787 and Li-ion

Geo-TH,In

Well-known Member
Seems like the 787 fires may be linked to the Li-ion batteries being overcharged. Or is the Li-ion battery have an issue with thermal run away?

When it's cold, my charger won't charge Li-ion batteries. It has to be very cold at 35000 feet.

I have 2 Li-ion batteries that are 4 years old. They hold their charge and take a full charge. However, they can't hold a candle to the batteries found in a Toyota prius, Ni-MH.

The price of Ni-MH batteries is close to the price of Ni-cd, but last for years. My 5 year old Ni-MH batteries are as good as the day I bought them.

Do you think Boeing will use Ni-MH?

George
 
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.
 
I've got 20 year old Nicads that still sort of work but my 10 year old NIMH's are all garbage. They just don't seem to have a good lifespan.

I moved all my tools to lithium ion, they have been great. The cold weather isn't the best for them but warm them up even a bit and they are fine.
 
Hello George Marsh,

I Have NiCad's, they work for me!
I get extra packs whenever someone gets tired of them. I recycle and make one out of two or three.
Original packs are as old as your Li-ion, and still going strong! With 4 packs I think I can drill all day,

Guido.
a97472.jpg
 
it doesn't take a whole lot of smoke to make a whole cabin seem as if its on fire. Most likely its getting over charged some how. The MD 88 still have a problem with the generator control units going bad. Use to have to do a test on one every time it landed. It will be figured out shortly.
 
All of the volume contained between the forward and aft pressure bulkheads is heated/cooled. Air is bled off the compressor sections on the engines and run through an air cycle machine if it needs to be cooled. That is true on transport category jets since the 707 days, but I think I did read that the 787 is somewhat different. It may use an electrically driven compressor to accomplish AirCon/Pressurization.

The FAA has certified 2 engine jets for over water operation since the advent of the Boeing 757/767 under a program called ETOPS, for extended range operations. Under a 180 minute ETOPS rule you can lose an engine and be allowed to fly for 180 minutes at single engine cruise to get to the nearest land.

Seems like the biggest worry with this 787 battery problem would be to have a battery fire or thermal runaway over the ocean and still have to fly 3 hours or so to land. UPS lost an airplane in Dubai when some computer batteries they were carrying as cargo shorted or ran away and started a fire. The pilots overflew a suitable airport while trying to get back to their departure airport. They were overcome by the smoke/fumes which was believed to be so thick they could not see, even with O2 masks and smoke goggles.
 
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.
 
Just simple matter of too many watts of power pushed into the battery and could not dissipate the heat.
System voltage has to be dropped to limit charging current and heating.
There should have been rtd's or thermal couples throughout the battery pack to monitor voltage.
Given the price of fuel over the lifetime of the airframe. Manufactures go to extreme lengths such as the lithium batteries and carbon fibre composite structure.
The more complicated you make anything, the more it will come back to bite you in the behind.
 
What passenger carrying, pressurized, jet transport aircraft does not have the cargo areas pressurized/heated?
 
Overnight stays are the reason that airplane electronics need to be qualified to operate at -40C after cold soak at -55C. Critical electronics and those needed to start the engines need to be qualified to operate at -55C. There are further requirements for equipment located outside the pressure hull, such as at the engines and control surfaces, to operate at the lowest temperature expected, which is a function of outside air temperature at altitude and minimum airspeed at that altitude. And of course there are corresponding qualification requirements for the high temperatures.
 
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
 
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
 
A big part of the exceptional life of the Ni-MH battery in the Prius (as much as 400K miles)is the fact that they are never charged above 80% charge,nor discharged below 20%. They trade 40% of battery capacity for exceptional long life.

They tell me those batteries make a lot of internal heat during the last 20% of a recharge, or the last 20% of a discharge, so Toyota just does not allow them to operate in those conditions.
 
Reports now say that it was not a too-high charge rate that caused the failure. Guess time will tell, or they hope the attention will fade.
 
My little (25 ton) airplane uses Ni-Cads, two of them right in the nose. They're outside the pressure vessel and get to go from soaking on a 120 degree ramp in DFW to -50 or -60 Centigrade in about half an hour and do that several times a day in the summer.

They seldom give trouble and are supposed to give me 40 to 45 minutes of power to the essential things while I'm in the air, though I've never had to test that out for myself. A battery overtemp condition is a big deal and on our "short list" of baddest of the bad emergencies.

The Lithiom Ion batteries are a big deal in aviation in that they (FAA) are looking to severely restrict their transport, banning them on cargo shipments. They're lighter for the same energy capacity, hence Boeing using them on the 787. If the membranes in the battery get damaged they can make their own thermal runaway. These are teething problems and not surprising considering the technology leap in the 787.
 

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