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Z-19 based block diagrams

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brianpublic2(at)starband.
Guest

Posted: Wed Sep 20, 2006 5:08 am Post subject: Z-19 based block diagrams

I am working on the wiring for my Eggenfellner Subaru based RV-7A.  I had

made up a wiring diagram, but then it was suggested that I redo it and

simplify it.  The original is a modified version of Z-19, with a couple more

circuits off each engine bus, and the substitution of Schottky power diodes

for the bridge diodes.



See the 2 block diagrams here:



http://brian76.mystarband.net/avionicsSep06.htm#sep15



The first one is the one I was going to go with, and the second one is a

proposed redesign.  As the picture caption states, I already have the 4PDT

locking switches, but I haven't bought the Schottky diodes yet.



The second one looks simpler, but is it perhaps too simple?  In the first

one, I can manually control which busses are "ON" with the 2 4PDT switches.

Normally, they'd both be on.  In case of loss of the single alternator, the

voltage will drop and the aux contactor will open (in either diagram).  Once

the 2 batteries are not tied together through the aux contactor, they will

have different voltages depending on load.  I can run the engine off one

battery it until it gets too low, then switch to using the other battery

(while looking for a place to land, of course).



With the second diagram, there is just one engine bus, instead of two, and

each battery feeds the bus through the 2 Schottky diodes.  But what if the

batteries are at different voltages?  How does the Schottky react in a case

like that?  Does the engine bus simply "see" the higher of the 2 voltages

passing through the 2 schottky diodes?



Any feedback or advice on these specific questions or on any general

observations about either block diagram will be greatly appreciated.

Thanks,

brian



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nuckollsr(at)cox.net
Guest

Posted: Wed Sep 20, 2006 7:11 am Post subject: Z-19 based block diagrams

At 09:00 AM 9/20/2006 -0400, you wrote:



 	  Quote: 	
		  

<brianpublic2(at)starband.net>



I am working on the wiring for my Eggenfellner Subaru based RV-7A.  I had

made up a wiring diagram, but then it was suggested that I redo it and

simplify it.  The original is a modified version of Z-19, with a couple more

circuits off each engine bus, and the substitution of Schottky power diodes

for the bridge diodes.



See the 2 block diagrams here:



http://brian76.mystarband.net/avionicsSep06.htm#sep15



The first one is the one I was going to go with, and the second one is a

proposed redesign.  As the picture caption states, I already have the 4PDT

locking switches, but I haven't bought the Schottky diodes yet.



The second one looks simpler, but is it perhaps too simple?  In the first

one, I can manually control which busses are "ON" with the 2 4PDT switches.

Normally, they'd both be on.  In case of loss of the single alternator, the

voltage will drop and the aux contactor will open (in either diagram).  Once

the 2 batteries are not tied together through the aux contactor, they will

have different voltages depending on load.  I can run the engine off one

battery it until it gets too low, then switch to using the other battery

(while looking for a place to land, of course).


	


    Why would your battery "get too low"? I presume you subscribe to

    the notion that careful load analysis, preventative maintenance of

    the batteries and operational testing is the best way to PREDICT and

    then MAINTAIN system performance to your DESIGN GOALS.

 	  Quote: 	
		  With the second diagram, there is just one engine bus, instead of two, and

each battery feeds the bus through the 2 Schottky diodes.  But what if the

batteries are at different voltages?  How does the Schottky react in a case

like that?  Does the engine bus simply "see" the higher of the 2 voltages

passing through the 2 schottky diodes?



Any feedback or advice on these specific questions or on any general

observations about either block diagram will be greatly appreciated.


	


    Failure Mode Effects Analysis (FMEA) is a process whereby you

    step through all discernable failures including poor design

    goals but NOT failure for due diligence in maintenance. Figure

    out a Plan-B for any failure of a component that might ruin

    your day and re-design the system for failure to meet design

    goals.



    First, I what way did you find Z-19 deficient? An admonishment

    to "make it simpler" is insufficient. You need to set design

    goals, operating limits for duration, then craft to those goals

    using only the parts necessary to comply. "Simplicity" becomes

    an automatic feature of the finished system because you didn't

    put a part in that wasn't necessary to the task.



    So, if Z-19 was attractive as a basis for the beginnings of

    you deliberations, what feature(s) fail to meet your design

    goals. Your first diagram appears to be Z-19 with a second

    fuel pump added. Perhaps all you need beyond Z-19 is a single

    switch that powers the aux pump (probably never used) from the

    engine battery bus.



    Bob . . .

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retasker(at)optonline.net
Guest

Posted: Wed Sep 20, 2006 7:12 am Post subject: Z-19 based block diagrams

Brian, your second design is almost exactly what I am doing (as you know 

I am also using the Egg Subaru).  It allows control over both system 

buses and makes sure that there is always power to the engine bus.  Yes, 

the engine bus will always "see" and draw power from whichever battery 

voltage is higher (less the Schottky drop).  I did add one "last resort" 

switch between the main battery and the engine bus.  While the Schottky 

diodes I am using are as bulletproof as you can get (175A continuous 

rating), I decided to set it up so I can connect directly to the main 

battery just in case.



I agree that your first design is too complicated.



All that said, I am not yet flying.



Dick Tasker



Brian Meyette wrote:



 	  Quote: 	
		  



I am working on the wiring for my Eggenfellner Subaru based RV-7A.  I had

made up a wiring diagram, but then it was suggested that I redo it and

simplify it.  The original is a modified version of Z-19, with a couple more

circuits off each engine bus, and the substitution of Schottky power diodes

for the bridge diodes.



See the 2 block diagrams here:



http://brian76.mystarband.net/avionicsSep06.htm#sep15



The first one is the one I was going to go with, and the second one is a

proposed redesign.  As the picture caption states, I already have the 4PDT

locking switches, but I haven't bought the Schottky diodes yet.



The second one looks simpler, but is it perhaps too simple?  In the first

one, I can manually control which busses are "ON" with the 2 4PDT switches.

Normally, they'd both be on.  In case of loss of the single alternator, the

voltage will drop and the aux contactor will open (in either diagram).  Once

the 2 batteries are not tied together through the aux contactor, they will

have different voltages depending on load.  I can run the engine off one

battery it until it gets too low, then switch to using the other battery

(while looking for a place to land, of course).



With the second diagram, there is just one engine bus, instead of two, and

each battery feeds the bus through the 2 Schottky diodes.  But what if the

batteries are at different voltages?  How does the Schottky react in a case

like that?  Does the engine bus simply "see" the higher of the 2 voltages

passing through the 2 schottky diodes?



Any feedback or advice on these specific questions or on any general

observations about either block diagram will be greatly appreciated.

Thanks,

brian

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klehman(at)albedo.net
Guest

Posted: Wed Sep 20, 2006 7:49 am Post subject: Z-19 based block diagrams

Hello Brian



I'm not really a proponent of running all the engine supplies through a 

diode. Redundancy is good but reducing the reliability of the primary 

system is a tradefoff worthy of careful consideration. I used a slightly 

different scheme that runs each fuel pump off a different battery with 

no diodes. If both pumps are running then no further action is required 

regardless of pump failure, diode failure, fuse blowing, etc. I have the 

option of running both pumps simultaneously at any time such as when 

landing or taking off. My first action in the event of an engine problem 

is to make sure all switches in my engine control row of switches are 

on. That insures both pumps are on. If I  had only one ecm, I'd really 

REALLY like the fuel pumps wired such that there is no way that a 

problem with one pump or its wiring could take out the ecm. For example, 

could a short take out a diode (or two?) before a fuse blows? Diodes 

have a tendancy to blow faster than fuses in my experience although 

perhaps you are planning very large diodes.



I must admit to not understanding why you'd need 4 pole switches in your 

first proposal. I can see the attraction of diodes for the ecm supply in 

your second proposal but I'd probably consider only routing the aux 

supply through a diode. Granted a short on the main system that did not 

isolate itself by blowing fuses could then disable your aux supply but 

I'm having trouble imagining that as a significant risk.



Regarding your diode question. It doesn't matter at all if the batteries 

are different voltages. Whichever is higher will supply the loads. As 

the voltage drops during discharge, the second battery will gradually 

share the load. From then on the battery voltages will be approximately 

equal. The key point is that the good battery will not transfer energy 

into a discharged battery regardless of whether a diode is present.



Ken L.



Brian Meyette wrote:



 	  Quote: 	
		  



I am working on the wiring for my Eggenfellner Subaru based RV-7A.  I had

made up a wiring diagram, but then it was suggested that I redo it and

simplify it.  The original is a modified version of Z-19, with a couple more

circuits off each engine bus, and the substitution of Schottky power diodes

for the bridge diodes.



See the 2 block diagrams here:



http://brian76.mystarband.net/avionicsSep06.htm#sep15



The first one is the one I was going to go with, and the second one is a

proposed redesign.  As the picture caption states, I already have the 4PDT

locking switches, but I haven't bought the Schottky diodes yet.



The second one looks simpler, but is it perhaps too simple?  In the first

one, I can manually control which busses are "ON" with the 2 4PDT switches.

Normally, they'd both be on.  In case of loss of the single alternator, the

voltage will drop and the aux contactor will open (in either diagram).  Once

the 2 batteries are not tied together through the aux contactor, they will

have different voltages depending on load.  I can run the engine off one

battery it until it gets too low, then switch to using the other battery

(while looking for a place to land, of course).



With the second diagram, there is just one engine bus, instead of two, and

each battery feeds the bus through the 2 Schottky diodes.  But what if the

batteries are at different voltages?  How does the Schottky react in a case

like that?  Does the engine bus simply "see" the higher of the 2 voltages

passing through the 2 schottky diodes?



Any feedback or advice on these specific questions or on any general

observations about either block diagram will be greatly appreciated.

Thanks,

brian



--

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dennis.glaeser(at)eds.com
Guest

Posted: Wed Sep 20, 2006 10:35 am Post subject: Z-19 based block diagrams

Brian,



My E-Sube architecture is shown here:

http://www.wideopenwest.com/~glaesers/RV7A/RV7A_Electrical.htm

I've put my batteries behind the baggage bulkhead, so the physical

layout is different than the diagram shows, but the architecture is the

same.  

I have a hot bus for each battery, instead of an engine bus, but

electrically pretty similar to your second diagram.



Dennis Glaeser

RV7A - finishing kit

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brianpublic2(at)starband.
Guest

Posted: Wed Sep 20, 2006 12:48 pm Post subject: Z-19 based block diagrams

About the battery voltage, I was referring to the case where the alternator

has died and I'm just trying to get to an airport on battery power.



I didn't find Z-19 deficient.  Yes, my first diagram is Z-19 with another

pump added, 4PDT switches instead of 2PDT, and Schottky diodes replacing the

rectifier bridges.  It was just suggested to me that I rethink it.   I

didn't at first, but then I had an epiphany a month or so later, and came up

with the second block diagram.



In looking at the first diagram again, it does appear that, with the pumps

switched with dedicated locking SPST switches, I probably don't need the

4PDT for the pumps circuits, as that just puts 2 switches in series.  So

that really leaves me with a SPST switch for each of; primary & secondary

fule pump and ECM.



So that leaves the question of "should I have 2 busses with diode bridges on

the output, or better to go with one engine bus with the diode bridge on the

input?"



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brianpublic2(at)starband.
Guest

Posted: Wed Sep 20, 2006 1:02 pm Post subject: Z-19 based block diagrams

A question for you, Dennis - where did you physically locate your Alt-B

current limiter and Hall Effect sensor?   I am a bit concerned about running

that #8 Alt-B wire all the way back from the alternator, through the

firewall and subpanel to the switches panel before it gets a current limiter

or breaker.  Is your current limiter mounted fwd or aft of the firewall?

Right now, I have more length of the Alt-B wire unprotected than protected,

and I don't like that.   I suppose I could put a breaker or limiter in the

wire right after it comes off the alternator, then fasten the

breaker/limiter to the top of the intake manifold.   How did you do it?



My plan calls for a 60a breaker in the Alt-B line at the switches panel.

Is the current limiter better for some reason?



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Dennis Glaeser

Joined: 10 Jan 2006
Posts: 53
Location: Rochester Hills, Michigan

Posted: Wed Sep 20, 2006 3:09 pm Post subject: Z-19 based block diagrams

Well, I haven't done it yet - don't get my engine until December...

My plan is to put both the current limiter and Hall effect sensor in the

engine compartment.  Since the alternator is on the firewall side of the

engine, I'll probably run the alternator B lead to a firewall mounted

current limiter, and then to the starter (of course, this may change once I

get the engine   The H sensor will probably be near the current limiter.

The only fat wire through the firewall is the starter wire (6AWG).  I am

going to splice an 8AWG wire on the 6AWG wire between the firewall and the

IP subpanel and that will feed the primary bus.



Dennis

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

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




A question for you, Dennis - where did you physically locate your Alt-B

current limiter and Hall Effect sensor?   I am a bit concerned about running

that #8 Alt-B wire all the way back from the alternator, through the

firewall and subpanel to the switches panel before it gets a current limiter

or breaker.  Is your current limiter mounted fwd or aft of the firewall?

Right now, I have more length of the Alt-B wire unprotected than protected,

and I don't like that.   I suppose I could put a breaker or limiter in the

wire right after it comes off the alternator, then fasten the

breaker/limiter to the top of the intake manifold.   How did you do it?



My plan calls for a 60a breaker in the Alt-B line at the switches panel.

Is the current limiter better for some reason?

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nuckollsr(at)cox.net
Guest

Posted: Wed Sep 20, 2006 6:03 pm Post subject: Z-19 based block diagrams

At 04:41 PM 9/20/2006 -0400, you wrote:



 	  Quote: 	
		  

<brianpublic2(at)starband.net>



About the battery voltage, I was referring to the case where the alternator

has died and I'm just trying to get to an airport on battery power.


	


   Okay. I think you'll find it useful to put bounds on "get to the airport".



   Too many of our brethren view the situation you've hypothesized as

   something that doesn't happen often (it doesn't) but is an emergency

   when it does (doesn't have to be) but is almost never covered by a

   Plan-B that is both calculated, designed and maintained so that the

   event is handled solely as a maintenance issue and not something likely

   to upset the wife and kids. They KNEW you were building death trap

   when you started the project, let's not prove them right.

 	  Quote: 	
		  I didn't find Z-19 deficient.  Yes, my first diagram is Z-19 with another

pump added, 4PDT switches instead of 2PDT, and Schottky diodes replacing the

rectifier bridges.  It was just suggested to me that I rethink it.   I

didn't at first, but then I had an epiphany a month or so later, and came up

with the second block diagram.



In looking at the first diagram again, it does appear that, with the pumps

switched with dedicated locking SPST switches, I probably don't need the

4PDT for the pumps circuits, as that just puts 2 switches in series.  So

that really leaves me with a SPST switch for each of; primary & secondary

fule pump and ECM.



So that leaves the question of "should I have 2 busses with diode bridges on

the output, or better to go with one engine bus with the diode bridge on the

input?"


	


   Diodes are more dependable than switches. The idea behind Z-19 as-drawn

   was to provide a plan-b for failure of either switch. Going from 2-pole

   to 4-pole devices is there wrong direction on the reliability curve.

   If I understand your system, you have Z-19 as shown plus an extra pump.

   If it were my airplane, I'd simply add a single-pole AUX PUMP switch

   to power the rarely (if ever) needed pump. Run it from either battery bus.



   You don't need a dual power path for this pump unless you're going for

   Part 25 certification where probability and statistical studies are

   required to analyze dual failures.



   Now, how about pre-flight. Is it harmful to power up the AUX PUMP and

   see that it develops pressure before you start the engine? If not,

   pre-flight is easy.



   This maintains the maximum separation of power paths for necessary

   systems by having them come together at the diodes.



   Bob . . .

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