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The Boeing Company Message Board

  • cbx6cylinder cbx6cylinder Jan 26, 2013 11:30 PM Flag

    Battery Choice Saved 40 Pounds

    These words are from an article I read.

    And the worst part of this is that a safer battery was available for the 787 all along. That safer battery would have come at a cost, however — adding 40 pounds — .01% to the 787′s 502,500 pound maximum takeoff weight.

    That’s the view of MIT professor, Donald Sadoway, who told the Times that a nickel-cadmium battery would have worked just as well without the little self-immolation problem that afflicts lithium-ion batteries. And the tiny additional weight of nickel-cadmium batteries — which would make the 787 a bit more costly to operate — hardly justified the fire risk of the lithium-ion ones.

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    • A lot of assumptions are being made about the 787 LI batteries, and just because some MIT professor throws his opinion into the fray doesn't mean anything unless he is a subject matter expert in batteries, especially LI batteries. Also I wouldn’t put too much weight into his opinion since his math isn't even close , 40 pounds of a 500,000 pound plane is 0.00008%, not .01%.

      Now there are some good ideas being passed around, but they are based on assumptions, like better cooling, but do we know if the batteries in normal use even get warm enough to benefit from it? I can think of some things too, like per cell voltage, temp monitoring, and per cell charging regulation, but how do I know if they have not all ready done so?

    • The lithium-ion batteries are faster charging and lighter than nickel-cadmium batteries.

      Add a cooling system to the lithium-ion battery and give up some of the weight advantage but keep the fast-charging advantage.

      The Tesla battery packs, for instance, are liquid-cooled.

      Going to a nickel-cadmium battery would require a re-design of the electrical system. Going to a liquid-cooled lithium-ion battery would be a quicker fix.

    • The Forbes article goes on to quote the professor: The lithium-ion battery in a cell phone, for example, is safer because the battery is so close to the outside of the phone that heat does not build up and cause a problem. In stark contrast, the 787′s lithium-ion battery is actually eight notebook sized batteries all packed next to each other in a closed box. This means that only the batteries on the ends have any hope of venting the heat they generate. The other six batteries just heat each other up since they can’t release their heat outside the box.... He also would put temperature sensors on each of the eight batteries and implement a “system of forced airflow” inside the box to help assure that the temperature of each battery stays below a threshold level.

      It pains me to think that Boeing would make a fundamental design error like this but in the context of outsourced design of systems with multiple sub contractors it makes more sense. The system issues, like overheating, can get lost in the rush to make schedules, reduce weight, integrate the parts, and keep the system within a specified size.

      I hope this doesn't turn out to be the problem (or part of the problem) because it's embarrassing. But, if it is it should be a relatively easy fix, particularly if Boeing is smart enough to bring in people like this to consult.

      Sentiment: Hold

      • 2 Replies to techpath2000
      • Did a patent search for Boeing, Thales, and GS Yuasa (as "assignee") using "abstract" terms "battery AND lithium AND thermal" which resulted in nothing for Boeing and Thales and nothing meaningful for Yuasa. (I ignored Secuarplane as they do not appear to have a direct physical/thermal responsibility.) However the same search for "Saft" (maker of commercial and defense Li-ion batteries, a French company with U.S. based manufacturing) resulted in a cogent patent involving understanding the potential runaway heating problem for Li-ion batteries and a patented method to control and remove the heat. The Saft Patent (5,187,030) was issued in 1993. (I am not offering that it is a profound patent, but it is there, nevertheless). The point being that many understand that the thermal management of Li-ion batteries is crucial. Satellite manufacturers, for example, like Boeing, Loral, and Lockheed Martin also "worry" the battery thermal management to the "nth" degree of everything, and especially the battery as its performance is greatly impacted by conditions too cold as well as too hot. Once in space, there is not much in the way of adjustments that can be made. The design of such thermal control is proved and shaken down in unit, subsystem, and system level testing. It is hard to believe that Boeing Airplane did not have an appreciation for Li-ion battery thermal issues but may have, as you suggested, lost control of the thermal systems discipline in the outsourcing process for the battery.

 
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