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kenryan

Joined: 20 Oct 2009
Posts: 429

Posted: Mon Mar 18, 2019 7:41 am Post subject: Battery BMS failures?

On the Aircraft Spruce page for the Aerovoltz battery, under the "Overview" tab, the following text appears:



"An Aerovoltz external BMS is in a prototype stage and will be made available to all Lithium Battery owners in the near future. Putting the unit internally dramatically drives up the battery cost and all batteries will wear out eventually so making it external will keep the cost of ownership lower down the road when it comes time to replace.

The current BMS systems on the market are very sensitive to damage and it can disable a perfectly good battery that will then need replacing. We donâ€™t feel thatâ€™s fair to our customers."

Has anyone heard about a rash of BMS failures?

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 18, 2019 9:48 am Post subject: Battery BMS failures?

 	  Quote: 	
		  

 Has anyone heard about a rash of BMS failures?

 	


   Good catch Ken. I'd be interested

   (as would we all) in knowing what

   kind of BMS failures have occurred.



   Unfortunately, every battery failure

   I've tried to follow up with the

   manufacture was greeted with a stone

   wall . . . take that back . . . used

   to get great data dumps from Skip

   Koss on Concorde product issues.



   I've asked to be the recipient of any

   failed batteries (or other devices)

   so that I might disassemble for close

   examination in a quest for answers . . .

   but those opportunities are rare

   to non-existent.



   The outcome of non-communication is

   ignorant assumption which gets traded

   around the various venues . . . with

   demonstrable data creep.



   The first difficulty we have is defining

   "Battery Management System".  Many

   lithium cylindrical cells are fitted

   with dead short mitigation and are

   advertised to be fitted with a "BMS".



   Batteries and array of series-parallel

   cells might include a cell balancing

   module and advertised to include

   a built-in "BMS".



   Then there are full-up BMS like EarthX

   and True Blue that will manage overheat,

   over volts, charge balance/limiting,

   fault mitigation and, in True Blue

   case, comfortable management of vented

   gasses in case the unthinkable does

   happen.



   Unless we're favored with a published

   product performance specification for 

   the failure being studied, any assertions

   about 'BMS failure' are exceedingly short

   on useful data.



   Keep your ears to the ground guys . . .

   we might get lucky . . . 



   



 

 

   Bob . . .

echristley(at)att.net
Guest

Posted: Mon Mar 18, 2019 4:47 pm Post subject: Battery BMS failures?

I have heard about the desulfater (sp?) charges killing the electronics due to their large voltage spikes.  The battery manufacturers themselves warn about those.

Otherwise....nada.



                  

                                                                    On Monday, March 18, 2019, 11:42:05 AM EDT, Ken Ryan <keninalaska(at)gmail.com> wrote:                 

                 



                 



                 On the Aircraft Spruce page for the Aerovoltz battery, under the "Overview" tab, the following text appears:



"An Aerovoltz external BMS is in a prototype stage and will be made available to all Lithium Battery owners in the near future. Putting the unit internally dramatically drives up the battery cost and all batteries will wear out eventually so making it external will keep the cost of ownership lower down the road when it comes time to replace.

The current BMS systems on the market are very sensitive to damage and it can disable a perfectly good battery that will then need replacing. We donâ€™t feel thatâ€™s fair to our customers."

Has anyone heard about a rash of BMS failures?

ceengland7(at)gmail.com
Guest

Posted: Tue Mar 19, 2019 12:34 pm Post subject: Battery BMS failures?

On 3/18/2019 12:47 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                [snip]

           Then there are full-up BMS like EarthX

           and True Blue that will manage overheat,

           over volts, charge balance/limiting,

           fault mitigation and, in True Blue

           case, comfortable management of vented

           gasses in case the unthinkable does

           happen.

         

           Unless we're favored with a published

           product performance specification for 

           the failure being studied, any assertions

           about 'BMS failure' are exceedingly short

           on useful data.

         

           Keep your ears to the ground guys . . .

           we might get lucky . . . 

         

           

         

         

                

             Bob . . .            	
     Bob,

     

     Speaking of  BMS, perhaps you can explain (since EarthX seems     unable) why EarthX batteries, with their 'full BMS', have a limit on     alternator current capability based on their battery capacity. I am     unable to see why a BMS that can manage individual cell charging,     and protect individual cells plus the entire battery, is unable to     limit overall charge current to the battery to a safe level. I've     repeatedly asked that question of their spokesperson on the VAF (RV)     forum, and gotten words without answers.

     

     Charlie

     	          		Virus-free. www.avast.com 		 	 [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Mar 20, 2019 7:15 am Post subject: Battery BMS failures?

 	  Quote: 	
		  Bob,



 Speaking of  BMS, perhaps you can explain (since EarthX seems unable) why EarthX batteries, with their 'full BMS', have a limit on alternator current capability based on their battery capacity. I am unable to see why a BMS that can manage individual cell charging, and protect individual cells plus the entire battery, is unable to limit overall charge current to the battery to a safe level. I've repeatedly asked that question of their spokesperson on the VAF (RV) forum, and gotten words without answers.



 Charlie 	


   Interesting question . . .



   I've oft asserted that batteries are

   like houseplants. Given the right treatment

   in proper proportions and protected from

   deleterious stress, they will 'bloom'

   and thrive.



   But the term 'battery' is not quantified

   and the selection of a battery is to

   craft a kind of marriage between a host

   of players not the least of which are

   the engine driven power source(s) and

   design goals for normal and abnormal

   operations.



   Lithium cells are the orchids of the

   battery family . . . capable of extra-

   ordinary performance in some respects

   but exceedingly sensitive to

   stress largely tolerated or

   shrugged off by the likes of

   Flooded, SVLA, gell and NiCad

   technologies.



   Lithium is extra-ordinarily vulnerable

   to over and under voltage conditions.

   Hence the 'real' BMS will strive to

   operate the array of cells between

   about 20 and 90 percent of charge.

   This is a goal stated by the electric

   and hybrid car folks. No doubt, EarthX

   has their own numbers but what ever

   the numbers, ignoring them risks

   premature battery failure.



   Then there's temperature . . . stuffing

   energy back into a lithium array 

   MUST raise the chemistry's temperature

   as does prolonged heavy rate discharge.

   So the agile BMS watches temperatures

   and strives to limit those effects

   on the cells irrespective of system

   demands from the outside.



   External hard faults cause spectacular

   current flows with a new constellation

   of risks for catastrophic failures.

   A BMS tailored for engine cranking

   expects to see some really high

   current flows for short periods of

   time . . . but it must differentiate

   between starter inrush/engine spin-up

   and a hard fault.



   I've mentioned that the enclosure

   for a True Blue, TC/TSO battery

   is filled with electronics . . .

   electronics with agility and robustness

   to accomplish all these things to

   prevent premature failure while packaged

   to keep the rare catastrophic failure

   from migrating to the rest of the

   aircraft.



   True Blue batteries are used on twin

   turbine aircraft with starter generators

   up to and including 400A per side or

   800A of recharge capability. Starter

   inrush is typically 1500-2000 amps

   followed by spin-up currents on the

   order of 500-700A lasting 20-30

   seconds. My hat is off to the folks

   who crafted an array of silicon that

   can operate in series with those loads

   yet meet design goals for safety and

   battery life.



   AeroVoltz seems to be moving toward

   offering an EXTERNAL BMS for their

   product line . . . methinks a fine

   idea. That way you don't trash a

   bunch of perfectly good transistors

   along with a shot battery.



   The most difficult thing for a BMS

   to do is throttle currents . . . in

   either a charge or discharge mode.

   The series connected control devices

   are either switched on hard (saturated)

   or totally open (off). This offers

   the smallest form factor of electronics

   to manage such current levels.



   Battery recharge limits are largely

   a thermal management issue. The

   very low internal impedance of the

   lithium cell COMBINED with its

   low mass raises concerns for overheating

   during prolonged high rates of charge.



   True Blue isn't immune to these

   forces either but they're designed to

   work in a world of currents a magnitude

   greater than piston driven light aircraft.

   EarthX and contemporaries are not immune

   from the need to make compromises in design

   goals. They are marketing good cranking

   performance and light weight. Light

   weight generally brings extra-ordinary

   requirements in thermal management.

   Light weight and small size puts limits

   on capacity . . . largely independent

   of short term cranking ability.



   Given the fact that a BMS cannot 'throttle'

   current into or out of the battery,

   they must be cognizant of the risks for

   marrying their 'orchid' to a system

   recently divorced from a 'bromeliad'

   that may not easily bloom but it doesn't

   lay down and die when insulted.



   So what's the responsible supplier of

   light cranking batteries to do when

   marketing to relative technical

   novices about the care and feeding

   of their products. To be sure, lots

   of their batteries are being married

   to systems that already have alternators

   that are too big.



   If the engine starts easily when

   smartly cranked time needed to recharge

   is limited even if too fast. If the

   operator NEVER allows the battery to

   be deeply discharged followed by

   an in-situ recharge by the ship's

   too-big alternator . . . then risks

   to the battery are low.



   At the same time, the operator purchased

   "light" and "whippy-starting" and made

   no demands for electrical and thermal

   robustness. So it makes sense that

   EarthX would recommend limiting the

   size of the alternator depending

   on size of battery . . . not a very

   realistic expectation but a good

   CYA move nonetheless.



   This raises a recollection of experiences

   with another shotgun wedding between

   poorly matched components. Waayyy

   back when we got all exercised about

   what was then a big quantum leap

   in light weight, robust cranking

   batteries with flooded NiCads.



   After setting a few airplanes on fire

   with a marriage of nicad and twin

   turbines, powers-that=be decided

   that the BEST thing to do was add

   a remote reading battery temperature

   meter paired with yellow warning

   and red danger lights designed

   to assist crews in managing their

   'orchids' to prevent overheat

   and thermal runaway.



   I argued then that we could craft

   an accessory to the starter-generator

   controllers that would automatically

   adjust bus voltage in response to

   battery overheat. That wasn't well

   received so we added another thing

   on the panel that was harder to

   install and drove up pilot work

   loads.



   The same thing could be done here.

   The BMS for the alternator/lithium

   marriage could easily include an

   regulator that would prevent an

   alternator of ANY SIZE from abusing

   the battery . . . maybe AeroVoltz

   will do it.



 

 

   Bob . . .

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Wed Mar 20, 2019 10:37 am Post subject: Re: Battery BMS failures?

 	  Charlie England wrote: 	
		  Speaking of BMS, perhaps you can explain (since EarthX seems unable) why EarthX batteries, with their 'full BMS', have a limit on alternator current capability based on their battery capacity. I am unable to see why a BMS that can manage individual cell charging, and protect individual cells plus the entire battery, is unable to limit overall charge current to the battery to a safe level. I've repeatedly asked that question of their spokesperson on the VAF (RV) forum, and gotten words without answers. 	




My guess is that it's a limitation of the cell balancing circuitry in the BMS.  As a cell within the battery reaches full charge, the BMS puts a resistance across it (either a fixed resistor hard-switched across the cell or a linear-mode transistor) to burn the current that would otherwise overcharge the cell while the others continue to charge.  There must be a limit to the power that this system can dissipate, which may explain the alternator output limitation.



 	  Robert L. Nuckolls, III wrote: 	
		  After setting a few airplanes on fire with a marriage of nicad and twin turbines, powers-that=be decided that the BEST thing to do was add a remote reading battery temperature meter paired with yellow warning and red danger lights designed to assist crews in managing their 'orchids' to prevent overheat and thermal runaway. 	




Indeed, the deHavilland DHC-8-202 that I flew in a previous life was fitted with battery temperature gauges on the overhead panel (just below the left fire t-handle in the linked image).



https://bitly.com/2uj9V9F+



The airline I worked for operated them in the desert southwest, where ambient temps routinely exceed 100Â°F.  Given the short-hop, quick-turn nature of the flying we did, and the eye-watering current required to start a >2,000shp engine, we kept a close eye on those gauges.



Eric

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 21, 2019 5:05 am Post subject: Battery BMS failures?

 	  Quote: 	
		    So the agile BMS watches temperatures

   and strives to limit those effects

   on the cells irrespective of system

   demands from the outside. 	


   Oh yeah, forgot to include charge balancing.

   Unlike most battery chemistries, individual

   cells in a series string of lithium may

   become 'unbalanced'. This simply means that

   one or more cells may 'top off' sooner than

   the rest. If the charging continues until

   all cells are topped off, there is risk

   for over-charging the fast learners thus

   insulting their sensibilities.



   This is generally accomplished by placing

   a load resistor across the faster cells

   thus forcing more charge energy into the

   slow cells until everyone is in lock-step . . .

   consider a cell balancer to be the

   ISO9000 of the lithium battery community.



   Here's an article from Battery University

   on the topic . . . 



  https://tinyurl.com/y3egekew



   . . . yesterday's missive was intended to

   illustrate that the term "BMS" is un-defined

   in the consumer world and maybe not well

   defined in the engineering world either. Unless you

   have access to the designer's product performance

   specification, it's wise to investigate

   before you plunk down your beer money

   for a battery upgrade. The full constellation

   of products offered are NOT interchangeable

   nor are they necessarily plug-n-play into

   our legacy electrical systems.



   In light of this fact, the phrase "BMS

   failure" in any dark-n-stormy-night 

   story is not very informative unless

   the narrator offers specific failure

   analysis data . . . almost NEVER a

   component of such stories. 



  



 

 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 21, 2019 7:37 am Post subject: Battery BMS failures?

 	  Quote: 	
		  

 Indeed, the deHavilland DHC-8-202 that I flew in a previous life was fitted with battery temperature gauges on the overhead panel (just below the left fire t-handle in the linked image).



  https://bitly.com/2uj9V9F+



 The airline I worked for operated them in the desert southwest, where ambient temps routinely exceed 100Â°F.  Given the short-hop, quick-turn nature of the flying we did, and the eye-watering current required to start a >2,000shp engine, we kept a close eye on those gauges.



 Eric 	


  Did you ever have occasion to take

  a hot battery off line?



 

 

   Bob . . .

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Thu Mar 21, 2019 8:52 am Post subject: Battery BMS failures?

 	  Quote: 	
		   On Mar 21, 2019, at 08:36, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

 

 Did you ever have occasion to take a hot battery off line?


	


Just once, but not in flight.  After flying three Phoenix-Yuma-Phoenix round trips on an especially brutal July day, we exceeded limits and couldnâ€™t start up for the fourth scheduled Yuma turn.  I canâ€™t say that either of us was particularly bothered by the forced break!



Eric

yellowduckduo(at)gmail.co
Guest

Posted: Thu Mar 21, 2019 9:30 am Post subject: Battery BMS failures?

On 21/03/2019 11:36 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		  >

> Indeed, the deHavilland DHC-8-202 that I flew in a previous life was 

> fitted with battery temperature gauges on the overhead panel (just 

> below the left fire t-handle in the linked image).

>

> https://bitly.com/2uj9V9F <https://bitly.com/2uj9V9F>+

>

> The airline I worked for operated them in the desert southwest, where 

> ambient temps routinely exceed 100Â°F.  Given the short-hop, 

> quick-turn nature of the flying we did, and the eye-watering current 

> required to start a >2,000shp engine, we kept a close eye on those 

> gauges.

>

> Eric



  Did you ever have occasion to take

  a hot battery off line?

   Bob . . .



An aircraft of that size and vintage may have had a battery charger that 
	


monitored temperature and could limit charging current??

It seems like the Lithium "BMS" strategies are moving in that direction.



Limiting the alternator size as per Earth-X recommendations is a small 

step in that direction which I applaud.  Even with VRLA batteries I 

tossed my 100+ amp alternator in favor of a 40 amp unit.

Ken

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Thu Mar 21, 2019 3:58 pm Post subject: Battery BMS failures?

 	  Quote: 	
		   On Mar 21, 2019, at 10:28, C&K <yellowduckduo(at)gmail.com> wrote:

 An aircraft of that size and vintage may have had a battery charger that monitored temperature and could limit charging current??


	


Donâ€™t quote me on this (itâ€™s been awhile...) but as I recall, the temperature monitoring was separate from the charger.  I think the chargerâ€™s only â€œdata inputsâ€ were weight-on-wheels and where its AC Power was coming from (external or engine-driven generator).



Eric

jimkale(at)roadrunner.com
Guest

Posted: Thu Mar 21, 2019 10:13 pm Post subject: Battery BMS failures?

I was a 28 year Army Active Duty helicopter pilot.  In the mid 70's I had a

Nicad helicopter battery completely melt down.  Just molton liquid in the

steel box container.  Fortunately the hydrogen did not ignite.   We smelled

it and then noticed a terrifically high charge rate.  We landed the CH-47

helicopter and we opened the battery box to find the mess.   A few years

later the Army put a warning in the manual to land if you smelled the rotten

egg smell and get out of the helicopter get away from it and not to touch

the battery.  Finally in the 90s the manufacturer put a battery charger in

the circuit which limited the charge current to about 10 amps.   It

prevented thermal runaway charging which could happen with the battery just

tied to the main bus and a 200 amp generator attached to the bus.



--

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 22, 2019 5:53 am Post subject: Battery BMS failures?

 	  Quote: 	
		  An aircraft of that size and vintage may have had a battery charger that monitored temperature and could limit charging current??

 It seems like the Lithium "BMS" strategies are moving in that direction. 	


   Don't think so. The 'charger' was not much

   different than what we have in our airplanes:

   An engine driven power source regulated to

   idealized charging levels for the battery.

   Some airplanes had two engine driven sources

   like starter generators. These would parallel

   for delivering up to 800A. The larger

   aircraft would also have a auxiliary power

   unit good for perhaps 200-300 amps that could

   be operated in parallel with ships generators.



   None of the generator controls were fitted with

   any way to monitor either battery temperature or

   current.



  	  Quote: 	
		  Limiting the alternator size as per Earth-X recommendations is a small step in that direction which I applaud.  Even with VRLA batteries I tossed my 100+ amp alternator in favor of a 40 amp unit. 	


   But suppose your running loads call for more

   current? Heated seats maybe? Electric cockpit

   heat a la LongEz? A B400 has electric

   de=ice on the tail feathers . . . lots

   of amps needed there.



   Virtually every rechargeable battery's maintenance

   instructions call for constant-current/constant-voltage

   recharge profiles.  I.e. limit current into the

   battery to some friendly level until the desired

   bus-voltage set point is reached whereupon you

   change to constant voltage operation.



   All it takes is a current sensor on the battery

   feeder to monitor the battery's recharge

   current and adjust bus voltage to maintain

   fast recharge at the recommended current

   until the battery is topped off whereupon

   the controller reverts to constant voltage.



   Not difficult to do for any combination of

   battery and engine driven power sources.



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 22, 2019 6:01 am Post subject: Battery BMS failures?

 	  Quote: 	
		  Don't quote me on this (it's been awhile...) but as I recall, the temperature monitoring was separate from the charger.  I think the charger's only data inputsâ€ were weight-on-wheels and where its AC Power was coming from (external or engine-driven generator). 	


   If the aircraft had 3-phase alternators

   and separate starters, then DC power was

   derived from transformer/rectifiers to

   run DC systems and recharge batteries.



   These aircraft were generally large enough

   to carry an APU which was used to start

   engines thus reducing demands on the battery.



   These systems could easily include features

   for battery management.



   But for twin-jets up through ships like

   the Hawker 800 series, batteries were

   connected to a bus powered by generators

   with a LOT of output capability. Any

   necessary monitoring of battery temperatures

   was a simple thermometer gage with warning

   and danger lights.



   It was up to crew to notice and then

   take an overheated battery off line until

   it cooled.



 

   Bob . . .

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Fri Mar 22, 2019 7:42 am Post subject: Battery BMS failures?

 	  Quote: 	
		   On Mar 22, 2019, at 07:00, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:

  If the aircraft had 3-phase alternators and separate starters, then DC power was derived from transformer/rectifiers to run DC systems and recharge batteries.

 

 These aircraft were generally large enough to carry an APU which was used to start engines thus reducing demands on the battery.


	


The Dash-8s of this vintage had Pratt & Whitney PW123Ds (2,150 shp/side) with starter/generators.  There were also AC generators (thatâ€™s what they called them!) and TRUs.  It was a complex electrical system, to put it mildly.



The planes were available with APUs, but the airline chose not to install them.  The reasons for that remained a mystery to most of us who flew them, as the plane was an overpowered beast that had no trouble hauling a full cabin and bulked-out cargo bins.  The extra couple hundred pounds would have made zero difference in performance, but would have improved interior comfort and reduced battery demands enormously.  As it was, all of our engine starts were battery powered for #2, then tie the DC buses to start #1 assisted by the #2 generator.



Eric

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