Dreamliner: Boeing 787 Aircraft Battery "Not Faulty"

SternisheFan writes "Airline safety inspectors have found no faults with the battery used on Boeing's 787 Dreamliner, Japan's transport ministry has said. The battery was initially considered the likely source of problems on 787s owned by two Japanese airlines. The world's entire fleet of 50 787s has been grounded while inspections are carried out. Attention has now shifted to the electrical system that monitors battery voltage, charging and temperature. Transport ministry official Shigeru Takano said 'we have found no major quality or technical problem' with the lithium-ion batteries. Shares in GS Yuasa, which makes the batteries, jumped 5% on the news. 'We are looking into affiliated parts makers,' he said. 'We are looking into possibilities.'"

Comments

Not entirely surprising

[vlm]

Not entirely surprising, its usually the charger and/or the discharge protection ckts. Ask the RC electric airplane people who have at least a decade or so experience with lithium batteries in airplanes and burning them up. I was into RC planes back when everyone used NiCad but I've kept up with recent events. The batteries themselves rarely burst into flame, they burst into flame when you connect them to something that does something very naughty well outside the limits of the datasheet.

I think this will probably, in the long run, turn into a "EE ethics and morals class" debate. So discharging 15 amps out of a 10 amp pack results in a 0.001% chance (actually pretty high) of blowing the pack up per the data sheet. However not supplying 15 amps to the engine control system during an alternator malfunction (or whatever) means the engine shuts down and 500 people have a near 100% chance of death. "just follow that datasheet" stuff could kill lots of people, then again "ignore the datasheet" could kill lots of people too. So if you must use lithium batteries (why?), then you can find a local minimum death rate which will not be zero... of course finding that might have to be done via experiment on unwilling crash victims, whole nother ethical issue. Basically, we're trading human life for slightly improved gas mileage, which certainly makes me want to fly on a carrier using airbus products instead of boeing products, which has other ethical issues, etc. Is the ethical/moral failure the managers for doing it despite advice against, the engineers fault for not committing career and economic suicide by refusing to design a lithium aircraft pack, the supplier for making batteries for an unsuitable purpose, the arabs fault for making jet fuel so expensive so we have to kill people with lightweight batteries, ...

The simplest thing is a battery drop tank arrangement or a rather stout thick wall steel case, making the works heavier than using old fashioned lead acid.

Re:Japanese covering their butts?

[AmiMoJo]

As opposed to the American company that is heavily supported by the American government telling us the fault must lie with the Japanese batteries it bought. I see where you are coming from.

Re:Oxygen is usually the culprit in most fires

[Anonymous Coward]

Actually it would not help. The nasty thing about these battery fires is the battery chemistry SUPPLIES OXYGEN.

Nuanced response

[Okian Warrior]

So what you're really saying is "Take the number of [batteries] in the field, A, multiply by the probable rate of failure, B, multiply by the average out-of-court settlement, C. A times B times C equals X. If X is less than the cost of a recall, we don't do one. "

The actual answer is more nuanced.

FAA regulations define 5 levels of critical for safety systems: levels A through E.

Level A is for things that can knock a plane out of the sky when they fail; for example the stall speed alarm.
Level C is for things that can cause injury or at most a single death; for example, the cabin pressurization system
Level E is for things that don't affect flight safety; such as, in-flight entertainment or the microwave in the galley

For reference, I wrote the software for cabin pressurization systems. It's level C (hardware == B), which means that failure in pressurization is an emergency situation, but isn't expected to kill everyone on board. The masks drop and the pilot immediately dives to under 10,000 feet to restore breathable air.

If the cabin fills with smoke, it's not life-threatening per se. The pilot can override the pressurization system and "dump" the cabin atmosphere, and it clears pretty quick. (The captain also dives to under 10,000 feet if necessary.)

The battery catching fire isn't a problem SO LONG AS the fire itself won't cripple the aircraft. The battery underpowering the plane when the alternator dies MAY BE a problem which would kill people.

The people who design these things take these levels into consideration, and the general rule is "fail safe". If you can't "fail safe", then "fail in the least dangerous way". In my experience, the engineer must make many choices when designing an aircraft unit. The answer is always "do it *this* way, because if *that* happens it will be less dangerous.

Let's wait and see what the investigation uncovers. Here are some Cliff notes:

1) Li-Ion batteries might behave differently at altitude (cabin pressure is reduced while flying)
2) The battery may be performing to spec, while trying to compensate for a more dangerous problem
3) Smoke in the cabin is not as dangerous as you might think
4) Things that burn are designed to not damage things when burning
5) People who design aircraft are pretty smart, and have a generally high moral standard.
6) People who investigate aircraft incidents are really, really thorough, and have a good track record.

(Note: Glossing over some details to make an easier read.)

Re:Japanese covering their butts?

[anubi]

The charge management circuit is what has me concerned. I have messed with plenty of failed power tool batteries, dissecting each, and finding common points of what caused the whole assembly to fail, and every time it has been the concept of cells in series.

The cells do not have identical leakage, so some cells tend to overcharge to compensate for the other cell in the stack which leaked its charge away.

This phenomena shows up after the cells have been in service for months to years.

The older chemistries I have worked with have been relatively tolerant of overcharge, converting the excess energy either to heat or hydrogen gas, which was silently vented. Lithium ion cells are not nearly as tolerant to overcharge as NiCd, LiMH, or Lead-Acid cells. Overfilling a lithium ion cell seems like overfilling a propane tank. Once it tops off, there is nowhere for the excess energy to go and POP goes the weasel.

If you are charging based on stack voltage, you will overcharge the hell out of a good cell as you try to bring the terminal voltage of a weak cell up. You will detonate your good cell in the process.

I am currently playing around with a lithium battery pack monitor with which I have individual chargers for each cell. There is no way I would consider charging all cells in series as is commonly done in the earlier packs. With the DC isolation I can easily get from high frequency inverters, it is quite easy for me to get matched voltages from multiple windings. I use supplemental converters to additionally charge individual cells that leak a bit more than others in the pack. I also have switched cell monitors which rapidly switch each cell onto a measurement buss along with three tightly controlled reference voltage sources. This results in a signal stream which indicates terminal voltage of every cell in the pack, cell by cell. This feeds a digitizer which constantly tracks each cell voltage and is instructed to terminate battery function if any cell shows over or under charge. If a cell simply needs a little help, the individual cell inverters kick in to boost the weaker cell and such activity logged.

A supplemental benefit of the serial analog data stream is that I can use any oscilloscope to see all the cells at once... I can sync to cell 0 which is the reference voltage. ( three references because this is so critical that if I have a reference drift I will have two others that hopefully are providing reliable data. Bad data = explosion; false trip=expensive downtime ).

Lithium batteries have a lot to offer, but they are also quite a bit more volatile than other chemistries I have worked with. Even YouTube has quite an assortment of videos of overcharged lithium cells igniting. Like a propane tank, they are quite useful if not mistreated, but can really take you to the cleaners if you do.