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Z101 switch state question: engine and main bus shutdown

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jun 09, 2023 7:45 am Post subject: Z101 switch state question: engine and main bus shutdown

 	  Quote: 	
		    I suggest two 

  independent switches, one for aux alternator and one for aux bus.

  	


   Under what condition would one wish to have independent

   control of battery and alternator that drives it? And

   how would one recognize and respond to that condition

   in flight?



   For a lot of years, the z-figures suggested a DPST

   on-off switch for battery/alternator. A pullable

   crowbar breaker offered means for achieving eliminating

   alternator drain for on maintenance on the ground.



   All busses in Z101 are dual feed paths for access

   to the battery. Driving the battery with short

   path from the alternator places it in the most

   strategic, worst case functionality.



   I think I've suggested before that the aux alternator

   be driven with an in-expensive 'ford' style 

   regulator. It's tested every pre-flight and then

   not used for remainder of 99.99% of all flights.

   Probability of it failing after successful pre-flight and

   for duration of one tank of fuel is vanishingly

   small. Using a full-up LR3 regulator in this

   service is overkill. 



 

 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 13, 2023 12:25 pm Post subject: Z101 switch state question: engine and main bus shutdown

 	  Quote: 	
		  Bob,

 For me, the critical factor here is not independent control of the battery; it's that the aux alternator is effectively playing the role of the internal generation system of a magneto; supplying electrical energy to the engine, even when the entirety of the airframe is made electrically 'cold'. As drawn in Z101: 	


   What accessories will be fed from your

   proposed aux bus loads that you would

   not want to power in combination with

   keeping the engine running?



   The fundamental premise for the aux bus

   is to power accessories most useful

   for continuation of flight with minimal

   energy demands. Primarily of concern

   where battery-only ops are part of

   the plan-b, i.e. no aux alternator.



   When an aux alternator is present,

   then battery-only ops are so statistically

   remote that battery selection can be

   minimized for weight and volume . . . 

   assuming that plan-b load analysis

   (and perhaps even flight testing)

   demonstrates that aux alternator will

   support necessary loads.



 

  	  Quote: 	
		  the aux alt cannot be working unless the aux bus is 'hot'. So,

 if we make the airframe 'cold', we're left with the battery running

 the high current-required engine control/injection system. 	


   Electrically induced smoke in cockpit is

   an exceedingly tiny risk. So aside from

   finding yourself on short-final-to-the-rocks,

   when would you expect to want the electrical

   system completely 'cold'? This condition

   would call for the engine to be shut down

   as well.



   So what's your FEMA/Plan-B analysis show?

   Will your anticipated aux alternator not carry

   the engine plus minimal flight accessory loads?



  	  Quote: 	
		  My choice on my project was to have both the output

 and the control source tied to the *engine* bus, so

 if muscle memory causes me to shut down the airframe

 in an emergency, I can react in the same way that I

 trained in old mag/carb aircraft. This leaves the aux alt

 supplying current to the engine bus. 	


   Muscle memory? When did this replace a

   well conceived and practiced check

   list?  When faced with a need to reduce

   energy consumption in a Z101 architecture,

   I would think that line item 1 would be to

   switch ENGINE BUS ALTERNATE source feeder ON.

   Item 2 would be to switch AUX BUS ALT FEEDER

   and AUX ALTERNATOR to ON. 3. Set master switch

   to OFF to kill any potential main alternator field

   drain and eliminate battery contactor drain.



   These steps carried out on the very compact

   DC POWER management panel will assure smooth

   transition to the Plan-B condition with no

   interruption of power to either engine or

   aux bus loads.



  	  Quote: 	
		  Running an automotive style high pressure fuel injection system/computer/ignition places significantly higher demands on the electrical system, making battery-only operation a poor choice if there's any way to avoid it. Real world in-flight tests using a good-condition PC680 has demonstrated a max endurance of about 40 minutes of battery-only operation, even if the rest of the airframe loads are minimal. Reading the PC680 capacity specs aligns with real-world experience. Not acceptable, when it's so easy to work around it. 	


   If you plan an aux alternator then without

   a doubt, due diligence is required to 

   confirm that it meets DESIGN GOALS for

   continued flight sans main alternator.



   Unlike the legacy considerations for sizing

   the main alternator, one doesn't have to

   consider excess capacity for battery

   recharging. You can PLAN for 100%

   utilization of alternator capacity for

   flight ops.  Ideally, the aux alternator

   would happily carry those loads. I.e.

   battery energy is not a factor for

   planning.



   I'm not seeing any value for plan-b ops

   sans AUX BUS. Energy to Comm, primary nav, panel

   lights and transponder should not

   represent a terrible concern for

   aux alternator energy management.



   Been out of pocket for a few days. Sons

   came to trim some trees around the house

   and yours truly spent a few hours dragging

   bush and trucking loads to the dump.

   Feel like I went too many rounds in 

   bar-room brawl! 



 

   Bob . . .



                    //// 

                   (o o) 

    ===========o00o=(_)=o00o========= 

    < Go ahead, make my day . . .   > 

    < show me where I'm wrong.      > 

    =================================

  

    In the interest of creative evolution

    of the-best-we-know-how-to-do based

    on physics and good practice.

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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