FAA, Boeing conclude 787 'safe' after battery problem

[Yancey Slide]

FAA, Boeing conclude 787 'safe' after battery problem (http://www.cnbc.com/id/101489044)

[RR_NDB]

"Without knowing precisely what caused the problem, Boeing developed more insulation between each battery's cells and a fireproof shell for the battery to starve it of oxygen if there is a fire. Each plane carries two batteries, which will each be surrounded by a stainless steel box. Each battery will have a titanium venting tube to a hole in the fuselage to carry flammable electrolytes and smoke overboard if a battery fails."

We should learn what was modified. Algorithms of chargers, circuitry or just the battery case?

This issue is very important. Batteries are essential so need to be safe and reliable.

Will go deeper to look what was changed. We discussed thoroughly the issue in another thread.

[VinRouge]

ETOPS implications anyone? In other words, battery may fail, not sure why, but let's wrap it in fireproof material so when it does, there is no problem. Hello?!

[RR_NDB]

Knowledge is essential in this issue. We must understand what caused Logan and Takamatsu cases. In this (ANA) i found little information. The equivalent circuit of the short circuit was very clear. I posted it on the BC thread. Will comment later on that. A wiring issue was reported. And the batteries are wonderful but critical. Must be inside tighter margins compared to other chemistries. (wrt to voltage and temperature)

On ETOPS the redundancy designed to 787 imho made the plane safe and adequately independent on the batteries. So, qualitatively speaking the redundancy is certainly good.

I will study the issue to be able to quantify. And be capable to answer your question.

I hope the redesign included algorithms. And even sensors per cell. Essential!

[EEngr]

RR_NDB
We should learn what was modified. Algorithms of chargers, circuitry or just the battery case?

It is my understanding that the case, inter-cell spacing and some over/under charge thresholds were changed.

The mechanical changes will minimize the spread of a single cell failure to other cells or the rest of the aircraft. Tighter over/under charge limits should cause more passive "battery fault" conditions. In other words, cases where the batteries operation has gone outside of limits and caused a shutdown.

It would be interesting to see how many modified batteries are being replaced for such shutdowns. Although that data may very well be proprietary.

[RR_NDB]

Tighter over/under charge limits should cause more passive "battery fault" conditions.

Not necessarily. Will comment thoroughly and deeply (circuit level) ASAP.

It would be interesting to see how many modified batteries are being replaced for such shutdowns. Although that data may very well be proprietary.

:ok:


It is my understanding that the case, inter-cell spacing and some over/under charge thresholds were changed.

Not enough! Per cell, TEMP and VOLTAGE is ESSENTIAL! Implemented?

[EEngr]

Per cell, TEMP and VOLTAGE is ESSENTIAL! Implemented?Per cell voltage was measured in the old battery configuration. What was done with this data is a good question. Undervoltage lockout on a 'lowest cell' voltage. Possibly also some input into the charging algorithm, but the battery assembly was never capable of individual cell charging.

Accurate per cell temp is difficult without modifying the cells to include internal temp sensors. The sensors in the battery assembly may have been relocated.

Tighter over/under charge limitsThere are two sets of limits to consider. The charging algorithm control thresholds. Modifying these will charge the battery 'more conservatively' and possibly avert thermal runaway and reduce lockout/maintenance replacement. The down side is that tightening these limits affects available battery capacity. The other set of limits are those that trigger lockout. Tightening these up could very well increase the number of lockouts, particularly if the charging algorithm isn't modified as well.

[RR_NDB]

Hi,

...but the battery assembly was never capable of individual cell charging.

IMHO it's much better and safer to do that. Thats the way i do. I posted yet in B&C thread.

What was done with this data is a good question.

:ok:

Accurate per cell temp is difficult without modifying the cells to include internal temp sensors.

Should be implemented yet. I consider ESSENTIAL. Outside is better than nothing.

The sensors in the battery assembly may have been relocated.

I hope the redesign made it.

The down side is that tightening these limits affects available battery capacity.

Sure, but i prefer lower capacity than an "offline" battery. ( i known on published the specs). If necessary larger batteries should be used. (derated).

Tightening these up could very well increase the number of lockouts, particularly if the charging algorithm isn't modified as well.

Ideally we should "learn" with the fleet batteries. Something like a holter. These wonderful and critical batteries "deserve".

[YeuEmMaiMai]

Lithium cells are very sensitive to manufacture processes, not sure how they are going to completely over come that one. I remember when my first employer started working with them, fires were not uncommon and even today when these cells fail, they do it in a spectacular fashion...

[EEngr]

Lithium cells are very sensitive to manufacture processes, not sure how they are going to completely over come that one.

True. But these particular GS Yuasa cells aren't unique to the 787 program. What is their service history to date in other applications? Manufaturing problems should show up across all customers.

How does Boeing's use of these differ from these applications?

[EEngr]

Sure, but i prefer lower capacity than an "offline" battery. ( i known on published the specs). If necessary larger batteries should be used. (derated).

The capacity of the battery, particularly the standby battery, is a matter of design certification. Early product development set this requirement and it would be expensive to change at this point. And it might introduce some operations changes that airline customers won't be happy with.

As to a larger battery, derated. That is possible. But the cells were selected off the shelf. The next increment in size might be quite a bit bigger physically and heavier. Again, design and certification costs.

But what it came down to was that Boeing "didn't know" what was causing the failures. So even with a bigger battery, the wisest decision was the fireproof box. Just in the event that the problem was not related to capacity.

[YeuEmMaiMai]

" How does Boeing's use of these differ from these applications? "

It really shouldn't differ. You have x amount of stuff that you need to have powered by y amount of batteries. Question is, how is the cell being managed? Is it getting too hot? Is it not being properly charged? I have no idea....

Just take a look at the consumer Lithium rechargeable battery problems over the years, Dell had problems with batteries that were made in Japan and were of decent quality under well controlled manufacturing process... Stuff happens and sometimes we just don't understand it until after the fact...

[EEngr]

Stuff happens and sometimes we just don't understand it until after the fact...

Not the sort of answer I'd expect when dealing with a manufacturer that self certifies their design. Aircraft need to be designed to a different set of standards than laptops due to the property value and lives at stake. The laptop industry has come up the learning curve and the issues of how to work with batteries is out there now. There are no more excuses of "we don't understand".

I think this goes beyond the battery issue and to the heart of certification itself. When someone signs certification documentation, they are claiming a level of expertise in the technology they are dealing with. If they "don't know" how it works, they shouldn't be approving it.

[YeuEmMaiMai]

Unfortunately like it or not, sometimes that answer is all we have... I am not any happier about it than you are....

[EEngr]

I am not any happier about it than you are.... Fine, but I want something done about it. The FAA shouldn't be accepting approvals from people that don't know what they are doing. The battery issue is water under the bridge, but the question of certification process needs addressing.