If the battery has a 75AH capacity (reported elsewhere) then the peak draw works out at about 9C (eg 700/75 = 9.3C).

I'm not sure this is the right data sheet (also reported elsewhere) because it's for a 65AH capacity but..

http://www.s399157097.onlinehome.us/...s/LVP10-65.pdf

It mentions a max discharge rate of 5C for the family. Obviously it's possible to trade off discharge rate vs time but 5C doesn't seem very high. I've seen other LI cells rated at 30C for model aircraft use.

The internal resistance for the 65AH cell is 0.3mohms. At 700A each cell would be dissipating 700 x 700 * 0.3 x10^-3 = 147W. There are 8 in the box so the battery might be dissipating >1kW for however long the APU is drawing 700A. Presumably it doesn't draw that much for long?

Is the battery ever used to start the APU in normal use or just emergency?

Peak current draw will only be for a fraction of the minute or so of the start up, especially with soft starts designed to reduce high torque induced damage of starter shafts.

cwatters, the 75Ah figure is the nominal capacity, ie. right down to total discharge, 65Ah is the usable capacity ie. down to immediately before the 'knee' part of the curve.

For unmatched, paralleled Li-Ion cells, 5C is already considerable. Or at least it was, not too long ago...
And references to model airplane batteries are a bit difficult as these are LiPo batteries and quite often end in smoke and tears, be it by faulty charging or mechanical damage. So let's keep them to the model world.

MoD (UK) has bags of experience with Lithium batteries exhibiting what they euphemistically call “flaming events”. In 2006 there was a total recall and destruction order on Li-Ion secondary batteries (rechargeables) supplied for the BOWMAN HF radio. It took well over two years to replace them, a period in which users had to largely do without; despite being a Critical Enabling Technology.

There were numerous problems, all known in advance and ignored; partly because batteries are seen as faffy and a largely ignored commodity. In short;


1. The battery case was meant to be welded to prevent moisture ingress. It was crimped to save money.


2. The internal sensing electronics were meant to be potted, as a back up to protect from moisture ingress but also to provide robustness. The potting was entirely missing, again to save money.


Additionally, the BOWMAN specification required the “system” (battery, chargers, human) to permit 500 charges before replacement. I include human, because obviously the user has to receive information as to state of charge and be properly trained.



3. A typical battery could be recharged 3-5 times, meaning stocks had to be replenished (typically) 100 times more frequently than anticipated, requiring money for which no provision had been made.
4. It could not be recovered from even moderately deep discharge.
5. The state of charge indicator was not visible to the user in normal use.



Despite users having no control, over 3, 4 and 5, it became an offence in the Army to “permit” a battery to go into deep discharge.
1&2 are clearly Quality Control and Quality Assurance failures on the part of the contractor and MoD respectively (as well as fraud). I won’t say manufacturer, because the selected company didn’t actually make the battery, they bought in and assembled the parts. This is a recipe for disaster when they are also responsible for the chargers; and, indeed, 3, 4 & 5 are primarily a systems integration failure. What realistic chance is there of an assembler having a deep understanding of the system integration requirements? The AC and DC chargers, I think around 12,000 of them, were bought-in and were incompatible with the batteries.



I point this out because, from what I read here (and many of the observations are excellent), there would seem to be some similarities. Much is said of the battery manufacturer, but that is always too simplistic. The first thing I’d look at is the Interface Definition Documents detailing the boundaries of responsibility. One of MoD’s failures was not to have IDDs, which is like handing out blank cheques. In part, this explained why they simply handed the replacement contract to the same company, without competition, paying them twice for the same thing. Despite proper manufacturers selling the same battery (and compatible chargers), manufactured and operating to specification, for half the price. If there is a lesson to be learnt here by Boeing and their suppliers, it is this. Don’t ask MoD for advice! Rather, seek out the company who advised MoD of these forthcoming problems in the first place.

Ground Politics

The chief of NTSB continues to repeat two basic themes, and Boeing responds in public with a type of response intended to resist these themes.

Theme #1 BOEING have experienced two very serious failures in the Battery system as certificated.

Theme #2 Lithium Ion Battery technology is under scrutiny as a whole, the format is in doubt, regardless of chemistry type.

BOEING answers by assertively requesting "test flights" and "repositioning".
They have got to keep at least a few aircraft operating, the chance that the public will see the fleet as collecting cobwebs on the ramp would be damaging.

BOEING answers by suggesting possible "fixes". Improvement to the case, as you propose, and similar, plus a scheme to keep each of the eight batteries isolated from each other, to prevent "propagation" of failure/fire in one cell.

The purpose of these proposed fixes is to plant their own theme, that the technology is "mature", and the failures are mitigable, in spite of the fact that their best efforts "Failed". (See Theme #2)

Technically, I think you have the solution at the ready. Some form of enclosure that will not conduct electricity, will contain explosive forces, flame, and electrolytic material.

These Press conferences are scripted, but that is to be expected. The playing out of the process at the public level is most instructive.

Hersman, to her credit, has outlined the interplay at each meeting. She is a consummate player, diplomatic, assertive, calm, and professional.

BOEING seem to have found their footing. Their initial response will eventually fade, but those who scrutinize the process will remember how they tipped their hand, and loudly (inadvertently) outlined the flawed relationships that exist in the industry.

FAA....speechless. Feckless, powerless, kept.

fdr: As I posted a week or two ago, there's nothing 'simple' about the 'solution' of changing to a different battery technology - and weight is the least of your issues.

First, the charging and monitoring systems and software would have to be redesigned and recertified.

Second, where would you PUT the damn things? Any alternative battery technology will not have the same energy density as lithium. Not only will batteries of equivalent capacity be heavier, they'll be bulkier. Much bulkier. They won't fit in the space available, the space Boeing carved out for lithium batteries. Mk 1 posted on this a few posts back.

They would have to reengineer the structure of the EE bay - or even carve a separate battery compartment out of the hold spaces. Now you have structural engineering changes to design, test, certify, put into the production process, and retrofit to the units already delivered. And do this while synchronized swimming with all those subcontractors you've parceled the project out to...

Now do you see why I said this airplane isn't going anywhere soon?

(the alternative - finding the root of the problem and proving lithium safe enough to use, all over again, could be even harder...)

Dimensions of a 50Ah NcCd aircraft battery,which easily will start the APU:
11,7in x11,8in x10,6in.Weight 94 lbs.

Original B787 battery:
19x13.2x10.2 inches and it weighs approximately 63 pounds

16" L, 10" W, 12" H. 80 AH. 105 lbs. Lead Acid?

Ultimately they'll have it fixed (possibly replaced), make FAA to re-certify, and resume selling again, I think. There's just no other way. The stakes are extremely high.

"there's nothing 'simple' about the 'solution' of changing..."
 

Hi,

Ranger One:

For the Main battery the task is much more complex than for the APU batt.

Suppose 2 Ni cd´s in two adjacent positions. Could solve the problem you mention.

How much? Let´s quantify?

Even optimizing (if possible like i am suggesting) would take months.

Problem is not just a BAD battery. There are MANY PROBLEMS. They yet know. We in pprune (with scarce information) detected SEVERAL.

I agree. And the consistency of this point certainly was taken into account by Chicago Boeing guys (most engineers are not there) in the Decision Making.

Boeing (airplanes) is now absolutely optmizing $. The dream is over. $ is the (only) name of the game. Insurance cover grounding. Further comments can be left to other posts...

They are facing other important problems. :{

It isn't that bad.... The elements of compliance with the Lithium Ion regs are all there.

BOEING (Thales, Yuasa, Securaplane) cut it too close. That is why BOEING pitched such a fit when FAA (AFTER JTSB) GROUNDED the 787.

Had they expanded by as little as 10 per cent their mitigations, well......

FAA and BOEING both knew a thermal runaway would happen; the problem is they were over confident in their design to mitigate a multiple (propagation).

That has been apparent from the outset, and all the way back.....

Now they have to do what they could have done before, and avoided all this nonsense.

Bigger case, more cell separation, stand off (raised) base, stricter assembly standards, etc......

Fix it. I cannot wait to fly in one.

:ok:

A very interesting read along those lines dealing with system safety asessments and how they failed is this great NASA report :
Why System Safety Professionals Should Read Accident Reports
And by the way, the "standard set by the FAA" of once in one billion flight hours is for catastrophic events, the one for hazardous events is once in ten million hours. So far the events have just been hazardous. Yes, an emergency landing did happen, and some passengers were injured. But there was neither the loss of an airframe nor did any fatalities happen, so formally once in ten million hours is the "correct" number to use. If only that number would have been met...

So maybe here as well the aircraft was desgned in a way that the effects of a thermal runaway were correctly recognized, but the likelihood was underestimated.

Safety first
 

Hi,

Volume,

:ok: Thanks

The low MTTR (in previous batt.) IMO should be used proactively by Boeing or Thales long before both battery fires.

Some years ago i´ve heard Boeing maintained in major airports a mechanic just to provide feedback to the 747 program.

Considering the innovations introduced on 787 i hope the data logging in the Systems are better than the HIGHLY PROBABLE loss of cell voltages history in both incidents.

MISCONCEPTION
 

Hi RR

You are proceeding along a path dictated by your preconception of the cause.

There are two causes here, as I see it. One is PROCURING, the other is PROXIMAL.

Your focus is on the proximal, aggravating cause. The smoking gun. The Electrical system.

There is a procuring cause, the Lithium Ion Battery. Procuring means 'Created'.

Proximal means 'aggravated to disclosure'. I am not sure the 'system' played any part at all. By the time the fire was uncontrolled, the system likely could not have had any effect on controlling it. Certainly not in preventing it.

RUNAWAY. OUT OF CONTROL, CANNOT BE CONTAINED, Land immediately, call the fire department.

That one cell could experience thermal runaway was a given, and the standard beyond which no further runaway would be tolerated.

That is what happened. NTSB told us that. "The fire started in one cell, #6".

That should have been the end of it. One cell self destructs, smoke vents, case contains the incident.

No monitoring can arrest a thermal runaway. Monitoring was intended to prevent Propagation. Boeing prepared for that, per the regulations.

It didn't work as designed. Because the design was insufficient?

NO. It did not work because something happened that exceeded the design's limits.

Boeing did everything just right. Just not enough of it.

Boeing knew what happened before the Fire Department arrived. And they have been working on re-certifying the new system since that day. Probably way before that.

I will be perfectly happy if Boeing provides a system that prevents PROPAGATION. Runaway int the problem.

imho

Scientific approach
 

Despite to have some models that could explain BOS and TAK i am completely open minded as any search of the truth should be and MUST be.

Obviously we don´t have all necessary information and so we need to be careful and REDUNDANT when expressing what is our models, what is our mind.

Not necessarily. E.g. the algorithms certainly respected design limits but could stressed the cells beyond safe levels. Only time can test certain design characteristics. (E.g. Comet, Electra, etc.)

Just (another :}) hyperbole or you indeed think this?
Certainly some Boeing engineers, some posting in many forums probably expected.

I am convinced NTSB will do an exemplar job when showing FAA their results. Propagation, runaway are important but they are looking to WHY the cell shorted. Runaway and propagation were consequences. In TAK a probable cell short resulted (posted earlier) in a devastating (external to the battery) short circuit. A battery failure DESTROYED an aircraft conductor during the flight. Fortunately transformed in a (non designed :} ) fuse. Thus saving Boeing from a much more serious case:




(The smoke in the vent was just a sample. TAK ATC could see the smoke:

http://i48.tinypic.com/55nrbn.png

Equivalent circuit of TAK case
 

Hi,

Reposting:

http://i45.tinypic.com/2nlqq79.png

ANA TAK short circuit of cell # 3 plus terminal to battery case.

ICAO moves to remove exemption to carry Li batteries on aircraft.

"A U.N. agency that sets global aviation safety standards is moving to prevent aircraft batteries like the one that caught fire on a Boeing 787 last month from being shipped as cargo on passenger planes, people familiar with the effort said.

Over the past few days, the members of the International Civil Aviation Organization's dangerous goods committee have proposed revoking an exemption that permitted lithium ion aircraft batteries as heavy as 77 pounds to be shipped on passenger planes, the sources told The Associated Press. All other lithium ion battery shipments on passenger planes are limited to 11 pounds or less because of the batteries' susceptibility to short-circuit and ignite."

UN agency moves to kill aircraft battery exemption | Boeing news | The Seattle Times

That didn't take long.

It's only been allowed for four weeks.... Does any body know what they're doing? Since it was the Department of Transportation that signed off on shipping the Batteries on pax flights, and that did not turn out, is that why the Department's chief, Ray LaHood, Resigned? Was he under pressure to allow the replacements to fly? How had Boeing been shipping the "replacements" before they were blessed by DOT? :ugh:

:E

Heading South:

Based on my experience I wouldn't be too quick to dismiss the relevance of lithium batteries as used in model aircraft . True, most batteries used for this application are lithium polymer and there have been a lot of flame events caused primarily by using the wrong or mis-set charger, the non use of a balancer (essential) as well as physical damage. I use these batteries for their high energy density, high discharge currents and quick charging ability and always remove the batts. from the airframe for charging due to the fire risk. For me so far so good, firewise, although failure rates (voltage collapse, and cell swelling) ) have been high !

However, I have also been using lithium Ion batteries for some years both for airframe electronics (numerous powerful digital servos) and engine power (ECU, Starter and ignition on gas turbine powered models). Although the packs I use have an internal balancer and dedicated, slowish, charger (about .2c) I have noticed a very high failure rate for LiIons compared with NiCd and NiMh chemistry even though the discharge currents on my applications are not excessive. The failures have been non "flaming" but many packs have lost voltage and the ability to accept a charge at way below the cycles one might reasonably expect (some have failed after less than 50 cycles).

With the fire/explosion risk of LiPos, the poor reliabiltity of LiIons a lot of us are moving over to LiFe batteries which appear safer chemistry even though they can't quite deliver the performance of other lithium chemistry but do show an ability to recharge VERY quickly and can deliver quite high currents without much voltage drop off. Never heard of a fire or explosion with LiFe cells, perhaps this may be the way to go.

Still putting my money on a single cell failure and the charger trying to bring the pack upto full voltage, but isn't that what a balancer circuit is supposed to do ?

So, don't totally dismiss our lithium experience !!

(and no, not an aeromodelling troll, ex 75/76 captain who once flew an earlier, nearly, all-electric aeroplane, the Valiant ! Not a lot of people know the Valiant was almost fully electric, inc engine duct anti-icing, except for hydraulic wheelbrakes and N/S, lipos in this days, never been heard of !!)

Anyway I wish Boeing every success in getting to the bottom of this, and rapidly too, the 787 should soon be helping pay my pension !