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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 15th Feb 2013, 12:59
  #701 (permalink)  
 
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All the talk about sensing temperatures at each battery, and even separate locations within each battery's cells, is a red herring. There is no way to "shut down" any one of the eight batteries connected in series.

One battery goes bad, the system shuts down. So why any more than one thermocouple?

The problem has always been propagation of thermal runaway.

When each battery of the eight battery group is short on life cycle, the entire group is short on life cycle.

This is all about compliance. The Backup 'system' flies in the face of even a one in ten million, the accelerated replacement program (ARP) is testimony to that.

Back to the regulations......

SoS... That "Thermocouple" is attached at......Battery #6? Almost as if it was planned that way?


Last edited by Lyman; 15th Feb 2013 at 13:04.
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Old 15th Feb 2013, 13:06
  #702 (permalink)  
 
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rogerg

Now that AB seems to be going back to ni-cad due to the uncertanty of lithium has the use of ni-nmh been considered.
I'm sure it has but Ni-Cad is what is used on the 380 so as a late 'fix', it is better to go with something that should be fairly straightforward to certificate.
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Old 15th Feb 2013, 13:31
  #703 (permalink)  
 
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Ni Mh

Hi,

rogerg:


Just a question. Now that AB seems to be going back to ni-cad due to the uncertanty of lithium has the use of ni-nmh been considered. In model use they do the similar job to ni-cd but are lighter and smaller and seem to be pretty safe.

The strategy of EADS seems very good. Aviation uses Ni Cad (successfully)
Probably Ni mh was not NOW considered for the IMO GOOD move from EADS. Certainly was studied prior decision to use Li ion.

AFAIK Ni Mh is not being used in airliners. In the mean time (A350) could still adopt Li ion. If possible.

I think may happen in the future. A battery redesign is not so complex.

A BAD design "burned" the name Li ion. It has merits.
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Old 15th Feb 2013, 13:46
  #704 (permalink)  
 
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FullWings
Contrast that with this, the battery pack for a self-launching glider.
Each cell is individually (and redundantly) monitored for voltage and
temperature, with the facility to automatically heat the batteries to
keep them in the ideal operating range if the OAT is low.
Amazing and looks like a beautifully engineered piece of kit. Shows how
it can be done / should be done and wonder how the 787 managed to get it
so badly wrong.

Even if that wiring harness on top of the cells uses high temperature
cable, it would have been far safer to have physical separation. Perhaps
an overall moulding plate covering the cells, with small access holes for
each of the wires to screw down to the terminals.

As for the thermocouple, the group here have already discussed the
merits of individual temp sensing, but even cheap computer power supply
temp sensors do a more workmanlike job than that and are never just glued
on.

What were these people thinking ?...

Last edited by syseng68k; 15th Feb 2013 at 13:51.
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Old 15th Feb 2013, 14:47
  #705 (permalink)  
 
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and are never just glued
on.
To be fair, if it was glued on there wouldn't be a drilled mounting hole for it.
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Old 15th Feb 2013, 14:50
  #706 (permalink)  
 
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In the photo of the damaged batteries, the "Gob of Resin" is plainly visible, intact.

Could the 'drilled' mounting hole have contained a frangible plug, to secure the thermocouple, without conducting heat to it?

Last edited by Lyman; 15th Feb 2013 at 14:52.
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Old 16th Feb 2013, 11:07
  #707 (permalink)  
 
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It looks to me like the thermocouple was mounted directly onto the inter cell shunt probably using something like this.



As I said earlier in the thread, this single sensor was more than likely just a way of monitoring the ambient temperature inside the battery casing rather than anything more subtle.
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Old 16th Feb 2013, 13:16
  #708 (permalink)  
 
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Hi SoS....

The resin gobbed "thermocouple". If a source of temperature sensing, could it be it is the sole sensor?

Would its placement more or less in the middle of the upper area be an attempt at a "generalized" reading?

It seems that no one battery can be "switched out" from the series?

The conjecture would depend on the design consideration. 170 degrees is the threshold of exothermic reaction at the Cathode, per the paper I linked. The Anode can go exothermic at lower temps, again the same paper.

Or could the "Thermocouple" be a fusible link of some description, tripping the main Battery breakers, in anticipation of runaway?

Is your photo of the "shadow" from the incident battery? Being empty, one wonders if the attachment itself might be the source of an open circuit, that trips the breakers? By design?

thanks for the photo
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Old 16th Feb 2013, 13:31
  #709 (permalink)  
 
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Lyman

Yes, the 'shadow' picture is from the incident battery.

The thermocouple I pictured is purely a generic device whose mounting tab looks like something that could have been bolted to that cell linking strap.

I really don't think this sensor had anything whatsoever to do with cell monitoring or even thermal runaway. I think it is purely something to record the ambient temperature of the battery to see that it is remaining within the -X to +Y degrees specified by Yuasa.
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Old 17th Feb 2013, 20:46
  #710 (permalink)  
 
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SOS:
To be fair, if it was glued on there wouldn't be a drilled mounting hole for it.
Agreed, just the idea of a casual blob of silicon rubber anywhere inside that battery does
look like a bodge...

Anyway, looks like it will be grounded for months at least, with Boeing apparently
talking about strengthened titanium boxes to contain any fires ...

Last edited by syseng68k; 17th Feb 2013 at 20:47.
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Old 17th Feb 2013, 23:08
  #711 (permalink)  
 
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Sort term fix?

This article confirm our concerns



Boeing will not disclose any details of the solutions it is working on.
Letīs exercise:

1) A conventional bus with Ni Cd (MAIN similar to 777) and redesigned Li ion as stand by. (maintaining diode module approach)

2) Smaller Ni cd (APU) with redesigned Li ion as stand by.

Note: Ni cdīs in current Li ion locations and redesigned Li ionīs in special compartments in close vicinity (nearby FWD and AFT EEbays).
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Old 18th Feb 2013, 04:45
  #712 (permalink)  
 
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From the second link, an apparent confirmation of speculation here about the temperature monitoring:
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.
(Although I find it hard to believe that the existing system did not in fact monitor individual cell voltages somewhere along the way.)

I do not think any EV or other high total-energy use tries to avoid monitoring individual cell temperatures or does not at least use temperatures more closely linked to cell temperatures than the Boeing design does.

Even if it would not allow effective corrective action, at least it could deliver early warning and perhaps reduce the contribution of external charging power to the spread of thermal runaway. If the system did not detect the short of a single cell and raise an appropriate warning, it may not have disabled the charging attempt either.

Last edited by inetdog; 18th Feb 2013 at 04:48.
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Old 18th Feb 2013, 05:43
  #713 (permalink)  
 
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From the first photo of the series connection of the eight single batteries, why speculate there was individual monitoring? What could be done? Only one thing, switch out the entire battery group, at least to prevent any aggravation from continued discharge/charge?

All the talk about sensing temperatures at each battery, and even separate locations within each battery's cells, is a red herring. There is no way to "shut down" any one of the eight batteries connected in series.
It appears attempts to insulate each individual from another were made. Even if one could be switched out, that leaves the remaining number to be vulnerable to abnormal current and voltages? I think this system works as a unit, or it shuts down. NTSB states that JAL started with a single cell failure; designed containment failed. ANA the same?

An argument could be made that containment did function satisfactorily. That is a judgment FAA makes. But then it remains to also argue there was no "thermal runaway", only something 'less'. That might be a tough sell.

Trying to improve 'containment only' does not meet the regs. That implies a thermal runaway is tolerable. If it was, it won't be now....

NTSB would have to clear the current manufacture as something it has shown itself not to be, 'resistant to flame/fire'.
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Old 18th Feb 2013, 09:29
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I'm sorry, but does anyone think there is a cat in hell's chance of the FAA certifying a stopgap where essentially the same arrangement is simply put in a bigger, more fireproof box?

Fair play to Boeing for perservering with Lithium Ion, but they need to face up to having to put the 787 on hold (alongside slowed production) for the best part of a year to do this. :-(
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Old 18th Feb 2013, 14:17
  #715 (permalink)  
 
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Yes, I believe in such a cat. The paper is being written.

The Box? A heavier Gauge with hemmed top, to accommodate more and heavier fasteners. Which might be a mistake, the original puffed up, and deformed, but remained affixed. Separate partitions for each individual battery?

Will the box be elevated above the floor, on a stand off base? Will the box have a heavy duct, to transport gases out the hull? More Temp sensors, to facilitate an early shut off? Which of course defeats the purpose of the Battery?

What are the calculations for the box' ability to withstand explosive forces?

These are things that would have been folded into the development phase, had the design more accurately anticipated these failures.

The Accelerated Replacement Program? Boeing obviously knew the problem was the battery. If they thought the case was the issue, would they not have replaced the case along with?

This is a solution. It does not solve the problem of the Batteries. It solves the problem of the grounding.
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Old 18th Feb 2013, 15:59
  #716 (permalink)  
 
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more from Boeing Land...

“The expectation in aviation is to never experience a fire on board an aircraft,” the NTSB chairwoman declared, her voice deliberate but dispassionate."


NTSB chief Hersman doesn’t mince her words | In Person | Business & Technology | The Seattle Times
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Old 18th Feb 2013, 16:02
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What is a Thermal runaway?

Hi,

Reading some posts in the many threads created after 787 battery incidents it seems useful to remember, some important points on "Thermal runaway":

1) Itīs a "positive feedback" mechanism. Once started (in a Li ion battery) it will make the device go to limits. E.g. leakage of electrolytes, generation of smoke and even fire outside the device.

2) A "positive feedback" to be interrupted (once started) would require to reduce the "device energy". In ANA TAK case this happened because battery was severely discharged by an "external short circuit". (caused by an internal short circuit of cell # 3 plus terminal region to ground through battery case). *

3) Electricity means (cut off, etc.) may be useless. It seems this is one characteristic of the BAD battery selected for the 787. This mean may be useless to stop battery charging or even delivering electricity (under load).

4) A simpler redesign of the battery would require reduce the likelihood of thermal runaway. For now a (technical) "quick fix" for 787 could be summarized:

a) Separate each LVP-65 ideally in individual chambers. (battery volume would be aprox. 30 ~ 40 % more)
b) Monitor each LVP-65 temperature (if not yet made)
c) Tweak software algorithms
d) Improve mitigation means. (better battery case, better venting, safer batteries location, etc.)

This is a Technical comment. Bureaucratic aspects (Cert., etc.) is another certainly much bigger issue for Boeing.

(*) This model can be explained by the ground wire that was fused by currents estimated in excess of 1,000 Amps. Itīs a model, that could be confirmed or not.
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Old 18th Feb 2013, 16:10
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RR,

Make the batteries round like they are supposed to be!
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Old 18th Feb 2013, 16:42
  #719 (permalink)  
 
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INFLIGHT FIRE MANAGEMENT SYSTEM

Flight Path

“The expectation in aviation is to never experience a fire on board an aircraft,” the NTSB chairwoman declared, her voice deliberate but dispassionate."
A little clarity from a public official. She is doing a good job under difficult circumstances. Instead of learning from her example, The Director of the Department of Transportation, Ray LaHood, simply resigned. FAA spokesperson Huerta is likewise performing spin duty.

RR NDB

a) Separate each LVP-65 ideally in individual chambers. (battery volume would be aprox. 30 ~ 40 % more)
That is the current design. Each battery (erroneously called "cell") is contained in its own plastic box. Between these batteries, is a layered steel, insulate sandwich. A new design would be Steel pigeon holes, or "egg crate" enclosures.

Does nothing to prevent a thermal runaway. NTSB have concluded the JAL failure began with a single battery, #3. So any egg crate mod merely isolates the batteries from each other. Still possible is the prohibited "fire" to which Ms. Hersman refers.....

b) Monitor each LVP-65 temperature (if not yet made)
A noble attempt to.....what? Try to prevent fire? Once the temp is thresholded, the Batteries are shut down, the back up system is off line, and the purpose of the system competes with its "shutdown" feature".

c) Tweak software algorithms
To better "balance" charging? algorithms only peripherally "control" temps., and cannot mitigate exothermic reactions, the source of "runaway".

d) Improve mitigation means. (better battery case, better venting, safer batteries location, etc.)
All this does is underscore how badly Thales and BOEING designed the system in the first place.

If Director Hersman is accurate regarding her interpretation of "fire", the word "mitigation" is in direct contradiction. Fire is PREVENTED, not MITIGATED....

A new system for Aviation: "INFLIGHT FIRE MANAGEMENT SYSTEM"

IFMS.... really?



edit. RR, just a suggestion re: the "short" at the connector strap. Look closely and see if you are not tempted to look at the deficit as "cut" by a gas jet, instead of a simple "fusion" due to heat of current. The battery case is aligned with the triangular "cut", and the metal has characteristics of a torch cut, complete with "beads" of molten metal along the very linear edges..... Is it completely severed?

Last edited by Lyman; 18th Feb 2013 at 17:12.
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Old 18th Feb 2013, 18:36
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RR, just a suggestion re: the "short" at the connector strap. Look closely and see if you are not tempted to look at the deficit as "cut" by a gas jet, instead of a simple "fusion" due to heat of current. The battery case is aligned with the triangular "cut", and the metal has characteristics of a torch cut, complete with "beads" of molten metal along the very linear edges..... Is it completely severed?
Just a suggestion: Since there are so many pictures circulating whose captions even mistake which of the two batteries is shown, could you add a link to a picture of the area you are discussing?
If you are talking about the one I am thinking of, with the attachment nut sitting loose on top of the cell, a large part of the connector appears to be totally missing, not just cut. That is more consistent with a high amperage vaporization of the metal than with a gas jet cut, although both events may have occurred as slightly different times.
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