FAA, Boeing conclude 787 'safe' after battery problem
Thread Starter
Joined: Jul 2008
Aviation Qualifications: CPL
Posts: 77
Likes: 0
From: MA, USA
FAA, Boeing conclude 787 'safe' after battery problem
Joined: Feb 2011
Posts: 876
Likes: 0
From: Nearby SBBR and SDAM
Redesign
"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."
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.
Last edited by RR_NDB; 19th March 2014 at 22:41.
Joined: Feb 2011
Posts: 876
Likes: 0
From: Nearby SBBR and SDAM
ETOPS implications anyone?
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!
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!
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
RR_NDB
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.
We should learn what was modified. Algorithms of chargers, circuitry or just the battery case?
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.
Joined: Feb 2011
Posts: 876
Likes: 0
From: Nearby SBBR and SDAM
Tighter over/under charge limits should cause more passive "battery fault" conditions.
It would be interesting to see how many modified batteries are being replaced for such shutdowns. Although that data may very well be proprietary.
It is my understanding that the case, inter-cell spacing and some over/under charge thresholds were changed.
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
Per cell, TEMP and VOLTAGE is ESSENTIAL! Implemented?
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 limits
Joined: Feb 2011
Posts: 876
Likes: 0
From: Nearby SBBR and SDAM
Safer Li batts
Hi,
IMHO it's much better and safer to do that. Thats the way i do. I posted yet in B&C thread.
Should be implemented yet. I consider ESSENTIAL. Outside is better than nothing.
I hope the redesign made it.
Sure, but i prefer lower capacity than an "offline" battery. ( i known on published the specs). If necessary larger batteries should be used. (derated).
Ideally we should "learn" with the fleet batteries. Something like a holter. These wonderful and critical batteries "deserve".
...but the battery assembly was never capable of individual cell charging.
What was done with this data is a good question.
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.
The down side is that tightening these limits affects available battery capacity.
Tightening these up could very well increase the number of lockouts, particularly if the charging algorithm isn't modified as well.
Joined: Mar 2014
Posts: 5
Likes: 0
From: Here and there
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...
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
Lithium cells are very sensitive to manufacture processes, not sure how they are going to completely over come that one.
How does Boeing's use of these differ from these applications?
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
Sure, but i prefer lower capacity than an "offline" battery. ( i known on published the specs). If necessary larger batteries should be used. (derated).
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.
Joined: Mar 2014
Posts: 5
Likes: 0
From: Here and there
" 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...
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...
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
Stuff happens and sometimes we just don't understand it until after the fact...
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.
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
I am not any happier about it than you are....
