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Tool Talk Discussion Forum

Re: 787 and Li-ion

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MarkB_MI

01-20-2013 09:35:39
75.198.35.49



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George, the batteries in question are within the pressurized fuselage, so ambient temperature is not an issue. And should the aircraft lose pressure, the passengers and crew are at much greater risk of dying than those batteries.

The choice of battery type is an engineering decision based on a number of factors, primarily cost and weight. Of course, mass reduction is an overriding concern in aircraft design, second only to safety. Lithium ion offers the highest energy density of the commercially available battery technologies, so it's hardly surprising that Boeing went with li-ion. My guess it was a global decision: "every battery in the aircraft must be li-ion". I don't think the batteries in question are that large, so they could have gone with a different technology for those particular batteries with a small weight penalty.

I doubt Boeing will switch to a different technology. More likely they will go with a modified battery or charging system. Switching technologies would require modifications to the charging system, so there's little to be saved in terms of cost by switching to NiMH.

With regards to your Prius, a hybrid like the Prius doesn't need a huge amount of storage capacity. Ni-MH makes a lot of sense, since it offers very good energy density, is reasonably cheap and reliable. On the other hand, a plug-in EV or hybrid like the Volt needs a lot of storage capacity. That's why the Volt uses li-ion batteries.

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scotc

01-20-2013 11:38:36
75.238.69.210



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 Re: 787 and Li-ion in reply to MarkB_MI, 01-20-2013 09:35:39  
Somehow I doubt that the entire fuselage is heated, even though it is all pressurized.



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MarkB_MI

01-20-2013 13:11:47
75.198.35.49



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 Re: 787 and Li-ion in reply to scotc, 01-20-2013 11:38:36  
Did you ever have your luggage frozen solid when you arrived? The entire pressure vessel uses the same conditioned air, including the baggage compartment. If it didn't, Fido and Fluffy would arrive as freeze-dried pets.



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Charles (in GA)

01-20-2013 19:38:55
24.178.124.21



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 Re: 787 and Li-ion in reply to MarkB_MI, 01-20-2013 13:11:47  
Been more than one frozen cat or dog, it does happen. The cargo areas are pressurized, but depending on the aircraft, usually only one area is heated for animals and other temperature sensitive items. In a Boeing 757 and 767 its the aft most bin area, know as the "bulk" bin since it is the area where loose cargo is loaded. Other bins get some amount of heat, but not much. The airplane is insulated, but the cold still soaks thru.

The batteries are mounted between the cargo bin sidewall and the outer skin of the aircraft usually (the APU battery in the aft bin).

The battery selection is based in large part on capacity of the battery. In event of electric failure, the battery must be able to power certain critical circuits for a given period of time, 30 minutes If I recall. Given all of the electric gadgets in the 787, there is a greater need for power, just for the essential stuff in an emergency, hence a more powerful battery is needed. I suspect Boeing went with the Li-ion battery to keep the weight down and still maintain capacity (amp/hrs) LiSO2 batteries have been banned in aircraft for some 30 years now. I don't know how different a Li-ion battery is, but its not uncommon to have a laptop catch fire, or a cell phone, when the sophisticated circuits that control the charge rate and such fail.

Too much new technology in one aircraft.

Charles

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buickanddeere

01-20-2013 15:02:05
74.220.189.226



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 Re: 787 and Li-ion in reply to MarkB_MI, 01-20-2013 13:11:47  
Depends on the plane. Not every cargo hold is pressurized and/or heated on every aircraft.



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steve706

01-20-2013 17:53:22
216.208.94.148



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 Re: 787 and Li-ion in reply to buickanddeere, 01-20-2013 15:02:05  
Out of interest buickanddeere, are you an AME?



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big fred

01-20-2013 19:31:22
174.21.209.92



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 Re: 787 and Li-ion in reply to steve706, 01-20-2013 17:53:22  
Aviation medical examiner?



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steve706

01-21-2013 13:56:25
216.208.94.172



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 Re: 787 and Li-ion in reply to big fred, 01-20-2013 19:31:22  
AME stands for aircraft maintenance engineer, the canadian version of an airframe& powerplant mechanic.



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big fred

01-21-2013 17:00:05
174.21.201.149



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 Re: 787 and Li-ion in reply to steve706, 01-21-2013 13:56:25  
My last doctor was an AME, aviation medical examiner.



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