion. I hesitate posting on these forums due to the Ã¢â‚¬Å“nay sayersÃ¢â‚¬Â when anything other than the simplest tech from the 50Ã¢â‚¬â„¢s is suggested. I have chosen to use a full EFII system and fully accept the additional complexities. I do appreciate your insight on things...



 As for the previous post about the B lead current limiters, I would disagree with putting the fuse at the other end as that would place it between the battery and starter.

I guess I should have been more specific. The other end of the *wire*; 
	


not the entire path. Look at the wire protection for the main alt, which 

is at the hot side of the starter contactor end of the 8 ga wire 

(correct). Now look at the protection on the aux alt B lead, at the 

alternator end, instead of at the source end, which is the cross-tie 

contactor.



When I took another look for this email, I also noticed that the 8 ga 

wires feeding both fuse blocks don't have any protection. 'Conventional 

wisdom' is that the battery contactor protects the 'fat wires', but 

smaller wires need protection.Â  What I see is 2 ga wires stepping down 

in size to 8 ga wires, with no switching (disconnect) and protection at 

the start of the 8 ga wires.



That's not a problem, as long as there isn't a problem. 



Charlie



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ceengland7(at)gmail.com
Guest

Posted: Fri Jun 29, 2018 7:17 am Post subject: Z-14 Question

Protection devices are to protect       *wires*. In our aircraft environments the source of damage to       wires is always the battery. Alternator B leads should be sized       big enough to handle the max that the alternator can deliver, so       they need no protection from the alternator. But the battery can       deliver hundreds of amps (sometimes *many hundreds* of amps). The       4 ga and larger stuff can survive long enough to use the master       contactor as protection, but smaller stuff runs a big risk of       lighting up the insulation if there's no circuit protection.

       

       No protection device on a wire is there to protect the battery.

       

       Charlie

       

       On 6/29/2018 9:58 AM, Bill Watson wrote:

     

      	  Quote: 	
		                Help me here Charlie, I'm not quite         following you.  The B-lead protection (current limiters) are         installed between the Alternator B-lead terminal and main bus         line.  The battery is not 'behind' the protection  and the bus.          Rather the battery has no protection between it and the bus fuse         block(s).

         

         What am I missing?

         

         Bill

         

         On 6/28/2018 9:56 PM, Charlie England wrote:

       

        	  Quote: 	
		                    Bill,

         

         Your install is obviously working, but it should be noted that         your alternator B lead protection should be on the other end. If         there's a fault in that wire, it should be big enough to handle         everything the alternator can throw at it, but it'll never be         big enough to handle everything the battery(s) can throw at it.

         

         FWIW,

         

         Charlie

         

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Mauledriver(at)nc.rr.com
Guest

Posted: Fri Jun 29, 2018 7:26 am Post subject: Z-14 Question

I think Bob refers to my Z-14 in an RV-10 as 'everything including the 

kitchen sink'.  I other words, a bit too much.



Ten years ago when I started laying out my electrical system, I went 

through the Z-schematics and frankly struggled to understand the various 

backup scenarios.  At one point I started sketching the Z-14 out and 

everything became simple and symmetrical (I may have an excess of the 

symmetry gene or something).  More important, my desire coming into this 

project was to have a state of the art panel which I could run for 10-15 

even 30 minutes on the ground without worrying about a subsequent engine 

start.



The need for this was driven home by 2 previous incidents; one being 

flying in to New Orleans less than a year after the big hurricane and 

finding myself sitting in my Maule staring at my Garmin 396 waiting for 

a break in the usual gulf coast cu-nims. Why couldn't I sit in the FBO 

and watch a Nexrad screen?  Because it was still under reconstructions, 

it lacked resources, and required a longish sprint to get to the 

tiedowns.  The other involved the Bahamas.



As my design came together, I ended up with (3) GRT HX EFIS screens and 

assorted accessories.  The GRTs did not have an integrated on/off switch 

(or backup batts) and I wasn't interested in adding any.  Main power on, 

EFISs on; no accidental power-offs or reboots in the soup.  Turned out 

that those (3) screens are real power hogs, even dimmed down.  Even now, 

to run them for 30 mins on one Odyssey 680 suggests pulling a fuse on 1 

or 2 might be a good idea (not really necessary).  It made me question 

the need for 3 screens but after encountering a couple of failures after 

6 years of operation, it's cool to be able to swap out one of the 2 

pilot oriented screens on the ramp at a remote location and fly with 

100% of your normally used panel working.



The Z-14 has turned out to be a simple solution for me.  I have 2 mags 

and no electrically dependent ignition.  I have 2 Odyssey 680s.  Either 

will start the engine, both guarantee it (I was happy to get rid of the 

light weight starters in favor of the slow turning but stronger standard 

starter).  I can run my panel as long as I wish with the engine off.  

Came in handy after the Breezy crash at Oshkosh a few years ago caused a 

conga line of epic proportions.  Etc etc.



I recently lost a voltage regulator.  What did it require me to do?  

Nothing except keep the x-feed switch on and turn off the non-working 

side.  No blip in the air, no shortened trip, no precautionary landing.  

Flew 2 more legs like that with the same redundancy that most pilots fly 

with most of the time.



Bill "I go what I wanted" Watson



On 6/28/2018 10:19 PM, Kelly McMullen wrote:

 	  Quote: 	
		   

 <kellym(at)aviating.com>



 Having a flying IFR RV-10 myself I question the benefits of dual 

 batteries along with dual alternators, etc. Almost all EFIS panels 

 these days offer a backup battery, good for 1 hour or more. I have one 

 for each of my EFIS screens. Most ship's batteries these days are good 

 for an hour or more of minimized current. An Ipad can provide hours of 

 moving map and GPS, and with some extras a nearly full EFIS screen.

 I can see if you choose to have dual electronic ignition systems that 

 then you are vulnerable to lack of electrons for at least one. It 

 seems to me that the SD-20 alternator for a backup source of power, 

 with a small, Odessey 680 or less mounted on the firewall should 

 handle any of those needs. You only need one good sized battery, such 

 as the Odessey 925 mounted in stock rear location, for starter 

 operation.s Or just keep one magneto for the backup, and eliminate 

 need for dual electric power sources. You get 85% of the electronic 

 ignition by replacing one mag.

 Just my opinion, but I would strive to keep the design as simple as 

 possible, and avoid having totally dual everything just because you can.

 Just thinking your goals might be achieved with a simpler system.

 Kelly



 On 6/28/2018 6:56 PM, Charlie England wrote:



>>>

>> I have a Z-14 in an RV10.  Bob's approach sounds great.  I like the 

>> symmetry.    Not having asked the question 10 years ago when laying 

>> my Z-14 out, I took a different approach.

>>

>> I have the Xfeed mounted with the other two contactors back on the 

>> battery tray.  2 AWG links them all up.  Then I have a single 2AWG 

>> lead going to the starter Contactor.  The other side has an 8AWG 

>> link going forward to one fuse panel (bus) and an 8AWG link going 

>> from the starter contactor to the other fuse panel (bus).

>>

>> The current limiters on mounted on the firewall and protect the 

>> lines going from the 2 alternators to the 2 main bus feeds.

>>

>> I've attached a schematic with the locations of devices implied.

>>

>> Bill "I love my Z-14" Watson

>>

> Bill,

>

> Your install is obviously working, but it should be noted that your 

> alternator B lead protection should be on the other end. If there's a 

> fault in that wire, it should be big enough to handle everything the 

> alternator can throw at it, but it'll never be big enough to handle 

> everything the battery(s) can throw at it.

>

> FWIW,

>

> Charlie

>






	




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Mauledriver(at)nc.rr.com
Guest

Posted: Fri Jun 29, 2018 8:43 am Post subject: Z-14 Question

I guess I didn't understand the fat       wire versus the less-than-fat wire exposure.  My take on       unprotected main power lines was that they can be run and       terminated in robust and simple ways with minimal exposure to       chafing, breaching of their insulation or shorting at the terminal       ends.  With that view in mind, I was thinking of my 8AWG wires as       'fat wires' just as my 2AWG wire is.  So I view the 8AWG on the       Aux side as a 'fat wire' with robust and simple terminations at       the contactor and the fuse block.... with a firewall stud in the       path which happens to be part of the current limiter unit.  I'm       quite confident that those 8AWG runs are simple and safe.

       

       I should note that the 8AWG runs from the current limiter firewall       studs to the fuse panels by the copilot's leg are quite short.        Putting the current limiter on the Aux side near the x-feed       contactor behind the luggage area would have required 2 long runs       of 8AWG instead of 1.

       

       I never considered the contactors as any kind of circuit       protection.  I thought of them as  simply switches, switches for       high current loads that can conveniently be thrown remotely by       small switches.  They enable you to manually disconnect a high       current line but there's no automatic protection.

       

       Bill

       

       On 6/29/2018 11:18 AM, Charlie England wrote:

     

      	  Quote: 	
		                Protection devices are to protect         *wires*. In our aircraft environments the source of damage to         wires is always the battery. Alternator B leads should be sized         big enough to handle the max that the alternator can deliver, so         they need no protection from the alternator. But the battery can         deliver hundreds of amps (sometimes *many hundreds* of amps).         The 4 ga and larger stuff can survive long enough to use the         master contactor as protection, but smaller stuff runs a big         risk of lighting up the insulation if there's no circuit         protection.

         

         No protection device on a wire is there to protect the battery.

         

         Charlie

         

         On 6/29/2018 9:58 AM, Bill Watson wrote:

       

        	  Quote: 	
		                    Help me here Charlie, I'm not quite           following you.  The B-lead protection (current limiters) are           installed between the Alternator B-lead terminal and main bus           line.  The battery is not 'behind' the protection  and the           bus.  Rather the battery has no protection between it and the           bus fuse block(s).

           

           What am I missing?

           

           Bill

           

           On 6/28/2018 9:56 PM, Charlie England wrote:

         

          	  Quote: 	
		                        Bill,

           

           Your install is obviously working, but it should be noted that           your alternator B lead protection should be on the other end.           If there's a fault in that wire, it should be big enough to           handle everything the alternator can throw at it, but it'll           never be big enough to handle everything the battery(s) can           throw at it.

           

           FWIW,

           

           Charlie

           

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ceengland7(at)gmail.com
Guest

Posted: Fri Jun 29, 2018 1:32 pm Post subject: Z-14 Question

Ah, the joys of trying to communicate       via the interwebs. 

       

       I'd agree that really short runs (the Aeroelectric 'gold standard'       seems to be 6", but I've probably fudged that in a place or two)       are low risk. But if that #8 from the right side of the x-feed       contactor to the current limiter runs the length of the plane, I'd       want protection at the source end. Not sure why moving the       protection would require two runs. If the protection is at the       contactor, the #8 could run to either fuse block #2, or to the aux       alternator B lead, as 'geographically convenient'. Then it would       continue to the other component. Electrically identical to what       you have now, except the long run (and the short run) of #8 would       be protected from the battery. If the current limiter is now on       the firewall, the only #8 in that run that's actually protected is       between the limiter and the alternator B lead.

       

       I'm not trying to tell you what to do; just wanted to mention a       potential vulnerability. If you're comfortable with the design,       then run with it. It's obviously been working ok so far. I know       I've done a few things that others wouldn't be comfortable with,       but I am, with my plane.

       

       FWIW, I have a similar arrangement for my engine bus (electrically       dependent alternative engine) to your fuse block #1, with the bus       being fed off the hot terminal of the contactor. In my case, it's       the master because everything's on the firewall in my plane, but       same risk of unprotected #8 wire. I protected it, and both my #8       alternator B leads, by using #12 fuse link wire on the 'battery       end' of each #8 wire. Just a 4"-6" long piece of the fuse link       wire soldered  on the end, with the joint insulated with heat       shrink. Then the fuse link gets the terminal that connects to the       contactor. The fuse link wire is an 'off the shelf' item available       from automotive supply houses; it has built-in insulation to       contain the heat if the protection is 'tripped'.

       

       Charlie

       

       On 6/29/2018 11:36 AM, Bill Watson wrote:

     

      	  Quote: 	
		                I guess I didn't understand the fat         wire versus the less-than-fat wire exposure.  My take on         unprotected main power lines was that they can be run and         terminated in robust and simple ways with minimal exposure to         chafing, breaching of their insulation or shorting at the         terminal ends.  With that view in mind, I was thinking of my         8AWG wires as 'fat wires' just as my 2AWG wire is.  So I view         the 8AWG on the Aux side as a 'fat wire' with robust and simple         terminations at the contactor and the fuse block.... with a         firewall stud in the path which happens to be part of the         current limiter unit.  I'm quite confident that those 8AWG runs         are simple and safe.

         

         I should note that the 8AWG runs from the current limiter         firewall studs to the fuse panels by the copilot's leg are quite         short.  Putting the current limiter on the Aux side near the         x-feed contactor behind the luggage area would have required 2         long runs of 8AWG instead of 1.

         

         I never considered the contactors as any kind of circuit         protection.  I thought of them as  simply switches, switches for         high current loads that can conveniently be thrown remotely by         small switches.  They enable you to manually disconnect a high         current line but there's no automatic protection.

         

         Bill

         

         On 6/29/2018 11:18 AM, Charlie England wrote:

       

        	  Quote: 	
		                    Protection devices are to protect           *wires*. In our aircraft environments the source of damage to           wires is always the battery. Alternator B leads should be           sized big enough to handle the max that the alternator can           deliver, so they need no protection from the alternator. But           the battery can deliver hundreds of amps (sometimes *many           hundreds* of amps). The 4 ga and larger stuff can survive long           enough to use the master contactor as protection, but smaller           stuff runs a big risk of lighting up the insulation if there's           no circuit protection.

           

           No protection device on a wire is there to protect the           battery.

           

           Charlie

           

           On 6/29/2018 9:58 AM, Bill Watson wrote:

         

          	  Quote: 	
		                        Help me here Charlie, I'm not             quite following you.  The B-lead protection (current             limiters) are installed between the Alternator B-lead             terminal and main bus line.  The battery is not 'behind' the             protection  and the bus.  Rather the battery has no             protection between it and the bus fuse block(s).

             

             What am I missing?

             

             Bill

             

             On 6/28/2018 9:56 PM, Charlie England wrote:

           

            	  Quote: 	
		                            Bill,

             

             Your install is obviously working, but it should be noted             that your alternator B lead protection should be on the             other end. If there's a fault in that wire, it should be big             enough to handle everything the alternator can throw at it,             but it'll never be big enough to handle everything the             battery(s) can throw at it.

             

             FWIW,

             

             Charlie

             

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jun 29, 2018 2:43 pm Post subject: Z-14 Question

At 11:36 AM 6/29/2018, you wrote:

  	  Quote: 	
		  I guess I didn't understand the fat wire versus the less-than-fat wire exposure.  My take on unprotected main power lines was that they can be run and terminated in robust and simple ways with minimal exposure to chafing, breaching of their insulation or shorting at the terminal ends.  With that view in mind, I was thinking of my 8AWG wires as 'fat wires' just as my 2AWG wire is.  So I view the 8AWG on the Aux side as a 'fat wire' with robust and simple terminations at the contactor and the fuse block.... with a firewall stud in the path which happens to be part of the current limiter unit.  I'm quite confident that those 8AWG runs are simple and safe. 	


    Agreed.



  	  Quote: 	
		  I should note that the 8AWG runs from the current limiter firewall studs to the fuse panels by the copilot's leg are quite short.  Putting the current limiter on the Aux side near the x-feed contactor behind the luggage area would have required 2 long runs of 8AWG instead of 1.



 I never considered the contactors as any kind of circuit protection.  I thought of them as  simply switches, switches for high current loads that can conveniently be thrown remotely by small switches.  They enable you to manually disconnect a high current line but there's no automatic protection. 	


   Correct . . . powers-that-be consider them

   'crew controlled protection', i.e. they're

   used to disconnect sources of energy to smallest

   practical footprint in times of stress . . .

   like smoke or . . . short approach to the rocks.



   B-lead protection is needed ONLY for the exceedingly

   rare instance of shorted alternator diodes so

   any such protection is located as close to the

   bus/distribution node as practical.



   Properly sized b-lead protection CANNOT be

   opened by alternator energy.



   Having recited the legacy philosophy I'll

   note that all three of the vehicles in my

   driveway ranging from 87GMC to 2006KIA

   ALL connect the b-lead directly to the battery . . .

   not even fusible links. In over 50 years

   of driving alternators, never had diodes

   short . . . I have had two instances of

   diodes opening . . . one just two weeks

   ago . . . but no shorts.



   Of course, smoke from the b-lead in a

   car is no big deal . . . as long as it

   doesn't set the engine grease on fire.

   Airplanes not so much.



   Current limiters scattered around the bus

   structures are very low return on investment . .. 

   probably zero.



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 01, 2018 9:20 am Post subject: Z-14 Question

At 08:22 AM 7/1/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>



 Bob,



 Along these same lines, I will have to run two battery buss leads from the aft batteries to the forward busses...about 8.5'.  



 Using the logic presented here, I need to install a current limiter in each battery lead, near the batteries...



 Does this sound like a good plan, or am I missing something? 	


     Yes, it's the NATURE of any probable fault that

     determines the value of upstream protection.



     Conduct a mental exercise considering all the

     ways that your 8AWG bus feeders might experience

     loads that put the 8AWG at risk for getting really

     hot, smoking lots of insulation and perhaps burning

     the wire in two.



     This kind of fault (hard fault) simply cannot

     arise in a properly installed/protected feeder

     (a condition cited by another Lister a few days

     ago). Fat wires in aircraft are at risk only

     for soft faults . . . conditions that cause

     arcing and heating levels too low to actually

     damage the wire. This exercise is called an

     FMEA (Failure Mode Effects Analysis).



     Example:  A C-90 on short final to Clovis NM about 1990 was

     suddenly stricken with complete disconnect of control in pitch.

     Elevator forces in wheel went to zero. The pilots did a go around

     and managed to land safely with power and pitch trim.



     A teardown revealed a mis-positioned wire bundle under the

     cockpit floorboards where a 40A protected wire for co-pilot's

     windshield heat had had been rubbing against the elevator

     cable for a considerable period of time.



     No smoke, no fire, no flickers in the electrical system, no

     trips of the 40A breaker. Over the pre-failure interval, 

     MegaJoules of energy were released in the erosion of steel

     wires (the copper wire was in pretty good shape . . . this

     demonstrates why layers of copper are included in the design

     of safes . . . nearly impossible to penetrate with a cutting

     torch).



     In other instances, it's easy to imagine a 10-cent resistor

     burning up in a radio and making lots of nasty smells in the

     cockpit while failing to open a 5A fuse that protects the

     feed wire to the failed device.



     Bottom line is that ALL thermally actuated protective devices

     (fuses, heater actuated breakers, current limiters, fusible

     links) and even magnetic breakers are incapable of reacting to

     the low-rate, long-duration soft faults that are exemplified

     by the two scenarios I offered above.



     In the case for your intended bus feeders, it is sufficient

     to route, support and otherwise eliminate probability

     of a soft fault (like rubbing an elevator cable or vibrating

     against the EDGE of a lightening hole in a bulkhead).



     The FAA acknowledges the unique fault probabilities

     of fat wires with words that speak to the design

     of light aircraft:



 

 [img]cid:.0[/img]

 [img]cid:.1[/img]



    Your proposed fat wires fall under

    clause (2).



 

   Bob . . .

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Rocketman1988

Joined: 21 Jun 2012
Posts: 63

Posted: Sun Jul 01, 2018 11:34 am Post subject: Re: Z-14 Question

Sooo...I do NOT need to use an ANL fuse on those 8AWG battery feeders...



Correct?

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 01, 2018 1:42 pm Post subject: Z-14 Question

At 02:34 PM 7/1/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Rocketman1988" <Rocketman(at)etczone.com>



 Sooo...I do NOT need to use an ANL fuse on those 8AWG battery feeders...



 Correct? 	


   yes



 

 

   Bob . . .

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