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Three Questions on Z-07

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markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Wed Mar 13, 2019 4:01 pm Post subject: Three Questions on Z-07

I am building an electrically dependent LSA Carbon Cub. I will be using the SDS EFI system. I am currently planning to use Z-07 as the basis for my electrical system architecture. 



I have three questions:



1. Using Z-07 as drawn my Endurance Bus (E-Bus) load is only 4.0 amps, due to high efficiency avionics, and my MOTIVE Power Distribution Bus (MPDB) load is 14 amps due to the EFI. In an alternator-out situation if I run the MPDB on one battery and the E-Bus on the other, wouldnâ€™t I be â€œwastingâ€ some of the E-Bus battery since its load is so much less than the load on the MPDB? Assuming that I want to keep the batteries the same size, would it be better to merge the MPDB and the E-Bus, keeping all connections the same?  In the alternator-out scenario I would then shut down my MAIN Power Distribution Bus to shed load and drive the E-Bus with both batteries, perhaps through a single relay.



In an earlier e-mail Bob said



 	  Quote: 	
		  During that discussion, we concocted the idea

of an ENDURANCE bus to (1) power a

minimally useful equipment list, (2) power

additional items easily turned off to shed

load and (3) have a battery energy path

around a de-energized battery contactor. 	




Essentially it seems to me that with an EFI the whole MPDB could be treated as part of the E-Bus. I realize that I may be missing something here.



2. I have been looking at using a pair of EarthX ETX680 (PC680-equivalent) LiFePO4 batteries since they have a BMS that will post info to my GRT EFIS about their condition. I would like to use both batteries for starting as in Z-07. I have read that people like to separate their avionics bus from the starting battery because of a potential voltage drop during starting. However, the BMS on the EarthX batteries takes their output to zero if it drops below either 12.8v or 11.5v (both are stated in their on-line documentation). Since the EarthX batteries can demonstrably start Lycoming 4 cylinder engines without dropping off line, does this in fact imply that there is not a voltage drop below 11.5v on starting with them? Is this a difference between LiFePO4 batteries and lead acid batteries?



3. Can someone tell me what the DSS2XC61-01A is? Is it a diode?



Thanks.



Mark[/quote]

JohnInReno

Joined: 08 Sep 2007
Posts: 150

Posted: Wed Mar 13, 2019 4:34 pm Post subject: Three Questions on Z-07

I have a couple of years experience with the EarthX batteries and I have 

some positive comments:



1.Â Â Â  The voltage should not drop during the engine start unless there 

is a dead stall.



2.Â Â Â  In a single battery installation, the battery is sized to the 

alternator output. A 70 amp alternator should have an EarthX900. I would 

ask EarthX about 2 batteries.



3.Â Â Â  I almost tested the BMS by leaving some electronics on for 2 days. 

The voltage dropped to just under 12 volts and it still had no trouble 

starting the engine. However, in that circumstance the battery absorbed 

60+ amps for at least 15 minutes. No harm done but if it happens again I 

will put it on the charger for a more leisurely charge rate.



john



On 3/13/2019 5:02 PM, markfw wrote:

 	  Quote: 	
		   



 I am building an electrically dependent LSA Carbon Cub. I will be using the SDS EFI system. I am currently planning to use Z-07 as the basis for my electrical system architecture.



 I have three questions:

 2. I have been looking at using a pair of EarthX ETX680 (PC680-equivalent) LiFePO4 batteries since they have a BMS that will post info to my GRT EFIS about their condition. I would like to use both batteries for starting as in Z-07. I have read that people like to separate their avionics bus from the starting battery because of a potential voltage drop during starting. However, the BMS on the EarthX batteries takes their output to zero if it drops below either 12.8v or 11.5v (both are stated in their on-line documentation). Since the EarthX batteries can demonstrably start Lycoming 4 cylinder engines without dropping off line, does this in fact imply that there is not a voltage drop below 11.5v on starting with them? Is this a difference between LiFePO4 batteries and lead acid batteries?



 Mark 	






 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=488059#488059



[/quote]

_________________
John Morgensen
RV-9A - Born on July 3, 2013
RV4 - for sale

markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Wed Mar 13, 2019 4:45 pm Post subject: Re: Three Questions on Z-07

thank you John. Very useful information. I will talk to EarthX about dual batteries.

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Wed Mar 13, 2019 6:47 pm Post subject: Re: Three Questions on Z-07

Electronic parts frequently become obsolete and are replaced by improved versions.

Search Mouser for part number DSS2x61-01A.

At the expected engine load, the diode will drop about 0.7 volts or less and could get hot consuming 10 watts of power.

Mount it to a heatsink using heat conductive paste.

_________________
Joe Gores

henador_titzoff(at)yahoo.
Guest

Posted: Thu Mar 14, 2019 2:31 am Post subject: Three Questions on Z-07

As Joe said, electronic parts frequently go obsolete; however, "improved versions" aren't always improved.  That's one reason companies keep engineers and quality control people around.  I remember once when Vishay obsoleted a part and replaced it with another part.  We looked at it and finally told our Air Force customer that the replacement part wasn't exactly an improved version.  The Air Force talked to the Vishay manufacturing engineer and got him to change the company's plans to obsolete the capacitor.  I wasn't sure what they said to him, but our defense department can pack a wallop, especially since Vishay was in Beersheba, Israel. I went there once with the quality manager to inspect their processes and that's when we got the real story.  I can't say publicly what the reason was, but it had something to do with shekels.  I do remember three of our engineers allowing a similar change without alerting our customer and working with them to accommodate it.  When the AF found out, it wasn't long before they were walked out the company door and possibly ostracized at other defense department contractors.  I haven't seen any of them since except one, and he started a company pouring concrete in our booming local commercial and residential industry.  It isn't exactly high tech, but he's making the big pesos.



For this application, though, Joe is correct in all statements below.  I particularly like the heat sink/conductive paste statement as temperature beyond rating is a killer on electronics.  I see heat sinks used widely in today's products, especially since miniaturization has become the norm, but power dissipation (not consumption) remains high.

Henador Titzoff



         



                  

                                                                    On Wednesday, March 13, 2019, 11:02:36 PM EDT, user9253 <fransew(at)gmail.com> wrote:                 

                 



                 



                 --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>



Electronic parts frequently become obsolete and are replaced by improved versions.



Search Mouser for part number DSS2x61-01A.



At the expected engine load, the diode will drop about 0.7 volts or less and could get hot consuming 10 watts of power.



Mount it to a heatsink using heat conductive paste.



--------



Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 15, 2019 4:36 am Post subject: Three Questions on Z-07

At 07:45 PM 3/13/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "markfw" <markwheelermd(at)icloud.com>



 thank you John. Very useful information. I will talk to EarthX about dual batteries.



 	


  Why dual batteries?



  When the alternator quits, you have to budget

  chemical energy on board to achieve design

  goals for altenrator-out endurance.



  The e-bus was crafted long before electrically

  dependent engines were popular . . . it's

  application was pretty narrowly focused on

  running the minimum suite of electronics

  to get you to intended destination with

  no alternator. I.e. ELECTRICAL endurance

  could easily outpace FUEL endurance.



  Now, with a 14A running load for an engine,

  you're probably not hoping for that kind

  of electrical endurance. An 18A total

  running load for 3+ hours is a pretty

  fat battery in lead acid . . . but maybe,

  just maybe achievable with a practical

  weight/volume in lithium.



  For all practical purposes, your alternator

  out energy needs for engine and avionics

  are the same . . . I think I'd concentrate

  on achieving the total energy package

  needed for what ever endurance number you

  pick. If you can make it equal or greater

  than fuel aboard, great. If not practical, then

  KNOW what that endurance number is and

  orchestrate your Plan-B operations to

  fit within that limit.

  

  Applying two batteries to separate

  tasks is not very helpful to that

  goal. An optimal two-battery configuration

  would call for the avionics battery to

  be about 1/3 the size of the engine

  battery. I think it more practical to

  treat the energy needs for flight as

  a total package than as two separate

  packages. Now, it MIGHT take two

  batteries in parallel . . . that's

  driven by the energy numbers and your

  weight/volume/dollars limits.



 



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 15, 2019 8:48 am Post subject: Three Questions on Z-07

At 07:35 AM 3/15/2019, you wrote:

  	  Quote: 	
		  At 07:45 PM 3/13/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "markfw" <markwheelermd(at)icloud.com>



 thank you John. Very useful information. I will talk to EarthX about dual batteries.

 	


  Why dual batteries?



  When the alternator quits, you have to budget

  chemical energy on board to achieve design

  goals for altenrator-out endurance. 	


   I'll have to dig back in the archives to

   retrieve the conversations going on while

   Z07 was being discussed. Note that the

   drawing is watermarked 'Work in Progresss'.



   Given the availability of high volume/energy

   ratio of lithium batteries; I'm having trouble

   justifying a Z07 architecture.



   If anyone can champion the idea, I'd be

   please to see their argument posted here

   on the List . . . but at the present time,

   I'm inclined to pull that drawing down.



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Fri Mar 15, 2019 10:52 am Post subject: Re: Three Questions on Z-07

I would leave that drawing available unless there is some unknown failure

mode.  There are different strokes for different folks.  Someone will have a 

perceived need that Z-07 will fill.

  I would like to see a very simple architecture without an endurance bus or 

diodes.  It would be designed with the low power requirements (<20Amp) of 

glass panels and LED lighting in mind.  Many glass panels have an internal 

backup battery good for an hour.

A builder of an IFR RV-10 might want all of the bells and whistles.  A builder of a 

small and slow two place airplane might prefer simplicity.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Mar 16, 2019 6:11 am Post subject: Three Questions on Z-07

At 01:52 PM 3/15/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 I would leave that drawing available unless there is some unknown failure

 mode.  There are different strokes for different folks.  Someone will have a 

 perceived need that Z-07 will fill. 	


   "Perception" is the key term here . . . where

   I have to ask, what are the failure modes being

   addressed and what are the numbers that support

   the selection of hardware.



   A finely tuned Z07 might call for a 24 a.h.

   engine battery and a 10 a.h. device for

   avionics. But to what end? BOTH batteries

   are expected and maintained to meet the same

   design endurance. What then is the value for

   having two batteries versus one battery

   with the same energy content?



   I don't recall the discussions now that

   prompted the Z07 explorations . . . but

   I don't see that it makes sense now.



 

 

   Bob . . .

kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Sat Mar 16, 2019 7:22 am Post subject: Three Questions on Z-07

The best reason I can think of to have two batteries is to get the engine started if the primary battery doesn't get the job done, and you happen to be on some remote Alaskan gravel bar. Many modern aircraft cannot be hand propped.



On Sat, Mar 16, 2019 at 6:15 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 01:52 PM 3/15/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>



 I would leave that drawing available unless there is some unknown failure

 mode.Â  There are different strokes for different folks.Â  Someone will have a 

 perceived need that Z-07 will fill. 	


 Â  "Perception" is the key term here . . . where

 Â  I have to ask, what are the failure modes being

 Â  addressed and what are the numbers that support

 Â  the selection of hardware.



 Â  A finely tuned Z07 might call for a 24 a.h.

 Â  engine battery and a 10 a.h. device for

 Â  avionics. But to what end? BOTH batteries

 Â  are expected and maintained to meet the same

 Â  design endurance. What then is the value for

 Â  having two batteries versus one battery

 Â  with the same energy content?



 Â  I don't recall the discussions now that

 Â  prompted the Z07 explorations . . . but

 Â  I don't see that it makes sense now.



 

 

 Â  Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Sat Mar 16, 2019 10:20 am Post subject: Re: Three Questions on Z-07

Sudden battery failure is rare, but it has happened . . . to me.  My PC680

 cranked the engine just fine.  Then later, when I reduced throttle to land, the 

EFIS rebooted.  The EFIS did not have an internal backup battery at the time, 

but now does.  I sent the battery to Bob N. and he found a broken 

internal weld.  I still only have one battery not counting the backup batteries inside of avionics.

  Each builder will wire their airplane the way that they want to.  All we can 

do is educate them so that they can make informed decisions.  A friend 

installed an avionics switch in his panel.  I told him that the need for that 

switch is based on an old wives tale that has been handed down from 

instructor to student.  And I told him that switch makes his airplane less safe.   

But I was only one person.  Several others told my friend to install that 

switch.  So he did.

  Some builders are willing to sacrifice money and performance for their 

peace of mind.  All we can do is look over their shoulder and point out 

anything that is dangerous.  If a builder wants to install two large 

batteries, he will do it whether there is a Z figure for it or not.

Without guidance, his architecture could have a design flaw

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 17, 2019 8:18 am Post subject: Three Questions on Z-07

At 10:19 AM 3/16/2019, you wrote:

  	  Quote: 	
		  The best reason I can think of to have two batteries is to get the engine started if the primary battery doesn't get the job done, and you happen to be on some remote Alaskan gravel bar. Many modern aircraft cannot be hand propped. 	


  One battery, sized and MAINTAINED for the

  task will never fail to get the engine

  started.



  Cranking the engine requires but 3-6

  percent of a battery's contained

  energy . . . a trivial sum. If the

  battery fails to get an engine started,

  it's axiomatic that it's suitability

  for continued flight has long since

  past.



 

 

   Bob . . .

kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Sun Mar 17, 2019 9:21 am Post subject: Three Questions on Z-07

"One battery, sized and MAINTAINED for the

Â task will never fail to get the engineÂ started."



I get your point Bob, but never say never. We already have one well respected report of battery failure, not attributable to abuse, just from the very small sample that consists of the current active members of this list. (You yourself did the autopsy.)



And remember, we are not all flying airport to airport, or landing in some farmer's field in Kansas, next to the Interstate (or even county road). Here in Alaska, we might be landing at some unimproved strip on the tundra, 150 miles from the nearest road. This would be commonplace here. Also consider cold weather operations where the battery might not be performing at 100% and the engine might be stiff (and you might be sitting at some remote landing spot with the 4 hours of available daylight fading quickly).

The consequences of a non-start on the engine vary so much depending upon the circumstances, I submit that it is not at all unreasonable to either incorporate a second starting battery, or at least carry one.

Ken



On Sun, Mar 17, 2019 at 8:22 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 10:19 AM 3/16/2019, you wrote:

  	  Quote: 	
		  The best reason I can think of to have two batteries is to get the engine started if the primary battery doesn't get the job done, and you happen to be on some remote Alaskan gravel bar. Many modern aircraft cannot be hand propped. 	


 Â One battery, sized and MAINTAINED for the

 Â task will never fail to get the engine

 Â started.



 Â Cranking the engine requires but 3-6

 Â percent of a battery's contained

 Â energy . . . a trivial sum. If the

 Â battery fails to get an engine started,

 Â it's axiomatic that it's suitability

 Â for continued flight has long since

 Â past.



 

 

 Â  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 17, 2019 10:53 am Post subject: Three Questions on Z-07

At 12:06 PM 3/17/2019, you wrote:

  	  Quote: 	
		  "One battery, sized and MAINTAINED for the

 Â task will never fail to get the engine

 Â started."



 I get your point Bob, but never say never. We already have one well respected report of battery failure, not attributable to abuse, just from the very small sample that consists of the current active members of this list. (You yourself did the autopsy.)



 And remember, we are not all flying airport to airport, or landing in some farmer's field in Kansas, next to the Interstate (or even county road). Here in Alaska, we might be landing at some unimproved strip on the tundra, 150 miles from the nearest road. This would be commonplace here. Also consider cold weather operations where the battery might not be performing at 100% and the engine might be stiff (and you might be sitting at some remote landing spot with the 4 hours of available daylight fading quickly).



 The consequences of a non-start on the engine vary so much depending upon the circumstances, I submit that it is not at all unreasonable to either incorporate a second starting battery, or at least carry one. 	


  No argument . . . that's what FMEA,

  load analysis, preventative maintenance,

  and matching the hardware to the mission

  is all about. How many of the GA fleet

  lands on floats anywhere much less

  on remote lakes in the NW Territories?



  (BTW, about 20 years ago, I did a drawing

   for an Alaskan bush pilot adding an

   auxiliary battery to the interior of

   one of his floats.



   Lots of unused volume there. Mounting

   the battery there didn't penalize

   volume in the aircraft and was easier

   to manage structurally)



  There are NO broad brush recommendations

  here . . . only an encouragement to

  match machine and pilot to the task

  while maximizing utility and minimizing

  risk . . . a start-stick might well

  fill the bill. But Z07 was never completed.

  If the List wishes to 'fine tune' this

  architecture, I'd be pleased to participate

  in cogent argument. 



 

 

   Bob . . .

markfw

Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

Posted: Sun Mar 17, 2019 12:43 pm Post subject: Re: Three Questions on Z-07

Bob,



I have assumed that I would use two batteries for 4 reasons:



1. I believed that there was a requirement to have a working battery to (magically to me) "cushion" delicate avionics from the alternator current;

2. I assumed that I could parallel the LiFePO4 batteries to aid in starting 

3. I was trying to guard against a battery failure "from bringing down the whole system".

4. It is easier for me to mount two smaller batteries in parallel than one large one given my alternator-out mission requirements.



It seems that reason #1 is bogus, since your discussion of "one large battery" assumes that the alternator alone can run everything required without a problem. I don't know where I got this idea.



Reason #2 turns out to (maybe) be bogus as well. Two manufacturers who supply a BMS with their LiFePo4 batteries recommend AGAINST running their batteries in parallel. Apparently, low resistance in a single cell of these multi-cell LiFePO4 batteries can greatly reduce capacity and longevity. The manufacturers take great care to match the resistance of the battery cells when they build them, and their BMS's spend a lot of time "optimizing" the batteries during charge and discharge. This is not possible between paralleled batteries and a Resistance mismatch between the batteries of (for example) 20% can reduce performance by 40%.



On the other hand another manufacturer who does not supply a BMS with their batteries says nothing about this. A friend of mine has used their product in parallel for 3 years without problem.



So, your Z-07 diagram without parallel batteries may still be useful for people who believe this is a problem for them.



Reason #3 was actually a quote from your 1998 paper "What's all this Battery Isolator Stuff Anyhow?". I have also heard it mentioned in various discussions of dual battery installations. As you point out in your 2008 paper "Myths of Multiple Battery Installation" a shorted cell is exceedingly rare. However, in an electrically dependent airplane, "rare" is in the eye of the beholder. Is there any data on this? Given the cell resistance issue LiFePO4 batteries might that chemistry be more susceptible to this problem?



Finally, reason #4 is a problem that you mention and is certainly not unique to my situation. My current theory is to use the TCW backup battery solution. It is automatic, does not parallel the batteries and is a lightweight LiFePO4 solution. The disadvantage is that (currently) it is limited to a 6 amp/hr capacity, which is 30 minutes for me throttled back if I lost BOTH my alternator and primary battery. 



Yes, this is non-FEMA thinking to worry about two failures at the same time. I think that it depends on what the definition of "bringing down the whole system" is. If a shorted battery cell can somehow stop the alternator from functioning, isn't that actually one failure?



Mark

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 18, 2019 7:20 am Post subject: Three Questions on Z-07

At 03:43 PM 3/17/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "markfw" <markwheelermd(at)icloud.com>



 Bob,



 I have assumed that I would use two batteries for 4 reasons:



 1. I believed that there was a requirement to have a working battery to (magically to me) "cushion" delicate avionics from the alternator current; 	


   not true



  	  Quote: 	
		  2. I assumed that I could parallel the LiFePO4 batteries to aid in starting 	


   sure . . . would one larger battery do it too?



  	  Quote: 	
		  3. I was trying to guard against a battery failure "from bringing down the whole system". 	


   battery failures don't bring down the whole system.

   The alternator will run self excited and you

   probably wouldn't know that the battery was

   gone until you shut the alternator off.



  	  Quote: 	
		  4. It is easier for me to mount two smaller batteries in parallel than one large one given my alternator-out mission requirements. 	


   available space can drive battery

   configuration . . . 



 

  	  Quote: 	
		  It seems that reason #1 is bogus, since your discussion of "one large battery" assumes that the alternator alone can run everything required without a problem. I don't know where I got this idea.



 Reason #2 turns out to (maybe) be bogus as well. Two manufacturers who supply a BMS with their LiFePo4 batteries recommend AGAINST running their batteries in parallel. Apparently, low resistance in a single cell of these multi-cell LiFePO4 batteries can greatly reduce capacity and longevity. The manufacturers take great care to match the resistance of the battery cells when they build them, and their BMS's spend a lot of time "optimizing" the batteries during charge and discharge. This is not possible between paralleled batteries and a Resistance mismatch between the batteries of (for example) 20% can reduce performance by 40%. 	


   I don't see how this is possible. How does one

   battery with a BMS know that there's another

   battery on line with it? The bus voltage is

   a function of regulator set point. Bus voltage

   is the sole determinant for optimal charging

   of the battery. The fact that a second battery

   shares the bus is totally transparent to the

   first battery.



 

  	  Quote: 	
		  On the other hand another manufacturer who does not supply a BMS with their batteries says nothing about this. A friend of mine has used their product in parallel for 3 years without problem. 	


   Exactly. This is what battery charge

   balancing is all about. If any single

   cell (or cell group) is lagging behind

   the rest in achieving full charge (due

   perhaps to slightly lower impedance)

   then the balancing system places an

   artificial load on the remaining cells

   in the string until the lagging cell

   catches up.



 

  	  Quote: 	
		  So, your Z-07 diagram without parallel batteries may still be useful for people who believe this is a problem for them. 	


   Believing is subordinate to knowing . . .

   knowing is subordinate to understanding.



  	  Quote: 	
		  Reason #3 was actually a quote from your 1998 paper "What's all this Battery Isolator Stuff Anyhow?". I have also heard it mentioned in various discussions of dual battery installations. As you point out in your 2008 paper "Myths of Multiple Battery Installation" a shorted cell is exceedingly rare. However, in an electrically dependent airplane, "rare" is in the eye of the beholder. Is there any data on this? Given the cell resistance issue LiFePO4 batteries might that chemistry be more susceptible to this problem? 	


    If it worries you, you'd better find out.

    Just suppose you have two batteries

    with their own contactors? How would you become

    aware that you had a shorted cell? How would

    you know which battery to take off line?

    If a cell were shorted in one battery, how

    do you know that taking the battery off

    line will markedly reduce risk? Each

    failure has it's own fingerprint (or

    failureprint) in how it manifests,

    progresses, propagates and terminates.

    Hence, each failure has an optimal

    response that drives toward a probable outcome.



 

  	  Quote: 	
		  Finally, reason #4 is a problem that you mention and is certainly not unique to my situation. My current theory is to use the TCW backup battery solution. It is automatic, does not parallel the batteries and is a lightweight LiFePO4 solution. The disadvantage is that (currently) it is limited to a 6 amp/hr capacity, which is 30 minutes for me throttled back if I lost BOTH my alternator and primary battery. 	


   Nobody looses BOTH unless they've done

   something really dumb. What kind

   of engine are we talking about?



 

  	  Quote: 	
		  Yes, this is non-FEMA thinking to worry about two failures at the same time. I think that it depends on what the definition of "bringing down the whole system" is. If a shorted battery cell can somehow stop the alternator from functioning, isn't that actually one failure? 	


   A shorted cell won't bring down the

   alternator. It will probably proceed

   to spectacular if not catastrophic

   failure in the battery itself . . . recall

   that a lithium cell contains a lot of

   energy with respect to weight/volume.

   That energy has to go somewhere . . . usually

   toward warming things up and making really

   bad smells. SVLA cells are not particularly

   failure friendly either.



   So the question before us is exactly what

   are the probabilities for an LiFePO4 cell-

   short? If it does short, what are the

   electrical and physical consequences?



   I used to have some friendly contacts at

   the Navy's battery testing facilities

   in Crane, Indiana. If any battery was

   purchased by the Navy, they had put it

   through rigorous tests including abuses

   designed to produce the greatest risks.



   TrueBlue has done extensive testing on

   LiFePo4, cylindrical cells used in their

   TSO/PMA offerings to TC aircraft. I've

   witnessed some tests where a constant

   42 volts was placed across the array

   of cells in a 24v battery. The poor things

   went into apoplectic self-destruction

   with considerable out-gassing. Gasses

   were vented overboard though the fitting

   on top. Outside of the case never reached

   temperatures hazardous to the aircraft's

   environs.



 [img]cid:.0[/img]



   I can also tell you that the volume of

   electronics in these products is roughly

   equal to the volume of batteries . . .

   the BMS is specifically tasked with

   preventing such a failure in the

   first place.



   It seems to be a choice of products. Just

   how much BMS you want to buy ranging

   from EarthX down to no BMS like Aerovoltz

   . . . or you could pop for True Blue.



   Aircraft Spruce covers the range . . .



  https://tinyurl.com/y4o5xwuz



   ACS has a world-wide market and 

   deep pockets at risk for very deep picking

   should one of their offerings prove

   dangerously unsuited to task.



   Z07 as last published has lots of

   bus structures which, in an electrically

   dependent airplane could probably go

   away. Wiring this up like a C150 but

   with engine dependency serviced directly

   from the battery bus is probably the

   way to go.



   You can go max-cold for smoke in the

   cockpit while keeping that whirrly thing

   up front turning. You can simply load-shed

   in case of alternator failure. If you've

   got enough chemical energy on board to

   meet satisfactory endurance goals, splitting

   that capacity between two, separately

   controlled batteries doesn't seem to make

   sense.



 

   Bob . . .

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