787 Batteries and Chargers - Part 1
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Technical concern
Hi,
Thinking on how different is the application of these (suposed) "proven" cells on the new design of 787 and:
1) The low MTTR
2) The "diode scheme"
3) The DC generation from redundant sources
4) The higher electric energy use for more functions
5) The ripple naturally present in busses
6) The Boeing selection of this battery
7) The offering of just une option: Li Ion
How is done the filtering of the busses? There are capacitors banks along the busses? Or any "sudden drop" of voltage makes the battery supply the energy (through the hi speed switch - the diode). If there are spikes (sudden negative going voltage levels) in the busses the battery is not as "offline" as previously thought.
OTOH we may imagine most high power loads (that required the 1.45 MW generation capability) are AC driven.
Thinking on how different is the application of these (suposed) "proven" cells on the new design of 787 and:
1) The low MTTR
2) The "diode scheme"
3) The DC generation from redundant sources
4) The higher electric energy use for more functions
5) The ripple naturally present in busses
6) The Boeing selection of this battery
7) The offering of just une option: Li Ion
How is done the filtering of the busses? There are capacitors banks along the busses? Or any "sudden drop" of voltage makes the battery supply the energy (through the hi speed switch - the diode). If there are spikes (sudden negative going voltage levels) in the busses the battery is not as "offline" as previously thought.
OTOH we may imagine most high power loads (that required the 1.45 MW generation capability) are AC driven.
fizz57:
From info we have, the ability to fast charge LI might have been
attractive for some operational reason. Of course, they are much
lighter, but the reason may also have been that it is a much more
modern technology, with many benefits over either lead acid or
nicad. Well proven, so why not use it ?.
Perhaps, but that's where the fault originated and in fact, the
NTSB focus has been in that area since the problem surfaced, right or
wrong. The battery data log is in the charger and it seems strange
to me that they spent a week tearing batteries, down, subjecting
them to minute examination, when the event timeline to failure may be
elsewhere. Nasrudin's Lost Key, or what ?.
More than just competent. Imho, the 787 is a revolutionary design,
in the same way that the A340 was when it was introduced. Technology
moves on and with any step change, there are far more risk than with
an incremental metoo design...
Regards,
Chris
A couple of thoughts....
Boeing's insistence on retaining the lithium batteries make me think
that they weren't chosen just for their size and weight, but that some
electrical characteristic (such a low internal resistance) make them
central to the design of the electrical system.
Boeing's insistence on retaining the lithium batteries make me think
that they weren't chosen just for their size and weight, but that some
electrical characteristic (such a low internal resistance) make them
central to the design of the electrical system.
attractive for some operational reason. Of course, they are much
lighter, but the reason may also have been that it is a much more
modern technology, with many benefits over either lead acid or
nicad. Well proven, so why not use it ?.
Secondly, I find the present focus and the batteries and chargers as
isolated systems to be pretty naive.
isolated systems to be pretty naive.
NTSB focus has been in that area since the problem surfaced, right or
wrong. The battery data log is in the charger and it seems strange
to me that they spent a week tearing batteries, down, subjecting
them to minute examination, when the event timeline to failure may be
elsewhere. Nasrudin's Lost Key, or what ?.
The engineers at the various plants involved can be assumed to be
reasonably competent...
reasonably competent...
in the same way that the A340 was when it was introduced. Technology
moves on and with any step change, there are far more risk than with
an incremental metoo design...
Regards,
Chris
Last edited by syseng68k; 31st Jan 2013 at 18:12.
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An analogy
Hi,
The (negative going) voltage spikes in the bus is similar to:
Imagine a large piston engine (mechanically) connected by a rod to a flyweel. The stress to the connection could destroy the rod. The diode could be viewed as "part of the rod". And the series connected cells must be capable to supply the large current spikes. The spikes could concentrate in some (area) concentrated points during the transient? And all these current spikes could even create oscillatory voltage transients increasing momentarily cell voltages above nominal levels?
The low MTTR reported probably was on MAIN batteries for other reasons. (supposing very rare use of APU battery discharging high current. And during towing the load is light. )
The (negative going) voltage spikes in the bus is similar to:
Imagine a large piston engine (mechanically) connected by a rod to a flyweel. The stress to the connection could destroy the rod. The diode could be viewed as "part of the rod". And the series connected cells must be capable to supply the large current spikes. The spikes could concentrate in some (area) concentrated points during the transient? And all these current spikes could even create oscillatory voltage transients increasing momentarily cell voltages above nominal levels?
The low MTTR reported probably was on MAIN batteries for other reasons. (supposing very rare use of APU battery discharging high current. And during towing the load is light. )
Last edited by RR_NDB; 31st Jan 2013 at 18:18. Reason: Typo
How is done the filtering of the busses? There are capacitors banks
along the busses? Or any "sudden drop" of voltage makes the battery
supply the energy (through the hi speed switch - the diode). If there
are spikes (sudden negative going voltage levels) in the busses the
battery is not as "offline" as previously thought.
along the busses? Or any "sudden drop" of voltage makes the battery
supply the energy (through the hi speed switch - the diode). If there
are spikes (sudden negative going voltage levels) in the busses the
battery is not as "offline" as previously thought.
have been similar failures in functionally different areas: Standby
power and APU start.
This would suggest that the problem is with the battery / charger
subsystem, as it's the only thing in common, afaik...
Regards,
Chris
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so many threads on this...
here is an interesting piece by Elon Musk...
An aerospace-capable version of Tesla's battery has been developed for use in SpaceX's Falcon 9 space launch vehicle. SpaceX, also owned by Musk, competes with Boeing/Lockheed Martin joint venture United Launch Alliance for customers. Boeing has thus far declined offers of assistance from Tesla and SpaceX, says Musk.
"They [Boeing] believe they have this under control, although I think there is a fundamental safety issue with the architecture of a pack with large cells," writes Musk in an email. "It is much harder to maintain an even temperature in a large cell, as the distance from the center of the cell to the edge is much greater, which increases the risk of thermal runaway."
"He's engineered [Tesla's battery] to prevent the domino effect, while Boeing evidently doesn't have that engineering," adds Sadoway.
Elon Musk: Boeing 787 battery fundamentally unsafe
here is an interesting piece by Elon Musk...
An aerospace-capable version of Tesla's battery has been developed for use in SpaceX's Falcon 9 space launch vehicle. SpaceX, also owned by Musk, competes with Boeing/Lockheed Martin joint venture United Launch Alliance for customers. Boeing has thus far declined offers of assistance from Tesla and SpaceX, says Musk.
"They [Boeing] believe they have this under control, although I think there is a fundamental safety issue with the architecture of a pack with large cells," writes Musk in an email. "It is much harder to maintain an even temperature in a large cell, as the distance from the center of the cell to the edge is much greater, which increases the risk of thermal runaway."
"He's engineered [Tesla's battery] to prevent the domino effect, while Boeing evidently doesn't have that engineering," adds Sadoway.
Elon Musk: Boeing 787 battery fundamentally unsafe
Last edited by FlightPathOBN; 31st Jan 2013 at 18:45.
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@syseng68k (if I had a name like yours it would end with 6502)
I'm referring to Boeing's latest statements on the batteries. There's no quibble with the design choice of Li-ion, despite all the scaremongers there aren't any insoluble technical problems and in a few years we'll be wondering what all the fuss was about. My point was just that if the batteries were simply reserve power banks then an interim replacement with Ni-Cds to get the planes flying again should have been the first option. This seems to indicate a more fundamental reason for the choice (probably on the A350 as well).
My second comment was based on the expected result that nothing was found wrong with either the batteries or the chargers. Expected because given the quality of the engineers (a bit of irony in my post there, as a sop to those wo think anything not Boeing shouldn't be in the air) I'm sure that both the batteries and the electronics are top-notch. So the reason for the failures, catastrophic or otherwise, must be elsewhere.
Given the novelty of the design, there are bound to be unknowns in the entire system even if the individual components are well understood. What margins were taken by the system integrators? Did Boeing construct a full-scale replica of the electrical system (as the Concorde engineers did with their fuel system) or was it all simulated? What were the inputs to the simulations? I think that these are the sort of questions that should be asked.
I'm referring to Boeing's latest statements on the batteries. There's no quibble with the design choice of Li-ion, despite all the scaremongers there aren't any insoluble technical problems and in a few years we'll be wondering what all the fuss was about. My point was just that if the batteries were simply reserve power banks then an interim replacement with Ni-Cds to get the planes flying again should have been the first option. This seems to indicate a more fundamental reason for the choice (probably on the A350 as well).
My second comment was based on the expected result that nothing was found wrong with either the batteries or the chargers. Expected because given the quality of the engineers (a bit of irony in my post there, as a sop to those wo think anything not Boeing shouldn't be in the air) I'm sure that both the batteries and the electronics are top-notch. So the reason for the failures, catastrophic or otherwise, must be elsewhere.
Given the novelty of the design, there are bound to be unknowns in the entire system even if the individual components are well understood. What margins were taken by the system integrators? Did Boeing construct a full-scale replica of the electrical system (as the Concorde engineers did with their fuel system) or was it all simulated? What were the inputs to the simulations? I think that these are the sort of questions that should be asked.
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Everything plausible and possible should be considered
Hi,
Chris,
I learned many years ago we must look to every possible detail. It could explain the fact(s).
Letīs wait to learn on % of failed batteries (MAIN or APU). One battery (BOS) is not an argument against the model.
The Decision Making on Li Ion usage as main certainly was more complex. (vs APU) The diode (if not used in other A/C) "protects" the (critical) battery in just one direction.
What is common:
1) Both batteries failed (APU and MAIN)
2) Battery of same type
3) Circuitry around (BC, BMs)
The higher electric power in 787 and the adoption of these higher capacity batteries must be viewed as something decided by fundamented reasons. The decision certainly was not trivial.
Chris,
I learned many years ago we must look to every possible detail. It could explain the fact(s).
Letīs wait to learn on % of failed batteries (MAIN or APU). One battery (BOS) is not an argument against the model.
The Decision Making on Li Ion usage as main certainly was more complex. (vs APU) The diode (if not used in other A/C) "protects" the (critical) battery in just one direction.
What is common:
1) Both batteries failed (APU and MAIN)
2) Battery of same type
3) Circuitry around (BC, BMs)
The higher electric power in 787 and the adoption of these higher capacity batteries must be viewed as something decided by fundamented reasons. The decision certainly was not trivial.
Last edited by RR_NDB; 31st Jan 2013 at 19:21.
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RR,
It appears hundreds of batteries have cycled down...with only a few of these birds in ops...
seems more like a fundamental failure of the assumptions...(supported by Musk, but perhaps biased)
obfuscation of the issue will not only lead to an extended process of this system,
but perhaps is the foundation of the unusual regulatory response to all processes...
It appears hundreds of batteries have cycled down...with only a few of these birds in ops...
seems more like a fundamental failure of the assumptions...(supported by Musk, but perhaps biased)
obfuscation of the issue will not only lead to an extended process of this system,
but perhaps is the foundation of the unusual regulatory response to all processes...
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Hi,
Elon Musk email touches in a VERY IMPORTANT point. He has concerns on the cell size and (seems) the temperature gradient inside. He would not emphasize in this "high rock style" message the correlation between cell size to the thermal runaway threat wirthout strong reasons backe by what he learned, know and consider a flaw.
PS
Fizz57 and syseng68:
My nickname could be 4004. Slower and less capable (just 4 bits) vs 6502 and 68000 but "the first one, years ahead"....
Elon Musk email touches in a VERY IMPORTANT point. He has concerns on the cell size and (seems) the temperature gradient inside. He would not emphasize in this "high rock style" message the correlation between cell size to the thermal runaway threat wirthout strong reasons backe by what he learned, know and consider a flaw.
PS
Fizz57 and syseng68:
My nickname could be 4004. Slower and less capable (just 4 bits) vs 6502 and 68000 but "the first one, years ahead"....
Last edited by RR_NDB; 1st Feb 2013 at 02:19. Reason: Improve text
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Hi,
FPO @ (#348)
Yes, FAA, NTSB and a lot of people around the world are concerned and working diligently to answer WHAT and WHY. Deborah Hersman expressed this very well in the briefing.
Boeing is in a defensive mode and i agree with your feeling.
FPO @ (#348)
Yes, FAA, NTSB and a lot of people around the world are concerned and working diligently to answer WHAT and WHY. Deborah Hersman expressed this very well in the briefing.
Boeing is in a defensive mode and i agree with your feeling.
rumor of improved protection approach
The Seattle area TV station King5 has posted a story simply attributed to "sources" asserting that Boeing is considering an approach to continuing to use the existing battery system with upgrades to containment and venting. As I doubt that even a profound understanding of just what happened in the JAL and ANA incidents will lead to a change which will have all stakeholders believing there will never be another one, I personally believe that continued use of these batteries requires improvement in precisely these two areas.
The idea here is that thermal runaway lithium cell failures should be rare, but that if one should happen anyway the design should safely contain damage to the battery itself, by adequate thermal and mechanical shielding to adjacent structures and equipment, and safer (which has to mean more constrained) venting of the unavoidable hot byproducts overboard.
I think this is on a correct track--though I certainly hope that improvements driven by real understanding make the cell failures far less common than they seem to be now. A complete redesign using a different chemistry is doubtless entirely possible, but the timeline when one includes all stakeholder approvals, testing, and regulatory hurdles would probably be very long even were the 777 solution "dropped in", and yet longer on a more original design.
The idea here is that thermal runaway lithium cell failures should be rare, but that if one should happen anyway the design should safely contain damage to the battery itself, by adequate thermal and mechanical shielding to adjacent structures and equipment, and safer (which has to mean more constrained) venting of the unavoidable hot byproducts overboard.
I think this is on a correct track--though I certainly hope that improvements driven by real understanding make the cell failures far less common than they seem to be now. A complete redesign using a different chemistry is doubtless entirely possible, but the timeline when one includes all stakeholder approvals, testing, and regulatory hurdles would probably be very long even were the 777 solution "dropped in", and yet longer on a more original design.
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Warning when approaching limits
Hi,
Archae86,
I liked it. Fault tolerance and Graceful Degradation will be improved with this approach.
This afternoon i was imagining special compartments with each battery, near plane outer surface with safety mechanisms. A bigger battery case with separated cells (ea one in a chamber), cell conections in the top, manifold with 8 bifurcations (metallic) and means to promote escape of cell leaks (even fire), etc.
All with improved battery management for charge and discharge. WRT to electrical circuitry:
Individual cell management, adaptive voltage (charge) CONTROL (not just monitoring).
Temp sensors PER CELL and other details like battery case geometry, parallel cell charger with extra features are being studied.
The opportunity was being motivating for me in an electric (actually hibrid) vehicle design, being R&Dīd. Safety first.
Archae86,
I liked it. Fault tolerance and Graceful Degradation will be improved with this approach.
This afternoon i was imagining special compartments with each battery, near plane outer surface with safety mechanisms. A bigger battery case with separated cells (ea one in a chamber), cell conections in the top, manifold with 8 bifurcations (metallic) and means to promote escape of cell leaks (even fire), etc.
All with improved battery management for charge and discharge. WRT to electrical circuitry:
Individual cell management, adaptive voltage (charge) CONTROL (not just monitoring).
Temp sensors PER CELL and other details like battery case geometry, parallel cell charger with extra features are being studied.
The opportunity was being motivating for me in an electric (actually hibrid) vehicle design, being R&Dīd. Safety first.
Last edited by RR_NDB; 31st Jan 2013 at 23:05. Reason: Typo
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From WSJ Dreamliner Batteries Needed Replacement Before Incident - WSJ.com
Sounds like a fair amount of mishandling rather than unexpected battery failures.
In the U.S., investigators have collected world-wide data for the 787 fleet indicating that as many as 160 batteries may have been replaced, including before and after delivery, according to people familiar with the details. The primary reason 787 batteries have been swapped out, these people said, are that they were improperly disconnected. They were left to discharge without any other power sources on the aircraft, causing a deep discharge; or they expired, people familiar with the matter said.
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Battery may request Help
Hi,
Ian W,
A battery or a System with them could (should) have means to warn when going below a given threshold. The circuit to perform it cost less than USD16.
Not just mishandling...
Ian W,
A battery or a System with them could (should) have means to warn when going below a given threshold. The circuit to perform it cost less than USD16.
Not just mishandling...
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Exactly..it seems much better to shut down the use of the battery power, than to permanently take down a cell...
this doesnt solve the thermal run away issue..
seems like the system is far too complicated, answering stop gap, (if/then) rather than solve the issues.
I think perhaps that Musk's opinions have some very good value...after all, look how many vehicles they roasted up...
this doesnt solve the thermal run away issue..
seems like the system is far too complicated, answering stop gap, (if/then) rather than solve the issues.
I think perhaps that Musk's opinions have some very good value...after all, look how many vehicles they roasted up...
Last edited by FlightPathOBN; 31st Jan 2013 at 23:20.
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RR_NDB
If someone wants to disconnect a battery incorrectly then it will still cause problems the quote actually goes on to say
I was just pointing out that the large number of battery failures seemed to be due to mishandling. Perhaps there needs to be more protection against that as well but its not an airborne occurrence - its a line maintenance issue.
A battery or a System with them could (should) have means to warn when going below a given threshold. The circuit to perform it cost less than USD16.
Not just mishandling...
Not just mishandling...
In many cases, according to these people, internal battery safety systems kicked in as designed, preventing maintenance officials from recharging the affected batteries.
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Major difference of Musk approach
Hi,
FPO,
Simple:
Smaller cells (iirc the popular "18650") separated and liquid cooled. Ea. About the volume of a stretched C type flashlight cell. (est. 10 ~ 20 % more volume)
The idea to use an "av. standard case" (we may comprehend the reasons) WITHOUT cell spacing and without "any" cooling certainly was an important factor to the outcome.
FPO,
Simple:
Smaller cells (iirc the popular "18650") separated and liquid cooled. Ea. About the volume of a stretched C type flashlight cell. (est. 10 ~ 20 % more volume)
The idea to use an "av. standard case" (we may comprehend the reasons) WITHOUT cell spacing and without "any" cooling certainly was an important factor to the outcome.
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APU battery usage depends on how diligent an airline is about not using the APU. Some airlines try to not use it at all costs. Some use it every flight, maybe twice (before engine start and before shutdown). Only one of those times will the APU battery be cycled. The other time it will probably started off the main buses. I don't work for ANA so I don't know what they do. A medium/long haul aircraft might start its APU 2-10 times per day.
The APU takes about a minute to start. So 30-40% of the battery capacity is used very quickly, and the battery will probably heat up a bit. If it is then recharged very quickly (10 minutes?), it will heat up even more.
The backup battery should not get much use. Starting up a "cold" airplane, the battery might be used just to get essential power up to do a APU start. Also cleaners might need a little light, so a mechanic might turn the batteries on. Opening and closing cargo doors. etc. Not high draw stuff, and not for very long.
I only saw a "dead" backup battery once. Someone left the battery switch on overnight, or maybe someone outside disconnected external power with the BATT switch on.
The APU takes about a minute to start. So 30-40% of the battery capacity is used very quickly, and the battery will probably heat up a bit. If it is then recharged very quickly (10 minutes?), it will heat up even more.
The backup battery should not get much use. Starting up a "cold" airplane, the battery might be used just to get essential power up to do a APU start. Also cleaners might need a little light, so a mechanic might turn the batteries on. Opening and closing cargo doors. etc. Not high draw stuff, and not for very long.
I only saw a "dead" backup battery once. Someone left the battery switch on overnight, or maybe someone outside disconnected external power with the BATT switch on.