Link to the previous topic FAA Grounds 787 Part 6 (by NZ1 Jan 26 2013 in Civil Aviation)

Please continue the discussion here

"Commercial Airplanes' 2013 deliveries are expected to be between 635 and 645 airplanes, which includes greater than 60 787 deliveries."

I think McN is just hedging his bets accounting for a little slippage due to the battery issue. I see a much better number (quality not quantity wise) coming in 3 months when things should be sorted out (hopefully).

Quotes from previous thread . . . .

Quoting PITingres (Reply 245): That's exactly what the design does. How is that not clear

We have been going back and forth over this for a couple of iterations now. I think what is meant is not so much why the battery goes to brick/dead/over-discharged or whatever definitions have been used. The question is why the BMS does not have a double threshold?

Threshold 2, 15-20% capacity left (forgive me, I lost the actual percentage). This is the brick condition, or dead as some referred to. In this state, it is not considered "safe" to recharge it, and it should definately not be attempted on the plane. You will have to send it to a specialized repair facility for refurbishment/repair/recharge.

Threshold 1, say 20-20% capacity left. The BMS shuts down the battery and airframe systems in a controlled fashion to prevent it from reaching threshold 2, where the battery must be replaced and sent to a specialized repair facility. This way, you end up with slightly less battery capacity, but you remain with a serviceable battery; all it needs to re-charge the battery is an external power souce. No hassles, no need to replace a $16000 battery, and face an undoubtedly significant repair bill, not to mention any operational inconveniences as these things by nature don't happen in a scheduled fashion.



Elon Musk / Tesla
I find his words very interesting. Basically what he said (and this was stated earlier in this thread by someone else), is that those eight cells are way too big. Boeing (read, the battery supplier) should have used many more cells, with 8 small cells in series to get the required voltage, and many many parallel groups of eight cells to get the required capacity.

There are a couple of problems with these big cells:

1. Local Zoning
They are so big that under some conditions they no longer behave as a homogeneous cell, they start to behave as individual mini cells. In other words, local zones can develop characteristics of mini cells. The problem now is that these local zones are not monitored in detail. Those zones apparently can develop local low voltage/high discharge condition inside the cell, without being detected.
The BMS only monitors the big cell (all 8 of them of course), but can not see in detail what is going on inside each cell, it can not see the local zones.

Basically Musk says this is why Tesla uses hundreds of mini cells instead of Boeing's large super cells (well, actually eight of them). Each Tesla mini cell is monitored indepently. That allows for so much better monitoring in great detail and oversight over the battery condition.
Where the 787 BMS monitors eight cells, Tesla would monitor dozens, of not hundreds of small cells for the same overall capacity.

The Tesla mini cells are so small that it is physically almost impossible for them to have their own small local zones.

2. Heat dissipation
The Tesla mini cells are separated sufficiently to be able to dissipate heat, without seriously affecting adjacent cells. That allows for much better battery temperature control and thermal management.

3.Thermal runaway
Even if a Tesla mini cell goes bezerk, it is sufficiently isolated from adjacent cells to prevent thermal runaway of the whole pack. The thermal runaway is a non-event as it is limited to a single mini cell, with a very small amount of energy (both electric and chjemical) being released.
When a 787 cell goes bezerk, you're pretty much guaranteed to have a big event.


BTW, apparently the Tesla BMS does have a sort of double threshold set-up, as I've not heard or read of any, let alone 100 - 150 of Tesla batteries, having to be changed where those batteries had to be returned to Tesla for safe recharge . . . . but that could be me not paying any attention from the other side of the pond.


Rgds,
PW100

Should Boeing offer a NiCad option? I think a lot of customers would take it up.

Quoting 7BOEING7 (Reply 1): Elon Musk / Tesla I find his words very interesting. Basically what he said (and this was stated earlier in this thread by someone else), is that those eight cells are way too big. Boeing (read, the battery supplier) should have used many more cells, with 8 small cells in series to get the required voltage, and many many parallel groups of eight cells to get the required capacity.

Tesla batteries put out 40, 60 or 85kwh are warranted for 8yrs or 100K, 125K, or unlimited miles. They are the entire bottom of he car +/- and weigh I'm guessing 1500-2000 lbs +/-. You replace the whole battery at once and if it's your nickel , it's $8-12K. How does their pwr/lb or pwr/volume relate to the 787 battery??

Quoting RickNRoll (Reply 3): Should Boeing offer a NiCad option? I think a lot of customers would take it up.

This question has been addressed; a NiCd battery of similar capacity would be too large to fit on the E&E racks. It could have been designed that way from the beginning, but with significant penalties, and at this point it's sort of a "gee-whiz, we coulda done..." head scratch thing.

Quoting 7BOEING7 (Reply 4): How does their pwr/lb or pwr/volume relate to the 787 battery??

8 - 12K vs 16K !! And warranted for 8 years !!

Can I ask all of you a favour? Can u end that endless discussion about the batteries? By now that should be moved over to Tech & Ops. There are so many other aspects which would be interesting to discuss, as the impact of the grounding on various issues. I am a bit fed up by now with that thread.

here is a grounding, period. If for good or not time will tell. But I would be much more interested in how that impacts supply chains, pilots, airlines, leases and other stuff. Unfortunately, that goes under.

Thanks

Apologies if this has been discussed already- there are too many posts and threads to check. I was wondering if the 787's bleedless engines were a factor in the amount of electric power this bird requires (considerably more than older planes of a similar size IIRC), and if so how this issue might affect future demand for bleedless engines.

I got the feeling that as far as Airbus and many airlines are concerned the jury was still out regarding whether bleedless engines are really the way forward before this problem arose. If using them means more batteries are required than aircraft with conventional engines, airlines might decide bleedless technology is not advantageous enough.

Quoting tropical (Reply 8): Apologies if this has been discussed already- there are too many posts and threads to check. I was wondering if the 787's bleedless engines were a factor in the amount of electric power this bird requires (considerably more than older planes of a similar size IIRC), and if so how this issue might affect future demand for bleedless engines. I got the feeling that as far as Airbus and many airlines are concerned the jury was still out regarding whether bleedless engines are really the way forward before this problem arose. If using them means more batteries are required than aircraft with conventional engines, airlines might decide bleedless technology is not advantageous enough.

I don't think the batteries power anything that uses bleed air on other airplane models.

Cheers

Quoting tropical (Reply 8): Apologies if this has been discussed already- there are too many posts and threads to check. I was wondering if the 787's bleedless engines were a factor in the amount of electric power this bird requires (considerably more than older planes of a similar size IIRC), and if so how this issue might affect future demand for bleedless engines. I got the feeling that as far as Airbus and many airlines are concerned the jury was still out regarding whether bleedless engines are really the way forward before this problem arose. If using them means more batteries are required than aircraft with conventional engines, airlines might decide bleedless technology is not advantageous enough.

No, the battery requirements would have been the same with engines using bleed air.

Quoting PW100 (Reply 2): Threshold 1, say 20-20% capacity left. The BMS shuts down the battery and airframe systems in a controlled fashion to prevent it from reaching threshold 2,

The problem with that is: think about the legal implications if the battery has to be used during a flight and it shuts down on threshold 1. Even if the flight lands safety, lawyers will be lining up to sue the airline and Boeing for emotional distress: "There was power still available, and your system didn't allow the plane to use it?" Now we all know what the deal is, but that's the sort of thing that can be demagouged to an ignorant jury.

Quoting tropical (Reply 8): I got the feeling that as far as Airbus and many airlines are concerned the jury was still out regarding whether bleedless engines are really the way forward before this problem arose. If using them means more batteries are required than aircraft with conventional engines, airlines might decide bleedless technology is not advantageous enough.

The battery really doesn't have much to do with that, though. Remember that the 787 batteries only have two jobs: (1) start the APU, and (2) power a few essential systems when there is no other source of power. The only time you'd need the batteries in flight would be if both engines flamed out (or all four engine generators failed), the APU was failed or not running, and the RAT failed to deploy.

Quoting macc (Reply 7): Can I ask all of you a favour? Can u end that endless discussion about the batteries?

Sir the batteries are the reason this a/c was grounded. The fact they necessarily must check the charging system and how the containment system worked adds to the complexity of the problem. If you don't want to deal with batteries, you'd best just ignore these "787 grounded" threads.

I'd love to stop reading and talking about the issue but that likely won't happen until the 787 returns to service.
  

Quoting PW100 (Reply 2): The question is why the BMS does not have a double threshold?

Just a guess on my part, but I'm going to suggest a) on-battery duration was thought to be more important than avoiding replacement (that's the "don't do that" argument), and possibly a related b) you'd have to allow several minutes at least for the power-up margin, and then a margin on top of that to make sure that you meet the specs for that power-up margin, and by that time you might be taking too large a slice out of the on-battery duration.

In other words, doing that might have required an x% larger battery for some significant x, and the designers didn't think it was worth it, and presumably whatever airlines were consulted agreed.

Whether anyone is regretting the decision at this point I've no idea.

Quoting PW100 (Reply 2): The question is why the BMS does not have a double threshold?

Because it increases complexity and the fault tree.

You have to prove that the battery will only disconnect at a level greater than 20% when another power source if available (Engine Generator, APU Generator, RAT) and would continue to discharge below 20% when it was the only power source for the airplane.

Quoting macc (Reply 7): Can u end that endless discussion about the batteries? By now that should be moved over to Tech & Ops. There are so many other aspects which would be interesting to discuss, as the impact of the grounding on various issues

We already know that even a permanent grounding of the 787 and cancellation of all outstanding orders, while a tremendous financial hit to Boeing, would not spell the end of Boeing Commercial. They'd sell hundreds of 767s and 777s in place of 787s because Airbus could not meet demand with the A330 and A350.

Anything less than a permanent grounding just defers Boeing's revenues to the right and temporarily increases inventory costs as frames back up prior to the fix being implemented and deliveries resume.

And I'd like to put to rest the idea that we'll know in the future if the grounding was a good idea or not. This is known right now, if not by us (if you're not convinced) then at least by the ones in charge. Even if it turns out, after a lengthy inquiry, that there was no danger of an accident, that has no impact on the initial decision to ground the plane.

Quoting Stitch (Reply 14): Anything less than a permanent grounding just defers Boeing's revenues to the right and temporarily increases inventory costs as frames back up prior to the fix being implemented and deliveries resume.

In the time that I worked at Boeing, the company surrendered up more than $1B thanks to the Uncle Mikey scandal, and wrote off $800M over a small accounting rules change. This 787 business looks like a drop in the bucket by comparison. It's never nice to lose money, but perspective.

The Seatlle times link has a video of a Lithium Ion Battery undergoing a meltdown with nothing more than a few wisps of smoke escaping from the containment. It appears it is possible to contain the result of a meltdown without creating an explosive effect.

I don't know whether this infornation has been posted before - if so, apologies for the repetition. But it appears to prove that a high proportion of the batteries have been giving frequent trouble ever since the aeroplane entered service; but the relevant authorities were simply not informed of the problems. The article is 'silent' on the question of how much Boeing knew about the problems:-

"Japan's two major airlines said Wednesday they had replaced a number of batteries in their Dreamliners after experiencing problems well before the worldwide grounding of Boeing's next generation plane.

A spokeswoman for All Nippon Airways said 10 batteries on its fleet had been switched, while a representative of rival Japan Airlines (JAL) said "quite a few" had needed changing.

"The lithium-ion batteries, made by Japanese manufacturer GS Yuasa, have been at the centre of a probe into the Dreamliner's airworthiness since a fire on a JAL plane in Boston and an emergency landing on an ANA flight in Japan.

"ANA, the launch customer for Boeing's lightweight plane, had to replace batteries 10 times ahead of the January 16 emergency landing forced by smoke apparently linked to the powerpack, company spokeswoman Naoko Yamamoto said.

"The airline, which started operating Boeing 787s in November 2011, had to replace some batteries after only a week while others lasted only a month, she said.

"In four cases, the main powerpack was only partially charged, while in two other cases a battery or an auxiliary power unit - which boosts the battery - failed to start, she said.

"All 10 replacements occurred last year - two in May, four in October, two on one day in November and two in December - involving seven Dreamliners, she said. The airline operates 17 of the planes.

"ANA had not reported the replacements to the Japan Transport Safety Board (JTSB) because "the ten problems were found before flights so were considered not to affect safety", Yamamoto said."

Read more: http://www.theage.com.au/travel/trav...-20130131-2dmbc.html#ixzz2JVwlxdTh

On the face of it, it looks as if Boeing will have no option but to replace ALL the batteries with more reliable and proven types? However long it takes to develop, test, and certify them?

[Edited 2013-01-30 18:09:22]

Quoting NAV20 (Reply 18): I don't know whether this infornation has been posted before - if so, apologies for the repetition. But it appears to prove that a high proportion of the batteries have been giving frequent trouble ever since the aeroplane entered service; but the relevant authorities were simply not informed of the problems.

It was discussed at length in Part 6.

The reason the relevant authorities were not informed of the problems is because these were cases of the battery's safety features working as designed. So there was no "problem" to report, at least in terms of safety. The authorities now want to review those batteries to see if they can shed insights onto the two that caught fire.

Quoting NAV20 (Reply 18): On the face of it, it looks as if Boeing will have no option but to replace ALL the batteries with more reliable and proven types? However long it takes to develop, test, and certify them?

I would expect Boeing will move to a safer electrolyte material, if not as a condition to return to service, then as a subsequent change to improve safety and reliability in conjunction with whatever measures are taken to return to service. Newer formulations that have been developed since the original battery was designed / certified are much stabler.

Quoting Stitch (Reply 19): I would expect Boeing will move to a safer electrolyte material

My bet too, Its the massive lead time to design and certify systems for Aircraft that really hurt innovation in the detail like a battery chemistry change. Who is going to be willing to pay huge money and wait years for a slightly better battery.

But it looks like in this case Boeing can select a much safer chemistry than was practical at the time they started designing the 787 battery system... and the FAA has some pretty huge incentive to do all it can to get it approved if it meets the requirements.

Quoting PW100 (Reply 2): Threshold 1, say 20-20% capacity left. The BMS shuts down the battery and airframe systems in a controlled fashion to prevent it from reaching threshold 2, where the battery must be replaced and sent to a specialized repair facility.

Why would you sacrifice the airframe to protect the battery?

Quoting PW100 (Reply 2): This way, you end up with slightly less battery capacity, but you remain with a serviceable battery; all it needs to re-charge the battery is an external power souce.

No, the whole point is that, once you hit what you're calling "Threshold 2" you have to electrically separate the battery from the aircraft. That's an FAA requirement. Once you do that, you can't recharge it without reconnecting it. That means either you replace it (the solution they chose) or you put in a reversible disconnect...the latter opens two huge fault options up, neither of which is good. Swapping LRU's is a whole lot simpler (and almost certainly cheaper).

Quoting PW100 (Reply 2): Basically Musk says this is why Tesla uses hundreds of mini cells instead of Boeing's large super cells (well, actually eight of them). Each Tesla mini cell is monitored indepently.

Each Boeing cell is monitored independantly too. I'm not a battery guy...does the size of the cell impact the ability to monitor it?

Quoting PW100 (Reply 2): Where the 787 BMS monitors eight cells, Tesla would monitor dozens, of not hundreds of small cells for the same overall capacity.

Doesn't that greatly increase the complexity off the BMS, an hence the probability of a BMS or cell failure?

Quoting PW100 (Reply 2): BTW, apparently the Tesla BMS does have a sort of double threshold set-up, as I've not heard or read of any, let alone 100 - 150 of Tesla batteries, having to be changed where those batteries had to be returned to Tesla for safe recharge . . . . but that could be me not paying any attention from the other side of the pond.

Tesla doesn't have a requirement from the FAA to sever the battery from the car, or to guarantee that the car is absolutely, positively, never without power. An unpowered car rolls to a stop. An unpowered airplane...

Quoting tropical (Reply 8): I was wondering if the 787's bleedless engines were a factor in the amount of electric power this bird requires (considerably more than older planes of a similar size IIRC), and if so how this issue might affect future demand for bleedless engines.

They're a huge factor in the amount of power the airplane requires. However, that has essentially nothing to do with the battery size or design. Also, "bleedless engines" are relatively easy to convert to bleed engines...the 747-8 flies around on what is basically a GEnX with a smaller fan and bleed ports.

Quoting tropical (Reply 8): If using them means more batteries are required than aircraft with conventional engines, airlines might decide bleedless technology is not advantageous enough.

It doesn't mean more (or bigger) batteries are required.

Quoting RickNRoll (Reply 17): It appears it is possible to contain the result of a meltdown without creating an explosive effect.

There is no evidence that the meltdown on either 787 created an explosive effect. A fire and leakage are not the same thing as an explosion.

Quoting NAV20 (Reply 18): I don't know whether this infornation has been posted before - if so, apologies for the repetition.

It's been posted before. The short version is that the vast majority of those replacements, assuming the articles are correct, are the result of the batteries operating *correctly* in the face of being run down in service.

Tom.

Quoting tdscanuck (Reply 21): There is no evidence that the meltdown on either 787 created an explosive effect. A fire and leakage are not the same thing as an explosion.

I didn't say there was. I had been saying they could just build a more substantial container, but people said that would just create an bomb that could explode. The video shows the container holding in the result of the thermal runaway with no hint of fire or solids breaking out.

Quoting Stitch (Reply 19): Newer formulations that have been developed since the original battery was designed / certified are much stabler.

Quoting XT6Wagon (Reply 20): But it looks like in this case Boeing can select a much safer chemistry than was practical at the time they started designing the 787 battery system...

Thanks for the replies, guys. But are those 'stabler' and 'safer' versions already in service and fully tested? Or will Boeing have to be the 'pioneer' again?

ok hello guys, I've pretty much handed off the whole "japan" side of things to the guys who are technically involved with the 787 (like tdscanuck), so pretty much anything translated or coming out of Japan is pretty much old news by now.

Now I have a question:
1) progress on the investigation?
2) Any guesses on when the 787 will fly again?
3) Rumors were floating in Japan about lawsuits coinciding with these batteries; would that happen?
4) According to Japan Today the JTM investigation shifted from Yuasa to a Kyoto company which makes products that monitors overcharge, charge exchange, and other components which allow the battery to work. Japan Today couldn't explain more about it; what's the investigation going to be like there?
5) What's the updates on the replacement service?

PHX787

Quoting PHX787 (Reply 24): 2) Any guesses on when the 787 will fly again?

next year . . .

If most of the problem with the Lithium Ion batteries has to do with improper charging and discharging, as the recent New York Times Article would suggest, how much of a design change would be required to make the batteries removable? Batteries could be charged and inspected at facilities on the ground and then changed in and out with every flight. If it works for Makita and DeWalt power tools, it should probably works for Boeing (tounge in cheek, of course).

Quoting ComeAndGo (Reply 25): Quoting PHX787 (Reply 24): 2) Any guesses on when the 787 will fly again? next year . . .

It won't be that long. There are too many engineers and too much riding on this a/c to have the grounding last that long.

Quoting NAV20 (Reply 23): Thanks for the replies, guys. But are those 'stabler' and 'safer' versions already in service and fully tested? Or will Boeing have to be the 'pioneer' again?

It would depend on the formulation.

As I understand it, the 787's batteries use lithium cobalt oxide with manganese. The manganese was added to improve service durability. Nissan and it's partners developed lithium nickel manganese cobalt (NMC) in 2008, and evidently the addition of the nickel reduces volatility. I could see Boeing looking at this formulation since it is similar to what they already have and it does have high energy density (like lithium cobalt oxide).

Quoting btfarrwm (Reply 26): If most of the problem with the Lithium Ion batteries has to do with improper charging and discharging, as the recent New York Times Article would suggest, how much of a design change would be required to make the batteries removable?

The current batteries are removable by design.

Quoting RickNRoll (Reply 17): It appears it is possible to contain the result of a meltdown without creating an explosive effect.

You can contain the result of a nuclear blast with a big and strong enough containment vessel (just watch an underground test from above sometime). That doesn't mean it's practical to carry on an airplane.

The whole point of the lithium ion batteries is to have a lighter battery. If the containment vessel makes the battery overall as big and heavy as a different, older technology, then you may as well just use that older technology.

Quoting tdscanuck (Reply 21): Each Boeing cell is monitored independantly too. I'm not a battery guy...does the size of the cell impact the ability to monitor it?

On small or large cells, it is possible to monitor the voltage of each cell with equal accuracy.

The problem with larger cells is that different areas of the electrode or plates within a single cell can see more current flow during charging and discharging than other areas, resulting in localized hot spots.

By having mutiple cells in a series/parallel arrangement (in the case of a 28V Li-Ion battery, maybe 24 or 32), the individual cells (and their electrodes or plates) get smaller, and can be montored for temperature with even more precision. As well as monitoring individual cell voltages, the current flow through each parallel group can be measured and compared for load balance vs. other parallel groups.

Proper voltage, current, temperature and cell load balance monitoring and control, coupled with cooling fins for individual smaller cells, and cooling fans can make for a very robust, reliable battery unit.



✈ LD4 ✈

Is their a chance that Boeing would take Musk on his offer or is it just PR stunt?

Elon Musk offers Boeing SpaceX batteries for the 787 Dreamliner
http://www.geek.com/articles/geek-ce...s-for-the-787-dreamliner-20130129/

[Edited 2013-01-30 21:21:38]

Quoting spacecadet (Reply 29): The whole point of the lithium ion batteries is to have a lighter battery. If the containment vessel makes the battery overall as big and heavy as a different, older technology, then you may as well just use that older technology.

I don't think that's the priority any more. Getting the planes in the air is. It has been suggested going back to the older technology, that's not an option apparently.

More from Boeing

http://www.independent.ie/breaking-n...xe-dreamliner-battery-3370880.html

A little more from Musk saying the 787 are fundamentally unsafe:

http://www.flightglobal.com/news/art...ttery-fundamentally-unsafe-381627/

Quoting p201055r (Reply 33): More from Boeing

Quote from this article:

"Boeing said about 2,000 batteries of all types were replaced every year on its various planes."


How many Boeing aircraft are currently flying? I'd guess more than 2.000, so less than 1 battery per year to be replaced. Apparently the number for the 787 is significantly higher - if the reported number of 100 to 150 was correct.

This higher replacement rate was certainly not intended. The higher maintenance cost it causes is not a security threat by itself, but still points to a design flaw in that area. At least, a less than perfect design.

[Edited 2013-01-31 00:46:28]

Quoting EBGflyer (Reply 34): A little more from Musk saying the 787 are fundamentally unsafe:

The war of words continues. Musk and the MIT professor Sadoway claim Boeing doesn't have the engineering to prevent the domino effect which increases the risk of a thermal runaway within the battery packs. Meanwhile, Boeing's Sinnett claims that not only do they have that engineering, they've also designed the appropriate containment to keep planes safe if thermal runaway does occur.

Where do they go from there?

From the last thread I only take over this quote, because PW100 wrote a great post about the rest:

Quote: Sinnett flat out said they designed for a battery fire...how can you say that they didn't anticipate the root cause?

Because very likely the nature of the found root cause will be so basic, that still saying "we fully trust our design" after these events have happened will a bit strange. I mean on the picture everybody can see that the design is not good at the prevention of failure propagation between cells. The picture and real world events are in an agreement. Boeings claims not.

Quoting PW100 (Reply 2):

Wise post!

Quoting PW100 (Reply 2): Threshold 1, say 20-20% capacity left. The BMS shuts down the battery and airframe systems in a controlled fashion to prevent it from reaching threshold 2

I have thought to quickly propose a draft for such such a two-level-battery controlling system, but then you did it!

I would propose in addition an emergency switch, that manually allows the crew to suppress Threshold1 in case every bit of power is needed up to the Threshold2. In that case the available power could be used in an emergency case until the battery locks. But not if the mechanics does a handling error like keeping a light on somewhere.

Quoting PW100 (Reply 2): There are a couple of problems with these big cells:

Again your wrote very precise what I think could be the case.

Quoting XT6Wagon (Reply 20): Quoting Stitch (Reply 19): I would expect Boeing will move to a safer electrolyte material My bet too, Its the massive lead time to design and certify systems for Aircraft that really hurt innovation in the detail like a battery chemistry change.

Any other electrloyte would reduce the batteries capacity. So there would be structural changes anyway to make the battery accordingly larger.

Quoting tdscanuck (Reply 21): No, the whole point is that, once you hit what you're calling "Threshold 2" you have to electrically separate the battery from the aircraft. That's an FAA requirement.

That's fine. And beside that there could a threshold 1, that would be reversible. Even my RC craft has two built in levels of low-voltage protection and additional levels are added by external gear.

Quoting tdscanuck (Reply 21): I'm not a battery guy...does the size of the cell impact the ability to monitor it?

Tesla and SpaceX say so. I could easily imagine this to be the case.

Quoting tdscanuck (Reply 21): Quoting PW100 (Reply 2): Where the 787 BMS monitors eight cells, Tesla would monitor dozens, of not hundreds of small cells for the same overall capacity. Doesn't that greatly increase the complexity off the BMS, an hence the probability of a BMS or cell failure?

You have to do what is required. For the cost of simple but burning batteries you can install a lot of (still simple) electronics.

Quoting tdscanuck (Reply 21): Tesla doesn't have a requirement from the FAA to sever the battery from the car, or to guarantee that the car is absolutely, positively, never without power. An unpowered car rolls to a stop. An unpowered airplane...

So one wonders why their design does properly cover all three safety levels, that are mentioned by Sinnet, while the Dreamliners design is poor in two of them. Had the dreamliner Teslas battery it would stay longer with battery power.

Quoting XT6Wagon (Reply 20): I would expect Boeing will move to a safer electrolyte material My bet too, Its the massive lead time to design and certify systems for Aircraft that really hurt innovation in the detail like a battery chemistry change. Who is going to be willing to pay huge money and wait years for a slightly better battery.

This was my previous thought until I read this.....

Quoting PW100 (Reply 2): 1. Local Zoning They are so big that under some conditions they no longer behave as a homogeneous cell, they start to behave as individual mini cells. In other words, local zones can develop characteristics of mini cells. The problem now is that these local zones are not monitored in detail. Those zones apparently can develop local low voltage/high discharge condition inside the cell, without being detected. ....... The Tesla mini cells are so small that it is physically almost impossible for them to have their own small local zones. 3.Thermal runaway Even if a Tesla mini cell goes bezerk, it is sufficiently isolated from adjacent cells to prevent thermal runaway of the whole pack. The thermal runaway is a non-event as it is limited to a single mini cell, with a very small amount of energy (both electric and chjemical) being released.....

If this is indeed true (The Tesla approach), it seems to me a permanent solution. Just a more robust (and larger and more expensive) design. It is a very simple principle used in many other solutions. Circuit board designs have limits on cross interferance from traces and limit the size of PCB's (can only make them so small). This may be the same phenomena here from a heat perspective. One day I think bigger cells can work with proper manufacturing, but apparently not there yet (impurities and other factors may cause this local zoning is a possibility).

The distributed approach mitigates risk on two levels, runaway and voltage/current loss of a cell (since a single cell is much less of the total pack). It seems a much better solution. Musk makes a compelling argument, with real world product experience to back it up; Tesla obviously took this expensive design path for a reason and apparently to avoid the incidents we are seeing now. I would think NTSB would be satisfied if such a solution was adopted to reduce incidents and was combined with neater containment/venting for accidental electrolyte discharge.

Quoting justloveplanes (Reply 38): (The Tesla approach)

The problem with the Tesla idea is certification. They don't have to certify it to any standard other than bad press, much less to FAA arbitrary and sometimes counterproductive regs.

ask yourself how many cells would the FAA let go dead before mandating a diversion. How many before replacement of the battery. Tesla wants to put hundreds of cells into a regulatory environment where even benign failure can be the source for massive trouble. Heck look at AA's trouble with the FAA being indecisive about ziptie spacing on MD80's with absolutely no evidence that there was a problem TO FIX. Now you are suggesting a large and massively complex battery replacing a simpler design.

You might convince me that doubling the cell count while running 1/2 the size might be possible, but 20x or more? hahaha good luck. At some point redundancy is counter productive. The Airline industry seems to quickly adopt solutions that while expensive mean that you only need a absolute minimum of back ups, extra capacity, or other redundancy factors. The fact that twin engine airliners are the safest, most reliable planes around should show you just how this ideal is achieved in the real world. More engines for the sake of "redundancy" just adds more potential failure points into the design.

Quoting justloveplanes (Reply 38): Just a more robust (and larger and more expensive) design. It is a very simple principle used in many other solutions. Circuit board designs have limits on cross interferance from traces and limit the size of PCB's (can only make them so small). This may be the same phenomena here from a heat perspective.

I agree. This might turn out to be the main contributing factor. I mean 76Ah from each single cell is huge.

Quoting justloveplanes (Reply 38): The distributed approach mitigates risk on two levels, runaway and voltage/current loss of a cell (since a single cell is much less of the total pack).

Correct.

Quoting XT6Wagon (Reply 39): The problem with the Tesla idea is certification. They don't have to certify it to any standard other than bad press, much less to FAA arbitrary and sometimes counterproductive regs.

No, it should be easier as it fulfills the standards of the FAA probably better than Boeings approach. So providing evidence for certification should be easier.

Quoting XT6Wagon (Reply 39): Ask yourself how many cells would the FAA let go dead before mandating a diversion.

The FAA has asked for zero cells to go dead (implicitely because even a single dead cell will infringe one or more of the defined requirements). This does not depend on the cellcount. So why not choose a cell size, that is inherently more stable?

Quoting tdscanuck (Reply 21): Tesla doesn't have a requirement from the FAA to sever the battery from the car, or to guarantee that the car is absolutely, positively, never without power. An unpowered car rolls to a stop. An unpowered airplane...

The whole point is, Tesla doesn't have to sever the battery because it's not a single string of huge cells. They can disconnect a single series of cells with very little impact on the battery capacity. A cell failure with them is almost unnoticeable. Potential for fire and loss of battery are pretty much eliminated.

Quoting XT6Wagon (Reply 39): The problem with the Tesla idea is certification. They don't have to certify it to any standard other than bad press, much less to FAA arbitrary and sometimes counterproductive regs.

Automobile certifications and aircraft certifications have some similarities and many, many differences, but autos are certainly very heavily regulated and have extremely detailed certification requirements. And just as with the 787 in the airline world the (re-) development of electric cars has caused thousands of pages of new cert reqs to be written. Again, may or may not be relevant to the 787 situation, but let's be technically and legally accurate in our discussion.

sPh

Tesla solution sounds possible, but then the whole pack with become larger and heavier and you will have to redesign and re-certify the whole rack installation, battery and charger system. I guess it would be way safer to switch the battery type in that case as well.

Quoting seahawk (Reply 43): Tesla solution sounds possible, but then the whole pack with become larger and heavier and you will have to redesign and re-certify the whole rack installation, battery and charger system. I guess it would be way safer to switch the battery type in that case as well.

In which case the Telsa solution goes away, if you are going to redesign to get that much space for the additional size of the batterires, may as well go ni-cad one time and be done with it, why continue with a technology that everyone is up in arms about?

Quoting RickNRoll (Reply 22): I didn't say there was. I had been saying they could just build a more substantial container, but people said that would just create an bomb that could explode. The video shows the container holding in the result of the thermal runaway with no hint of fire or solids breaking out.

The argument about explosion risk was about *sealed* battery cases. As you said:

Quoting RickNRoll (Reply 17): nothing more than a few wisps of smoke escaping from the containment.

If wisps of smoke are escaping, it's not a sealed case, hence doesn't build pressure, hence isn't explosive. We already had people yelling, at considerably length, that release of flammable gas was totally unacceptable and that's what the battery you describe was doing.

Quoting PHX787 (Reply 24): 3) Rumors were floating in Japan about lawsuits coinciding with these batteries; would that happen?

I'm not sure...who, exactly, would they sue and for what? Airliner contracts are *huge*...it's hard to imagine there is some wrong that's sue-able that isn't already covered in the contract.

Quoting btfarrwm (Reply 26): If most of the problem with the Lithium Ion batteries has to do with improper charging and discharging, as the recent New York Times Article would suggest, how much of a design change would be required to make the batteries removable?

They're already removable. In aviation parlance, the battery is an LRU (Line Replaceable Unit). There's usually a design goal that all LRU's should be able to be replaced in some finite time for maintenance reasons...on the order of 30-60 minutes is common. Some LRU's are worse, some are better. Swapping a battery is actually on the faster end.

Quoting Unflug (Reply 35): How many Boeing aircraft are currently flying? I'd guess more than 2.000, so less than 1 battery per year to be replaced. Apparently the number for the 787 is significantly higher - if the reported number of 100 to 150 was correct.

Quite a lot more than 2,000...the active Boeing fleet (including heritage MD) is close to 10,000. However, it's a mistake to think the battery replacement rate should be constant across the fleet...electrical demand (and certification requirements) have gone *way* up. The battery situation on an MD-80 is not remotely close to that of a 777.

Quoting rheinwaldner (Reply 37): Quoting tdscanuck (Reply 21): Doesn't that greatly increase the complexity off the BMS, an hence the probability of a BMS or cell failure? You have to do what is required. For the cost of simple but burning batteries you can install a lot of (still simple) electronics.

I didn't ask about cost, I asked about complexity and probability of failure. The battery is the last line of defense for the electrical system and (for the main battery) not on the MMEL. Reliability is a lot more important that cost. I fully agree that having batteries catch fire is not an indication of reliability but I don't see how injecting even more complexity and failure modes into the BMS is going to to help the reliability situation.

Quoting rheinwaldner (Reply 37): Had the dreamliner Teslas battery it would stay longer with battery power.

Had the Dreamliner the Tesla's battery it would not have been certified and would not be flying today.

Quoting rheinwaldner (Reply 40): Quoting XT6Wagon (Reply 39): The problem with the Tesla idea is certification. They don't have to certify it to any standard other than bad press, much less to FAA arbitrary and sometimes counterproductive regs. No, it should be easier as it fulfills the standards of the FAA probably better than Boeings approach

It fails the FAA special conditions for battery certification on its face:

Quoting nomadd22 (Reply 41): The whole point is, Tesla doesn't have to sever the battery because it's not a single string of huge cells. They can disconnect a single series of cells with very little impact on the battery capacity.

Without a rewrite of the regulations or a redesign of the battery, Tesla's battery is blatantly uncertifiable.

Quoting rheinwaldner (Reply 40): Quoting XT6Wagon (Reply 39): Ask yourself how many cells would the FAA let go dead before mandating a diversion. The FAA has asked for zero cells to go dead (implicitely because even a single dead cell will infringe one or more of the defined requirements). This does not depend on the cellcount. So why not choose a cell size, that is inherently more stable?

The probability of a cell failure sounds like it goes up with cell size, but it also scales up with the number of cells...if you go from 8 to 800 cells, you need to improve the cell reliability by a factor of 100 to maintain the same system-level reliability. Is that realistic?

Tom.

Quoting tdscanuck (Reply 45): The probability of a cell failure sounds like it goes up with cell size, but it also scales up with the number of cells...if you go from 8 to 800 cells, you need to improve the cell reliability by a factor of 100 to maintain the same system-level reliability. Is that realistic?

I sure the heck don't know anything about the certification, but that just doesn't make sense to me. A cell failure when you have 800 cells isn't a system failure and has no real impact on the system. Writing the standard so a cell failure that has no impact other than a 1% drop in battery capacity is the same as a cell failure that causes total battery failure and meltdown sounds more than a little insane to me. By disallowing the Tesla type architecture, the FAA has required a battery that's less reliable, and has a much greater chance of causing real problems when it fails.

[Edited 2013-01-31 06:34:52]

Quoting tdscanuck (Reply 45): I fully agree that having batteries catch fire is not an indication of reliability but I don't see how injecting even more complexity and failure modes into the BMS is going to to help the reliability situation.

You have to weight up the complexity increase by the risk reduction of going to smaller cells.

What we do know, is that millions small-cell batteries (less than maybe 10Ah per cell) are in use and can be considered as proven. They did cause troubles to some degrees in consumer applications, but in a professional environment they should be manageable to perform safely.

The Dreamliners >70Ah cells are called inherently unsafe by people who only build vehicles that can be left at the roadside the latest 15 seconds after the wish to do so.

Quoting tdscanuck (Reply 45): Without a rewrite of the regulations or a redesign of the battery, Tesla's battery is blatantly uncertifiable.

It does not need to be Teslas battery. There are different requirements for cars e.g. in the area of crash impact.

But the principles of the Tesla battery should be valid for the dreamliner:
- Reduce cell size.
- Have a layout, where at least a bit better separation can be achieved.

Quoting tdscanuck (Reply 45): The probability of a cell failure sounds like it goes up with cell size, but it also scales up with the number of cells...if you go from 8 to 800 cells, you need to improve the cell reliability by a factor of 100 to maintain the same system-level reliability. Is that realistic?

Tesla's batteries seem to be more stable overall. Otherwise we would have heard the incidents by now. So the 100 times more complex BMS seems to be outweighted by more than 100 times more stable cells.

Quoting rheinwaldner (Reply 47): So the 100 times more complex BMS seems to be outweighted by more than 100 times more stable cells.

If that's really true, I can't see why they'd go for the giant-cell architecture, except maybe maximum power density.

Quoting nomadd22 (Reply 46): I sure the heck don't know anything about the certification, but that just doesn't make sense to me. A cell failure when you have 800 cells isn't a system failure and has no real impact on the system.

What the FAA wrote (that's relevant here) was:
(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.

I think the applicability would require the FAA to concede that the over-temperature of a *cell* was permissible as long as it didn't over-temp the battery, and that failure of a cell could not be considered failure of the battery.

My read on it is that the FAA special condition wasn't written to take that kind of hundreds-of-levels-of-redundancy at the cell level into account.

Tom.

Quoting nomadd22 (Reply 46): I sure the heck don't know anything about the certification, but that just doesn't make sense to me. A cell failure when you have 800 cells isn't a system failure and has no real impact on the system. Writing the standard so a cell failure that has no impact other than a 1% drop in battery capacity is the same as a cell failure that causes total battery failure and meltdown sounds more than a little insane to me.

Consider the reliability and redundancy requirements. If you have 800 cells, you have a massively complex BMS with 800 sets of sensors, 800 signal conditioning circuits, and 800 relays so that individual cells can be taken off line. Can the BMS detect faults in all of that circuitry so as to maintain redundancy? What happens if an isolation relay fails to switch? Can you detect it, and if you can, do you take the whole battery offline? Even if you can line up all of the testing and all of the paperwork to show that it's safe and get it certified, you've created a maintenance nightmare due to the complexity of the system.

As far as Elon Musk goes, if I was working for him right now, I'd be ashamed. His remarks have not been helpful, and his using the issue to grandstand and draw attention to himself is very unseemly. He seems to forget that a lot of the people he's calling idiots are the same people that he's trying to get to come work for him.