Lithium ion/Boeing 787

Discussion in 'Fred's House of Pancakes' started by tochatihu, Jan 18, 2013.

  1. Flaninacupboard

    Flaninacupboard Senior Member

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    From that article:





    32 Divided by 8 is 4. Did I just clear up this investigation? :D
     
  2. FL_Prius_Driver

    FL_Prius_Driver Senior Member

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    Since designing power electronics for aircraft is my primary job presently, I'll give you my take based on what little I have seen in the press.

    1) My first shock was the battery cells being in the same box as unprotected circuit cards. Even automakers know that control electronics should be protected in dedicated enclosures, especially any that have a safety function. Nature puts our brains inside a skull for the same reason. If the box were to fill up with any fluid from any source, the electronics that should protect it are filling up with the same fluid from the same source. Some supplier did a song and dance about how that would be OK and some Boeing approval authority bought the song and dance. Double Fail.

    2) Zero defect detection ranges from the routine to the impossible depending on what is called a defect. Various X-ray views, charge leakage test, and many other Non-Destructive Tests exists (at some breakpoint cost) that for every very large batteries those have an impressive defect detection capability. Usually, the final defects are hard to find in the end product, then effective testing during the manufacturing process is possible. Virtually never is it a matter of physics that limits defect detection. Almost always it is a matter of cost that determines how much screening and testing is applied.

    3) As for your "non-degrading" torture test, there are none. Aviation equipment is required to be subjected to the full spectrum of either DO-160 (FAA) or MIL-STD-810 (Military) or extremely similar equivalent testing. Those tests are intense and brutal. Any items subject to those tests are considered expended after the testing. It is basically illegal to put in service any items subject to any testing that could degrade equipment (vib, shock, temp, drop, etc.). Now incompetent or greedy folks can always find ways around the intended testing, so there is always the possibility the correct testing was sidestepped.

    4) What is usually done in production is a couple of units are sacrificed for full testing of all aspects as described about to show the design works. Then in production, each unit is subject to "ESS", Environmental Stress Screening. This usually is a limited (e.g. watered down) set of vibration and temperature cycles to ensure all units work as specified, find infant mortality failures, and establish reliability statistics. ESS parameters are determined by the manufacture more so than the airworthiness authority, unlike the qualification test of the previous paragraph. So a manufacture intent on ESS being an ineffective rubber stamp of approval can easily do so.
     
    dave77, cwerdna, tochatihu and 2 others like this.
  3. tochatihu

    tochatihu Senior Member

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    Thanks a bunch FL. I am going to presume that someone with your level of insight is in the NTSB investigation.

    The (previously) active 787 fleet numbered about 50 and were in service for about a year. They had a few other incidents, unrelated to power electronics. Then two planes with similar serial numbers (-> completion dates) got smoked. If I got all that right, it may lend credence to the notion that some production run of batteries got through with defects. Or, that some run of Securaplane controllers did.

    In no way is this meant to counter FL's compelling point about being in the same box. That really rings true. In fact, he made the point with humor - "Even automakers know..."

    Dumb automakers...
     
  4. xs650

    xs650 Senior Member

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    Maybe Boeing should have hung onto Alan Mulally and made him CEO instead of letting him be lured away by dumb automaker Ford. :D Mulally had a solid engineering background with an excellent high level management track record at Boeing while the present CEO is a BA-MBA business type with no obvious technical background.

    Boeing’s 787 Problems Never Would Have Happened if Alan Mulally Was CEO: Clive Irving | Daily Ticker - Yahoo! Finance
     
  5. tochatihu

    tochatihu Senior Member

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  6. xs650

    xs650 Senior Member

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  7. wjtracy

    wjtracy Senior Member

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    ...more comments about the chemistry of Li Ion batts. I am not a battery expert, but this reference seems to say what Li batts do have in common is organic (flammable) liquids used as electrolytes. I think this answers the questions I have had - why would salts of lithium be flammable?
    New Lithium-Ion Battery Woes | January 28, 2013 Issue - Vol. 91 Issue 4 | Chemical & Engineering News
     
  8. JMD

    JMD 2012 Prius 4 Solar Roof

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    My cousin is a Former Boeing employee. Graduate of Cooper Union. He never flew, drove everywhere. I thought he was eccentric since he is a Aeronautical Engineer and never flew. In retrospect he knew how unpredictable man made can be.
     
  9. FL_Prius_Driver

    FL_Prius_Driver Senior Member

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    This article is by far the most important. It matches my first hand experience of how an operational shortcoming can easily translate an equipment weakness into an equipment fault. Specifically, while many are expecting some explicit fault to be uncovered, most aviation big problems occur as the accumulation of many small issues combined in a very bad way.

    Imagine someone who only recharges their electric car when the last "99% depleted" alarm finally goes off (instead of recharging routinely). Then when they recharge, they use the emergency rapid charge rate (and only the emergency charge rate). When their battery fails earlier than the expected life, they claim it is entirely the battery makers fault. (Is it the battery maker's fault?, the car makers fault?, the owner's fault?)

    So what makes the Boeing 787 situation interesting is the possibility not of a battery defect, but of insufficient battery protection from operational abuse. I'm not claiming I know this is a factor in the problem, but this report is worth reading.
     
  10. xs650

    xs650 Senior Member

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    In your posited case of the car battery it would be clearly the car makers fault. They know (how could they not know?) the low level of technical knowledge of the average car owner and the don't give a toot level of care the average car gets. If they don't make the battery system highly idiot resistant, as Toyota did with the regular Prius traction battery then shame on the car maker.
    Considering the potential consequences of a battery fire in an aircraft, that system should also be robustly idiot resistant with a possible over-ride for the pilot in case of emergency. Although, with some pilots I'm not so sure about the desirability of an over-ride:)
     
  11. wjtracy

    wjtracy Senior Member

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    I thought the Elon Musk comments were a pretty bad omen. If he is correct, sounds to me like we might be talking extended down time for redesign/revamp. If he is not correct, then he (Musk) loses some credibility. I suppose there could be some kind of temporary work-around in terms of operating envelope/flight time.
     
  12. rcf@eventide.com

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    Seems to me that Elon Musk is definitely correct. If one cell goes into thermal runaway, the whole assembly will be destroyed. The real question, though, is why even one cell would self-destruct. I'm sure that Boeing tested the batteries at simulated altitude and temperature. What they may not have been able to do is test with a simulated radiation environment equivalent to the real one at 40,000 feet. I wonder what would happen if an energetic particle hit a cell and left an ionization trail through the separators. Would that be enough to allow an unintended current to flow, which would in turn create heat, which in turn might increase the width of the channel, and so forth? No idea, really, if this is plausible. But if it is, it means that there really is no "flaw" in the design of the electronics or the batteries, and it will take quite a while to prove this is the cause since it happens only randomly and only at altitude.

    This problem reminds me of the weird issue they had with memory chips in the 70s, when bits would flip for no apparent reason. Turned out to be alpha particles from radioactive materials in the chip packaging material.

    Richard
     
  13. FL_Prius_Driver

    FL_Prius_Driver Senior Member

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    I agree with you on the car makers responsibility, but making the 100% foolproof car certainly limits responsible drivers with a lot of extra expense and constraints. I would note that the 2001 Prius does not have the discharge protection put in the later versions, so Toyota did good, but not great protection from those trying the 2001-3 out as a fully electric car. You could damage the 2001 battery with excessive discharge from driving after the gas tank runs dry. It's truely amazing how hard it is to put in protection from every possible idiotic tactic. There are more creative idiots than 100% hermetically competent engineers.

    Boeing is the responsible party here, whether they agree or not. What could be a future problem is many thinking that Li-Ion must be dangerous when in fact it is poor engineering or poor operational constraints that are the entire issue. Any car or aircraft battery can be misused if the pilots, maintenance, or repair personnel are determined to be destructive. That said, what the real 787 battery problem turns out to be awaits expert facts.
     
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  14. tochatihu

    tochatihu Senior Member

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    "Boeing is the responsible party here."

    I double down on this. Let's find out what went wrong and make sure it will not prevent commercial aviation from using 'secondary cells' from contributing to more efficient flying in the future. We need that. I don't care if one or another company gets shamed in the process.
     
  15. wjtracy

    wjtracy Senior Member

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  16. FL_Prius_Driver

    FL_Prius_Driver Senior Member

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    I read the opposite, that the mentioned solution addresses the issue Musk stated. Specifically that a thermal chain reaction between cells must be prevented with proper design techniques. Small Cell are much easier to handle, but Boeing is probably quite happy to put an very expensive, but rapidly issued, isolation solution in place to resolve the humongously expensive pain of having the whole fleet grounded.
     
  17. wjtracy

    wjtracy Senior Member

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    ^^^good, well I thought Musk might be correct...though I don't know if this solution solves all the shortcomings he saw
     
  18. SPEEDEAMON

    SPEEDEAMON Professional Car Nut

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