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Z diagrams and fuseable links

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Jekyll

Joined: 22 Feb 2006
Posts: 44

Posted: Mon Mar 20, 2006 3:11 pm Post subject: Z diagrams and fuseable links

I'm planning my electrical system and am intending to use a cludge of the Z-13/8 and Z-12. Basically, I'm deleting the SD-20 circuits from the Z-12 and inserting the SD-8 circuitry from the Z-13/8. Said another way, my intent is to use the Z13/8 but substituting the B&C VR (LRC3-14) for the VR shown. I'm using an E-Mag/P-Mag combination. I thought the remainder would be identical but close examination shows some differences (other than the ignition) which I don't understand.



a. The E-Bus alternate feed in Z-13/8 has a fuseable link and a 7A fuse but the Z-12 has just the fuse. Why the difference between the drawings? Why have both a fuseable link and a fuse in the same wire? I thought thier purpose and function were the same.



b. The Z-13/8 has a fuseable link and a 5 amp pullable CB between the main bus and the DC master power switch. The Z-12 just has the CB. Why the difference and should I use the fuseable link or just the CB?



c. The Z-13/8 indicates the E-bus and the main bus should be no more than 6 inches apart. Am I to read that as no more than 12 inches because of the isolation diode (6 inch max on each side of the diode) or should it be a combined total of 6 inches? The Z-12 doesn't identify this requirment. Should the 2 Z figures be the same in this regard and if not, which should I use (6 inches each or in total)?



d. The avionics ground bus shows a connection to the instrument panel ground bus indicated as 5X20AWG. I'm thinking this indicates a ground connection based on 5 seperate 20 AWG wires to individual faston tabs between the busses. Please confirm or correct my read on this.



Thanks



Jekyll

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nuckollsr(at)cox.net
Guest

Posted: Mon Mar 20, 2006 6:47 pm Post subject: Z diagrams and fuseable links

At 03:11 PM 3/20/2006 -0800, you wrote:



 	  Quote: 	
		  



I'm planning my electrical system and am intending to use a cludge of the 

Z-13/8 and Z-12. Basically, I'm deleting the SD-20 circuits from the Z-12 

and inserting the SD-8 circuitry from the Z-13/8. Said another way, my 

intent is to use the Z13/8 but substituting the B&C VR (LRC3-14) for the 

VR shown. I'm using an E-Mag/P-Mag combination. I thought the remainder 

would be identical but close examination shows some differences (other 

than the ignition) which I don't understand.


	


     How does figure Z-13/8 fall short of your design goals?

     I presume you understand that if you close the master

     contactor during main alternator inop operations that

     you have the same functionality as replacing the SD-20

     with an SD-8 in Z-12 . . .



     However, when wired as Z-13, you can continue flight

     to airport of intended destination with minimal loads

     thus saving the battery for approach to landing by reclosing

     the master contactor and powering up everything you need

     knowing that the battery's full capacity + SD8 output

     is available for completion of flight.



     I don't understand what you want to achieve with the

     architecture you've suggested.

 	  Quote: 	
		  a. The E-Bus alternate feed in Z-13/8 has a fuseable link and a 7A fuse 

but the Z-12 has just the fuse. Why the difference between the drawings? 

Why have both a fuseable link and a fuse in the same wire? I thought thier 

purpose and function were the same.


	


     Sorta . . . the operating time constant between fuses and fusible links

     could not be further apart. Circuit breakers reside in between.

     Sizing of fuses, breakers, wire and choices for style of

     protective devices are all up to you. When you see protection

     at both ends of a wire, it suggests that their are sources

     of energy that put the wire at risk from either end.



 	  Quote: 	
		  b. The Z-13/8 has a fuseable link and a 5 amp pullable CB between the main 

bus and the DC master power switch. The Z-12 just has the CB. Why the 

difference and should I use the fuseable link or just the CB?


	


     I'll suggest you review the fusible link discussion

     at



http://aeroelectric.com/articles/fuselink/fuselink.html





 	  Quote: 	
		  c. The Z-13/8 indicates the E-bus and the main bus should be no more than 

6 inches apart. Am I to read that as no more than 12 inches because of the 

isolation diode (6 inch max on each side of the diode) or should it be a 

combined total of 6 inches? The Z-12 doesn't identify this requirment. 

Should the 2 Z figures be the same in this regard and if not, which should 

I use (6 inches each or in total)?


	




    There are no requirements, only recommendations based on

    carry-overs and rules-of-thumb from the certified world.

    The rule-of-thumb for leaving a wire "unprotected" is 6"

    of length. If your own thumb is longer, feel free.

    If you're not comfortable/conversant with the tradeoffs

    for selection of protection, go for breakers/fuses sized

    for your particular load analysis. Fusible links are limited

    use devices and not universal replacements for more

    conventional device.

 	  Quote: 	
		  d. The avionics ground bus shows a connection to the instrument panel 

ground bus indicated as 5X20AWG. I'm thinking this indicates a ground 

connection based on 5 seperate 20 AWG wires to individual faston tabs 

between the busses. Please confirm or correct my read on this.


	


    Yes, this is one option. See Figure 18-17 in:



http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf



    You can use multiple pins within the bus connector or

    take a couple of fatter from the bus to firewall ground

    block.

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Jekyll

Joined: 22 Feb 2006
Posts: 44

Posted: Mon Mar 20, 2006 7:57 pm Post subject: Re: Z diagrams and fuseable links

 	  nuckollsr(at)cox.net wrote: 	
		  At 03:11 PM 3/20/2006 -0800, you wrote:



     How does figure Z-13/8 fall short of your design goals?

     I presume you understand that if you close the master

     contactor during main alternator inop operations that

     you have the same functionality as replacing the SD-20

     with an SD-8 in Z-12 . . .

	




Well, I think I said that 13/8 is using a generic Ford VR and that I looking at using the B&C VR part number LRC3-14. In looking at 13/8 and 12, I at first thought the only difference in the main alternator wiring is that the crow bar and low voltage monitoring portions depicted in the 13/8 are internal to the B&C VR used on the Z-12. But then I noticed subtle differences in the form of the fuseable links I mentioned. 



I'm no genius at this stuff so I bought your book and use your site for assistance. Though I'm a babe in the woods with wiring airplanes, the main alternator circuitry and the logic flow between the e-bus, main bus, bat bus and instrument bus appear to be the same. This causes me to wonder why the differences I mentioned exist namely the fuseable link between the e bus and switch, the fuseable link between the main bus and the alt CB. With the similarities between the 2 drawings, I would have expected the same callouts in these areas.



So- why fuseable links in one and not the other? I'm not critisizing your designs, just trying to understand so that I can wire my bird with the confidence that comes from understanding.



Jekyll

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Bill Schlatterer

Joined: 09 Jan 2006
Posts: 195

Posted: Mon Mar 20, 2006 9:15 pm Post subject: Z diagrams and fuseable links

Bob, your original Z13 from a couple of years back used the LRC3-14

regulator but recently you pulled that one and substituted a diagram using

the Ford Regulator.  I understood Jekyll to say that he was using the Z13

diagram but needed to pull the regulator circuit from Z12 which you still

show with the LRC3-14.  Thus the blend of Z13 and Z12.  I have an old copy

of the original Z13 with the B&C regulator if that would help!



If I were to ask you for my perfect Z13 it would be the Z13/8 with B&C

regulator and one P-Mag,... But then you always said "they are just

architecture examples, modify as needed".  



Thanks for all your help!



Bill S

7a wiring 



--

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blackoaks(at)gmail.com
Guest

Posted: Wed Mar 22, 2006 2:41 pm Post subject: Z diagrams and fuseable links

<snip> When you see protection

    at both ends of a wire, it suggests that their are sources

    of energy that put the wire at risk from either end.

<snip>



Bob,

This brings up another question.  I have a Lancair ES and the weight and

balance requires the batteries to be aft of the baggage compartment.  I have

the battery contactor within 6 inches of the battery but then have about a

12 foot run up to the main bus.  If I need to have the battery contactor in

the rear to keep from having a long 'hot'  wire why don't I need something

at the front end to keep the alternator from making the long wire 'hot' from

the other end?



--

John McMahon

Lancair Super ES

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klehman(at)albedo.net
Guest

Posted: Wed Mar 22, 2006 7:14 pm Post subject: Z diagrams and fuseable links

I think because the long wire is thick enough to not overheat from max 

alternator output.

A 40 amp alternator can't put much more than 40 amps into the wire and 

it is sized to handle that. A battery can put out many hundreds of amps 

and overheat that wire. Remember overcurrent protection is only to 

prevent overheating of the wire. A fuse won't shutdown something like a 

high resistance arcing short to ground that draws less current than the 

fuse rating. Hopefully you'd also be able to shut down the alternator if 

you were experiencing smoke or obvious electrical distress.

Ken



John McMahon wrote:



 	  Quote: 	
		  



<snip> When you see protection

    at both ends of a wire, it suggests that their are sources

    of energy that put the wire at risk from either end.

<snip>



Bob,

This brings up another question.  I have a Lancair ES and the weight and

balance requires the batteries to be aft of the baggage compartment.  I have

the battery contactor within 6 inches of the battery but then have about a

12 foot run up to the main bus.  If I need to have the battery contactor in

the rear to keep from having a long 'hot'  wire why don't I need something

at the front end to keep the alternator from making the long wire 'hot' from

the other end?



--

John McMahon

Lancair Super ES

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