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Z-19 hypothetical question

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user9253

Joined: 28 Mar 2008
Posts: 1935
Location: Riley TWP Michigan

Posted: Fri May 23, 2008 4:42 pm Post subject: Z-19 hypothetical question

Here is a hypothetical question for you electrical gurus.  A pilot is flying on trip in a plane wired according to schematic Z-19.  Shortly after takeoff the main battery contactor fails open.  The pilot does not notice anything wrong because the engine battery contactor is closed and the alternator is still functioning.  Eventually the main battery discharges due to loads on the main battery bus, and the pilot notices some things not working.  He knows there is a problem but does not know the cause.  Just to be safe, he closes the Endurance-Bus Alternate-Feed switch.  The question is, does the charging current blow a fuse?  (either one or both fuses)  The current path is from the Main Power Distribution Bus, 7A fuse, diode, Endurance Bus, Alternate-Feed switch, fuse, Main Battery Bus, to the main battery.



If the answer to the above question is yes, then everything on the Endurance Bus might not work for the remainder of the flight.  I think the best solution is to increase the wire and fuse sizes in the above circuit.  What size is required?  Other possible solutions such as another diode or relay create additional problems.



Joe Gores

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_________________
Joe Gores

nuckolls.bob(at)cox.net
Guest

Posted: Sat May 24, 2008 9:59 am Post subject: Z-19 hypothetical question

At 05:42 PM 5/23/2008 -0700, you wrote:



 	  Quote: 	
		  



Here is a hypothetical question for you electrical gurus.  A pilot is 

flying on trip in a plane wired according to schematic Z-19.  Shortly 

after takeoff the main battery contactor fails open.  The pilot does not 

notice anything wrong because the engine battery contactor is closed and 

the alternator is still functioning.  Eventually the main battery 

discharges due to loads on the main battery bus, and the pilot notices 

some things not working.  He knows there is a problem but does not know 

the cause.  Just to be safe, he closes the Endurance-Bus Alternate-Feed 

switch.  The question is, does the charging current blow a fuse?  (either 

one or both fuses)  The current path is from the Main Power Distribution 

Bus, 7A fuse, diode, Endurance Bus, Alternate-Feed switch, fuse, Main 

Battery Bus, to the main battery.


	


   EXCELLENT question!



   It's that "just to be safe" thinking that causes

   joe-pilot to stubs his toe. Every design feature

   of a system is (or at least should be) put in place

   for a specific purpose. In this case, the E-bus alternate

   feed switch is intended to provide an alternative power

   for e-bus powered electro-whizzies WHEN the main bus

   voltage falls too low to be a practical source of energy.



   99.9+ percent of the time this is because the

   alternator is no longer supporting ship's loads for

   what ever reason.

 	  Quote: 	
		  If the answer to the above question is yes, then everything on the 

Endurance Bus might not work for the remainder of the flight.  I think the 

best solution is to increase the wire and fuse sizes in the above 

circuit.  What size is required?  Other possible solutions such as another 

diode or relay create additional problems.


	


   Controls in our aircraft have beneficial

   effects that are addressed as part of a constellation

   of design goals. Some controls are not totally

   free of misadventure or even hazard for having been

   operated at an inappropriate time or inappropriate

   way.



   The only time I would close the e-bus alternate feed

   switch is after the low voltage warning light has

   informed me of a need for completing the flight battery(ies)

   only.



   Referring to . . .



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z19m_1.pdf



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z19m_2.pdf



   In the hypothetical you posed, electro-whizzies to

   first start spinning down would be the clock and the

   #2 fuel pump. Also, the engine would be complaining if

   the current configuration of switches had the engine

   running from the main battery instead of the engine

   battery. In this case, the first thing to do is bring

   the engine's alternative power switch ON to see if the

   engine gets happier. This is the hazard-free thing

   to do irrespective of how the engine was being powered

   before the "event".



   Once the engine is happy, use the voltmeter to explore

   the condition of the two batteries. One would quickly

   discover that for whatever reason, one of the batteries

   is low.



   Now is not the time to initiate trouble shooting

   procedures with switch-flipitis and non-piloting

   thought processes. Save all that fun stuff until

   parked on the ramp.



   Now, suppose a contactor fails during flight but

   the battery does not fall so low that electro-whizzies

   start complaining. It's conceivable that the airplane

   gets parked with an undiscovered latent failure. This

   is why the pre-flight check for dual battery airplanes

   is to turn battery switches on one at a time before starting

   the engine and comparing similarity of voltage readings

   for the two batteries under the same load.



   This will catch the latent failure before next flight.



   This brings up the rationale for separate normal

   and alternative engine power control switches as opposed

   to the multi-pole, two-position switches suggested by

   other designers. This hypothetical illustrates the

   feature of being able to ADD the alternative engine

   source to the current engine source . . . I.e. disturb

   as few controls in the present configuration as possible

   while resolving the appropriate plan-B for comfortable

   termination of flight. It also eliminates having mechanical

   failure of the single switch taking the engine power down.



   More than one dark-n-stormy night story has related

   situations where pilot fiddle-itis made things

   progressively worse. I had this conversation with

   a client just yesterday when the question was asked,

   "what happens if the warning light comes on, the pilot

   pulls the breaker and resets it, the warning light goes

   out and he tries to operate the system AGAIN and

   further aggravates the out-of-rig condition?"



   My answer was, "If the pilot survives to tell you

   about it, yank his job if not also his ticket". If the POH

   or the check-pilot that approved him for the aircraft

   doesn't cover the proper procedure for responding to

   that particular warning, then yank HIS job and/or ticket."



   The point is that carefully crafted systems need to

   be supported not just with good systems and human

   factors engineering. The teachers charged with

   insuring skill and understanding on the part of

   future users are just as critical as the designers.

   More folks die out of apathy/ignorance than of systems

   failure.



   Bob . . .

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nuckolls.bob(at)cox.net
Guest

Posted: Sat May 24, 2008 10:25 am Post subject: Z-19 hypothetical question

P.S. A product under development . . .



http://www.aeroelectric.com/Catalog/AEC/9011/9011-700-1C.pdf

has two channels of LOW Voltage warning. The second specifically intended

to watch the aux battery for failure of contactor or failure of

pilot to close said contactor.



I don't think I'd put a low voltage warning in just for that purpose

but in this case, it was about a 7% increase in parts count to

add the feature to an existing design.



Just some additional food for thought.



Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1935
Location: Riley TWP Michigan

Posted: Mon May 26, 2008 7:31 am Post subject: Hey Bob, were you referring to me as joe-pilot? LOL

Hey Bob, were you referring to me as joe-pilot?  LOL



Ok, to keep me from stubbing my toe, how about the attached schematic?  It features circuit breakers within reach of the pilot, dual alternate feed for the essential bus, relays to isolate power from the cockpit, one power wire between engine compartment and essential bus with fusible links to protect it.



Any suggestions, comments, or improvements are welcome.



Joe Gores

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AeroElectric Z-19Aa1.gif

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Modified Z-19 Dual batteries without fuel injection or electronic ignition

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_________________
Joe Gores

longg(at)pjm.com
Guest

Posted: Tue May 27, 2008 6:23 am Post subject: Z-19 hypothetical question

Bob,

Let me know if you need another mule to test the below. I am very

interested (no, make that a must have) in dual battery monitoring. A

quick google turns up a few options.



High tech job.

http://store.solar-electric.com/xalidubamo.html



Gizmo.

http://www.piranhaoffroad.com.au/products/dualbattery/dualbatteryinfo_ac

cessories.htm



Do not archive.



--

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nuckolls.bob(at)cox.net
Guest

Posted: Tue May 27, 2008 4:32 pm Post subject: Z-19 hypothetical question

At 08:31 AM 5/26/2008 -0700, you wrote:

 	  Quote: 	
		  



Hey Bob, were you referring to me as joe-pilot?  LOL



Ok, to keep me from stubbing my toe, how about the attached schematic?  It 

features circuit breakers within reach of the pilot, dual alternate feed 

for the essential bus, relays to isolate power from the cockpit, one power 

wire between engine compartment and essential bus with fusible links to 

protect it.



Any suggestions, comments, or improvements are welcome.



Joe Gores


	


   I'm having trouble putting my arms around the rationale

   for the double alternate e-bus feeds. The original design

   goal for dual batteries under Z-19 was to make sure the

   LAST piece of equipment on board to loose power after

   alternator failure was the engine.



   Further, with the double-alternate feed scheme you seem

   to be worrying about double failure . . . alternator

   followed by a failure of your non-engine battery to carry

   e-bus loads.



   For the first 25% or so of capacitor discharge, voltage

   falls at the approximate rate of:



    Volts/Second = Amps/Farad



    Assuming a 4A bus, then 4A/.05F yields a rate of

    80 volts/second. If your hoping to keep the e-bus

    at say 10v or above, then starting with a fresh battery

    (12.5 v) you can tolerate a drop of 2.5 volts during

    transition.



    At 80 volts/second decay, you can tolerate an open supply

    line for 2.5/80.0 or 32 milliseconds. Hmmm . . . you

    can probably get the transition over with in that time.

    But suppose you're switching from a discharged battery

    at 10.5 volts. Now the capacitor starts at 10.5 and

    transition has to be completed in 0.5v/80vps

    or 6 milliseconds.



    This exercise illustrates why we don't attempt these

    kinds of things in the big iron birds. Every piece

    of equipment we install is qualified to make graceful

    recoveries from total loss of power during switch

    or relay transitions.



    Let's revisit Z-19 as published and you tell us

    what failure mode is not addressed.



    Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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