# lithium battery fire on dreamliner



## GerhardRP (Nov 17, 2009)

http://www.cnbc.com/id/100364588
No details yet.


----------



## PStechPaul (May 1, 2012)

A video:
http://live.wsj.com/video/boeing-dr...4F.html#!7034E8F9-92AD-473D-BCFD-A9D930E0934F


----------



## Elithion (Oct 6, 2009)

It's getting worse.


----------



## GerhardRP (Nov 17, 2009)

Seem to be these batteries:
http://www.gsyuasa-lp.com/aviation-lithium-batteries
http://www.s399157097.onlinehome.us/SpecSheets/LVP10-65.pdf


----------



## GerhardRP (Nov 17, 2009)

Elithion said:


> What makes you think so?


sorry, maybe you read my post before I added the press release link.


----------



## Ziggythewiz (May 16, 2010)

Even the news articles said they were using yuasas. The problem with lithium cobalt is that it maximizes specific energy at the expense of safety. Anyone in the airline industry should know better. Hmmm...30% more energy, and 100% more smoke. Win win!!

Additionally, these cells have the vent on the side, which would make a bad scenario much worse when they try to vent and can't.










Our batteries (LiFePO4) maximize safety and cycle life, which would make them a much better choice for airlines.


----------



## Elithion (Oct 6, 2009)

Good find!

Now the question is: what BMS? Or, more to the point, was it hooked up properly to shut down charging and discharging when needed?










The picture is from this article.


----------



## GerhardRP (Nov 17, 2009)

GerhardRP said:


> Seem to be these batteries:
> http://www.gsyuasa-lp.com/aviation-lithium-batteries
> http://www.s399157097.onlinehome.us/SpecSheets/LVP10-65.pdf


"An examination of the flight data recorder indicated that the battery didn't exceed its designed voltage of 32 volts, the National Transportation Safety Board said in a statement."
So, they designed it for 4 volts/cell.
http://abcnews.go.com/US/wireStory/ntsb-plane-battery-burned-overcharged-18265254


----------



## Ziggythewiz (May 16, 2010)

How do you know that?

Just crappy batteries with a crappy BMS that burns power without telling the charger to turn off.


----------



## kennybobby (Aug 10, 2012)

Ziggythewiz said:


> How do you know that?
> 
> Just crappy batteries with a crappy BMS that burns power without telling the charger to turn off.


The LVP datasheet indicates nominal voltage 3.73, all the discharge curves start at 4 volts, and the notes on the graphs indicate CC/CV charging at either 4.0 or 4.025 volts. The data sheet also has errors/blunders and reads like the chinglish typically seen for the batteries we get...maybe Yuasa subbed out the job too? lol Anybody know at what charging voltage the cobalts start to cook off or go into thermal runaway?


----------



## Ziggythewiz (May 16, 2010)

I'm sure 4 is fine for those, but they said the problem was the charger cooking the cells, which means if it didn't go too high it was pumping juice into shunt regulators at a higher rate than they could handle.

It doesn't take much for a BMS to make a toasty day.


----------



## Elithion (Oct 6, 2009)

Based on what we heard so far, I would say that it was an over current due to a short circuit.


Short across the battery (or some cells)
High current
High temperature
Thermal runaway (which LiCoO2 cells can suffer from)
Fire (contained in the metal box)
Edit: this report says that the "battery" voltage was correct (32 V). It doesn't say that the cell voltages were correct.
Did the BMS not monitor each individual cell voltage?
Did a cell short out, and the rest of the cells (7) got slightly overcharged (14 % higher voltage)?
I can't see that resulting in a catastrophic event.
I stick with my first hypothesis.


----------



## Karter2 (Nov 17, 2011)

So, no "cell level" overload or thermal protection ?
Even the cheap ass Tesla has that !
Hard to believe that somebody would approve that sort of design for commercial aviation use ?


----------



## PStechPaul (May 1, 2012)

I wonder who actually does the design assessment and approval? Probably a bunch of managers who fired the engineers so they could keep their jobs and get bonuses for cost reduction. Engineers are expensive, and they are so darn critical. I've expressed my reservations about some designs, while the manager said "ship it"!


----------



## Karter2 (Nov 17, 2011)

PStechPaul said:


> I've expressed my reservations about some designs, while the manager said "ship it"!


 Thats why managers are paid a higher rate... they take "risk" decisions.
As an engineer, you work with data and facts, making "rational" decisions.
But in the Aero industry, those "risk" decisions must be eliminated.


----------



## kennybobby (Aug 10, 2012)

*Securaplane...i feel safer already*

It looks like the top has blown off of cell number 3, the third from the pack anode. All the rest still have exposed terminals. 

Battery Charge Unit, BCU:
Securaplane Technologies (that's a great name, George Jetson) located in Tucson, AZ says they supply the BCU. 
Info from their site:
Founded in 1986, Securaplane was the pioneer of security systems for aircrafts and has remained the world leader in these systems since...Securaplane was acquired by Danaher Corp. in 2000 and incorporated best practices in Lean Manufacturing and Lean Enterprise through the application of Danaher Business System....In April 2011, Securaplane was acquired by Meggitt PLC as part of a broader acquisition of Pacific Scientific Aerospace. Headquartered in the United Kingdom, Meggitt PLC is an international group operating in North America, Europe, and Asia. Known for its specialized extreme environment engineering,..

They also make some LiFePO batteries:
Lithium batteries: Through its expertise in power electronics and experience in energy storage, Securaplane has developed a unique architecture for lithium batteries, both for mainship applications as well as emergency backup applications. *Integrating all electronics into the battery offers unique benefits in terms of power/energy performance, long-life reliability, and safety.*

Their Sealed Lead Acid batteries are made from 0.028 inch pure lead sheets and even come with a warranty--wonder if Yuasa has a warranty form that requires 2 cycles of capacity check before return?


----------



## Elithion (Oct 6, 2009)

There is a fuse mid-pack (white component between cells 2 and 3 (counting clockwise). That would discount the external short circuit hypothesis. It would still be possible that the current was very high, but still below the fuse threshold. The voltage is too low for the idea of an arching fuse.

There doesn't appear to be a switch for the pack current: the bus bars go straight from the end cells, through current sensors on the BMS PCBs, to the outside. The BMS can only monitor and report, but it is not a protector (it is powerless to protect the battery on its own). So, if the hypothesis of excessive current is correct, the BMS may have known of the problem, but would have been powerless to do anything about it.

I hate it when people play expert and expound based on too little information; and here I am doing exactly that. But I can't help myself!


----------



## Ziggythewiz (May 16, 2010)

I still say a cell got too hot (due to shunting or just charging faster than it wanted to) and tried to vent, but couldn't due to idiots designing the vent on the side instead of the top.


----------



## Elithion (Oct 6, 2009)

This morning I wrote an article about this, and EEWEB already published it.


----------



## PStechPaul (May 1, 2012)

It looked like a 4S4P configuration but if it's a 32V pack then more likely would have been 8S2P (if there were 16 cells, as I had thought). One problem with cells in parallel is that, if one fails as shorted, the other cell(s) discharge their energy into it, which would not be detected by the BMS except as a low cell, and it couldn't do anything about it anyway. That's why I like strings of cells in series, with parallel connections on the ends where protection can be provided. 

Davide posted the link to his excellent article which explains the possibilities better than my conjectures above. I see now that these were prismatic cells in series, so my parallel cell hypothesis (and number of cells) were wrong. It will be interesting to learn of the true cause for this destructive event, if we will ever be privy to the details and the truth. I can see a huge fight among engineers, management, lawyers, government officials, insurance adjusters, and media people, trying to come up with a statement with the right "spin" to satisfy everyone. 

According to the brochure on the BCM, its output is limited to 1500 watts (32V 47A) with a 24V 80A input supply, so it is unlikely that it supplied excessive current during charging.


----------



## Elithion (Oct 6, 2009)

a) it's a 8S1P
b) inside each and every cell case, there are cells in parallel. Therefore, the fear of paralleling cells, while all too common, is purely a matter of perception, and is not technically based.


----------



## Ziggythewiz (May 16, 2010)

Elithion said:


> This morning I wrote an article about this, and EEWEB already published it.


Wow...you really do hate to play expert and expound based on too little information.


----------



## Elithion (Oct 6, 2009)

Ziggythewiz said:


> Wow...you really do hate to play expert and expound based on too little information.


 _Touché_ . Guilty as charged.


----------



## Coulomb (Apr 22, 2009)

Elithion said:


> Based on what we heard so far, I would say that it was an over current due to a short circuit.
> 
> 
> Short across the battery (or some cells)


That's the Achilles' heel of off-cell BMS; you need individual wires to the BMS, and it seems too much trouble to fuse each wire. And if you do fuse each wire, then if its a removable fuse, you have the trouble of corrosion because the current is too small to provide "wetting". So it's unreliable.

So designers just leave out the fuses, and hope that the BMS doesn't short the cells, or a fault develops in the wiring, or insulation breaks, or a washer falls into the box during assembly.

At least with cell-top BMUs (battery management units), you can put a surface mount fuse on each one. That overcomes the problem of reliability, at the cost of difficulty replacing the fuse. It's till not fool proof, of course; a badly placed washer could still bypass the fuse. But it seems lot better than lots of wires (redundant wires, even!) that are all capable of starting a fire.

The BMS must be pretty impressive; two printed circuit boards that take up one end of the box. It's a shame with all that circuitry that it failed to do its job.

[ Edit: disclaimer: I have co-designed a cell-top BMS for lithium iron phosphate cells, and may end up selling them at some point. So I have a bias away from off-board BMS. I claim that this was a result of thinking through the various options, and deciding that cell-top with fuse is the safest option. ]


----------



## piotrsko (Dec 9, 2007)

I dunno: after being a 2nd tier subcontractor production manager for BMAC, I am guessing somebody either got the shutoff voltage wrong, or isn't checking charge current levels.

32v sounds high for a 8S1P pack.


----------



## PStechPaul (May 1, 2012)

32 volts is 4V/cell, which should be OK for charging. Nominal 3.7V/cell is 29.6V.

I think having exposed studs for terminals is asking for trouble. It would be better to have recessed female threads that require a copper washer under the bus bar (and attached to it) so that it would be almost impossible to short the terminals accidentally. You could also have one terminal as a stud and the other recessed, as a "foolproof" polarity indicator. The interconnecting bus bars could be insulated except for a small area for contact, and the bolts and nuts used for connection could have a plastic cap. However, those precautions may not be necessary, if once the cells are installed and tested, an adequate insulating shroud would be installed over the connections. That flat plastic shield seems to be (and perhaps was) inadequate.

I'm also working on a system with cell-top BMUs, although for smaller cells such as AA and 18650s. I think Li-Ion can be made almost as safe as LiFePO4, with a more capable BMS, with the possibility of much lower cost per Wh. From what I've seen, Li-Ion may be about half the cost of LiFePO4.


----------



## Karter2 (Nov 17, 2011)

PStechPaul said:


> I think Li-Ion can be made almost as safe as LiFePO4, with a more capable BMS, with the possibility of much lower cost per Wh. From what I've seen, Li-Ion may be about half the cost of LiFePO4.


 For Boeing, it would be better to have LiFePO4 with the performance/ weight of LiCo ...no matter what the cost !
In fact, i bet they now wish they had bought out the A123 business!


----------



## Zappo (Sep 1, 2011)

I'm not sure what they will eventually find but my wife is thinking I'm an effing genius right now. I had heard on the news that the battery had just been discharging pretty hard and then had just started charging when the fire happened. Later that day, the Japanese investigators were speculating that the cause was possibly over voltage. I told her that given the heavy discharging just before, it was highly unlikely that there was an over-voltage condition. The next morning on the news, they were saying it was determined it wasn't from over voltage. My wife just looked at me and started laughing.


----------



## Karter2 (Nov 17, 2011)

Elithion said:


> This morning I wrote an article about this, and EEWEB already published it.


 Davide
In that article you propose 3 possible hypotheses..

1) Unbalanced overcharge.
2) Over current charging 
3) Over current discharge

but reported data and logic would suggest that high rate discharge is unlikely as the pack was still at peak voltage 32v ?.. implying that no discharge had occurred ?
Also, the 1000+ Amp "over current charge" you theorized is unlikely since..
A) a charger capable of that level current would be excessively large and heavy and over spec'd for the application ( remember the primary focus of the 787 is weight reduction and space is always at a premium.
B) Also Where would a 30-40 kW supply come from on board ? ..or even on the ground ?
C) surely any systems on board would have protection ( breakers, fuses etc) against any such massive excessive current levels.

so it would seem that your option 1 is the most likely of those theories ?


----------



## kennybobby (Aug 10, 2012)

*my money is on overcharge of cell #3*

the third from the anode in the pack. i don't see any shunt wires in the loom that could handle 20 amps, much less 47 at max BCU current.

I'll bet $100 that #3 had a lower capacity than the others or had gotten out of "balance" with the rest of the pack somehow. When #3 got full and the rest were still being charged it went thermal from the overcharging current it had to endure. Maybe some reporter will get their hands on the cell logs in the flight recorder data...


----------



## Coulomb (Apr 22, 2009)

*Re: my money is on overcharge of cell #6*



kennybobby said:


> the third from the anode in the pack.


Pardon a dumb question, please. Which end are you saying is the anode? I didn't see any indication of a negative or positive sign. I assume you mean the one furthest from the fuse; it seems to be the most beaten up.


----------



## Jan (Oct 5, 2009)

*Re: my money is on overcharge of cell #6*

And what about the fact the BMS side of the box is more damaged on the outside than the rest of the box?


----------



## Karter2 (Nov 17, 2011)

Elithion said:


> This morning I wrote an article about this, and EEWEB already published it.


Davide,
you state in that article .....


> Electrical, power circuit
> • 8S1P arrangement
> • 29.6 V nominal, 32 V max
> • 65 Ah, 1.9 kWh
> ...


 Where does that value of 580A peak ..come from ?
It doesnt seem to correlate to the 65Ahr, and 5C rating of the cells .


----------



## Elithion (Oct 6, 2009)

Karter2 said:


> Where does that value of 580A peak ..come from ?


It's the current at which the efficiency of those cells is 1-e^-1. Reference, (search for "Ultimately, we chose a factor of e because").

By all means, I am not saying that that is the current that the manufacturer rated these cells at.


----------



## Karter2 (Nov 17, 2011)

So the 580 A is just a theoretical figure calculated by you...not an "official" figure from the pack specification or a system design parameter ?


----------



## Elithion (Oct 6, 2009)

Karter2 said:


> So the 580 A is just a theoretical figure calculated by you...not an "official" figure from the pack specification or a system design parameter ?


> theoretical 

I wouldn't quite say that: you can get that much current out of those cells. 

> calculated by you

Yes, from their Short Discharge Time.

> not an "official" figure

Correct.


----------



## kennybobby (Aug 10, 2012)

*LiCoO2 Cathode, Carbon Anode in Yuasa?*

Looking at it some more it appears that the carbon anode (-) terminal of cell #3 exploded and pushed the positive cathode terminal over against the side wall of the box. To me this all points to a 'charging' event as that is when the Li+ ions are moving into the carbon lattice of the anode (intercalation) as shown below.


----------



## GerhardRP (Nov 17, 2009)

*Re: LiCoO2 Cathode, Carbon Anode in Yuasa?*

More info:
https://www.federalregister.gov/art...7-8-airplane-lithium-ion-battery-installation
http://www.nytimes.com/2013/01/24/b...vercharged-japanese-investigators-say.html?hp


----------



## Zappo (Sep 1, 2011)

FINALLY! A couple of reporters for the New York Times addressed the whole lithium-ion confusion:

“Lithium-ion” is a vague term that is used in the battery industry to describe a variety of chemistries. This particular battery was built specifically for the 787 and, according to the safety board on Thursday, used an aluminum strip coated in lithium cobalt oxide in its positive electrode. That is an older technology and is more prone to thermal runaway; it also generates oxygen as it heats, making combustion more likely.

Hiroko Tabuchi in Tokyo contributed reporting, and Christopher Drew and Jad Mouawad in New York.

Thanks guys!


----------



## EVfun (Mar 14, 2010)

*Re: Not dumb at all...*



kennybobby said:


> i just don't know how to upload a picture into a post properly--i didn't mark the anode (-) terminal but hopefully this picture shows where #6 blew it's top...


You have the cells labeled exactly backwards. The fuse is between cell 2 and 3, so the cell that appears most damaged is cell 3.


----------



## Coulomb (Apr 22, 2009)

*Re: LiCoO2 Cathode, Carbon Anode in Yuasa?*



GerhardRP said:


> More info:
> https://www.federalregister.gov/art...7-8-airplane-lithium-ion-battery-installation
> ...


Thanks!

I think they might have overlooked some of the special conditions, like:

"(7) Lithium ion battery installations must have a system to control the charging rate of the battery automatically, so as to prevent battery overheating or overcharging, and,
(i) A battery temperature sensing and over-temperature warning system with a means for automatically disconnecting the battery from its charging source in the event of an over-temperature condition, or,
(ii) A battery failure sensing and warning system with a means for automatically disconnecting the battery from its charging source in the event of battery failure."


Or if they did have the above in place, they just happened to have two failures in a very short time.


----------



## lithiumlogic (Aug 24, 2011)

I'm rather shocked at how little effort seems to have gone into mitigating the risks of the battery chemistry compared to say, Tesla motors or other automotive manufacturer. I mean if your battery starts smoking midway across the Pacific all you got to do is hit the airbrakes, open the door and step out, right?

The cobalt oxide cathode starts to decompose at temperatures above 70C, producing heat. The hotter it gets, the faster the reaction and therefore heat production. Working against this is the dissipation of heat into the environment. At some point, heat production exceeds dissipation and the temperature will continue to rise to ignition point with no further heat input. With a fully charged , freestanding 18650 this may not occur till 130C or so when the separator melts, creating a short circuit. However the same cell in a very well insulated container will eventually go into runaway if heated to just 70C, though apparently it can take two days to get there. 

The thing is these large format cells have a much lower surface area to volume ratio than 18650s and they're wrapped tightly in a metal box. So I suspect the temperature at which the positive feedback loop sets in is going to be lower than with 18650s. The runaway in the destroyed battery could have been initiated some time before there was smoke. Perhaps when the ground crew started the APU, one of the cells has a higher internal resistance than the rest and heated up to 80C?

How much more likely is this when you go to start an airplane that's been sat for a couple of days in Riyadh i wonder?


Jack Rickard had a fire in one of his A123 packs a week after overcharging it. It was one heck of a big pack and was encased in foam, so imagine the middle cells were pretty nicely insulated.

It does look like they're undercharging the cells to try and improve stability however. 4V per cell fully charged is only about 80% on Li-Co - the fully charged voltage is 4.2V.
The battery sits in the plane's EE bay, so if it vents, flammable vapours accumulate around high voltage switchgear etc. Water is the best extinguishing medium for a lithium battery fire because not only does it put out the flames from the burning electrolyte, it cools the cathode below the temperature where the reaction occurs. But the fire crew didn't want to be spraying water around in that compartment where there's high voltage switchgear.

Perhaps they could rig a system to discharge water from the plane's fresh water tank (or even the waste water tank ) in an overheat scenario. You get to fly the rest of the way across the Pacific with no toilets or handbasins but at least you are not on fire.

Starting from scratch, how i'd have done it :

1) I'd not put the battery in the EE bay, for the above reason. It can go in the tail , behind the aft pressure bulkhead, nearer to the APU it is supposed to start. Any fire/venting occurs outside the pressure hull and where flammable materials are less likely to be present (cabin insulation etc). The air from the cabin outflow valve can be blown through the battery compartment to keep them at room temperature, though they'll be unpressurised.

2) i'd take a leaf out of Tesla's book and use 8S30P 18650s. Better surface area to volume ratio so less likely to overheat, and a fire in one cell is less threatening to the aircraft. I wouldn't use a liquid cooling system (adds weight) but since we have plenty of spare space, i'd have each cell separated from its neighbour by a substantial air gap. One cell catching fire can't send it's neighbour into thermal runaway.


----------



## Elithion (Oct 6, 2009)

Inspectors: cell maker GS Yuasa off the hook, BMS manufacturer now under the microscope


----------



## PStechPaul (May 1, 2012)

Thanks for the link. Some of the comments were interesting and well-informed. I think some of the suggestions, such as using a Lipo-Safe bag for the cells and using a sealed enclosure filled with Argon may be advisable, but perhaps a change to LiFePO4 would be best. Even though no fault was found with the manufacturing of the batteries, I think it was still inherent in their chemistry to go into thermal runaway and melt-down if the BMS did not detect a dangerous condition and effectively act on it soon enough. Hopefully the investigators can duplicate this and zero in on the root cause and take effective action.


----------



## Ziggythewiz (May 16, 2010)

The problem is that Boeing likely considered the batteries to be a minor part of the build, and instead of saving them for last like any experienced EV builder would do, they must have selected the batteries and designed that part first...before either of the huge Sony fire recalls.

Not only are these cells far less safe than LiFePO4, they're not even as dense, so they're losing on cost, space, and weight as well.

They may have chosen these cells before LiFePO4 even existed, but they could have easily changed midcourse during one of the many lithium fire panics over the last decade. Now they'll have to change anyway, but they'll probably just slap in a new BMS and do tons of battery maintenence over the years.


----------



## PStechPaul (May 1, 2012)

Ziggythewiz said:


> Not only are these cells far less safe than LiFePO4, they're not even as dense, so they're losing on cost, space, and weight as well.


It is my understanding that LiCo is much higher in energy density than LiFePO4. See the following:
http://batteryuniversity.com/learn/article/types_of_lithium_ion

Lithium Phosphate is about 105 Wh/kg which is only about 20% higher than NiMH at 90, while LiCo is about 170.

I'll use these figures to do a reality check on the Li-Ion and NiMH cells I just purchased and tested, and the LiFePO4 which are on order.

The Li-Ion 18650 is rated at 3600 mAh and 3.7 V, for 13.3 Wh, and its weight is 41g, so energy density is supposedly 325 Wh/kg. Thus I would expect an actual capacity of 1883 mAh or 6.9 Wh, which coincides with another report that states these cells actually produce half of their advertised rating.

The LiFePO4 18650 is rated at 1800 mAh and 3.2V, for 5.76 Wh, and about the same weight 42g, so energy density is 137 Wh/kg. From the chart I linked above, this is still a little high, so I should expect 1380 mAh or 4.4 Wh.

The NiMH AA cells are rated 3000 mAh and 1.2V, or 3.6 Wh, and weigh about 19g, so energy density is 189 wH/kg, or more than twice what should be expected. So reality would be 1430 mAh or 1.7 Wh.

Now the expected true costs based on my small quantity purchases are:

NiMH $0.92/1.7 = $0.54/Wh
Li-Ion $3.54/6.9 = $0.51/Wh
LiFePO4 $4.20/4.4 = $0.95/Wh

These are total cost including shipping. Larger quantities roughly cut these costs in half. I will need to do testing on the NiMH and the LiFePO4 to see what their actual capacities are. The Li-Ion cells, as received, measured about 1.78 Wh and 0.83 Ah.

The results are tabulated here:
http://enginuitysystems.com/files/DischargeTest_3600mAh_Li-Ion.ods
http://enginuitysystems.com/files/DischargeTest_3600mAh_Li-Ion.xls


----------



## PStechPaul (May 1, 2012)

Another report questions the apparent lack of cooling system:
http://www.designnews.com/document....84,industry_aero,aid_257987&dfpLayout=article

But I also wonder if the batteries could have been too cold and charging or discharge current was excessive in respect to temperature. These failures occurred in winter, and also it's colder at high altitudes. Maybe a heater would also be needed?


----------



## Ziggythewiz (May 16, 2010)

PStechPaul said:


> It is my understanding that LiCo is much higher in energy density than LiFePO4. See the following:
> http://batteryuniversity.com/learn/article/types_of_lithium_ion
> 
> Lithium Phosphate is about 105 Wh/kg which is only about 20% higher than NiMH at 90, while LiCo is about 170.


Usually (now) they are, but cells are always getting better, and these were developed so long ago they are only 87-101 Wh/kg according to the spec sheet linked on the first page.


----------



## PStechPaul (May 1, 2012)

The 100 Ah Hi-Power cells advertised here are 80 Wh/kg:

http://www.electriccarinternational.com/Lithium-Prismatic-Batteries.php

Those from Tornado Batteries are 3.5 kg or 91.5 Wh/kg.

http://www.tnd-battery.com/html_products/LiFePO4-Prismatic-Cells-Catalogue-263.html

Their 18650 1500 mAh LiFePO4 cells are 120 Wh/kg:

http://www.tnd-battery.com/html_products/LiFePO4-Battery-32V-18650--1500MAH-cell-270.html

That's the maximum for their cells, so the 1800 mAh figure for the cells I ordered must be inflated!


----------



## Karter2 (Nov 17, 2011)

Its not just energy density that is important in some situations.
Specifically , Boeing required a very fast charge rate ..
.. apparently, and other chemistry cells could not meet that requirement at the time.
.. but there are certainly LiFePO4 cells that would easily satisfy that now. 
Just goes to show how dated some technology can be on a brand new aircraft !


----------



## mizlplix (May 1, 2011)

It seems that so far they have eliminated the GPU, battery construction and materials from consideration for the failures (2).

I also note that the batteries in question were only used for back-up and ground power systems and not the main flight systems.....Interesting.

The AirBus people recommended encasing the batteries in a secondary box to catch and vent any smoke from a potential battery failure...Short for 
"Our designs are flawed, but we will use then anyways." 

I can not wait to see just what is at fault after they eliminate *everything* from the cause list....LOL

Miz


----------



## Salty9 (Jul 13, 2009)

In my experience it will be blamed on the lowest level employee possible.


----------



## PStechPaul (May 1, 2012)

It will be found to be a gremlin :


----------



## GerhardRP (Nov 17, 2009)

The plot thickens:
http://www.nytimes.com/2013/01/30/b...ls-before-the-fires.html?pagewanted=2&_r=0&hp


----------



## mizlplix (May 1, 2011)

What I find interesting is this statement: 


> Boeing has said its system has safeguards that prevent a drained battery from being recharged without first being sent back to the manufacturer for reconditioning.


Which I take to mean there IS a way to rescue overly discharged cells.....

Now we have to send a Mole to work at Yuasa and find out how. 

Any volunteers?

Miz


----------



## mizlplix (May 1, 2011)

A cute article:

http://www.bbc.co.uk/news/business-21256486



> Japan's transport ministry said that safety inspectors had found no faults with the battery


What did they expect? Yuasa IS a Japanese company. "We no sell bad cell." "You plane is fault." 

I think Boeing has a problem when a nation is protecting an indigenous company. 
Meaning that even if Boeing finds cell defects, they will have to pay to get it 
corrected even if it means having a Chinese firm make replacements.

Boeing needs to tool up and make their own......

I will take care of all the "old, defective, cells" for them.<LOL>

Miz


----------



## mizlplix (May 1, 2011)

I take that to mean the BMS, not the aircraft system. If the BMS was doing it's job, the cut-off point would have been before cell damage happened.

Unless the discharge curve in the BMS was not correct and allows the cells to be damaged before cut off, like 99% instead of a safer 80%. 

It seems they are going the same learning curve we have regarding the actual safe cell operating range (If you want a long life span without damage).

So their "fix" seems to be to add a few AH's and set the BMS to limit the discharge to 80% or so (Like we have found).

Whatever, I wish them a fast resolution to the problem. We do not need another defunct American company. 

Miz


----------



## Karter2 (Nov 17, 2011)

Its very possible they have a "Low voltage lockout"..... which requires a factory inspection and "reset" to ensure cell integrity,..... before the battery pack can be reused. ?
But I sure hope someone kept records of those pack serial numbers, which aircraft had these "defective" packs, ( removed and installed ?), and has done a check to see if there are any common factors !


----------



## Coulomb (Apr 22, 2009)

Karter2 said:


> Its very possible they have a "Low voltage lockout".....


Huh! I wonder if it's staff avoiding what they see as "excessive servicing". Imagine you're prepping for a big international flight, everything is rush rush rush, and damn it! You see the BMS light on, again! That only happened a month ago, and now it's back again! By the book, that thing has to go back to maintenance, and that will put us half an hour behind, minimum. Maybe there's a way to trick the thing into forgetting the alarm... it's only for backup lighting after all, it's just a big nuisance. I bet the manufacturers set the limits too tight deliberately to get extra service work. I'll just jiggle the controls till the alarm goes off.... ah, there it is. Problem solved!

Total fantasy, and I'm not accusing anyone of anything. But this sort of thing can arise when an alarm seems to go off "too often". Of itself, this is bad design, if you have humans in the loop.


----------



## Elithion (Oct 6, 2009)

The guardian quotes me: "My gut feeling is that there was something wrong with the management here" 

I am always amazed by how one's words are interpreted by journalists.


----------



## GerhardRP (Nov 17, 2009)

Anybody read Japanese?
http://www.mlit.go.jp/jtsb/flash/JA804A_130116-130205.pdf


----------



## Elithion (Oct 6, 2009)

GerhardRP said:


> Anybody read Japanese?
> http://www.mlit.go.jp/jtsb/flash/JA804A_130116-130205.pdf


Google does.

Page 1
Japan Transport Safety Board
Serious incident investigation aviation
•
Genus where
All Nippon Airways Co., Ltd. (Flight 692)
Transportation
•
The expression of type
Boeing 787-8 type formula
•
JA804A registration symbol
Registration symbol
•
January 16, 2013 date and time of occurrence at around 08:26 (Wed)
•
Above an altitude of about 32 Takamatsu Airport near the place of occurrence
,
000
ft
Above an altitude of about 32 Takamatsu Airport near the place of occurrence
,
000
ft
February 5, 2013
Transportation Safety Board
One


----------



## Elithion (Oct 6, 2009)

GerhardRP said:


> Anybody read Japanese?
> http://www.mlit.go.jp/jtsb/flash/JA804A_130116-130205.pdf


Google does.

PAGE 1 ------------------------------------------------------------
Japan Transport Safety Board
Serious incident investigation aviation
•
Genus where
All Nippon Airways Co., Ltd. (Flight 692)
Transportation
•
The expression of type
Boeing 787-8 type formula
•
JA804A registration symbol
Registration symbol
•
January 16, 2013 date and time of occurrence at around 08:26 (Wed)
•
Above an altitude of about 32 Takamatsu Airport near the place of occurrence
,
000
ft
Above an altitude of about 32 Takamatsu Airport near the place of occurrence
,
000
ft
February 5, 2013
Transportation Safety Board
One

PAGE 2 ------------------------------------------------------------

1. Overview of the main battery


The airplane is equipped with two batteries


Main Battery
APU battery (Auxiliary power unit)

The lithium ion secondary batteries are identical
Eight cells are connected in series

Specifications are as follows:


Lithium-ion battery
Nominal voltage: 29.6 Vdc (3.7 V × 8 cells)
Nominal capacity: 75Ah
Weight and Size: 28.5kg, 215H × 280W × 335L mm
(According to the manufacturer's documentation)

PAGE 3 ------------------------------------------------------------
2. Battery location
Main Battery [left side of picture] APU battery [right side]
Damaged normal 

PAGE 4 ------------------------------------------------------------
3. Battery Analysis


APU battery and main battery
Japan Aerospace Exploration Agency (JAXA, Mitaka) carried out a CT scan 
The main battery manufacturer in Kyoto performed a 
CT scan of each cell and the decomposition study



Battery Battery Monitoring Unit (BMU)
The manufacturer in Fujisawa conducted an analysis

Battery Charger
The manufacturer in the USA conducted an analysis

Contactor and battery diode module (BDM)
Will be studied by manufacturer in France

PAGE 5 ------------------------------------------------------------​


----------



## Ziggythewiz (May 16, 2010)

So...3rd party inspection of the battery and only manufacturer denials of the rest.


----------



## Elithion (Oct 6, 2009)

PAGE 5 ------------------------------------------------------------

4.CT scan image

Main Battery

APU Battery (Normal)
Main Battery (CT scans into 3D images taken by JAXA)

PAGE 6 ------------------------------------------------------------

5. Degradation of the battery in the manufacturer's

Main Battery

PAGE 7 ------------------------------------------------------------
6. Appearance of the battery (main battery)

PAGE 8 ------------------------------------------------------------
7. Appearance of each cell (main battery)
Cell 1.... cell 8

PAGE 9 ------------------------------------------------------------
8. CT scan image of each cell

Cell 5 - Hole in positive electrode - Internal wiring is melted, next to cell 6
Cell 7 - Dent and bulge
Cell 6 - The internal wiring of the positive electrode is melted
Cell 3 - Damaged positive electrode
CT scan converted into a 3D image

PAGE 10 ------------------------------------------------------------
9. Battery cell status (Summary)


Damage seen in all eight cells - damage particularly large in cells 3 and 6
Thermal damage is seen in all cells
Thermal runaway seen
Most damage seen on the positive electrode of cell 3
Melting was observed inside six of the positive electrodes (cells 4 and 5 did not)
PAGE 11 ------------------------------------------------------------
10. Other

Ground wire of the enclosure battery is disconnected.

PAGE 12 ------------------------------------------------------------
Summary



Investigate further the status of the battery cell damage
Decomposition study

Continue looking for the cause of the damage
Perform data analysis, such as of flight-data recorder, battery charger etc.

Continue the investigation of the disconnection of the enclosure grounding wire 

When did it happen, and why


----------



## Karter2 (Nov 17, 2011)

That sound like just a Japanese translation of the US reports we have already seen..with the CT scans etc.


----------



## Elithion (Oct 6, 2009)

Karter2 said:


> That sound like just a Japanese translation of the US reports we have already seen..with the CT scans etc.


Damn! I wasted all that time translating? I haven't seen the English version. Can you point me to it?


----------



## Ziggythewiz (May 16, 2010)

Don't feel too bad Just think how much time those idiots spent designing and testing the BMS, and Boeing spent testing the battery packs...


----------



## GerhardRP (Nov 17, 2009)

Karter2 said:


> That sound like just a Japanese translation of the US reports we have already seen..with the CT scans etc.


Actually, the US reports were quoting from this presentation by the Japanese equivalent of the NTSB. None I could find had the pictures. 
Thanks for translating, Davide.
Gerhard


----------



## Karter2 (Nov 17, 2011)

GerhardRP said:


> Actually, the US reports were quoting from this presentation by the Japanese equivalent of the NTSB. None I could find had the pictures.


 Scans shown here..
http://www.ntsb.gov/investigations/2013/boeing_787/JAL_B-787_1-24-13.pdf


----------



## kennybobby (Aug 10, 2012)

So it was the cathode terminal, not the anode, on cell #3 that exploded.

That would explain how the green ground cable fused--the pack anode is tied to the aircraft chassis for some reason, and the battery box was grounded to the chassis by the green cable. When #3 blew the cathode terminal, the jumper bar was pushed over to touch the inside of the battery box and shorted the pack to ground thru the green "fuse" wire, which looks to be aluminum?


----------



## PhantomPholly (Aug 20, 2008)

This is all such a shame for Boeing, but they violated a primary rule of aviation: Don't introduce too many new technologies at once. I realize they probably saved a couple of hundred pounds of paying payload with their solution, but in the end it cost them a lot more.

They should have just let Tesla make them some proven last-gen battery packs with balancers. Would have been almost as light, but less likely to fail.


----------



## Karter2 (Nov 17, 2011)

PhantomPholly said:


> .... but they violated a primary rule of aviation: Don't introduce too many new technologies at once..


 Actually, i think their problem may be that they used an OLD battery technology rather than the more stable newer technologies. !
They just didnt do their homework well enough.


----------



## PStechPaul (May 1, 2012)

More information, pointing to an internal short circuit, but still many questions:
http://www.designnews.com/document....84,industry_aero,aid_258717&dfpLayout=article


----------



## Elithion (Oct 6, 2009)

Wall Street Journal

"Microscopic 'Dendrites' a Focus in Boeing Dreamliner Probe"

"The critical factor is charging too fast on some cells,"

May or may not be related: dendrites are likely when charging below 0°C.


----------



## Ziggythewiz (May 16, 2010)

Karter2 said:


> They just didnt do their homework well enough.


Sure they did...20-30 years ago. They just failed to regrade their work when the answer key was altered by huge recalls using the same old battery chemistry and new (safer and more energy dense) technologies became established.


----------



## Ziggythewiz (May 16, 2010)

"May or may not be related: dendrites are likely when charging below 0°C. "

I would also wonder how pressure (or lack thereof) affects the cells, as well as the BMS.


----------



## piotrsko (Dec 9, 2007)

well, we know that we got dendrites up in space, took forever to duplicate down earth side. But that was tin, I believe, or possibly also aluminum.


----------



## kennybobby (Aug 10, 2012)

Can't dendrites form on either the cathode or the anode depending upon the over-current direction, at any temperature? 

update friday feb 15: 
NEW YORK: US aerospace giant Boeing said Friday it will continue to use lithium-ion batteries, despite rival Airbus saying it would avoid them following two incidents on the Boeing 787. "Boeing is confident in the safety and reliability of lithium-ion batteries," said Boeing spokesman Marc Birtel. 

"Our years of experience and deep expertise confirm that, like other technologies, when the appropriate battery, system and airplane protections are in place, lithium-ion batteries deliver significant benefits," Birtel said.


----------



## kennybobby (Aug 10, 2012)

*Shear the Sheep it's time to Pull Wool...*

This really gets interesting...go read the 56 page court document found in this story for details: http://www.nextgov.com/emerging-tec...estroyed-boeing-787-suppliers-facility/60809/ Securaplane builds the battery charging units. They had a lithium battery fire back in 2006 that burned some of their facility to the ground while testing the BCU. The test technician found an error in schematic, got nervous and wouldn't ship hardware, blew the whistle, later fired. Tries to sue for getting fired due to whistleblowing, but has poor legal counsel (himself) and loses a slamdunk case in court. Of course he got fired for squealing to the feds about the BCU--that's how that business works. But we've all read that the voltage to the battery never exceeded 32 volts...so what could it be? Nobody knows to look at the individual cell voltage? Wonder what the inside story is on the BMS for this 8-pack...


----------



## Elithion (Oct 6, 2009)

NTSB Interim Factual Report, released yesterday.


----------



## Coulomb (Apr 22, 2009)

Elithion said:


> NTSB Interim Factual Report, released yesterday.


Fascinating.

The things that stand out to me are:

1) The voltage of the battery reduced from 31 to 30 about 3 seconds before charging started. Maybe this was a timing error in the logs.
2) Only the positive pin of the power connector showed evidence of overcurrent. There was evidence of high current in the earth strap from case to aircraft earth, and on the shield on the charger cable.
3) These overcurrent events don't seem to be documented in the logs.
4) The charge current of some 44 A doesn't seem to have lasted long. But surely the terminals of J3 were designed to carry 44 A. So there must have been hundreds of amps flowing at some point, that wasn't logged.
5) The BMU system doesn't seem to be logged at all. This seems a significant oversight. I guess there isn't a logging requirement for earlier batteries, but with lithium, the BMU would seem to be critical, in my opinion. I hope that as a result of this, that BMU operation is logged in the flight recorders.
6) The following requirement (one of the 9 special conditions that Boeing needed to get lithium cells allowed on aircraft) seems impossible to achieve with Lithium Cobalt cells: "Safe cell temperatures and pressures must be maintained during any foreseeable charging or discharging condition and during any failure of the charging or battery monitoring system not shown to be extremely remote."
(7) "The lithium ion battery installation must preclude explosion in the event of those failures." Well, one of the fire personnel received a burn to his neck when something inside the battery, in his words, exploded. So with the benefit of hindsight, it would appear that they didn't achieve that requirement either.


----------



## PStechPaul (May 1, 2012)

Very detailed and interesting report. It appears that there was an initial drop of 1 volt which may have been a partial short in one of the cells. This was followed by a charging current of 45 amps, which may have been triggered by the voltage drop. The pack voltage further decreased to 29 volts indicating a nearly full short in one cell, then the voltaged increased to 31 volts, and then a failure was reported and the charge current was removed. The voltage dropped to 28 volts which was the nominal for the remaining 7 cells at 4 volts each.

It is possible that the four seconds of charging at 45 amps into a damaged cell with a voltage drop of 4 volts, or 180 watts, may have been enough to start ignition at the failure point, and then there was a chain reaction that involved adjacent cells. It may be difficult to detect a failed cell when its voltage drops only about 1 volt, and the charger may simply try to recharge the pack as if it had just been slightly depleted. This would be appropriate if all cells were balanced, but perhaps the BMS did not react in time, and the charging current appeared to restore balance.


----------



## Ziggythewiz (May 16, 2010)

Coulomb said:


> "Safe cell temperatures and pressures must be maintained during anyforeseeable charging or discharging condition and during any failure of thecharging or battery monitoring system not shown to be extremely remote."


It didn't happen every time, so how 'bout here's $5,000 and we'll call that extremely remote?


----------



## GerhardRP (Nov 17, 2009)

Coulomb said:


> Fascinating.
> 
> T<snip>
> 2) Only the positive pin of the power connector showed evidence of overcurrent. There was evidence of high current in the earth strap from case to aircraft earth, and on the shield on the charger cable.
> ...


The schematic on page 8 shows the current sensor only in the negative lead.


----------



## kennybobby (Aug 10, 2012)

*Re: lithium battery fire(s) on dreamliner(s)*

The cells are housed in a stainless steel case that is somehow not isolated from the cell terminals(?). At 4.025 volts they reported 1 to 1.4 volts from (+) to case and 2.6 to 3.0 (-) to case.

After reading the reports for the Boston incident it looks to me that the case of cell 5 shorted to the inside of the battery cover which is connected to the airframe vehicle chassis thru the ground stud. The battery pack negative terminal is also connected to the chassis at some undefined point, which creates a ground loop thru the vehicle chassis. When cell 5 shorted to chassis then you had at least a very low impedance 18.6 to 19 volt potential looking for a current path back home. It appears to have used the chassis-grounded J1 signal shields as part of that path too.

For the ANA incident it appears that the cathode of cell 3 was blown asunder--why? Same reason, but it was a different cell that shorted to the chassis, although the outcome was the same.

Now i know the root cause but need to verify something before i post my theory...


----------



## Coulomb (Apr 22, 2009)

GerhardRP said:


> The schematic on page 8 shows the current sensor only in the negative lead.


Duh! I missed that one.  Thanks.

That sure sounds like it has something to do with it. They should either move the sensor to the positive lead, or put a second sensor on the positive lead.

That still won't prevent a fire with two shorts to chassis, but hopefully they will catch the first short to chassis with this, and the "extremely remote" fiction becomes a little more believable.


----------



## kennybobby (Aug 10, 2012)

*NTSB hearing on this incident is today and tomorrow*

ntsb.gov has a webcast of the hearing. 

Concerning the DCA13IA037 airworthiness factual report dated march 5,2013: The Flight Data Recorder report shows measurement DCBus_APU_Battery_Current (A) in figure B-12 on page 10B-13 only discharging an average of about 20 amps for the APU start with a momentary spike up to 30 amps during the 35-second discharge. 

This would only be 640 watts average with the spike at 960 watts, not the 9.6 kW (32V x 300A) mentioned in your report. Some of the other power figures in that paragraph appear incorrect also and should be re-checked. 

In addition I wanted to point out that same FDR current data also shows that the APU battery was constantly being overcharged by trickle-charging at 1 to 2 amps during the 14 minutes between Last Engine Shut Down and the APU Shuts Down. 

The Securaplane battery charging patent #5,780,994 is based upon a Ni-Cd battery charging profile and assumes a trickle-charging phase of indefinite length following the fast-charge phase. 

GS Yuasa does not include trickle-charging in the CC/CV charging procedure of their cells, nor does any other manufacturer of Lithium chemistry batteries. 

The CT Scan report also provides evidence of overcharging in the x-ray scans of the 'normal undamaged' Main battery. The cell walls are clearly seen to be bulging outward and there may be cell-to-cell wall contact. This swelling of the cells is also seen in the CT scans shown in the JTSB reports for the 'undamaged' APU battery. 

I have a copy of a mechanical load analysis that shows that only a couple of psi delta-pressure is necessary to deform the 0.031 inch thick stainless steel material used as the cell case. A deformed cell case would likely cause internal short-circuit contact of the current collector bars to the case. 

The source of the pressure delta could be internal due to overcharging, or external due to operation at reduced atmospheric pressure such as in high altitudes (e.g. 6000 ft).


----------



## JRP3 (Mar 7, 2008)

PStechPaul said:


> 32 volts is 4V/cell, which should be OK for charging.


Unless they keep trickle charging it at reduced current after it's already full. Repeat this every time and eventually you'll get swelling and then shorting.


----------



## kennybobby (Aug 10, 2012)

*Charging Requirements*

A new set of documents was just released on the NTSB Docket site. On docket # SA-536, exhibit # 17-A, Airworthiness Excerpts from Boeing Battery Specification Control Drawing:

page 89, section 3.2.4.13, Charging Requirements
*The fully charged battery shall accept continuous overcharge at _ V without explosion or damage to the battery case.*

The blanked out voltage was redacted due to proprietary concerns.

So it looks like Boeing wrote a requirement on the battery that violates the fundamental law of Lithium battery chemistry... 

Edit notes: In the second day of hearings the GS Yuasa representative mentioned that they have built over 14,000 cells since 2001 and have never seen an internal short. These are the industrial cells of the same construction as the 787 cells, but using a different chemistry. 

For the battery charger unit, Thales provided test reports which show that there is no actual battery used in testing the charger--a battery simulator, 3kW low impedance resistor, is used instead. 

Boeing, Thales and Yuasa all claim that over-charging was not involved in the battery fire because they have 4 BMU's providing multiple layers of redundancy against over-charging, so it just never could have occurred. Even though the fault tree in the safety assessment report indicates over-charging is the only way to cause venting with fire. But with a 4 layer BMU the probability of occurrence was deemed improbable over the life of the fleet with only 1 chance in 10 billion flight hours...How can anyone argue with such brilliant logic? Yet it happened twice, and one plane only had 150 flight hours.


----------



## kennybobby (Aug 10, 2012)

The NTSB has released a final report on this incident, here is an excerpt:

The NTSB determines that the probable cause of this incident was an internal short circuit within a cell of the APU lithium-ion battery, which led to thermal runaway that cascaded to adjacent cells, resulting in the release of smoke and fire. The incident resulted from Boeing’s failure to incorporate design requirements to mitigate the most severe effects of an internal short circuit within an APU battery cell and the FAA’s failure to identify this design deficiency during the type design certification process. 


As a result of this investigation, the NTSB makes safety recommendations to the FAA, Boeing, and GS Yuasa. The NTSB previously issued safety recommendations to the FAA regarding (1) insufficient testing methods and guidance for addressing the safety risks of internal short circuits and thermal runaway and (2) the need for outside technical knowledge and expertise to help the FAA ensure the safe introduction of new technology into aircraft designs.


----------



## PhantomPholly (Aug 20, 2008)

Yeah, the NTSB isn't exactly rapid about making a determination - what is this, 3 years now?


----------



## Karter2 (Nov 17, 2011)

"Probable cause" ..!!
That doesn't exactly sound like they actually know what the root cause was.
It is no more reassuring than Boeings multilevel BMU was in preventing the original failure .


----------



## Karter2 (Nov 17, 2011)

PhantomPholly said:


> Yeah, the NTSB isn't exactly rapid about making a determination - what is this, 3 years now?


January 2013.......


----------



## pdove (Jan 9, 2012)

*Re: Charging Requirements*



kennybobby said:


> The NTSB has released a final report on this incident, here is an excerpt:
> 
> The NTSB determines that the probable cause of this incident was an internal short circuit within a cell of the APU lithium-ion battery, which led to thermal runaway that cascaded to adjacent cells, resulting in the release of smoke and fire. The incident resulted from Boeing’s failure to incorporate design requirements to mitigate the most severe effects of an internal short circuit within an APU battery cell and the FAA’s failure to identify this design deficiency during the type design certification process.



That is not a cause that is a result. What caused the Short???


----------



## lithiumlogic (Aug 24, 2011)

Is the battery prevented from charging at temperatures below zero?

Example, aircraft is parked somewhere cold overnight. Crew start the APU ... electrical power from the APU becomes available to charge the battery almost immediately, but it'll be some time before the cold soaked cabin gets above zero.


----------



## Karter2 (Nov 17, 2011)

Whilst i am not impressed with the NTSB's conclusions, they have had 20 months with full access to evidence , expert resources, manufacturers data , etc etc....
..so to throw out a wild guess, like low temp charging, is a pretty optimistic stab at a potential cause !
If that wasnt covered off and eliminated in the first days of investigation, then the NTSB should be disbanded. !!
..together with all the experts involved in designing the battery system !! 
The conclusion that the "probable cause" was an internal short, seems odd if YUASA,s claim never to have had any previous evidence of such occurring in 14,000 operational units is true.
Unless the NTSB have seen other cells of this make , with positive evidence of I'S' to suggest a causal link, then a "possible" cause maybe, but _probable_ ?


----------



## EVfun (Mar 14, 2010)

*Re: Charging Requirements*



pdove said:


> That is not a cause that is a result. What caused the Short???


Contamination in the manufacturing process is considered to be the cause. The clean room environment for building these batteries is important because very small contamination can be a problem since low ESR cells are comprised of many thin layers.


----------



## Karter2 (Nov 17, 2011)

*Re: Charging Requirements*



EVfun said:


> Contamination in the manufacturing process is considered to be the cause..


 But , unless they have confirmed evidence of such contamination,...
...its only a "possibility"


----------



## JRP3 (Mar 7, 2008)

Plus this was not an isolated incident, there have been other Dreamliner battery failures that resulted in swollen cells but didn't necessarily cause a fire. Unless Yuasa had a chronic manufacturing defect in these cells I'm still inclined to think it has more to do with this particular application and associated parameters. Repeated over charging and/or charging below freezing are still likely candidates. I don't think they reached the root cause at all.


----------



## pdove (Jan 9, 2012)

JRP3 said:


> repeated over charging and/or charging below freezing are still likely candidates. I don't think they reached the root cause at all.


If you look at the design the root cause was obvious. The voltage was held at 32 volts on eight cells the whole time the APU is running. So the batteries were charging. Boeing denied that they over charged the batteries because they claimed 4 volts was nominal voltage.


----------



## Karter2 (Nov 17, 2011)

pdove said:


> If you look at the design the root cause was obvious. The voltage was held at 32 volts on eight cells the whole time the APU is running. So the batteries were charging. Boeing denied that they over charged the batteries because they claimed 4 volts was nominal voltage.


 Well, 4 volts is well within the operation range of those cells, so its only going to be "Charging" if there is something drawing the pack voltage down below 32 volts .
If the charge circuit is worth anything at all, it will be well into CV mode- (current limiting down to a fraction of an amp) - at that voltage.

And i doubt the NTSB just took Boeing's word for the correct charging protocol, ..they have other expert sources to cross check these things ( i hope !) .. not least the cell Manufacturer, and the charger suppliers.


----------



## Coulomb (Apr 22, 2009)

Karter2 said:


> Well, 4 volts is well within the operation range of those cells, so its only going to be "Charging" if there is something drawing the pack voltage down below 32 volts .


Huh? Let's say 3.60 V is the equivalent on LiFePO4 to these LiCo cells. 3.60 V is "within the operation range" of LiFePO4, but if you leave them at 3.60 V continuously, you *will* overcharge them, they will at least bloat, and worse things could happen. I can imagine LiCo going into thermal runaway.

Disclaimer: I don't know much at all about the LiCo chemistry, so I could be way off base there. So this is mostly by analogy to LiFePO4, which I know better (but I'll admit I'm not an expert there either).

You can't "float" LiFePO4 above a certain voltage, from memory it's around 3.40 V. It could well be that 4.0 V is above the "float voltage" of LiCo. Or maybe there isn't a safe float voltage at all.

Edit: on second reading, I may have misunderstood your post. But leaving the cells at 4.0 V is surely bad.


----------



## PStechPaul (May 1, 2012)

I'm not sure that there was an adequate individual cell BMS on that pack. It's been a while since I waded through the official (and non-official) data, but I recall some speculation about that. It's possible that one cell may have become weak and leaky or even partially shorted, which may not have been properly identified and addressed. If the charger monitored the pack voltage with the assumption of 8 cells at 4.0V each for 32 volts, but one cell was low, the 7 good cells would see 4.57 volts which is considerably beyond the safe level. In that case, some of the adjoining cells might have swelled and put pressure on others, or even created a conductive path to the cell which was identified as the source of the fire, and the stored energy and high temperature may have contributed to the runaway failure condition.


----------



## EVfun (Mar 14, 2010)

LiCoO2 batteries have a full charging voltage of 4.15 to 4.20 volts, and a nominal voltage of 3.60 volts. The LiFePO4 batteries we often use in conversions have a full charging voltage of 3.60 to 3.65 volts, and a nominal voltage of 3.20 volts. 

All Lithium batteries seem to last longer if undercharged, but there is more available capacity sacrificed when undercharging LiCoO2 cells, compared to LiFePO4 cells. 

The information publicly released today also speaks of changer to the charging routine and changes in battery box design so that one cell going into thermal runaway won't cause adjacent cells to go into thermal runaway. LiCoO2 cells are more prone to thermal runaway and need to be charged closer to the voltage limit of the electrolyte.

Here is a link to a Reuters article about the findings.


----------



## PStechPaul (May 1, 2012)

I wonder how much the increased protective packaging and safe venting hardware, and other safeguards, adds to the total weight, compared to a battery pack of similar capacity but with greater intrinsic safety, such as perhaps NiMH or NiZn, or even LiFePO4?


----------



## pdove (Jan 9, 2012)

EVfun said:


> LiCoO2 batteries have a full charging voltage of 4.15 to 4.20 volts, and a nominal voltage of 3.60 volts.
> 
> Here is a link to a Reuters article about the findings.


It is a starter battery. It starts the APU. How much energy could that take? 10% of the capacity maybe. Then the APU runs for hours with voltage on the bTtery. Unless they lowered that system voltage we will see more fires.

You can not continue to charge a full lithium battery without damaging it and 4 volts will cause charging. Nominal on those cells is 3.7 volts. Cutoff voltage on charging is 4,2 not the resting voltage.


----------



## Karter2 (Nov 17, 2011)

pdove said:


> It is a starter battery. It starts the APU. How much energy could that take? 10% of the capacity maybe. Then the APU runs for hours with voltage on the bTtery. Unless they lowered that system voltage we will see more fires.
> 
> You can not continue to charge a full lithium battery without damaging it and 4 volts will cause charging. Nominal on those cells is 3.7 volts. Cutoff voltage on charging is 4,2 not the resting voltage.


The way you put it implies there is no control of the charge system at all !
Do you actually believe that is the case ?
And do you not think the NTSB investigation might have picked up on that also ?
Even the most basic $10 Chinese LiPo chargers have profiled CC/CV charge control .


----------



## pdove (Jan 9, 2012)

I was not referring to the charger. I could be wrong but when I looked at the design the battery was always. Injected to the bus. The APU generates the :2 volts to power the airplane and thus is inadvertantly charging the pack as well.


----------



## JRP3 (Mar 7, 2008)

Yes, unless the generator is completely disconnected from the pack after hitting 4V then it's constantly being overcharged, and if it's constantly being held at 4V then it's being held at an excessively high SOC for a long time as well. Let's face it, Tesla managed 6831 cells in each Tesla Roadster without thermal runaway issues.

The ridiculous part is the LiCo cells that were used were of a similar energy density as current LiFePO4 cells. Any one of us could put together a pack of CALB's that would be safer than this setup, and without the giant sarcophagus they ended up putting around it would have better energy density. Part of the problem is the design parameters were locked in place many years ago and ignored lithium ion battery advances.


----------



## Coulomb (Apr 22, 2009)

Karter2 said:


> The way you put it implies there is no control of the charge system at all !


It it is indeed staying at 4.0 VPC for long periods of time, like when the APU is running, then yes, that's exactly what it sounds like. Maybe it cuts back from 4.2 VPC to 4.0 VPC, but that's not enough.



> Even the most basic $10 Chinese LiPo chargers have profiled CC/CV charge control .


Yes, but the situation here is different, I think. It seems to me that the battery stays online, powering loads and/or smoothing the output of the APU. I don't think it's purely a starter battery. So that means it can't be like the Chinese LiPo chargers and switch off after charge is "complete"; it seems to need to replenish charge taken continuously out of the battery. So it's either always charging, or is alternating between charging and a kind of floating mode, like the MPPT charger on a battery solar electric system. My apologies if I've gotten this screwed up.


----------



## JRP3 (Mar 7, 2008)

*Re: NTSB hearing on this incident is today and tomorrow*

As previously posted in this thread:



kennybobby said:


> In addition I wanted to point out that same FDR current data also shows that the APU battery was constantly being overcharged by trickle-charging at 1 to 2 amps during the 14 minutes between Last Engine Shut Down and the APU Shuts Down.
> 
> The Securaplane battery charging patent #5,780,994 is based upon a Ni-Cd battery charging profile and assumes a trickle-charging phase of indefinite length following the fast-charge phase.
> 
> ...


----------



## PhantomPholly (Aug 20, 2008)

Karter2 said:


> January 2013.......


Oh, "only" 2 years...


----------



## PhantomPholly (Aug 20, 2008)

JRP3 said:


> The ridiculous part is the LiCo cells that were used were of a similar energy density as current LiFePO4 cells. Any one of us could put together a pack of CALB's that would be safer than this setup, and without the giant sarcophagus they ended up putting around it would have better energy density.


The root problem here is getting approval from the FAA. We pilots are still stuck with 1940's technology because the cost to get FAA approval for something as ordinary (at least today) as electronic ignition can be millions of dollars.

Example: ElectroAir has been making electronic ignition kits to replace 1940's Magneto technology in Experimental aircraft for over a decade for about $2k. There are other vendors in the Experimental world doing the same, and pricing is similar. The kits typically let you replace expensive aircraft spark plugs with automotive plugs having a much hotter spark and providing between 5-10% improvement in power (or in fuel economy at a given power setting). That much improvement is like having a turbocharger giving you a "free" boost equivalent to flying 2-3k' lower, and for many planes can make the difference between going over or going around.

The exact same kit with an FAA STC is about double the cost.

At $5 / gallon for AvGas, 10% can pay for itself over some period of time. However, most pilots will never buy the upgrade because the payback period is almost forever in aircraft terms.

You can take it to the bank that any approval process for the Airlines is 10x, 100x, or even 1000x more expensive than for light aircraft.

So for all you lovers of Big Government - this is what you get. Stupidity by Political committee instead of technology by technologists.


----------



## Karter2 (Nov 17, 2011)

Sorry, but I find it impossible that Boeing/YUASA/ etc etc.... Would spend so much resource and effort to convert to a newer battery type, with a custom charge/BMS etc ....and yet retain a NiCad charge profile !
That would be a fok up of ridiculous magnitude !
IF... This constant "overcharging" / use of a incorrect charge protocol.....is in fact the case ..( hard to believe such a basic mistake).. Then why is it not mentioned as a "probable cause" in the NTSB report.
IF correct, it would seem to be a much more likely failure mode than blindly pointing the finger at a "probable". Internal short !
IF.. The NTSB missed that minor fact they are a waste of space also !


----------



## Hollie Maea (Dec 9, 2009)

Karter2 said:


> If the charge circuit is worth anything at all, it will be well into CV mode- (current limiting down to a fraction of an amp) - at that voltage.


It is the batteries themselves that determine current in CV mode.


----------



## Hollie Maea (Dec 9, 2009)

PhantomPholly said:


> So for all you lovers of Big Government - this is what you get. Stupidity by Political committee instead of technology by technologists.


Save it for the Atlas Shrugged thread, dude.


----------



## Karter2 (Nov 17, 2011)

Hollie Maea said:


> It is the batteries themselves that determine current in CV mode.


Agreed, but the effect is that the current will reduce to millamps as the cell voltage nears the charge voltage where it will be shut off ....on any sensible LiPo charger !


----------



## PStechPaul (May 1, 2012)

The situation might be similar to that in a vehicle where the batteries could be charged either from an external charging source, or through regeneration. Some means must be in place to maintain the batteries in a state perhaps 10-20% less than full charge so that they might accept regenerative energy. But the BMS and charging and controller circuitry should also be able to dissipate the excess energy rather than overcharge the batteries. Perhaps some hysteresis should be built in so that the charge alternates between 80% and 90% SOC rather than dancing around a certain point.


----------



## Karter2 (Nov 17, 2011)

There is much speculation about what may or may not be happening with regards to charging, BMS , etc. But how much hard information is actually available ?
If these are modern control systems, they are likely to be firmware/ software operated and as such easy to change in many respects ?
Do we know these details, ( ie actual program logs) ,...or are we just guessing ?


----------



## PhantomPholly (Aug 20, 2008)

Karter2 said:


> Sorry, but I find it impossible that Boeing/YUASA/ etc etc.... Would spend so much resource and effort to convert to a newer battery type, with a custom charge/BMS etc ....and yet retain a NiCad charge profile !
> That would be a fok up of ridiculous magnitude !
> IF... This constant "overcharging" / use of a incorrect charge protocol.....is in fact the case ..( hard to believe such a basic mistake).. Then why is it not mentioned as a "probable cause" in the NTSB report.
> IF correct, it would seem to be a much more likely failure mode than blindly pointing the finger at a "probable". Internal short !
> IF.. The NTSB missed that minor fact they are a waste of space also !


Welcome to the Libertarian Party!


----------



## PhantomPholly (Aug 20, 2008)

Hollie Maea said:


> Save it for the Atlas Shrugged thread, dude.


Really - stating the obvious is now politically incorrect? 

Get over it.


----------



## kennybobby (Aug 10, 2012)

There is documentation such as the contract specifications and acceptance data packages available at the NTSB docket site and i have spent a few hours reviewing it. Some of this was identified in an earlier post, http://www.diyelectriccar.com/forums/showpost.php?p=351224&postcount=91

Look at that contract requirement that a fully charged battery must tolerate being held at a constant voltage...xxx Volts without failure. We don't have access to the 'xxx' because it was redacted, but someone at the NTSB has access and knows.

So in this case a company (Boeing) writes a contract spec for a battery that defies the laws of chemistry; the contractor (Thales) is not going to tell them they can't do it; the subcontractor (Yuasa) is not going to tell them they can't do it--They are going to try their best to build a battery to meet the spec and pass the acceptance test. 

Boeing can write a contract spec for a charger with a trickle-charge mode to keep the battery topped up at 100% all the time; the contractor (Securaplane) is going to do their best to build a charger that meets the spec and passes the acceptance test. 

Back in 2006 when the charger and battery were first tested together, the battery caught fire and burned the Securaplane facility to the ground. And for acceptance testing of the chargers now they don't use a real battery, but a battery simulator. This is all found in the details of the documentation.

It sure seems from the evidence in the data that they were overcharged because the APU and Main batteries are held at 32 V all the time while in flight (i.e. trickle-charge mode). As a result cells were overcharged and the subsequent swelling that occurs from overcharge caused the internal short (layer separation, current collector breakage, etc.) This swelling can be seen in the xray images on the 'good' battery packs, also found in the documentation.

So the NTSB final report says the battery wasn't overcharged, but the only evidence that they weren't overcharged is that Boeing said so, because there is a contract spec and the battery passed the acceptance test...Here is part of Boeing's statement:
In 2005, the FAA determined that special conditions would be necessary to address the use of lithium ion batteries on the 787. Later that year, Boeing proposed a high-level summary of how it would show compliance with those special conditions. 
Throughout development and certification, the battery was subject to roughly 40,000 hours of testing, including 5,000 hours of dedicated battery testing, 10,000 hours of airplane ground and flight testing, and 25,000 hours of integrated power system testing. The development process for the battery system was conducted by technical experts in accordance with standard industry practices. During all developmental endurance testing, which included testing at low temperatures, and cold weather flight testing, no internal short circuits were observed. 
During development and certification, it was concluded based on testing and GS Yuasa’s experience that an overcharge was the only failure that could result in fire; as a result, the battery had multiple redundant protections against overcharging. 



...

• The root cause investigation 
The evidence from the investigation has conclusively ruled out certain potential causes. It can be said with confidence that the cause was not an external short circuit, overcharge, over- discharge, or external heating. 
The most likely cause was an internal short circuit. Because of thermal damage during the event, the precise root cause of the internal short circuit cannot be determined. Mechanical abuse of the cell, however, can be ruled out as a possible cause of the internal short circuit. The three remaining potential causes for an internal short circuit are: 
o foreign objects in the cell;
o failure of internal separator film between cell electrodes; o redeposition of conductive materials within the cell.


----------



## kennybobby (Aug 10, 2012)

How Boeing defines overcharge:

Overcharge – A battery cell is overcharged when the total energy input during charging exceeds the storage capacity of the cell resulting in voltage between its terminals above its maximum design limit. 

Overcharging a cell may result in irreversible damage and cell venting. A battery composed of multiple cells requires monitoring of each cell voltage and the battery voltage to ensure overcharging does not occur for any cell. 

Aircraft recorded data confirms the battery voltage did not exceed its upper design limit prior to and during the event.43 

Because an overcharge would result in a catastrophic failure, the battery and charger system was designed with four layers of protection against the possibility of an overcharge. The first layer monitors the individual cell voltages and stops the BCU from charging when any cell voltage exceeds a set point. The second layer independently monitors cell voltages and stops the BCU from charging at a slightly higher set point. The third layer monitors the battery voltage and stops the BCU from charging once it exceeds a set point. The fourth layer will stop the BCU from charging by shutting off the input to the BCU at a slightly higher battery voltage set point.44 Should any of these protections be activated, an electronic error signal will be sent to the BMU which is subsequently recorded by the aircraft’s recording system. 45 

There was no evidence these protections were activated—the recorded battery voltage was below its upper design limit throughout the event and no associated error messages were recorded.46 Thus, overcharge can be ruled out.

43 NTSB Interim Factual report, March 7, 2013, page 11.
44 NTSB Airworthiness Group Chairman Factual Report, 5 March 2013, page 32.
45 NTSB Airworthiness Group Chairman Factual Report, 5 March 2013, pages 32-36.
46 NTSB Flight Data Recorder Group Chairman’s Factual Report, 25 February 2013, pages 4-5, 8.


----------



## aeroscott (Jan 5, 2008)

32 volts RMS would be higher then 32 volts . I wonder how much higher?
I'm going to call Midnight and ask how high my solar charger is spiking the lithium pack passed the 4.1/ cell I am set at.


----------



## dcb (Dec 5, 2009)

@kennybobby, nice work. I hope the NTSA will be appraised of your research. It sounds much more plausible than random internal short.

These things should never be trickle charged as far as I know. Was there any battery thermal data during the event that you know of?


----------



## PhantomPholly (Aug 20, 2008)

KennyBobby, excellent synopsis. Thanks for posting.


----------



## aeroscott (Jan 5, 2008)

Just called Midnight Solar and talked to teck . My question was too advanced for their understanding so advanced teck will get back to me this afternoon . 
Teck did say a bms was important. I don't see how bms is going to solve 
a voltage spike that causes a dendrite / plating caused by a micro voltage spike.
As for trickle charging , it would seem that by definition it would be a over voltage condition if the battery is fully charged to start with.


----------



## aeroscott (Jan 5, 2008)

Just got called into work.


----------



## Karter2 (Nov 17, 2011)

kennybobby said:


> )
> 
> It sure seems from the evidence in the data that they were overcharged because the APU and Main batteries are held at 32 V all the time while in flight (i.e. trickle-charge mode). As a result cells were overcharged and the subsequent swelling that occurs from overcharge caused the internal short (layer separation, current collector breakage, etc.) This swelling can be seen in the xray images on the 'good' battery packs, also found in the documentation.


.accepting that I have not read all the background papers,...
I fully agree that the NTSB report appears to have overlooked some serious potential issues,..
..... But being open about the facts...

32v (4v per cell) , is NOT overcharged for LiPo chemistry .
I'm unclear if ..."Trickle-charge mode" ....is your interpretation, or as described in the report or by Boeing/Thales ?
I ask because there is a big difference between constant "trickle charge" and " holding" at a set voltage with voltage control/ monitoring.
What evidence is there for LiPo cells "held" at 4v swelling ?

Where did any mention of "RMS" voltage appear ?. Did I miss it ?


----------



## aeroscott (Jan 5, 2008)

I talked to teck from Midnight yesterday and he said the Clasic charge controller is not pwm but mppt. Some charge controllers are pwm and would have a spike relating to rms, but how much?
I came up with the RMS not the report. I am speculating on reasons for unintentional over charging.
Trickle charging is a common nicad battery killer in the form of wall warts (and my be aero nicad systems) 
ie: dumb charger just putting small amount of over voltage into battery with no regulation .


----------



## Karter2 (Nov 17, 2011)

I understand what trickle charging is, and it's potential effect on LiPo cells.
I just wanted to know if that charge method had been confirmed by Boeing, Thales, or just a term introduced in the debate by one of us ?
It is possible to "hold" a cell at a nominal voltage (+_ 0.1v or less) without a constant trickle charge.


----------



## Coulomb (Apr 22, 2009)

Karter2 said:


> It is possible to "hold" a cell at a nominal voltage (+_ 0.1v or less) without a constant trickle charge.


I believe so. But whatever that voltage is for LiCo, 4.0 VPC seems too far past their nominal voltage (3.7 VPC) to be under that "safe float" limit.

This battery system would have been designed some ten years ago, I think, with the long design, test, and approval times. Not only was LiFePO4 not viable back then (OK, maybe to to industry it might have been), but experience with any kind of Lithium cells would have been rather limited. So it seems to me that a little "lead thinking" creeping in might not be as unthinkable as it would be today.


----------



## Karter2 (Nov 17, 2011)

Coulomb said:


> ?....
> This battery system would have been designed some ten years ago, I think, with the long design, test, and approval times. Not only was LiFePO4 not viable back then (OK, maybe to to industry it might have been), but experience with any kind of Lithium cells would have been rather limited. So it seems to me that a little "lead thinking" creeping in might not be as unthinkable as it would be today.


Commercial LiCo cells were available from the very early 1990's, non commercial ( military, aerospace industry etc) most likely well before that.
There is a lot of experience using these cells in a "backup" mode or just keeping them charged at/near max voltage.
How many millions of laptops are there that sit with their chargers permanently connected ?
I cannot believe that Boeing/Thales/YUASA were not aware of that kind of experience !


----------



## PStechPaul (May 1, 2012)

Lawyers, CEOs, spin doctors, and the media may be engaging in a game of CYA and sensationalism, and the truth, as might be revealed by scientists and engineers, be damned.


----------



## pdove (Jan 9, 2012)

Coulomb said:


> I believe so. But whatever that voltage is for LiCo, 4.0 VPC seems too far past their nominal voltage (3.7 VPC) to be under that "safe float" limit.
> 
> This battery system would have been designed some ten years ago, I think, with the long design, test, and approval times. Not only was LiFePO4 not viable back then (OK, maybe to to industry it might have been), but experience with any kind of Lithium cells would have been rather limited. So it seems to me that a little "lead thinking" creeping in might not be as unthinkable as it would be today.


They could have done it with LiFePO4 batteries and no BMS at all. It's a starter battery. Charge it to 80% after each start of the APU and then disconnect it from the system. None of what they did made sense to me.


----------



## kennybobby (Aug 10, 2012)

This is from Yuasa's datasheet for the LVP 65 found on their website, nominal voltage 3.7, rated capacity 65 Ahr, nominal capacity 75 Ahr (?). Picture of some discharge curves tested, the charging was CC/CV at 70 A/ 4.025 V, details in bottom left corner of picture.

The NTSB docket has a report submitted by Thales of their testing and root cause investigation. Their root cause seems to be internal short due to high frequency (~1 MHz) noise (1.5 mV) causing cell over-voltage (~4.5V) due to resonant amplification (30 dB) from ground strap inductance and cell-to-case capacitance.

One interesting finding by Thales is they made decompression tests for a 6000 ft altitude simulation and found (surprise!) that the cell cases (0.031" stainless steel) would swell and puff out up to 3 mm, about an 1/8th of an inch.

And the CT xray images by the NTSB of undamaged battery packs showed separation of the foil layers in every cell of 4 battery packs they scanned.

Thales also reported finding various voltages present between the cell case and the cell terminals--so it's like some of the foil layers are touching the inside of the cell case to where it is no longer isolated from the terminals...

Sounds like internal shorting has a couple of contributing factors: either overcharging puffing out a cell and letting the foils contact internally, or altitude decompression puffing out a cell and letting foils contact. 

All of the cells examined have shown some separation of internal foil layers.

Yuasa reported they have never had an internal shorting event in over 14,000 of these cells built and used in industrial applications-- so what is different in this case? Either decompression swelling or overcharge swelling causing separation of layers which allows for internal contact and shorting is my guess.


----------



## aeroscott (Jan 5, 2008)

I have some !/2" and 5/8" ss tubing at .030" wall. What was the cell size?
A 9" dia. water fire extinguisher , 2 1/2 gallon about .030" can take 100psi.
Or could they be box shaped?


----------



## aeroscott (Jan 5, 2008)

Could that 1Mhz be the pwm cycles.


----------



## Coulomb (Apr 22, 2009)

Karter2 said:


> How many millions of laptops are there that sit with their chargers permanently connected ?


Excellent points. I concede that my thoughts were not well considered.

I will however point out that laptop batteries are continually cut short in life by leaving the cells at very high states of charge a lot of the time. It would be much better for longevity if the cells were kept at more like say 75% SOC, and you had to press a button to go to 100%, if you knew you needed a long session. But of course that's less convenient, and a little more expensive, so they don't do it.


----------



## Coulomb (Apr 22, 2009)

aeroscott said:


> Could that 1Mhz be the pwm cycles.


Not directly, no. 300 kHz is considered the bleeding edge right now, and only the latest wide bandgap devices can achieve it. But PWM pulses are sharp, so they have many harmonics. So it's possible that say the 15th harmonic or so of a roughly 8 kHz switching frequency (wild guess) could possibly have triggered the resonant circuit. But it seems unlikely to me. Aircraft would have other sources of radio frequency energy, but 1 MHz (right in the middle of the AM radio band) seems unlikely, at least from communications equipment, and also I would expect electromagnetic interference to be strictly controlled in aircraft.


----------



## pdove (Jan 9, 2012)

kennybobby said:


> One interesting finding by Thales is they made decompression tests for a 6000 ft altitude simulation and found (surprise!) that the cell cases (0.031" stainless steel) would swell and puff out up to 3 mm, about an 1/8th of an inch.
> 
> And the CT xray images by the NTSB of undamaged battery packs showed separation of the foil layers in every cell of 4 battery packs they scanned.
> 
> ...


Looks like you were right Kenny. It's interesting that they tested this. Good find!


----------



## JRP3 (Mar 7, 2008)

Coulomb said:


> I will however point out that laptop batteries are continually cut short in life by leaving the cells at very high states of charge a lot of the time.


Exactly, the cells are damaged by being kept at this high SOC. The difference is laptop cells are never asked to put out high C rates, the way starting batteries are. By the way some laptops do allow setting charge levels.


----------



## Karter2 (Nov 17, 2011)

JRP3 said:


> Exactly, *the cells are damaged by being kept at this high SOC. * The difference is laptop cells are never asked to put out high C rates, the way starting batteries are. By the way some laptops do allow setting charge levels.


Do you have any data or references to support that statement ? 
...or is it just another convenient assumption ?
I might suggest that laptop packs have a much harder life than starter packs (that usually only cycle <5% of their capacity ) 
Laptops are frequently cycled to full discharge (BMS limited hopefully ) and fully recharged at max rate, often on a daily basis, and if you have ever felt the pack temperature of your Laptop or Ipad etc, you will know that they spend most of their working life at 50+ degC !
18650 cells generally have a cycle life rating of a few hundred cycles, so it doesn't take many months to reach that limit for a weak cell.
Most of the Laptop packs I have dismantled (many!). have a single cell failure, for non apparent reasons.... But the remaining cells function normally for many more months. I might expect high SOC damage to affect most of the cells, rather than just an individual one.


----------



## Karter2 (Nov 17, 2011)

kennybobby said:


> One interesting finding by Thales is they made decompression tests for a 6000 ft altitude simulation and found (surprise!) that the cell cases (0.031" stainless steel) would swell and puff out up to 3 mm, about an 1/8th of an inch.
> 
> And the CT xray images by the NTSB of undamaged battery packs showed separation of the foil layers in every cell of 4 battery packs they scanned.
> 
> ...


This certainly appears to be a potential explanation for internal cell failure with plenty of actual evidence to verify the theory.
....so I wonder why the NTSB report focused on the "possibility" of internal contamination...... Which was a theory with no hard evidence to support it !
.....other than the fact that it shifts the blame to the cell manufacturer, and away from the "user" or systems designer who decided on the application !


----------



## JRP3 (Mar 7, 2008)

It's no secret that laptop packs die prematurely, so I'm not sure how it's a convenient assumption. My last laptop lost almost all battery capacity after less than 3 years and 99% of the time it was plugged in and never deeply cycled, until capacity dropped to such levels it wouldn't hold for even 15 minutes. It's also well known that keeping cells at a higher SOC shortens their cycle life, which is why no OEM EV builder allows a cell to get to 100% full. Tesla also recommends timing charge to end just before you drive the vehicle, further limiting time spent at high SOC.

Sure laptops can get warm, but usually the battery pack is not near the processor. The pack on this laptop right now is cool to the touch, but the center of the laptop is warm. On the many laptop packs you have taken apart, did you do a capacity tests on the remaining "good" cells, and if so how close were they to new capacity?


----------



## Karter2 (Nov 17, 2011)

3 years seems a fair run for a pack used daily!
Your "convenient assumption" was not that they died prematurely, but that they failed due to being held at a high SOC. ,!
Laptop packs are commonly 3s, 2p or 4s, 2p, strings with internal BMS?
2.2 , 2.4, and 2.6 Ahr cells are most common.
Salvaged "good" cells generally show capacities in line with those values also
I'm sure you realise that you only need to lose one cell in a series string, for the whole pack to appear to have lost capacity (voltage or watt monitored).
Unless you strip the pack and test individual cells, it's hard to know exactly the state of play, but my suspicion is the cells go out of balance (cheap/weak BMS )
And eventually one cell(or pair) goes low voltage and holds the pack down.
I suspect that laptop manufacturers view battery,s as a potential source of future income, and don't put their best efforts into ensuring a long life span !
They can take $20 worth of cells, add $5 of case and circuitry, then sell it to consumers for $100+ ...... Several times for one single laptop !


----------



## JRP3 (Mar 7, 2008)

I"ll agree that laptop cell behavior is not the best indicator of cell performance in general. Some people have claimed they took apart "bad" laptop packs and all cells were in good shape with good capacity, but the firmware or software was limiting capacity in the laptop.


----------



## Karter2 (Nov 17, 2011)

We went a bit off track with the laptop packs, 
...but I believe they are an example that LiCo ( ET al) can be " held" at high SOC without dramatic consequences.


----------



## Coulomb (Apr 22, 2009)

Karter2 said:


> ...but I believe they are an example that LiCo ( ET al) can be " held" at high SOC without dramatic consequences.


Agreed. But note that high SOC isn't the same as "considerably higher than nominal voltage". This is likely to take a cell well above 100% SOC eventually.


----------



## pdove (Jan 9, 2012)

JRP3 said:


> I"ll agree that laptop cell behavior is not the best indicator of cell performance in general. Some people have claimed they took apart "bad" laptop packs and all cells were in good shape with good capacity, but the firmware or software was limiting capacity in the laptop.


That is fact I took apart many packs and only found one or two bad cells out of the whole lot. it is better than before because laptop batteries used to swell and burn now at least they cut off the charging. They used to believe you could trikle charge these batteries by holding the voltage up with very little current flow. Why do you think they were burning up. This is an excellent example as to what happens when you do.


----------



## dougingraham (Jul 26, 2011)

Coulomb said:


> Agreed. But note that high SOC isn't the same as "considerably higher than nominal voltage". This is likely to take a cell well above 100% SOC eventually.


LiCo cells can be held at 4.2 volts pretty much forever. The nominal voltage of 3.7 volts is about the middle of the typical operating range. Fully charged at 4.2 and empty at 3.2 volts. They are not stiff cells like LiFe.

The manufacturers use a charge algorithm to let you know when you can stop charging which is similar to that given for LiFe cells. CC to 4.2 and CV until the current reaches C/20. If you hold it at 4.2 you get a little more capacity but the charge rate is so low that it takes a long time to see anything. If you let them CV at 4.2 volts for several days and then rest them the voltage will rest down very little. One problem with going to 4.2 volts is if you have an imbalance and a cell goes over 4.35 volts you will see a breakdown in the electrolyte and in the case of pouch cells they will puff up. This is only 0.15 volts and would be an instrumentation error of 3.6%.

It is still considered a good idea to stay away from the endpoints as that seems to be where the cell damage most occurs. But it is not in and of itself harmful to hold this cell type at 4.2 volts. And at 32 volts for 8 cells this would be holding the cells at 4 volts which I would consider conservative for a full charge voltage. Around 80% of full charge.


----------



## JRP3 (Mar 7, 2008)

Tesla would disagree about charging to and holding at 4.2V.


----------



## pdove (Jan 9, 2012)

dougingraham said:


> LiCo cells can be held at 4.2 volts pretty much forever. The nominal voltage of 3.7 volts is about the middle of the typical operating range. Fully charged at 4.2 and empty at 3.2 volts. They are not stiff cells like LiFe.
> 
> The manufacturers use a charge algorithm to let you know when you can stop charging which is similar to that given for LiFe cells. CC to 4.2 and CV until the current reaches C/20. If you hold it at 4.2 you get a little more capacity but the charge rate is so low that it takes a long time to see anything. If you let them CV at 4.2 volts for several days and then rest them the voltage will rest down very little. One problem with going to 4.2 volts is if you have an imbalance and a cell goes over 4.35 volts you will see a breakdown in the electrolyte and in the case of pouch cells they will puff up. This is only 0.15 volts and would be an instrumentation error of 3.6%.
> 
> It is still considered a good idea to stay away from the endpoints as that seems to be where the cell damage most occurs. But it is not in and of itself harmful to hold this cell type at 4.2 volts. And at 32 volts for 8 cells this would be holding the cells at 4 volts which I would consider conservative for a full charge voltage. Around 80% of full charge.


Not sure where you heard that but it is incorrect. Cell damage has been proved to occur at voltages above 3.7 volts. The goal for longevity would be to have a balance between maximum capacity and time above 3.7 volts.

I will find the paper where this was proven and post it later today


----------



## kennybobby (Aug 10, 2012)

Notice in the datasheet that the LVP 65 is a slightly different chemistry and that the CV charge voltage is only 4.025--just 25 mv above the airliner hold voltage and no where close to the 4.2 LiPO cells. 

What is the resting OCV of a LiPO after CC/CV at 4.2 anyway--has anyone actually measured that voltage?

The nominal LVP 65 cell voltage is listed as 3.7 but one of the 4 BMU's was designed to latch the battery open-circuit and require factory reset if one of the cells went below 3.89 Volts.

Why did they have 4 BMU systems? And how could such an over-engineered battery with so much redundancy and monitoring features catch on fire? It appears that they kept patching or adding on a BMU or a contactor everytime they had a fire (known to be at least 2 fire incidents during development). Keep modifying the contract specs and requirements until the problems are eliminated is one approach to getting hardware built...


----------



## pdove (Jan 9, 2012)

pdove said:


> Not sure where you heard that but it is incorrect. Cell damage has been proved to occur at voltages above 3.7 volts. The goal for longevity would be to have a balance between maximum capacity and time above 3.7 volts.
> 
> I will find the paper where this was proven and post it later today


One of the main reasons for capacity fade in Li-ion cells is overcharging the cell. Li-ion batteries operate safely within their normal operating voltage. However, they become increasingly unstable if charged to higher voltages. Above 4.3 V, Li metal deposits on the anode. In addition, the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging also causes the cell to heat up. According to Aurbach et al. [17], the onset of electrolyte oxidation in Li-ion cells may be as low as 3.7 V. This oxidation of the solution produces a sufficient concen- tration of Lewis acids, which interact with the active mass and lead to its partial dissolution.


----------



## dougingraham (Jul 26, 2011)

pdove said:


> Not sure where you heard that but it is incorrect. Cell damage has been proved to occur at voltages above 3.7 volts. The goal for longevity would be to have a balance between maximum capacity and time above 3.7 volts.
> 
> I will find the paper where this was proven and post it later today


I would like to read that paper.

It is the act of charging and discharging that partially causes the damage. For EV use you certainly don't want to overcharge. Charging and holding at 4.2 for months does not seem to have adverse effects on the cell. If I were using this kind of cell in my EV I would probably set the charge stop point at somewhere between 4.0 and 4.1 volts so as to undercharge somewhat. Tesla has a setting that stops the charge early and they only recommend you do a max charge when you really need to.

Laptops that use LiCo cells horribly mistreated their cells when plugged into a charger. They would charge to 4.2 and then turn off until the voltage dropped some and then charge back up cycling the cell constantly at the region where the most damage is done during charge. This was done to get the maximum run time (when new). They also like selling you batteries when they wear out.


----------



## Karter2 (Nov 17, 2011)

kennybobby said:


> Notice in the datasheet that the LVP 65 is a slightly different chemistry and that the CV charge voltage is only 4.025--just 25 mv above the airliner hold voltage and no where close to the 4.2 LiPO cells.
> 
> What is the resting OCV of a LiPO after CC/CV at 4.2 anyway--has anyone actually measured that voltage?
> ...


Kenny, 
I don't know , but that looks like any other LiPo discharge curve....just with the top 0.2 v missed off ! It's pretty obvious from the slope of the curve, that there is potentially more capacity available above 4.025v, we need to see a charge curve to be sure, but that cell has not stopped accepting charge..
....maybe they were just avoiding the "extremes" or even simulating the capacity available from the 4.0v charge that Boeing intended using. .?
Every LiPo and LiCo cell I have charged to 4.2 volts has "rested" or settled to stay very close to that (4.18-4.19v minimum) for days.


----------



## JRP3 (Mar 7, 2008)

> Most Li-ions are charged to 4.20V/cell and every reduction of 0.10V/cell is said to double cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.00V/cell should deliver 1,200–2,000 and 3.90V/cell 2,400–4,000 cycles.


http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


----------



## Karter2 (Nov 17, 2011)

Cycle life is useful and interesting and important in some applications..
..but it very different to catastrophic cell failure from thermal runaway!

PS , is anyone else having problems accessing the PDF of the YUASA LPV 65 cell ?.. none of the links i have will work currently ???
Kenny, which link are you using ?
www.gs*yuasa*-lp.com/SpecSheets/*LVP65*-MSDS.pdf
http://www.gsyuasa-lp.com/aviation-lithium-batteries
http://www.s399157097.onlinehome.us/...s/LVP10-65.pdf


----------



## pdove (Jan 9, 2012)

dougingraham said:


> I would like to read that paper.


I quoted it above. Not sure why the link didn't show in my post I'll try again.

http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/capacityfade_jpspaper2.pdf


----------



## Karter2 (Nov 17, 2011)

Really ! .. a 12 year old paper as a reference for current lipo technology ! ?


----------



## pdove (Jan 9, 2012)

Karter2 said:


> Really ! .. a 12 year old paper as a reference for current lipo technology ! ?


Time does not change fact.


----------



## JRP3 (Mar 7, 2008)

Karter2 said:


> Cycle life is useful and interesting and important in some applications..
> ..but it very different to catastrophic cell failure from thermal runaway!


It's clear evidence that higher voltage damages the cell. What might happen to a damaged cell called on to do high C rate engine cranking over and over again?


----------



## Karter2 (Nov 17, 2011)

It's clear evidence that higher charge voltages reduce cycle life (which is capacity reduction) ..that is known fact.
Beyond that you are just speculating.
What evidence do you have that it can lead to cell failure, thermal runaway, puffing, smoke, or any other catastrophic problem ?


----------



## Karter2 (Nov 17, 2011)

pdove said:


> Time does not change fact.


No , but it certainly allows for immense changes in cell chemistry, construction, and performance .


----------



## pdove (Jan 9, 2012)

Notice figure 1b and figure 5. The fully charger voltage of the cell is 3.82. Any voltage above that and you will get current flow. That is why they used 4, 4.05 etc. as charging voltages.


----------



## Karter2 (Nov 17, 2011)

Ok...
Even ignoring the fact that this is 12+ yr old cell chemistry,...
..what exactly do you think this is showing ?
Fig 3 clearly shows that whilst a higher charge voltage (4.17v) resulted in faster capacity loss (AKA. .cycle life) , it also shows that even with that capacity loss after 100 cycles, the 4.17v charge still gives DOUBLE the capacity of a 4.0v charge !
Also, keep in mind that cycle life test results reflect full charge/discharge cycles, which is not necessarily the kind of "short" cycling that back up or starter pack cells ever see.!
And I repeat ..reduced cycle life is not cell failure.
Further, if you research the NTSB report data on that LVP 65 cell, you will notice that is is actually a 75ahr cell that is de-rated to 65ahr to reflect its useable capacity after a stated number of charge cycles....
...IE , that cell was heavily over rated for it's intended use .


----------



## pdove (Jan 9, 2012)

Karter2 said:


> Ok...
> Even ignoring the fact that this is 12+ yr old cell chemistry,...
> ..what exactly do you think this is showing ?
> Fig 3 clearly shows that whilst a higher charge voltage (4.17v) resulted in faster capacity loss (AKA. .cycle life) , it also shows that even with that capacity loss after 100 cycles, the 4.17v charge still gives DOUBLE the capacity of a 4.0v charge !
> ...


I think it shows that any voltage over 3.82 will cause the cells to charge. If you hold them at 4 v they will draw current and eventually swell and perhaps short.


----------



## Karter2 (Nov 17, 2011)

A couple of key phrases there are.....


pdove said:


> I think ..."
> ........... and perhaps ....


 All you need is evidence and examples to support your thinking.
Of course if you keep supplying current into a cell, it will inevitably fail.
But in order to do that you have to apply a voltage above the cell voltage, which we know can be 4.1+ volts. So you would have to increase the charge voltage accordingly above 4.1 volts to continue charging.
That would not be considered to be holding 4.0 v

This all hinges on what we understand by "Hold at 4.0 v ". 
Some of us are assuming this means a "trickle" charge at constant applied voltage...
Others might assume it is referring to a "maintenance" charge mode that cycles the cell between some preset limits (EG, 3.95 and 4.05 v ?)
Do we actually know for certain ?


----------



## JRP3 (Mar 7, 2008)

Karter2 said:


> ...IE , that cell was heavily over rated for it's intended use .


It's intended use was for a starter battery, and LiCo is not known as a high C rate chemistry. Do we know what the cranking amps and duration were for this application?


----------



## Karter2 (Nov 17, 2011)

Maybe this will help us understand the BMU's and if the cells were "overcharged" or not ....
According to the NTSB Airworthiness Report on page 37:



> The contactor is identified as part number 104CZ02Y01 from the French company Zodiac Aerospace. It is a normally-closed solenoid with single-pole single-throw contacts and does not have a latching feature.
> ....the contactor is normally closed and was designed to open in the event of an overcharge situation.
> .
> 
> ...


----------



## Karter2 (Nov 17, 2011)

JRP3 said:


> It's intended use was for a starter battery, and LiCo is not known as a high C rate chemistry. Do we know what the cranking amps and duration were for this application?


 Just to be clear, there are two different packs involved..
The APU starter pack
and a totally separate Systems Back up pack
Same type and construction , but in diferent locations in the aircraft.
Both have suffered fiery failures !


----------



## Karter2 (Nov 17, 2011)

> Do we know what the cranking amps and duration were for this application?


 From another forum..


> *How much current does an APU on a 787 actually take to start?*
> The FAA noted this disparity (562A or more called for by Boeing vs. 375A maximum available from the Yuasa batteries).
> 
> They then noted that the APU on the incident aircraft actually used less power than the Boeing SCD called for, and that there were sudden changes in power consumption during the start sequence, but that testing was done with “resistive banks”.
> ...


 As with much of this issue, there is confusion over the specification of those YUASA cells, ( not helped now by their apparent loss of on line documents ??)
I believe from memory they were officially "10C" cells ( 650A ) rated, and there have even been comments quoted from YUASA stating 1000A pulse rating, but the test documents only show 250A discharge curves, and YUASA told the NTSB they were rated for 375A. ! ????
I suspect there was some confusion over the "continuous" and the "pulse"
ratings.
Also we know the pack was "protected " by a 400A contactor.


----------

