787 Batteries and Chargers - Part 1
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I have a fair amount of experience in laminates. If I had to be restricted to one facet of this failure, I would look at the performance (in service) of the roll.
Expansion and contraction, (with and without heat) would happen at variable rates, and substrate performance would be related to the shear of the adhesive relative to the binding strength of the separate layers.
Each cycle would aggravate any weakness from the manufacture, and new and variabe failures would propagate. The system would break down over time, and penetration of electrolyte (conductor) would occur. Hotspots and potential thermal runaway would likely appear, well ahead of optimistic projections.
The evidence is in the photography of the MAIN Battery in the report. The tortuous and serpentine folds show the results of repetitive expansion, contraction, and variable "return Rates" to original.
Conclusion? Each of the layers present in the roll is fragile, in its own way. Each exhibits particular responses to the stresses of environmental and mechanical challenges. The elastic value of the laminated roll is near zero, it wants to remain in the "last" position it had. forcing it to contort in these conditions is degrading the performance of its intended use.
Layerman (Acryl Cellulosic, monolithic Alumina/acrylate, glassfibre/epoxy, two phase cellulosic/phenolic, etc.) Certified in Epon.
Expansion and contraction, (with and without heat) would happen at variable rates, and substrate performance would be related to the shear of the adhesive relative to the binding strength of the separate layers.
Each cycle would aggravate any weakness from the manufacture, and new and variabe failures would propagate. The system would break down over time, and penetration of electrolyte (conductor) would occur. Hotspots and potential thermal runaway would likely appear, well ahead of optimistic projections.
The evidence is in the photography of the MAIN Battery in the report. The tortuous and serpentine folds show the results of repetitive expansion, contraction, and variable "return Rates" to original.
Conclusion? Each of the layers present in the roll is fragile, in its own way. Each exhibits particular responses to the stresses of environmental and mechanical challenges. The elastic value of the laminated roll is near zero, it wants to remain in the "last" position it had. forcing it to contort in these conditions is degrading the performance of its intended use.
Layerman (Acryl Cellulosic, monolithic Alumina/acrylate, glassfibre/epoxy, two phase cellulosic/phenolic, etc.) Certified in Epon.
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Most of my experience with heat damage has to do with monolitic structure, depending on the purity of the mix, failure is propagated with variable absorption/loss of heat. Fractures are frequently complete, through the width of the material.
With a laminated application, geometry plays an important part, introducing radial differentials at adhered surfaces, and mechanical stresses that vary dependent on the expansion rate of each layer. It strikes me the rate of heat gain and loss would be different at the rolled returns of each layered mass.
How brittle is the paste? How resilient? The metal foil would behave well in mechanical stress, but conduct heat very differently than the anode cathode.
The Poly film would seem to be the most vulnerable to heat and mechanical stress.
There must be a Thermal engineer here?
With a laminated application, geometry plays an important part, introducing radial differentials at adhered surfaces, and mechanical stresses that vary dependent on the expansion rate of each layer. It strikes me the rate of heat gain and loss would be different at the rolled returns of each layered mass.
How brittle is the paste? How resilient? The metal foil would behave well in mechanical stress, but conduct heat very differently than the anode cathode.
The Poly film would seem to be the most vulnerable to heat and mechanical stress.
There must be a Thermal engineer here?
That's all very well Lyman, and I do not doubt your experience in this field.
However,
The original single battery (constructed of three cells if you will) appears to perform well ON IT'S OWN,
It is only when as, Eeng has alluded, Boeing/Thales bung eight of them together and attach them to an aeroplane that it all goes wrong.
However,
The original single battery (constructed of three cells if you will) appears to perform well ON IT'S OWN,
It is only when as, Eeng has alluded, Boeing/Thales bung eight of them together and attach them to an aeroplane that it all goes wrong.
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There must be a Thermal engineer here?
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TURIN
Is there precedent for a single battery in service aboard an aircraft?
In "Large Format"?
All of Boeings propositions have to do with protecting seven cells from just one.
So, when was this single battery tested under CFR? Cold soak, pressure cycles, charge discharge, load, SOC over time (storage). Inert storage?
I think it has more to do with aeronautical conditions, than keeping company with other batteries.
The obvious possibility is degradation of capacity and performance, faster than was predicted on the bench. Boeing, (No one) tested this battery in the sky, integrated with all systems.
Of all the removed Batteries, did some of the locked out cells migrate back into the fleet? Disassemble, test, recharge, assemble and ship? Yuasa had a sole source contract for this battery, Take note of the "tamper proof seal" on the APU BATT......
Demands of service would have everything to do with performance, whether solitary, or grouped in eights?
It is only when as, Eeng has alluded, Boeing/Thales bung eight of them together and attach them to an aeroplane that it all goes wrong.
In "Large Format"?
All of Boeings propositions have to do with protecting seven cells from just one.
So, when was this single battery tested under CFR? Cold soak, pressure cycles, charge discharge, load, SOC over time (storage). Inert storage?
I think it has more to do with aeronautical conditions, than keeping company with other batteries.
The obvious possibility is degradation of capacity and performance, faster than was predicted on the bench. Boeing, (No one) tested this battery in the sky, integrated with all systems.
Of all the removed Batteries, did some of the locked out cells migrate back into the fleet? Disassemble, test, recharge, assemble and ship? Yuasa had a sole source contract for this battery, Take note of the "tamper proof seal" on the APU BATT......
Demands of service would have everything to do with performance, whether solitary, or grouped in eights?
Last edited by Lyman; 11th Mar 2013 at 19:35.
Is there precedent for a single battery in service aboard an aircraft?
The ACE (Actuator Control Electronics) backup Batteries are also Li-Ion. Much smaller than a main battery and only designed to last about ten minutes. As far as I know there have been no reported problems with these, even the one that got charred by the APU battery at Boston.
The 777 has a similar ACE backup battery. I wonder if it too is Li-Ion?
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@EEngr
Per quotes in the media from GS Yuasa, the cell design and construction used in the LVP65 battery was first put into production batteries by them around 1999 and was considered the best choice for the LVP65 based on how well it had worked in previous batteries in other applications.
But what is the service experience with the GS Yuasa LVP65 battery in other applications? Good? Bad?
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Syseng68k, #911
Yes, wind energy systems.
This can be mitigated by ensuring the system can detect and isolate the first fault, and prevent further fault.
The high number of failing batteries could indicate that either the cells are having quality issues, or the cells are operating outside limits.
I'm not sure that number of thermal runaways would be zero, even if the cells are perfect and running under perfect conditions.
Each cell has many square meter of foil, in multiple layers separated with a tin layer of metal oxide.
An imperfection in the metal oxide layer could result in a short.
If the cell is large (or multiple cells are connected in parallel), then the amount of energy that can be dissipated in a fault area is higher, and may reach the combustion/runaway temperature.
Measures sufficient for small cells, might be insufficient for large cells.
Yes, wind energy systems.
There's stiil the problem of >1 cell shorting to case, but I guess
that scenario could be covered by fusable links between the cells, rather than the existing copper straps.
that scenario could be covered by fusable links between the cells, rather than the existing copper straps.
However, my point would still be that if the cells are properly managed and run within data sheet limits, the problem won't arise in the first place.
I'm not sure that number of thermal runaways would be zero, even if the cells are perfect and running under perfect conditions.
Each cell has many square meter of foil, in multiple layers separated with a tin layer of metal oxide.
An imperfection in the metal oxide layer could result in a short.
If the cell is large (or multiple cells are connected in parallel), then the amount of energy that can be dissipated in a fault area is higher, and may reach the combustion/runaway temperature.
Measures sufficient for small cells, might be insufficient for large cells.
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Maybe simply too much current demand while the battery is still too cold ... pity there are no more details re. the Boeing tests (NTSB report page 33, end of paragraph 1.7).
On the other hand, post# 1222 in the Other thread, re. E/E cooling, mentions air drawn from the cabin (?) ; however the FDR data has things like Cooling_Sensor_Aft_Temp_EE, about 20 degree F. How does it work really?
On the other hand, post# 1222 in the Other thread, re. E/E cooling, mentions air drawn from the cabin (?) ; however the FDR data has things like Cooling_Sensor_Aft_Temp_EE, about 20 degree F. How does it work really?
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On the other hand, post# 1222 in the Other thread, re. E/E cooling, mentions air drawn from the cabin (?) ; however the FDR data has things like Cooling_Sensor_Aft_Temp_EE, about 20 degree F. How does it work really?
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TURIN
The ACE is single purpose, a true 'Backup', not integrated into the distribution system for general purpose.
If only the APU/MAIN had similar function....
This 'large format' (scaled up) battery as used in the Dreamliner suggests that LiIon is suited to standby power only...
@HighWind... I think the Yuasa program shows challenges to materials/methods as regards spontaneous failure.....also. The pastes, but especially the oxide, must be scrupulously blended, (powder/binder) without imperfection of powdery occlusions, or viscosity variation. Add to that the loss of symmetry of the roll in service, and.....poor performance.
The ACE (Actuator Control Electronics) backup Batteries are also Li-Ion. Much smaller than a main battery and only designed to last about ten minutes. As far as I know there have been no reported problems with these, even the one that got charred by the APU battery at Boston.
If only the APU/MAIN had similar function....
This 'large format' (scaled up) battery as used in the Dreamliner suggests that LiIon is suited to standby power only...
@HighWind... I think the Yuasa program shows challenges to materials/methods as regards spontaneous failure.....also. The pastes, but especially the oxide, must be scrupulously blended, (powder/binder) without imperfection of powdery occlusions, or viscosity variation. Add to that the loss of symmetry of the roll in service, and.....poor performance.
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Weight saving in airliners
So true, those comments about save a pound and cost a hundredweight...
Been saying for decades that so much booze and pop being carried about the planet unused is more than foolish, its criminal when effectively its responsible for major incidents due over zealous weight saving....
I've seen a 5/32" instead of a 3/16" shear pin cause a fatal in a light aircraft, saved all of another spoonful of cornflakes at breakfast for the pilot but was in a critical position..
Been saying for decades that so much booze and pop being carried about the planet unused is more than foolish, its criminal when effectively its responsible for major incidents due over zealous weight saving....
I've seen a 5/32" instead of a 3/16" shear pin cause a fatal in a light aircraft, saved all of another spoonful of cornflakes at breakfast for the pilot but was in a critical position..
Last edited by HarryMann; 12th Mar 2013 at 10:22.
Do a Hover - it avoids G
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Weight saving in aircraft
Saving weight is what life is all about when you start the original design process of any aircraft. This applies whether the aircraft is one powered by rubber that you wind up as a kid or is the next generation airliner or combat aircraft. Unless you are totally ruthless about weight the resulting aircraft will be hopelessly out performed by any competitors.
Judging the weight benefits and penalties in the design stage is where the skill comes in. Once you have an aircraft to ground test and later flight test then we start to get the benefit of hindsight as to whether the design choices were flawed.
While it is NOW as obvious as the balls on a dog that the 787 battery choices have produced more penalties than benefits criticising the original choice on the lines of “everybody knows those things are trouble etc” is easy but does not reflect what went on at the paper design stage. I am quite sure one of the battery people might well have preferred NiCads (or whatever) but I am also sure another guy wanted more weight in the bracket that the main gear is fixed to. Detailed designers are conservative people who do not want their part of the design to let down the team.
Enter the chief designer. If he allowed every designer to have his conservative choice they would probably have to strengthen the hangar floor. So where does he draw the line? – because it is HE who has to draw it. If he does not push towards the dodgy end of the spectrum we would never have got the continually better aeroplanes that the world has seen for the last 100 years.
Working on a VTO aircraft in the early 60s I asked the chief designer why on earth the cockpit had to be so low because it was going to ruin the rearwards view and he replied “to save aluminium on the fuselage sides”. At the time I thought he was wrong. Later I understood his problem and where he was coming from.
Judging the weight benefits and penalties in the design stage is where the skill comes in. Once you have an aircraft to ground test and later flight test then we start to get the benefit of hindsight as to whether the design choices were flawed.
While it is NOW as obvious as the balls on a dog that the 787 battery choices have produced more penalties than benefits criticising the original choice on the lines of “everybody knows those things are trouble etc” is easy but does not reflect what went on at the paper design stage. I am quite sure one of the battery people might well have preferred NiCads (or whatever) but I am also sure another guy wanted more weight in the bracket that the main gear is fixed to. Detailed designers are conservative people who do not want their part of the design to let down the team.
Enter the chief designer. If he allowed every designer to have his conservative choice they would probably have to strengthen the hangar floor. So where does he draw the line? – because it is HE who has to draw it. If he does not push towards the dodgy end of the spectrum we would never have got the continually better aeroplanes that the world has seen for the last 100 years.
Working on a VTO aircraft in the early 60s I asked the chief designer why on earth the cockpit had to be so low because it was going to ruin the rearwards view and he replied “to save aluminium on the fuselage sides”. At the time I thought he was wrong. Later I understood his problem and where he was coming from.
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Puffy cells and stuff, the root cause
Excessive cell case flexing due to either overcharging or reduced external pressure cycling will cause internal shorting of the electrodes, fatigue of the aluminum and copper current collector fingers, etc. This is the root cause.
When a Lithium cell is "puffy" it typically has a reduced capacity and is an indication of over-charging. i.e. it is damaged goods.
But what else can puff out a cell?
How about the 3 psi differential pressure between the inner volume of the cell case (@14.7) and the reduced pressure of the E/E bay at 6000' (@11.8 psi) -- the deflection of the 5" x 7" sheet of 0.031" thick 304 stainless steel that is the S1 and S3 cell case will experience plastic deformation. You can see it in the CT scans of the Main, Fig 22. That expansion creates voids in the windings and separates the poly separator from the foils--it is now damaged goods and its charging profile will no longer follow the sinc and exponential model assumed by the Battery Charging Unit software as described in the patent.
Is it possible that three 45-second 450Amp APU starts with 60 seconds rest in-between would pull the pack down below the 15% capacity lock-out of the BMU.
What is the 15 % lock-out? That is the condition when the BMU energizes the contactor to open-circuit the battery and render it useless unless returned to the vendor for reset/recharge.
When a Lithium cell is "puffy" it typically has a reduced capacity and is an indication of over-charging. i.e. it is damaged goods.
But what else can puff out a cell?
How about the 3 psi differential pressure between the inner volume of the cell case (@14.7) and the reduced pressure of the E/E bay at 6000' (@11.8 psi) -- the deflection of the 5" x 7" sheet of 0.031" thick 304 stainless steel that is the S1 and S3 cell case will experience plastic deformation. You can see it in the CT scans of the Main, Fig 22. That expansion creates voids in the windings and separates the poly separator from the foils--it is now damaged goods and its charging profile will no longer follow the sinc and exponential model assumed by the Battery Charging Unit software as described in the patent.
Is it possible that three 45-second 450Amp APU starts with 60 seconds rest in-between would pull the pack down below the 15% capacity lock-out of the BMU.
What is the 15 % lock-out? That is the condition when the BMU energizes the contactor to open-circuit the battery and render it useless unless returned to the vendor for reset/recharge.
Last edited by kenneth house; 16th Mar 2013 at 13:59.
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@kenneth house
- Hull and eebay is at cabin altitude ~6000 feet
- Cells are derated to 4.025V / ~80%SOC
- BCU was not connected to charger / test rig at 2006 incident
- OV/UV is being considered as part of investigation
- Exemplar batteries showing deformation - CT report pg 26, img 22 - of cells are being examined
Last edited by saptzae; 12th Mar 2013 at 21:34. Reason: Fixed cabin alt 6000, Thanks Turin!
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The FAA has given Boeing permission to move forward with their proposed fix.
The Federal Aviation Administration (FAA) today approved the Boeing Commercial Airplane Company's certification plan for the redesigned 787 battery system, after thoroughly reviewing Boeing's proposed modifications and the company's plan to demonstrate that the system will meet FAA requirements...
...The FAA will approve the redesign only if the company successfully completes all required tests and analysis to demonstrate the new design complies with FAA requirements. The FAA's January 16, 2013 airworthiness directive, which required operators to temporarily cease 787 operations, is still in effect, and the FAA is continuing its comprehensive review of the 787 design, production and manufacturing process.
...The FAA will approve the redesign only if the company successfully completes all required tests and analysis to demonstrate the new design complies with FAA requirements. The FAA's January 16, 2013 airworthiness directive, which required operators to temporarily cease 787 operations, is still in effect, and the FAA is continuing its comprehensive review of the 787 design, production and manufacturing process.
•Hull and eebay is at cabin altitude ~6000 feet
Fixed it for ya.
The ACE is single purpose, a true 'Backup', not integrated into the distribution system for general purpose.
The APU battery has a single purpose, mainly. It is not integrated into the system. It starts the APU (occasionally) or powers the Nav lights (very occasionally).
But still failed.
The main battery has extra functions compared to say, the 777 main batteries, and that is to power emergency brakes (hardly ever) or towing without a generator (rare).
And also failed.
General purpose? No.
Fixed it for ya.
The ACE is single purpose, a true 'Backup', not integrated into the distribution system for general purpose.
But still failed.
The main battery has extra functions compared to say, the 777 main batteries, and that is to power emergency brakes (hardly ever) or towing without a generator (rare).
And also failed.
General purpose? No.
Last edited by TURIN; 12th Mar 2013 at 21:34.
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"The FAA also granted Boeing permission to begin flight test activities on two airplanes: line number 86, which will conduct tests to demonstrate that the comprehensive set of solutions work as intended in flight and on the ground; and ZA005, which is scheduled to conduct engine improvement tests unrelated to the battery issue."
Engine improvement tests??
Here is the FAA link...(sorry, but due to budget cuts, the FAA cannot afford the word wrap in a press release)
Press Release – FAA Approves Boeing 787 Certification Plan
edit: Waiting on the NTSB repsonse...
and of course, the last line of the news release..
"The FAA’s January 16, 2013 airworthiness directive, which required operators to temporarily cease 787 operations, is still in effect, and the FAA is continuing its comprehensive review of the 787 design, production and manufacturing process."
Engine improvement tests??
Here is the FAA link...(sorry, but due to budget cuts, the FAA cannot afford the word wrap in a press release)
Press Release – FAA Approves Boeing 787 Certification Plan
edit: Waiting on the NTSB repsonse...
and of course, the last line of the news release..
"The FAA’s January 16, 2013 airworthiness directive, which required operators to temporarily cease 787 operations, is still in effect, and the FAA is continuing its comprehensive review of the 787 design, production and manufacturing process."
Last edited by FlightPathOBN; 12th Mar 2013 at 21:50.
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Does the ACE perform other, occasional duty? How many discharge/charge cycles per flght? Is it enclosed, with a tamper proof seal? Is it not a true "Backup" storage battery, where the APU/MAIN batteries do extra duty?
Do you know if the ACE storage battery is part of the AD?
Do you know if the ACE storage battery is part of the AD?