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Rear Mounted Batteries - more questions

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nuckolls.bob(at)cox.net
Guest

Posted: Thu Apr 17, 2008 3:56 am Post subject: Rear Mounted Batteries - more questions

At 02:54 PM 4/16/2008 -0700, you wrote:



 	  Quote: 	
		  



Bob and list,

    Using the previously attached document as reference...



Assumptions... rear mounted batteries.  Main Bat Cntctr, Aux  Bat cntctr 

and Xfeed Cntctr all mounted in rear beside the batteries.


	


    Hmmmm . . . normally we'd like to see the cross-feed contactor

    mounted on the firewall. This provides nice fat-wire terminals

    from both batteries to serve as distribution points for the

    two batteries in addressing their respective tasks.



 	  Quote: 	
		    2awg ground wire to fwd central gnd bus attached to the engine via stud 

 through firewall. XFEED cnctr closed for starting.  2AWG wire from the 

 same side of XFEED cntctr that the main bat cntctr is connected to 

 starter cntctr.


	


     Okay . . .



 	  Quote: 	
		  Questions.... Can I then run appropriate sized wire (tbd) from the same 

side of the starter cntctr as the 2awg wire is attached to the main pwr bus?


	


     Yes. If your cross-feed contactor were up front

     then the battery distribution tie point would be

     on the cross-feed contactor. With the configuration

     you've described, then the starter contactor becomes

     the tie point.

 	  Quote: 	
		  If so, I also assume I would run appropriate sized wire ~8-10 awg (but not 

the heavy 2awg) from aux bat side of the XFEED to the Aux bus and use same 

wire to from the aux alt (prob 8 amp b&C alternator).


	


     Oops . . . sounds like you're describing a Z-14

     architecture using an SD-8 on the aux side. Not

     recommended due to aux battery contactor loads being

     such a significant portion of the SD-8's output.

     Suggest a Z-13 architecture is more appropriate to

     maximizing the capabilities of the SD-8.

 	  Quote: 	
		  Hope this makes sense.  Really just trying to understand if I can only run 

two fat wires from the batteries to the firewall if I want to ground at 

the firewall  or need to pull the extra "hot fat wire".


	


     Let's talk about your architecture and choices

     of hardware to fill the various slots. What

     shortcomings do you perceive with a Z-13 architecture

     that drives you toward dual batteries?



     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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n277dl

Joined: 28 May 2007
Posts: 49
Location: Muscatine IA

Posted: Thu Apr 17, 2008 2:07 pm Post subject: Re: Rear Mounted Batteries - more questions

Bob,

  Thanks for the response and heres some more details....



building a rv10, dual grt hx, 430w, sl30, tt - ap, lycoming io540 - one lightspeed ignition and one mag.  Will have basic airspeed round gauges  for backup... ie groudspeed, vsi, altimeter and an electric gyro attitude indicator.  Have similar systems in RV7A except dynon not grt, no sl30 and all both mags.  



Why two batteries...primarily rumblings on those with efis to the need to have the two batteries in starting to keep from resetting the boot-up operation of the efis's during engine startup (honestly, unverified by me). Adding an extra battery is an insignificant expense (relatively speaking).  Having two batteries would make me more comfortable with dual electronic ignition in the future. I won't start that way as engine already ordered and configured but it's much easier to plumb for future than redo later.



 	  Quote: 	
		  

Hmmmm . . . normally we'd like to see the cross-feed contactor 

mounted on the firewall. This provides nice fat-wire terminals 

from both batteries to serve as distribution points for the 

two batteries in addressing their respective tasks. 

	




In a previous post on the original thread you stated....

 	  Quote: 	
		  

Quote: 



The crossfeed contactor, starter contactor and current limiter 

block can be mounted within inches of each other and "wired" with 

flat strap like the pictures found in this directory . . . 



http://www.aeroelectric.com/Pictures/Wiring_Technique/ 



The short straps are much easier to fabricate and install than 

very short hunks of fat wire with terminals. 



Bob . . .

	




So I'm a little confused.  Maybe I took this one out of context and was specifically directed at firewall mounted batteries.  



I've actually already ran the two 2awg fat wires to the front where I could mount the xfeed contactor but then found the above post and thought maybe it should only be one.



I'm on the road this week but will review the z13 tomorrow night.  Maybe all I need and don't need the extra complexity.  



Thanks again,

Doug

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_________________
Doug
"Fools" are always more creative than process people and will always find ways to ruin a perfectly good set of processes.

nuckolls.bob(at)cox.net
Guest

Posted: Fri Apr 18, 2008 7:17 am Post subject: Rear Mounted Batteries - more questions

At 03:07 PM 4/17/2008 -0700, you wrote:

 	  Quote: 	

Bob,

   Thanks for the response and heres some more details....

building a rv10, dual grt hx, 430w, sl30, tt - ap, lycoming io540 - one 

lightspeed ignition and one mag.  Will have basic airspeed round 

gauges  for backup... ie groudspeed, vsi, altimeter and an electric gyro 

attitude indicator.  Have similar systems in RV7A except dynon not grt, no 

sl30 and all both mags.

Why two batteries...primarily rumblings on those with efis to the need to 

have the two batteries in starting to keep from resetting the boot-up 

operation of the efis's during engine startup (honestly, unverified by 

me). Adding an extra battery is an insignificant expense (relatively 

speaking).  Having two batteries would make me more comfortable with dual 

electronic ignition in the future. I won't start that way as engine 

already ordered and configured but it's much easier to plumb for future 

than redo later.

 >

 > Hmmmm . . . normally we'd like to see the cross-feed contactor

 > mounted on the firewall. This provides nice fat-wire terminals

 > from both batteries to serve as distribution points for the

 > two batteries in addressing their respective tasks.

 >

In a previous post on the original thread you stated....

 >

 > Quote:

 >

 > The crossfeed contactor, starter contactor and current limiter

 > block can be mounted within inches of each other and "wired" with

 > flat strap like the pictures found in this directory . . .

 >

 > http://www.aeroelectric.com/Pictures/Wiring_Technique/

 >

 > The short straps are much easier to fabricate and install than

 > very short hunks of fat wire with terminals.

 >

 > Bob . . .

 >

So I'm a little confused.  Maybe I took this one out of context and was 

specifically directed at firewall mounted batteries.

I've actually already ran the two 2awg fat wires to the front where I 

could mount the xfeed contactor but then found the above post and thought 

maybe it should only be one.

I'm on the road this week but will review the z13 tomorrow night.  Maybe 

all I need and don't need the extra complexity.

Thanks again,

Doug

  My apologies, I may have stuck my foot in it . . . my reason

  is too many balls in the air at once . . . but no excuses.

  Have I seen a power distribution diagram on your project? My

  mental images of our discussion may well be tainted with

  artifacts from discussions on other projects. My comment about

  x-feed contactor on the firewall was based on some discussions

  about rear mounted batteries when I produced a sketch that

  looked like this:

http://www.aeroelectric.com/Pictures/Schematics/Z-14_w_Rear_Batteries_Metal_Aircraft.pdf

  The thrust of this reasoning addressed the need to

  have a convenient, robust place to tie off fatwires that

  come forward from rear mounted batteries in a Z14-like

  architecture. The most obvious solution was to place

  the cross-feed contactor on the firewall irrespective

  of where the batteries were located.

  This provides the sought-after tie point for tying

  the battery fat-wires into the rest of the system.

  Let's back-track as needed to make sure my words are

  supportive of your design goals. Do you have a z-figure

  like drawing to share?

  Bob . . .

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n277dl

Joined: 28 May 2007
Posts: 49
Location: Muscatine IA

Posted: Fri Apr 18, 2008 2:33 pm Post subject: Re: Rear Mounted Batteries - more questions

Bob….



Started out with your published z14 drawing and began to understand the flow with them…



Then found the string referencing the z14_rough that uses non-local ground.  Reviewed options and decided I wanted to use a central primary ground on the firewall / engine block.



That particular string also is where the discussion of keeping the XFEED CNTCTR and the Battery Cntctr’s located close and connected using copper/brass strapping which drove me to drawing up the very rough sketch with only one “+” fat wire running from the back to the front.  



I think the biggest weakness of the “one wire” concept is that I would loose some of the benefit of the aux alternator as it would have to keep the aux battery  cntctr closed.  Think I read in either the “connection” or the list that it takes about 1amp to keep the contactor closed. Obviously, I’d lose 1/8th of the output of the SD8 in that scenario.  Assuming that it’s okay to physically mount the xfeed contactor at the front instead of with the battery contactors, the only real advantage is one less “+” fat wire.  Would still have to run something from the Aux alt and aux bus to the rear but it could be a smaller wire.



So all that said, maybe the simplest most efficient design would be moving the xfeed contactor to the front.  



Also pondering the physical location of the battery bus (ie, the always hot bus).  From what I can read it appears the recommendation is always having this bus physically located within 6-8 inches of the battery.  Obviously this requires running wiring from the front to the back for all devices that you want powered via the battery bus.  An option that I never see mentioned and therefore assume is a bad idea is to run one heavier wire from the rear mounted battery and physically locate the battery bus in the front.  Again, I assume this is a bad idea but would you comment on why…  I’m assuming that you wouldn’t want a non-fused wire ran that distance but thought I’d ask anyway.



These rear-mounted batteries are requiring some noodling as to where to physically mount things. Guess that's why they call it experimental 



Thanks again for all your input.  It sure helps to bounce things off someone that has done this more than once before.



Doug

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_________________
Doug
"Fools" are always more creative than process people and will always find ways to ruin a perfectly good set of processes.

nuckolls.bob(at)cox.net
Guest

Posted: Tue Apr 22, 2008 5:53 am Post subject: Rear Mounted Batteries - more questions

At 03:33 PM 4/18/2008 -0700, you wrote:



 	  Quote: 	
		  



Bob….



Started out with your published z14 drawing and began to understand the 

flow with them…



Then found the string referencing the z14_rough that uses non-local 

ground.  Reviewed options and decided I wanted to use a central primary 

ground on the firewall / engine block.



That particular string also is where the discussion of keeping the XFEED 

CNTCTR and the Battery Cntctr’s located close and connected using 

copper/brass strapping which drove me to drawing up the very rough sketch 

with only one “+” fat wire running from the back to the front.



I think the biggest weakness of the “one wire” concept is that I would 

loose some of the benefit of the aux alternator as it would have to keep 

the aux battery  cntctr closed.  Think I read in either the 

“connection” or the list that it takes about 1amp to keep the 

contactor closed. Obviously, I’d lose 1/8th of the output of the SD8 in 

that scenario.  Assuming that it’s okay to physically mount the xfeed 

contactor at the front instead of with the battery contactors, the only 

real advantage is one less “+” fat wire.  Would still have to run 

something from the Aux alt and aux bus to the rear but it could be a 

smaller wire.



So all that said, maybe the simplest most efficient design would be moving 

the xfeed contactor to the front.



Also pondering the physical location of the battery bus (ie, the always 

hot bus).  From what I can read it appears the recommendation is always 

having this bus physically located within 6-8 inches of the 

battery.  Obviously this requires running wiring from the front to the 

back for all devices that you want powered via the battery bus.  An option 

that I never see mentioned and therefore assume is a bad idea is to run 

one heavier wire from the rear mounted battery and physically locate the 

battery bus in the front.  Again, I assume this is a bad idea but would 

you comment on why…  I’m assuming that you wouldn’t want a non-fused 

wire ran that distance but thought I’d ask anyway.



These rear-mounted batteries are requiring some noodling as to where to 

physically mount things. Guess that's why they call it experimental 



Thanks again for all your input.  It sure helps to bounce things off 

someone that has done this more than once before.



Doug


	


   I've been pondering this discussion for the last day or so and

   I wasn't pleased with the lack of elegance. It seemed that your

   design goals were not well served with the present suite of hardware

   (too heavy).



   An FMEA study of Z-13/8 yields and excellent reliability scenario

   but it cannot address the fact that some modern EFIS products are

   unable to deal with the real world of millisecond long, bus brownout

   during starter-inrush loads. See:



http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1.jpg



   Indeed, all single-battery systems are not designed to provide

   a constant source of power that stays inside the operating

   envelope of these computer based products.



   One obvious solution is a second battery. The question is

   how big? It only needs to supply power to a limited suite of

   ship's hardware for a few tens of milliseconds while the starter

   motor spins up at the onset of each cranking cycle. In terms

   of ENERGY, the requirements are trivial. So the real sizing

   considerations are for internal impedance of the battery. Ideally,

   we'd like to put an array of AA NiMh cells in to support the e-bus

   during brownout . . . but these cells have finicky charging

   requirements. It's not that they wouldn't do the job . . . but

   system design issues are more complex and parts count goes

   up.



   So what's a reasonable middle ground? Take a peek at:

   Take a peek at this drawing I did last night:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8A(BrownOutBattery).pdf



   Here I've suggested that you dump the #2 fat battery and

   the fat contactors associated with #2 master and crossfeed.

   Install a much smaller (7.2 AH, 5.5# 0.04 ohm) "brownout

   battery" and a pair of cube power relays wired such that

   the e-bus is supported ONLY by the brownout battery during

   engine cranking and only while the main bus is loaded so

   heavily that it cannot keep the EFIS from resetting.



   This same technique could be added to any single battery

   system (or even Z-14 where you wanted to use both batteries

   for cranking). This modification to Z-13 does not burden the

   SD-8 with supporting fat contactors that are never expected

   to carry cranking currents . . . hence may be ably replaced

   with smaller, plastic relays.



   Bob . . .

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nuckolls.bob(at)cox.net
Guest

Posted: Tue Apr 22, 2008 7:33 pm Post subject: Rear Mounted Batteries - more questions

At 10:42 AM 4/22/2008 -0700, you wrote:



 	  Quote: 	
		  Bob,  Very interesting discussion....



We are (were) planning on using Z19RB architecture.  Granted, that 

requires 2 full size batteries (17- 20 AH) which we feel would provide 

sufficient backup power in the event of alternator failure, redundant 

power sources for the dual fuel pump and ignition required for the 20b 

Mazda rotory engine and avoids the added expense and complication of the 

extra alternator.  To insure good batteries one would be replaced each year.



Our thought was the two batteries would provide adequate power even during 

starts to prevent brownouts and a minimum of one and a half hours battery 

power (with load shedding of course) in the event of an alternator failure.


	


   That's consistent with the processes by which Z-19 was crafted.

   Dual alternators is simply not a practical option for many

   of the automotive conversions.



 	  Quote: 	
		  We have not tested this battery endurance yet as the panel is not finished.


	


   You should be able to predict e-bus performance. The

   Discharge curves for various battery products are generally

   available from the manufacturer. Just keep in mind that

   the useful capacity is not consistent with variable loads.

   The higher the load, the more energy is lost internal to

   the battery. In this family of curves . . .



http://www.aeroelectric.com/Pictures/Curves/17AH_12V_Capacity_vs_Load.gif



   we see that a new 17 a.h. battery is good for

   just over 2 hours with a 4 amp load. So about 1.5

   hours when time to toss the battery. On the other

   hand, a 10A load is good for about 60 minutes. If

   one hour is the new-battery design goal, then end

   of service life will be at about 45 minutes.



 	  Quote: 	
		  The brownout relay got me thinking about Z13/8 again....

Any thoughts????


	


   It's up to you to decide what goodies are operated

   during the alternator out operations and then decide

   how much payload you're willing to trade for battery-

   only endurance with those loads.



   In VMC, your other-than-engine loads can probably

   be VERY low thus offering more hours of electrical

   support than you have fuel support. A set of pre-flight

   tested hand-helds can certainly be part of your plan-B

   equation.



   Being limited to two batteries, one alternator and

   a couple of hand-helds doesn't need to present a

   worrisome situation.



        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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