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Z-14 extrapolation

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CBarber(at)TexasAttorney.
Guest

Posted: Fri Dec 26, 2008 1:48 am Post subject: Z-14 extrapolation

Pardon my sophmoric ignorance on this question (sophmore = wise fool) but I 

have installed my Z-14 system in my Velocity with a Mazda Rotary.  I am 

using two standard/stock alternators for this engine rated at 80 amps each. 

The Z drawing uses two 40 amp alternators and mostly 20 awg wire.  Do I need 

to increase the wire size to perhaps 10 awg for my larger alternators?  This 

is becoming an issue as after finally seeming to get my system to "work" 

mostly properly after having my EE friend come out and figure out some basic 

switch functioning that I missed I am having my two Bat circuit breakers 

trip whenever the engine is running and the crossover toggle is in the NON 

crossover mode.



My friend, Blain (who formed and owns the company who supplies air 

conditioner units for smaller airplanes such as Cirus, Moody, 

Columbia/Cessna and now developing for the EXP market, namely Velocity) is 

very versed in electrics but was unable to stick around once this issue came 

up.  He had already spent the day helping me get things right and had a 

family to tend to for the holidays. He did suggest that I may need to change 

the 5 amp CB to 7.5 but cautioned to find out more before going too much 

further by simply adding higer CB's ect.



Back to my problem.  As mentioned, when in the "crossover mode", ie both 

alternators acting together the CB's do NOT trip.  However, when I put the 

toggle in the center position (from down) having the systems act 

indipendently, both trip.  It happens only when the engine is running thus 

the alternator, well, alternating...so to speak.  I did change to the 7.5 

amp CB's but when I tested it tonight, they both tripped as well.  My 

thought is since I used the 20 awg wire as in the Z drawing, but am using 

higher output alternators that my system is not up to the task and that I 

may need to beef things up with larger wire.  Again, pardon my 

ingonrance...even though the fog lifts a bit every day.



So, thoughts, concerns, insight????  All is appreciated.



Thank you.



All the best,



Chris Barber

Houston

www.LoneStarVelocity.com

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Dec 26, 2008 7:04 am Post subject: Z-14 extrapolation

At 03:45 AM 12/26/2008, you wrote:

 	  Quote: 	
		  

<CBarber(at)texasattorney.net>



Pardon my sophmoric ignorance on this question (sophmore = wise 

fool) but I have installed my Z-14 system in my Velocity with a 

Mazda Rotary.  I am using two standard/stock alternators for this 

engine rated at 80 amps each. The Z drawing uses two 40 amp 

alternators and mostly 20 awg wire.  Do I need to increase the wire 

size to perhaps 10 awg for my larger alternators?  This is becoming 

an issue as after finally seeming to get my system to "work" mostly 

properly after having my EE friend come out and figure out some 

basic switch functioning that I missed I am having my two Bat 

circuit breakers trip whenever the engine is running and the 

crossover toggle is in the NON crossover mode.


	


   The Z-figures are to illustrate architectures and

   are not intended to drive alternator size, wire

   sizes, fuse/breaker sizes. Nor are they intended

   to drive the selection of what devices are fed

   from which bus.



 	  Quote: 	
		  My friend, Blain (who formed and owns the company who supplies air 

conditioner units for smaller airplanes such as Cirus, Moody, 

Columbia/Cessna and now developing for the EXP market, namely 

Velocity) is very versed in electrics but was unable to stick around 

once this issue came up.  He had already spent the day helping me 

get things right and had a family to tend to for the holidays. He 

did suggest that I may need to change the 5 amp CB to 7.5 but 

cautioned to find out more before going too much further by simply 

adding higer CB's ect.


	


    The very FIRST thing you do in crafting an

    electrical system is make a list of every device

    that needs DC power to function and you decide

    what that device's position is in the hierarchy

    of necessity. If it's functionality is highly

    desirable for comfortable completion of flight,

    then you have TWO of those devices fed from

    separate power sources. Design goals for achieving

    comfortable termination of flight after some

    component failure are outlined in Chapter 17

    of the 'Connection.



    Next you select an architecture that mitigates

    the effect on outcome of flight for having lost

    one of the devices. Unless you plan on boring

    long holes in the most marginal kinds of weather

    AND you're planning on full-up capability of

    flight in IMC on both sides of the panel, it's

    not clear that the features offered by Z-14 is

    really all that useful to you.



    However, if you're already a long way down that

    path, so be it.



    Have you conducted a load analysis on your proposed

    system and filled out forms like:

    http://www.aeroelectric.com/PPS/Load_Analysis/Blank_Form.pdf



    Fill out one sheet for each bus in your proposed

    design with the goal of deducing what your electrical

    system load are for each flight condition AND insuring

    separate power sources for systems that back each other

    up.



    Or you can take advantage of the load analysis exercises

    conducted by a number of List members and offered in

    Excel spread sheets. You can download those for study

    or modification to your needs in this director from

    my website:



http://www.aeroelectric.com/PPS/Load_Analysis



    After ALL the electrico-whizzies in your airplane

    have been identified, quantified and assigned functionality,

    then you pick fuse/breakers and wire sizes to accomModate

    the needs of each system.



 	  Quote: 	
		  Back to my problem.  As mentioned, when in the "crossover mode", ie 

both alternators acting together the CB's do NOT trip.  However, 

when I put the toggle in the center position (from down) having the 

systems act indipendently, both trip.  It happens only when the 

engine is running thus the alternator, well, alternating...so to 

speak.  I did change to the 7.5 amp CB's but when I tested it 

tonight, they both tripped as well.  My thought is since I used the 

20 awg wire as in the Z drawing, but am using higher output 

alternators that my system is not up to the task and that I may need 

to beef things up with larger wire.  Again, pardon my 

ingonrance...even though the fog lifts a bit every day.



So, thoughts, concerns, insight????  All is appreciated.


	


     There are no positions of switches in Z-14 or

     any other Z-figure that would cause a breaker

     to trip. The cross-feed contactor is there to

     (1) PERMIT running both sides from one alternator

     should one alternator become inoperable and (2)

     using both batteries to crank the engine. But

     if the crossfeed is closed during normal operations,

     no untoward behaviors should be expected. One

     alternator (with the higher voltage setting) will

     hog the load but no breakers will pop.



     I'm not sure of the 20AWG wire reference. Wires

     this small are used in power distribution and

     control downstream of the appropriately sized

     fuse or breaker. The wire is selected to meet

     requirements for carrying current in that particular

     task and the PROTECTED by the appropriate size

     fuse or breaker.



     If you've strung a lot of 20AWG wire into your

     airplane without having evaluated each of those

     wires with respect to their current carrying

     function, then you've not conducted the load

     analysis exercise suggested above.



     Bob . . .

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