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Z-13/8 Switch Question

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george(at)georgejenson.co
Guest

Posted: Wed Jan 31, 2007 12:23 pm Post subject: Z-13/8 Switch Question

Listers / Bob,



I'm planning my electrical system (Z-13/8, Plane Power main alt) and panel 

and want the switches and layout to be as simple and logical as possible. I 

am considering using two 2-1 switches for the master and the alternators as 

follows:



Master Switch

Down EBUS: Closes circuit between battery bus and  E-bus.

Middle BATT: Only Battery bus is live.

Up MAIN: Normal flight position, grounds contacter making Main bus live, 

E-bus is live via diode from Main.



Alternator Switch

Down BKUP: Grounds contactor making SD-8 backup live to battery.

Middle OFF: No power source available.

Up MAIN: Closes circuit between Main bus and main alternator field.



To my thinking, this is plenty logical and user-friendly. In effect, these 

two would replace the following three switches in Z-13/8:

1. DC Power Master Switch (2-3)

2. E-Bus Alternate Feed (1-3)

3. Aux Alt Off/On (1-3)



Questions:

1. Is this a bad idea in terms of failure exposure - does my risk go up by 

using fewer switches or by using 3-position switches? If so, the next three 

questions are largely moot.



2. Can it be done such that the first is BATT / EBUS / MAIN and the second 

is OFF / BKUP / MAIN such that fully down is off, fully up is normal, and 

middle is "Houston, we have a problem"? This is my first choice, but I 

haven't been able to work out a way to do it with any other 3-position 

switch that I'm aware of. If there is an Off-On-On like a 2-1 but with Off 

on bottom, that would do it, if there is some cool way to do it with a 2-10 

I haven't conjured it.



3. I lose the ability to have both alternators plugging away at the battery 

at the same time, is this a bug or a feature?



4. I also lose the ability of having both the Main bus live, and the E-Bus 

live direct from the Battery bus w/o the attendant voltage drop from the 

diode. Again, bug or feature?



Thanks in advance,



George Jenson

Tucson, AZ

RV-7 standard build, fuselage underway

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nuckollsr(at)cox.net
Guest

Posted: Wed Jan 31, 2007 1:46 pm Post subject: Z-13/8 Switch Question

At 01:21 PM 1/31/2007 -0700, you wrote:



 	  Quote: 	
		  

<george(at)georgejenson.com>



Listers / Bob,



I'm planning my electrical system (Z-13/8, Plane Power main alt) and panel 

and want the switches and layout to be as simple and logical as possible. 

I am considering using two 2-1 switches for the master and the alternators 

as follows:



Master Switch

Down EBUS: Closes circuit between battery bus and  E-bus.

Middle BATT: Only Battery bus is live.

Up MAIN: Normal flight position, grounds contacter making Main bus live, 

E-bus is live via diode from Main.



Alternator Switch

Down BKUP: Grounds contactor making SD-8 backup live to battery.

Middle OFF: No power source available.

Up MAIN: Closes circuit between Main bus and main alternator field.



To my thinking, this is plenty logical and user-friendly. In effect, these 

two would replace the following three switches in Z-13/8:

1. DC Power Master Switch (2-3)

2. E-Bus Alternate Feed (1-3)

3. Aux Alt Off/On (1-3)



Questions:

1. Is this a bad idea in terms of failure exposure - does my risk go up by 

using fewer switches or by using 3-position switches? If so, the next 

three questions are largely moot.


	


   Combined functions open opportunities for single

   failures of a switch to affect more than one function.

   Choose your combinations carefully. Also be aware that

   fewer switches is "simpler" but combined functionality

   is more "complex."

 	  Quote: 	
		  2. Can it be done such that the first is BATT / EBUS / MAIN and the second 

is OFF / BKUP / MAIN such that fully down is off, fully up is normal, and 

middle is "Houston, we have a problem"? This is my first choice, but I 

haven't been able to work out a way to do it with any other 3-position 

switch that I'm aware of. If there is an Off-On-On like a 2-1 but with Off 

on bottom, that would do it, if there is some cool way to do it with a 

2-10 I haven't conjured it.


	


     This could turn into a long debate as to the desirability

     of doing (or not doing) any particular thing. Keep in mind that

     the Z-figures have been combed for a number of years to keep

     the operation logical and produced an attractive failure mode

     effects analysis. While the switch panels illustrated to support

     Z-13/8 may have a lot of features, I've resisted efforts to

     combine functionality for systems other than cabin comfort,

     landing/taxi/wig-wag and other lighting.  See:



http://www.aeroelectric.com/PPS/Switch_Panels/Z13-30-ElexIgn.pdf



 	  Quote: 	
		  3. I lose the ability to have both alternators plugging away at the 

battery at the same time, is this a bug or a feature?


	


     13/8 is not intended to be run with two alternators.

 	  Quote: 	
		  4. I also lose the ability of having both the Main bus live, and the E-Bus 

live direct from the Battery bus w/o the attendant voltage drop from the 

diode. Again, bug or feature?


	


     What you propose will predictably function as you've suggested.

     Just be aware that the considerations for architecture and

     functionality goes deeper than numbers of switches and occupied

     panel space. Consider further that you'll no doubt want to

     sell this airplane at some future date. The more familiar your

     prospective customer is with the functionality of the controls,

     the better.



     Bob . . .

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george(at)georgejenson.co
Guest

Posted: Wed Jan 31, 2007 2:51 pm Post subject: Z-13/8 Switch Question

Bob,



Thanks for the quick reply and solid logic.



1. I'll stick with the Z-13/8 as shown - losing one switch isn't worth 

gaining an unknown amount of risk and giving up being "more likely to be 

familiar" to a prospective future purchaser.



2. Thanks for the switch layout link - hadn't seen those and they are very 

useful.



3. You wrote:

 	  Quote: 	
		  13/8 is not intended to be run with two alternators.


	


I was referring to the main alternator and the SD-8 backup as two 

alternators. Either that wasn't clear, or I mistakenly called it an 

alternator. I was basing that on B&C's description:



 	  Quote: 	
		  SD-8 Alternator

Click picture for description Spline-driven 8 AMP - 14 Volt power system 

for mounting on vacuum pump pad. Price includes alternator assembly with 

male spline and regulator (protrudes 4.75" from mounting surface.)


	


Am I misunderstanding what you meant by 13/8 not having two alternators? In 

any case, as 13/8 appears, you could indeed have both the Main Alternator 

and the Backup SD-8 "whatever its called" both connected to the battery at 

once. I'm assuming this is OK but I was asking if it is necessary or 

beneficial? A better question would be under what circumstances would you 

want them both connected and charging?



Thank you again for all you do,



George Jenson

Tucson, AZ

RV-7 Std Build, fuselage underway

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nuckollsr(at)cox.net
Guest

Posted: Wed Jan 31, 2007 3:40 pm Post subject: Z-13/8 Switch Question

At 03:50 PM 1/31/2007 -0700, you wrote:



 	  Quote: 	
		  

<george(at)georgejenson.com>



Bob,




	


   <snip>

 	  Quote: 	
		  >SD-8 Alternator

>Click picture for description Spline-driven 8 AMP - 14 Volt power system 

>for mounting on vacuum pump pad. Price includes alternator assembly with 

>male spline and regulator (protrudes 4.75" from mounting surface.)


	


    OOPS . . . a better word would have been OPERATED.

 	  Quote: 	
		  Am I misunderstanding what you meant by 13/8 not having two alternators? 

In any case, as 13/8 appears, you could indeed have both the Main 

Alternator and the Backup SD-8 "whatever its called" both connected to the 

battery at once. I'm assuming this is OK but I was asking if it is 

necessary or beneficial? A better question would be under what 

circumstances would you want them both connected and charging?


	


   Your load analysis for NORMAL ops should be well satisfied by

   the main alternator. The standby alternator is to enhance ALT

   FAILED operations to support 8+ amps of E-bus loads indefinitely

   while en route. This saves 100% of battery charge in reserve for

   loads that exceed the SD-8 output during approach and landing.

 	  Quote: 	
		  Thank you again for all you do,


	


   My pleasure sir.



    Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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