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Failure modes with Z12

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jpx(at)qenesis.com
Guest

Posted: Thu Feb 18, 2010 11:42 am Post subject: Failure modes with Z12

I am still vacillating between Z13/8 and Z12.



I intend to use two electronic ignitions.  The only thing that  

concerns me is an overvoltage event that burns out both ignitions.   

Probably very rare, considering the robust design, but perhaps a  

lightning strike, or the failure of an overvoltage module ?  Z12 would  

isolate the two and alleviate my concern.



Second, I frequently cruise at 2200rpm and the output of the SD-8  

would be only about 5A.  For 0.8 pounds and $79 more, with an  

insignificant balance improvement, I can buy a 40A and 20A alternator  

instead, which is very tempting.



The concept of the essential bus diode is not used in Z12, so now we  

get to my question.  It appears that after a failure of either battery  

contactor, there is no configuration to supply power to the  

corresponding battery bus.  So duration of flight is limited by the  

battery capacity, rather than the capacity of the remaining alternator  

to supply all the ships loads with the cross feed contactor engaged.   

What change could be safely made to provide power to both battery  

buses without negatively impacting other features of Z12 ?



Thanks !



Jeff Page

Dream Aircraft Tundra #10

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 19, 2010 1:29 am Post subject: Failure modes with Z12

At 01:34 PM 2/18/2010, you wrote:

 	  Quote: 	
		  



I am still vacillating between Z13/8 and Z12.



I intend to use two electronic ignitions.  The only thing that

concerns me is an overvoltage event that burns out both ignitions.

Probably very rare, considering the robust design


	


    correct . . . not a useful point of concern . . .

 	  Quote: 	
		  but perhaps a lightning strike,


	


   No guarantees at all for lightning strike. I'm pretty sure

   Klaus hasn't included lightning immunity in his design

   goals . . . and in any case, system architecture wouldn't

   offer any 'protection' except for a few of the possible

   energy conduction pathways. One just generally needs to

   stay away from

 	  Quote: 	
		    or the failure of an overvoltage module?


	


   Ov module failures don't cause ov conditions.

   OV module failures would not catch and stop

   an OV condition . . . AFTER a regulator failure.

   That's dual failures on a single tank of fuel.

   Exceedingly unlikely to the point



 	  Quote: 	
		     Z12 would isolate the two and alleviate my concern.


	


   Z12 is a single system with two alternators. Z13/8

   is a variation on the same theme. Only Z-14 provides

   near-total isolation between separate systems  . . .

   assuming your willing to let this concern drive

   you decisions.



 	  Quote: 	
		  Second, I frequently cruise at 2200rpm and the output of the SD-8

would be only about 5A.  For 0.8 pounds and $79 more, with an

insignificant balance improvement, I can buy a 40A and 20A alternator

instead, which is very tempting.


	


   What are your design goals? Under conditions of

   main alternator failure, could you NOT cruise as

   fast as red line for the remainder of the flight?



 	  Quote: 	
		  The concept of the essential bus diode is not used in Z12, so now we

get to my question.  It appears that after a failure of either battery

contactor, there is no configuration to supply power to the

corresponding battery bus.  So duration of flight is limited by the

battery capacity, rather than the capacity of the remaining alternator

to supply all the ships loads with the cross feed contactor engaged.

What change could be safely made to provide power to both battery

buses without negatively impacting other features of Z12 ?


	




   You must be talking about Z-14. Are you telling us that

   both batteries are critical for sustained flight? What

   loads are you running from each of the battery busses that

   offers this condition?



   Elegant system design eliminates all single points of

   failure that put the mission at risk. You need to

   make a list of the things you absolutely need to

   continue flight to airport of intended destination.



   For me, flying a spam can, that means shut down the

   electrical system entirely and go to flight-bag

   hand-helds. When I have the airport in sight, I've

   got what ever the battery contains to finish the

   flight.



   The decision is not made by asking us for advice on

   your concerns. The decision is driven by failure mode

   effects analysis stacked against the equipment you

   plan to carry on the panel and in the flight bag. Where

   will those devices will get a couple hours of energy when

   the alternator quits (which is increasingly rare).



   Confidence only arises from a calculated Plan-B.



   Bob . . .

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longg(at)pjm.com
Guest

Posted: Fri Feb 19, 2010 8:09 am Post subject: Failure modes with Z12

Jeff,



Bob's last 3 paragraphs put everything together. The risk adverse

individual (my wife) will question every level and only accept one final

outcome - total assumed security. That isn't going to happen. Look at

all the GA wrecks in the last few days - yikes. In a few year we'll be

lucky if we're allowed to fly.



So let's talk about failure modes as Bob mentions below. For your

example assume the worst case which is probably over water, right? Ok,

personally I have two Klaus jobs (wow, this guy is famous - just the

mention of the name Klaus, I'm so jealous), any-who I have the SD-8 and

a Dynon with HSI. So everything goes to hell, Don't tell Bob but I use

two batteries with Z-13 like Klaus recommends to run one module, so live

it up. This battery is 4.5 ah (very small), but the Klaus job will run

down to 5 volts (now, you're heading for the Bahamas and both

alternators die (hardly likely unless you've been pouring sand into

them) halfway between Palm Beach and Bimini - oh sh*%). 



Ok, with my 1-2 amp Dynon (internal battery) and my sometimes 3 amp SL30

I can still do a non-precision landing at Bimini after running for an

hour (the 50 miles or so) on battery(s). Everything else is off and my

Dynon is running on internal battery (that sucker runs min 1.5 hours

just on the internal 16 volts it has saved up, and oh, since I have two

Dynons I can then turn on the other one and..) When I get near Bimini, I

turn on the radio because I've been monitoring my progress as Bob

mentioned with my handheld GPS and spare batteries. Hell, if I'm really

nuts I can even use my handheld radio to talk to the Bimini approach.



The Klaus jobs won't know the difference and if you're really cocky you

can turn one off and pull 5 volts for several hours before even the 17

ah battery dies. If that's used up, I kill it and move to my backup 4.5

ah battery and skip over Bimini and keep going to Nassau.



You get the point. Once you get setup, you simulate this on the ground.

If your system is 100%, you'll be sitting in your plane a long time

waiting for the battery to give up.



Moral of the story - Keep the batteries in your toys fresh and you'll

keep flying. Batteries and oil are cheap, don't skimp on either.





 	  Quote: 	
		  From Bob N>

" Elegant system design eliminates all single points of
	


   failure that put the mission at risk. You need to

   make a list of the things you absolutely need to

   continue flight to airport of intended destination.



   For me, flying a spam can, that means shut down the

   electrical system entirely and go to flight-bag

   hand-helds. When I have the airport in sight, I've

   got whatever the battery contains to finish the

   flight.



   The decision is not made by asking us for advice on

   your concerns. The decision is driven by failure mode

   effects analysis stacked against the equipment you

   plan to carry on the panel and in the flight bag. Where

   will those devices will get a couple hours of energy when

   the alternator quits (which is increasingly rare)."



 	  Quote: 	
		  


	






--

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Fri Feb 19, 2010 8:44 am Post subject: Re: Failure modes with Z12

 	  Quote: 	
		  "I am still vacillating between Z13/8 and Z12." 	
  If you are undecided, go with Z-13/8.  It is simpler, costs less, and weighs less than Z-14 and is more reliable than most factory-built systems.

  You are concerned about a battery contactor failure.  How will you recognize that a battery contactor failure has occurred?  There might not be any symptoms because the alternator would probably keep working.  It would be necessary to monitor the battery voltage to recognize a problem.  Even with a failed battery contactor, voltage on the main power distribution bus will be normal as long as the alternator keeps working.  The low voltage warning light on the regulator does not warn of low battery voltage due to contactor failure.

   If using Z-13/8, turning on the E-Bus Alternate Feed Switch will provide a parallel path around the contactor from the main alternator to the battery.  Although voltage will be dropped across the diode and current is limited by the 15 amp fuse, it should be adequate for a fuel pump and ignition.  In addition, the aux alternator is connected to the battery side of the main contactor.  Multiple failures would have to occur before power is lost to critical engine ignition and fuel systems that are connected to the battery.  You might consider connecting one ignition and fuel pump to the battery bus and the other set to the E-Bus.  Doing so insures that one set will keep working in the event of a bad electrical connection.

   What do you think Bob N.?

Joe

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 19, 2010 10:17 am Post subject: Failure modes with Z12

At 10:44 AM 2/19/2010, you wrote:

 	  Quote: 	
		  

 > "I am still vacillating between Z13/8 and Z12."

   If you are undecided, go with Z-13/8.  It is simpler, costs less, 

 and weighs less than Z-14 and is more reliable than most factory-built systems.

   You are concerned about a battery contactor failure.  How will 

 you recognize that a battery contactor failure has occurred?  There 

 might not be any symptoms because the alternator would probably 

 keep working.  It would be necessary to monitor the battery voltage 

 to recognize a problem.  Even with a failed battery contactor, 

 voltage on the main power distribution bus will be normal as long 

 as the alternator keeps working.  The low voltage warning light on 

 the regulator does not warn of low battery voltage due to contactor failure.

    If using Z-13/8, turning on the E-Bus Alternate Feed Switch will 

 provide a parallel path around the contactor from the main 

 alternator to the battery.  Although voltage will be dropped across 

 the diode and current is limited by the 15 amp fuse, it should be 

 adequate for a fuel pump and ignition.  In addition, the aux 

 alternator is connected to the battery side of the main 

 contactor.  Multiple failures would have to occur before power is 

 lost to critical engine ignition and fuel systems that are 

 connected to the battery.  You might consider connecting one 

 ignition and fuel pump to the battery bus and the other set to the 

 E-Bus.  Doing so insures that one set will keep working in the 

 event of a bad electrical connection.

    What do you think Bob N.?

Joe



--------

Joe Gores





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=287195#287195




	




   Bob . . .



                    ////

                   (o o)

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

    < Go ahead, make my day . . .   >

    < show me where I'm wrong.      >

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

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Fri Feb 19, 2010 1:56 pm Post subject: Re: Failure modes with Z12

Bob,

I can not show you where you are wrong because you said nothing wrong and your electrical drawings are very hard to improve upon.  Comments in my previous post were not meant to criticize or to suggest changes.  I was only trying to explain how the circuit worked and that there is no reason to be overly concerned about a battery contactor failure in flight and that no changes to Z-13/8 are required for dual electronic ignition (other than to tap power from two separate points).  When I asked for your opinion at the end of my previous post, I was asking for your approval and to correct anything that I may have said that was incorrect.  I hope that you did not take it any other way.  I have been reading the AeroElectric List for a couple of years and have learned a lot and respect your work and opinions.  I commend you for offering free advice and taking time to answer electrical questions from home-builders.

Joe

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 19, 2010 9:10 pm Post subject: Failure modes with Z12

 	  Quote: 	
		     When I asked for your opinion at the end of my previous post, I 

 was asking for your approval and to correct anything that I may 

 have said that was incorrect.  I hope that you did not take it any 

 other way.  I have been reading the AeroElectric List for a couple 

 of years and have learned a lot and respect your work and 

 opinions.  I commend you for offering free advice and taking time 

 to answer electrical questions from home-builders.


	


   Joe, I just re-read my posting. I'm sorry if

   I sounded reproachful in any way. Please know that

   it was unintentional. I abhor such behavior in

   myself and discourage it in others. In fact, I think

   I complimented your organization of the FEMA thought

   process and attempted to amplify that stream of ideas.



   To the best of my recollection, your postings have

   always been helpful and technically accurate.

   I value your participation on the List.



   Bob . . .

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