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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 22nd Feb 2013, 21:05
  #801 (permalink)  
 
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Lyman,

JTSB said this week it had found the ANA APU had been erroneously wired to the main battery that overheated.

Last edited by FlightPathOBN; 22nd Feb 2013 at 21:05.
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Old 23rd Feb 2013, 21:41
  #802 (permalink)  
 
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From this:

Boeing readies short-term battery fix, facing uncertainty | Business & Technology | The Seattle Times

The battery control system will have sensors to monitor the temperature and
voltage of each individual cell rather than the battery as a whole, one source said.
...and this:

FAA Says Boeing Needs to Address Battery Risks Before Dreamliners Will Fly Again | Frequent Business Traveler

Boeing also said it plans to develop a new battery design that will measure
the temperature and any voltage changes in individual cells.
Looks like the original design did in fact only have a single temp sensor,
even if they were managing individual cell voltages. Beats me how such a
design ever got past engineering.

I wonder if the group here will be able to send bills for consultancy fees
to Boeing ? ...

Last edited by syseng68k; 23rd Feb 2013 at 21:42.
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Old 24th Feb 2013, 01:00
  #803 (permalink)  
 
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I wonder if the group here will be able to send bills for consultancy fees
to Boeing ?
at the same time they pay the airlines for the parked aircraft!
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Old 24th Feb 2013, 16:34
  #804 (permalink)  
 
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Why Didn't the Airlines Object?

Looks like the original design did in fact only have a single temp sensor, even if they were managing individual cell voltages. Beats me how such a design ever got past engineering.
I don't understand why the airlines bought off on this Rube Goldberg arrangement. This hugely complex battery system clearly is unsuitable for the intended use and is an obvious hazard to safe flight. They threw KISS out the window and sacrificed safety on the altar of weight reduction.
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Old 24th Feb 2013, 17:01
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smilin ed:

The way I see it, it's inadequate oversight of the complete battery
subsystem by any sufficiently qualified and experienced engineer. Perhaps
that's what happens when you hand over the company to beancounters, who
then fire all the older engineers who really knew what they were doing
and understood the meaning of the expression "due diligence".

What is interesting is why Yuasa, who know how these cells need to be
managed, didn't raise questions about the design, but perhaps they did
and were overuled. Hopefully the final report will be more enlightening.

Glass is half full though, right ?. It will be fixed and be a better
a/craft because of it...
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Old 24th Feb 2013, 17:11
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As complex as it is, it is not complex enough. If they wire each individual battery for a heat signature, they are acknowledging how unreliable the system is. Any outlier temperature above the threshold would cause a shutdown of the entire assembly.

An admission that fire is possible in one cell is an admission that the design is unreliable, per se. And not just because of fire.

"Separation"... Ostensibly to prevent heat transfer. This system is eight batteries, in series. Lose one, lose them all. It does not matter how well the offending cell is isolated, isolation for overtemp fails the system and takes it off line.

There will be fire, that is the purpose of the upgraded box. No one installs a heavy fireproof enclosure if the chance of fire is manageable above its predicted rate of failure. And the rate of failure is not acceptable, box or no box....

Fire or no fire. Why fireproof a system that doesn't work even when it is not burning? The LiIon technology is cargo, in the hold, or as equipment.

Fire is prohibited, not mitigated.

IanW.... Functionality, (Does it "Work"?) is not required to own a Patent.

New? check.... Unique? check..... Does it work? no check.....

Last edited by Lyman; 24th Feb 2013 at 17:22.
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Old 24th Feb 2013, 17:16
  #807 (permalink)  
 
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Syseng68k
Looks like the original design did in fact only have a single temp sensor,
even if they were managing individual cell voltages. Beats me how such a
design ever got past engineering.
Back at the beginning of the thread there was detail about the BMS using a patented system that managed the charging of the cells using software that predicted the temperatures from the voltage across the cells. It would appear that 'patented' is not the equivalent to validated as working.

What is Thales saying about this?- They provided the entire battery assembly and BMS.

Last edited by Ian W; 24th Feb 2013 at 17:18.
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Old 24th Feb 2013, 21:02
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from Boeing Land....

Another person familiar with the engineering work said the new box would be made of stainless steel nearly half an inch thick. It would be capable of containing an explosion, and would have a tube to vent smoke and flame outside the jet.
However, the source said engineers have raised questions about the safety of venting flames outside the plane, especially if it is on the ground and being fueled. The effect could be something like a flamethrower, this person said.

final solution?
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Old 24th Feb 2013, 21:13
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Add a flame arrestor?
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Old 24th Feb 2013, 21:56
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Back at the beginning of the thread there was detail about the BMS using a
patented system that managed the charging of the cells using software that
predicted the temperatures from the voltage across the cells. It would appear
that 'patented' is not the equivalent to validated as working.
Actually, the patented method doesn't look at temperature, but fwir, tracks
the voltage curve towards the inflexion point. Then when it gets a match
with an internal model of a cell's charging characteristics, predicts end of
charge from that. Might be a very good idea, but is a bit simplistic in terms
of what else needs to be done to properly manage the cells. While temperature
and voltage are loosly related, you can't predict temperature from voltage
alone. Edit: In fact, you can't predict temperature with any degree of accuracy
at all.

It's much easier and more complete to measure each cell's temperature and
voltage, since they are the critical limiting factors in terms of maximum
charge or discharge currents...

Last edited by syseng68k; 24th Feb 2013 at 22:09.
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Old 24th Feb 2013, 22:04
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Add a flame arrestor?


mid-air fueling

edit: maybe they looked up how Titanium burns!

Last edited by FlightPathOBN; 25th Feb 2013 at 01:14.
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Old 25th Feb 2013, 21:51
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I'll just reiterate what i posted l ooo ooo ng ago.

place each sub-cell in an insulating ceramic pot (which could have a screw-on lid in the same material.

Make the cell-tails from heat- sensitive alloy
fit each one with a temp-probe and voltage-monitoring wire.
place all three in a second fireproof ceramic pot.

The main terminals each have a busbar to which the tails are attached.
each subcell individually monitored,so much tighter control. any high current or overheating will melt the tail (fusible link) thus disconnecting the individual sub-cell. THE BATTERY WOULD MAINTAIN IT'S AVAILABILITY (unless all 3 sub-cells in a single-cell failed O.C.

Thermistors cost buttons-even "certified "ones should be well affordable within the current 16,000 dollar postulated ripoff price.

Controller/memory/discrete components are all pennies and there is no earthly reason why 48 temp and 25 voltage wires should present a problem to the control/monitoring/charging unit.

It seems no-one is willing to lose face by admitting this fitment was ill-thought-out and piss-poorly executed.

PROPERLY engineered, I'm sure the initial objectives could be met and the fusing/monitoring/insulating (heat, as well as electrical) regime would probably allow a thinner,lighter containment-vessel (sorry, "container")
Fingers crossed they rejig the charging/monitoring wherein I feel the problem lies. They're determined to stick with the technology, they HAVE to respect it's limitations and keep within the SAFE operating envelope.
@Smilin' Ed.
They threw KISS out the window and sacrificed safety on the altar of weight reduction.
Unfortunately, the sodding great tin fire- box added back all the weight .

not to mention the cost of this fiasco ,to both finances and reputation.

Perhaps, the engineers KNEW but were overruled by arrogant "suits" "know it all all. Perhaps it was a genuine oversight or omission and nobody recognised the importance of a building burning.......et al.
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Old 25th Feb 2013, 23:01
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CS,

How much of the rest of the aircraft was designed and implemented the same way?

Perhaps, the engineers KNEW but were overruled
fitting a square peg in a round hole has NEVER worked....the batteries need to be round, the 'engineers' blew it on the design..like many of the other assemblies that have gone wrong...

finite element computer engineering disconnected with manufacturing capability.

Last edited by FlightPathOBN; 25th Feb 2013 at 23:06.
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Old 26th Feb 2013, 00:34
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Controller/memory/discrete components are all pennies and there is no earthly reason why 48 temp and 25 voltage wires should present a problem to the control/monitoring/charging unit.
At least for the temp sensors there is no need for more than 3-6 wires (depending on any redundancy desire) since there are plenty of serial bus (more than one flavor) temp sensors available.

Some of these also have voltage monitor inputs but then things get a bit complex due to common mode issues etc.

Accuracy is not a major factor, +- 1 degree C would suffice, rates are probably as interesting as absolute.
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Old 26th Feb 2013, 10:54
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@ Murphy...I was trying to make the point that, even doing it on the cheap with discrete components and maximum redundancy, it wouldn't exactly be overwhelmingly complex. Every single sub-cell could be monitored and contained thus giving a hugely enhanced safety-cushion.


@flightpathOBN I still think that GS-Yuasa's construction is beyond reproach....yes, I take on board the issue of folds, expansion and contraction.

WOUND CONSTRUCTION WILL NOT STOP THAT THERMAL MOVEMENT
It is arguable that, given the binding -effect of the spiral-wrap, the crushing-pressure in the core will be far higher than in the flat-folded construction. Not to mention the heat buildup in the core....this could be mitigated by using very tall electrodes with fewer turns...then you're on to 24 long-slim, cigar-shaped cells wired in series-parallell.
Ever wound a ball of wool or string over your fingers? coiled rope round hand and elbow? Gets tight, doesn't it!
the batteries in service(and changed) have been abused!
other discussion in R&N, but not of the quality of this one
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Old 26th Feb 2013, 14:38
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Cockney Steve
the batteries in service(and changed) have been abused!
This was my feeling as well - perhaps not deliberate abuse but slavishly following the laid down procedures which perhaps have some instructions that 'assume' that nobody-would-do-that. Or perhaps procedures that assume that the aircraft will be in a particular state when something is done (e.g. all electrics powered down for a battery change.) but don't actually require it.

What abuse do you think could cause a single cell to be on the edge so recharge or even use while parked would cause a problem?
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Old 26th Feb 2013, 14:52
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Ian W

How about...
1. Overcharging
In general, lithium ion batteries are significantly more susceptible to internal failures that can result in self- sustaining increases in temperature and pressure (thermal runaway) than their nickel-cadmium or lead-acid counterparts. This is especially true for overcharging, which causes heating and destabilization of the components of the cell, leading to formation (by plating) of highly unstable metallic lithium. The metallic lithium can ignite, resulting in a self-sustaining fire or explosion. Finally, the severity of thermal runaway from overcharging increases with increasing battery capacity, because of the higher amount of electrolytes in large batteries.
"We may never know the cause..."

The cause is part of the problem, known since the advent of the technology. Given "mystery" how can anyone in their right mind propose a "fix"?

Without eliminating each possible cause, one is left with a known fire, of unknown origin...

So at least in service to the regs, and the English language, absent a known cause, there is no "fix", interim, permanent, or otherwise.

Only a "method to control spread of fire"....

Last edited by Lyman; 26th Feb 2013 at 15:00.
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Old 26th Feb 2013, 16:33
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CS:
@ Murphy...I was trying to make the point that, even doing it on the cheap with discrete components and maximum redundancy, it wouldn't exactly be overwhelmingly complex. Every single sub-cell could be monitored and contained thus giving a hugely enhanced safety-cushion.
I understand your were providing a "proof of existance" not a necesarily a final dessign.

Depending on location of monitor PCB, preferably outside the "fire box" so logging would survive an 'incident', serial bus sensors would almost certainly be cheaper than individual wires given the cost of certified connectors and wire harnesses etc.

Have to say I am very puzzled that the cells are not individually monitored in the current design since that would give the best early warning of problems.
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Old 26th Feb 2013, 16:42
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cockney steve said:
WOUND CONSTRUCTION WILL NOT STOP THAT THERMAL MOVEMENT
Equally important as, or perhaps more important than, the thermal expansion is the roughly 10% change in volume of the combined electrodes, active material and separator between fully discharged and fully charged state. This is a characteristic of the LiCo electrode chemistry.
Repeated wide range State of Charge cycling may potentially be more damaging to the electrode structure than thermal cycling, especially if there are other contributing factors such as debris from manufacturing or dendrite growth.
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Old 26th Feb 2013, 16:57
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Murph...

Have to say I am very puzzled that the cells are not individually monitored in the current design since that would give the best early warning of problems.
There are at least two reasons Boeing is not puzzled. (in my opinion).

They were overconfident in the single Temp system, or they knew multiplying the sensors would result in a higher number of Battery failures.

I lean toward the latter; Boeing knew the more data they had regarding the system performance, the more failures they would incur.

This is not sinister, necessarily, it is a judgment call within the rather loose confines of their self inflicted Regulatory restrictions.....

Their decisions were based on on over reliance on optimism....

No harm, no foul.....But Hell to pay if it goes up in smoke....
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