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Electrical System Reliability (and other ???)

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nuckolls.bob(at)cox.net
Guest

Posted: Mon Jan 07, 2008 8:29 am Post subject: Electrical System Reliability (and other ???)

At 02:23 AM 1/7/2008 -0800, you wrote:



 	  Quote: 	
		  Hi Bob:



I'm in the beginning phase of designing my electrical system.  The 

following are the particulars of my setup:



         Aircraft Mission - IFR (IMC is a likelihood), night and remote 

 backcountry operations.

         Engine - Lycoming IO-540.

         Glass Panel - One Dynon D180 EFIS/EMS and one Dynon D120 EFIS 

 both with internal battery backup.  They are supposed         to be able 

 to cross-display via Dynon's D-SAB.

         Avionics - Garmin GMA-340 Audio, SL30 Nav/Com, SL40 Com, GTX 327 

 Transponder, GPS 496, Dynon AOA/Heated pitot             tube.  All of 

 the avionics were pre-wired by Approach/FastStack using their connecting 

 hub.  The GPS 496 has internal                 batteries as well as an 

 external power source.  I also have a ICOM IC-A23 handheld Com/VOR that I 

 always carry with me.

         Electronic Ignition - LASAR controller with dual Slick mags.  One 

 mag is equiped with a sensor for the LASAR system and             the 

 other is impulse coupled.  Both are inop while the electronic system is 

 operating.  The system has the "Bush Kit"                     which is 

 supposed to default to operating on the mags alone in the event of 

 electrical or software failure.  The controller is             supposed 

 to operate with voltages down to 5.5volts.

         Vacuum System - None

         Alternator/Regulator -  B&C L-60 Alternator and B&C LR3C-14 

 Regulator.

         Fuel Injection - Bendix style fuel injection with Airfllow 

 Performance auxiliary fuel pump.

         Electrical Controls -  Three axis RAC trim system, Electric 

 flaps, Electric cowl flaps.

         Lighting - Dual Strobe lights, Nav Lights, Dual taxi lights, Dual 

 landing lights,  Dual "Type C4A" military style cockpit lights.

         Autopilot - TruTrak Digiflight II two-axis autopilot.

         Battery(s) - My intent is to use the Odyssey series battery(s).



Before I go any further with the design I need to make the following 

decisions:



         1. Single or Dual Alternator. If dual alternator, size of second 

 alternator and type of second regulator.

         2. Single or Dual Battery.  If dual battery, isolated systems or 

 combined and capacity of each battery.

         3. Glass Panel alone or Glass Panel with back-up "Steam 

 Gauges",  Airspeed, Altimeter, Turn Coordinator, Compass.



I have read through Sections 2, 3 and 17 of your book several times as 

well as the wiring diagrams and various articles on your site.  These 

offer a great amount of information and advice which I'm sure would allow 

a knowledgeable person to make the proper decisions.  However, my 

knowledge, experience and confidence are limited so I would like to 

confirm with you my interpretation of the information and get your 

confirmation/critique thereof.  Here goes:



         The first is that designing for complete battery failure i.e. a 

 dead short that would take down the whole system in 

 NOT                     necessary.  This seems to be covered well on page 

 17-11 in a paragraph that contains the following, "Last, the 

 antiquated             concerns for battery "failure"....RG battery 

 reliability....drives the probability of gross battery failure to 

 zero."  However, I would         like to confirm that the Odyssey 

 batteries would fall under the same class as "RG battery reliability" and 

 that I would NOT             need to design for battery failure given my 

 intended mission and battery selection.  Would you concur with that??



         Regarding decision number #1:  Your comments on several pages of 

 sec. 17 clearly indicate your preference for 

 dual                     alternators.  My setup in heavily dependent on 

 electrical systems for normal operations. Based on that and on 

 your                     comments, I would opt for a second alternator 

 using B&C SD-20 Alternator and B&C SB1B-14 Standby Controller.  Given 

 the         need of a second alternator, the weight penalty between the 

 20amp and 8 amp models is 3 pounds.  It would seem 

 the                 20amp would provide near normal operations for as 

 long as it works should the primary alternator fail.  Would you concur 

 with         that??




	


   Is it your design goal to have 100% capability of

   the panel with one alternator out . . . or sufficient

   snort to comfortably complete the mission?



 	  Quote: 	
		           Regarding decision number #2:  This has several sub-parts.



             A - Your comments in sec. 17 seem to indicate that with a 

 dual alternator setup as I opted for in #1, dual batteries 

 with                 isolated systems are NOT necessary as a design point 

 for in-flight electrical failure.  I would like to avoid the 

 dual                         battery contactors and the crossfeed 

 contactor by using a single battery source.  Would you concur with 

 that??  If it                     makes a difference, the battery(s), 

 regulators and LASAR controller will be located on the cabin side of the 

 firewall.

             B -  One of the mission requirements is backcountry 

 operations.  Given that, one my design points was the ability to 

 start             the plane with a completely dead primary (cranking) 

 battery, say as a result of leaving the master on.


	


    Why would you even consider that? You're obviously very

    concerned about NOT having necessary things operate 100%

    of the time but stacking lots of hardware on top of the

    probability that a pilot walks away from the airplane leaving

    things turned on is running off in the wrong direction.



    The most reliable system is that which has the fewest parts.

    The most reliable flight system has a minimum of options for

    the pilot consider when something is not working. A simple

    flashing low voltage warning light (comes with the LR3) tells

    you that a master switch is ON after engine shutdown . . .

    so that scenario is unworthy of consideration . . .



 	  Quote: 	
		     That is the reason I             opted for the LASAR system with the 

 bush kit.  However, given my configuration I would need some sort of 

 standby                     electrical power.  To that end I am 

 considering two options:



                     Option 1:  Design in a permanent Non-Cranking (Aux) 

 battery and bus as shown in fig. Z-35. to power the Fuel 

 Pump,                     LASAR system, and one EFIS/EMS.



                     Option 2:  Design in an external power plug for the 

 fuel pump ONLY and carry a small battery with me 

 during                                 backcountry operations 

 ONLY.   With my configuration I do not need the EFIS/EMS or the LASAR 

 system to                                 function to just start the 

 engine.  The only thing I really need is a few seconds of fuel pump 

 operation to pressurize the                     system in order to hand 

 prop the engine.  If I was backcountry I would have 12 volts of battery 

 power someplace                             anyway.



                     My choice would be for Option 2.  Would you concur 

 with that???



                     C -   Odyssey offers several batteries ranging in 

 capacity form 14 to 28AH, in cranking power from 535 to 

 925CCA                         and in weight from 12.0 to 26.0 lbs.  In 

 the unlikely event of the same flight failure of both 

 alternator/regulator systems                     opted for in #1, and 

 according to the method used on page 17-6, any of the batteries would 

 satisfy the requirements                     of my E-bus.  However, I am 

 not so sure about starting power for normal operations.  My engine is 

 fuel injected and                     high compression.   My space 

 limitations would preclude me from installing the 28AH/925CCA/26lb 

 battery.  That                         would leave two preferred 

 batteries; The PC545 (14AH/545CCA/12.6lbs) and the PC680 

 (17AH/680CCA/15.4lbs).  If                     necessary I could install 

 two of either the PC545 or PC680 batteries wired together to act as 

 one.  My first preference                     would be a single PC680, 

 second would be two of the PC545's and lastly two of the PC680's.



                     Here I would simply ask for your recommendation as to 

 which way to go??.



         Regarding decision #3:  Well this started out to be a long and 

 involved question but as I was typing out my reasoning 

 and             explanation, I made the decision to opt for the back up 

 gauges.  I intend to file IFR for trips and that means at some point 

 I             will probably be in IMC and there is just no way that I am 

 going into IMC without them.  Thanks for helping me get that 

 one             out of the way.  Its been bothering me for months.



There are a couple of other questions I have:



         On page 17-10 you say, "When you trade generators for 

 alternators, loss of a battery contactor may well precipitate total loss 

 of electrical power.  Alternators, don't run well without a 

 battery".  Yet when I look at Figs 17-2,3,4,5,6, and 8, all of them place 

 the Alt field switches on the main bus with the contactor in the path to 

 the battery.  If I understand your statement correctly, it seems that if 

 you loose a single contactor in any except fig 17-5 & 6, Dual Batteries, 

 you would lose all charging systems.  Shouldn't there be a pathway to 

 energize the Alt fields thru the E bus in case of a contactor 

 failure.  Is my reasoning correct??  It looks like Fig Z-13/20 does that 

 for the Aux Alt only and  Fig Z-12 doesn't for either Alt.  Is that 

 correct??  Wouldn't you want to be able to energize both Alt systems from 

 the  E-bus in case of contactor failure with a single battery??? Or 

 alternatively, what about two contactors for a single battery??? They're 

 cheap enough??? Would that work???


	


   The z-figures are crafted to offer comfortable continued

   flight to intended destination while having suffered the

   failure of one piece of the DC power generation and distribution

   system.



 	  Quote: 	
		  

         I really don't understand what P-leads are or the difference 

 between P-mags and E-mags.  What do I have with the LASAR system???


	


   A lot of unnecessarily complex and expensive hardware.



 	  Quote: 	
		     I looked but couldn't find any articles to explain mag operation or 

 what they are.  Could you point be to the proper article???


	


   I'm not sure it would benefit you to delve into the technical

   merits of the various ignition systems at this point. You're

   getting wrapped around too many axles at the same time.

   Unless you're anticipating replacing the Lasar system with

   something else based on new knowledge, the I'll suggest you

   go with what you have.



   If I were building your airplane, I'd figure out a way to

   make Z-13 work. The Lasar system doesn't need extra-ordinarily

   reliable electrical energy . . . that's why it was designed

   that way . . . which is true of the PMag as well. But Z-14

   can and does offer the ultimate in overall system reliability

   and versatility for keeping plenty of stuff on the panel

   working in spite of one and in some cases two failures of

   equipment on one tank full of fuel.



   It's my recommendation that you go with Z-14 as published

   and start filling out your load analysis forms for all the

   busses. Go to my website and search on "load analysis". Then

   print out copies of



http://www.aeroelectric.com/articles/LoadAnalysis.pdf



   for each of the four buses and decide what items will

   be fed from each bus.



   I presume that you presently fly the same kinds of missions

   in a type certificated aircraft. Know that ANY of the choices

   offered in the Z-figures will offer you a "step up" from

   that which is already flown in hundreds of thousands of

   spam-cans for nearly 100 years. Electrical system failures

   as the precipitating event in a disaster are an exceedingly

   tiny portion of root cause.



   Don't spend a lot of time worrying this. Your craftsmanship

   is going to have a stronger influence on success than selection

   of parts and/or architecture.



   Bob . . .

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flagstone(at)cox.net
Guest

Posted: Mon Jan 07, 2008 11:55 am Post subject: Electrical System Reliability (and other ???)

Bob:



You're right.  Ignorance is bliss.  Z-14 it is.



Thanks.



Mark

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