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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 10th Feb 2013, 02:11
  #601 (permalink)  
 
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Cockney Steve

I am sure Turin can weigh in as well but there seems to be a slight misperception about what the purpose the aircraft main battery serves in a degraded power state. Indeed if it it a race to the aerodrome the battery should last for 30 minutes to provide absolute essential power-think in this case of the captain's flight instruments. This has been pretty much the standard on every Boeing that I have flown as well as MD, Lockheed, and narrow body Airbus.

What really should be going on however, is that the battery is providing power long enough until you can climb back out of the degraded power state. This might mean the RAT starts powering the busses, the apu comes on line, or you can get a generator back. It should be just an interim power source at most.

I know you realize this but I am not sure some that are following this thread do.

Btw. I have a colleague who landed in South America on battery power only in a 767. 40 minutes on this power source. 10 more than advertised but it was drained on the rollout....close...
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Old 10th Feb 2013, 07:29
  #602 (permalink)  
 
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I am glad to be wrong. The NTSB said both failures were caused by the same thing. I cell failed (for some reason).

The only thing I don't like in the battery is what Cockney Steve said. I want a metal contact for all those little wires. Not mechanical. Too mainy points to corrode, poor installation, etc.
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Old 10th Feb 2013, 08:18
  #603 (permalink)  
 
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Seattle Times:

NTSB challenges Boeing estimates of 787 battery safety

Some well chosen and rather salutary quotes in the piece...

Last edited by robdean; 10th Feb 2013 at 08:22.
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Old 10th Feb 2013, 17:08
  #604 (permalink)  
 
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Li ion can be used in airliners today?

Hi,

Question:

Airliners benefits today and will benefit in near future in using Li ion batteries?

Some facts:

Question 2: Limited test activities are being planned with just Li ion batteries?
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Old 10th Feb 2013, 17:22
  #605 (permalink)  
 
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The NTSB has narrowed the failure down to some criteria. Internal defects are on the list, and cannot, by their nature, be monitored, or even known, until failure. They are mentioned as related to the folding of the electrode, pinching and wrinkling, and foreign object contamination.

This report is not a new revelation. This failure is well known in the industry, see Failure Analysis Associates, Exponent evaluation.

NTSB may appear to be discovering this problem just now. Wrong, it was on their list, it was on the list prior to the wording of the FAA special circumstances.

Try to avoid the propaganda that somehow something mysterious is happening.
Any Drama is Public Relations.

As has been said here before, this is "Mature Technology". That is true, but "Mature" is not a synonym for "Safe in Commercial Aviation".

As to Boeing writing the regs. Let's see. I am in a spelling Bee, as a contestant.

May I submit the word which I will be required to Spell?

Last edited by Lyman; 10th Feb 2013 at 17:29.
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Old 10th Feb 2013, 17:30
  #606 (permalink)  
 
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Surrounding electric environment

Hi,

syseng68k:


Negative going voltage spikes in DC bus could "turn on" diode module

An analogy can be made
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Old 10th Feb 2013, 17:55
  #607 (permalink)  
 
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Li ion 787 previous battery replacements

Hi,

Low MTTR:

"...the top three reasons for Boeing returning batteries” as batteries running down, being improperly disconnected, or exceeding their expiration date."


A battery that’s left on with no other power source, Gunter said, “will deep discharge (and) cannot be recharged or reused.”


And one that’s improperly disconnected, she added, “trips one of the protection features and renders the battery unusable.”


Because lithium-ion batteries can be dangerously volatile if undercharged, as well as when overcharged, an automatic cutoff is built into the 787 batteries so that if the charge falls below 15 percent of full, the battery locks.
After some problems during trips, some years ago i opened and analyzed the 6 cell battery pack of my main laptop. The voltage span from empty to full used in that design was just one volt. IIRC 11.6 to 12.6 Volts. I decided to use an external battery for my main and spare laptops. Currently i use 12 cells, charging each one up to 4.2 volts with constant voltage monitoring. Warning me if a given cell falls below 3.3 volts during operation. Result: 10 hour plus operation. Ea. cell can be replaced. (18650)
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Old 10th Feb 2013, 18:10
  #608 (permalink)  
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Lyman:
The standard set by the FAA for this safety critical event is one occurrence in one Billion flight hours.

FALSE.

That standard does not apply to the battery system, as it is not critical for flight.

I urge contributors to this thread to please refrain from posting unfounded hyperbole. It does nothing to further our understanding of the technical issues at hand, bothers those professionals well versed in the industry standards, and misleads the gullible.
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Old 10th Feb 2013, 18:17
  #609 (permalink)  
 
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Regulating agencies are always a step behind the industries that they regulate. If they were not, there would be no innovation. Banks, airplanes, whatever. I don't blame the FAA. They did the best they could with the info they had.
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Old 10th Feb 2013, 18:28
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Batteries cell voltages in JA829J and JA804A were recorded?

Hi,

NTSB and JTSB mentioned cell voltages?
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Old 10th Feb 2013, 18:49
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Another battery

Hi,


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Old 10th Feb 2013, 19:16
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@RR_NDB

CVR/FDR are recorders for investigative purpose.

QAR records more in detail, with maintenance in mind.

Subsystems do their own recording. Frequently, investigations looked for example at FADEC NVM.

So far, there is no hint on availability of any per cell recordings. Sensibly, the BMS would record (amongst others) things like
  • Event time stamp
  • Cell #
  • Cell voltage
  • Cell short/over voltage/under-voltage
  • Charger on/off
  • Failure notification
  • Breaker tripped / disconnected
  • Battery temperature/fire
At BOS smoke/fire was observed, but no hint on any prior battery related alert.

IMHO, NTSB based their BOS related analysis, as of 6 Feb brief, on FDR (32V, no overcharge), and on physical evidence / examination after disassembling battery and cells.

We know that 32V during a cell short will result in destruction of remaining cells. To figure it out, the following info is needed.
  • Battery temperature history
  • Per cell voltage history
  • Per cell voltages prior to Primary failure
  • BMS response to Primary failure
  • Battery voltage after Primary failure - Has it reduced or remained at 32V
  • Precise failure sequence

Last edited by saptzae; 10th Feb 2013 at 19:28. Reason: Typo
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Old 10th Feb 2013, 19:45
  #613 (permalink)  
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Lyman:
having been reduced from the one billion figure

FALSE. No such reduction ever took place.

Posting nonsense incorrectly extrapolated from opinions collected by journalists doesn't lead to a better understanding.

There is an immense difference between the designed failure rate requirements for flight critical systems and other systems and components.

One may opine what qualifies as such, but that doesn't make it so.
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Old 10th Feb 2013, 19:49
  #614 (permalink)  
 
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Black box own data recorder

Hi,

saptzae:

Battery temperature history
Per cell voltage history
Per cell voltages prior to Primary failure
BMS response to Primary failure
Battery voltage after Primary failure - Has it reduced or remained at 32V
Precise failure sequence




But, if Investigators were with only "Per cell voltage history" like the old CVR approach (endless tape) probably they would be ready (some time ago) to deterministically say the "WHAT and WHY" in these BAD batteries that initiated the thermal runaway, GROUNDING THE 787.
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Old 10th Feb 2013, 20:04
  #615 (permalink)  
 
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In a poor design

Hi,

saptzae:

We know that 32V during a cell short will result in destruction of remaining cells.


Yes, with a poorly designed system you even display fireworks.

(When a cell starts to exhibit anomalies YOU CAN IMMEDIATELY process the info and decide what to do. AFAIK the people that worked in the algorithms had this techniques available to implement a "world class" design. 787 deserved it!

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Old 10th Feb 2013, 20:24
  #616 (permalink)  
 
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I urge contributors to this thread to please refrain from posting unfounded hyperbole. It does nothing to further our understanding of the technical issues at hand, bothers those professionals well versed in the industry standards, and misleads the gullible.
I couldn't agree more


Last edited by CliveL; 10th Feb 2013 at 20:29.
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Old 10th Feb 2013, 22:34
  #617 (permalink)  
 
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Ether former safety board member John Goglia was misquoted by the interviewing journalist, or he would be well advised to refrain from making erroneous statements about matters he doesn't understand.
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Old 10th Feb 2013, 22:47
  #618 (permalink)  
 
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HazelNuts39

I quoted the article in good faith, and will retain it in my files.

I will remove all reference to the remarks from this thread.

Your information I consider to be the gold standard, here.

Thanks for your intercession...
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Old 10th Feb 2013, 23:06
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How long will be the grounding of 787?

Hi,

In first NTSB briefing Deborah Hersman emphasized WHAT and WHY on BOS 787 incident.

WHAT: A short circuit inside a cell.

Problem now (WHY) seems much more complex. Even impossible to conclude:

1) PCB´s probably were FUBAR

2) Cell voltage history (before and after thermal runaway) probably were lost

If this is true, the only way to recover cell voltage history would be if battery voltage was measured and recorded. (NOT THE DC bus as happens in a conventional plane) Remember that between the cells plus terminal (the right position to measure) and the bus you have a relay/contactor and a diode module (this one specific to 787, because using Li ion that only "goes to the bus" if it drop below, i estimate 30 V)

So, if the voltage at battery plus terminal of cell # 8 was not measured or recorded NTSB will have two possibilities:

1) A cell failure from a non electric reason. (process, etc.)

2) A cell failure from a cell voltage balancing failure when battery was being charged. (Series charging, IMO not the best approach)

Considering JA829J started flying few weeks before the incident, very probably no other battery was used (and replaced) in that plane. So not possible (very probably) to look to other battery used in (APU) this plane.

So i don´t expect a conclusive WHY from NTSB for this particular battery failure. Simply i cannot imagine how to conclude. (the WHY)

The fact they are going to see process (manuf., design and chargers) is an indication they had no means to find the WHY in using the shortest procedure: Looking to the smoking gun.

On the question in the Title: What concerns me most is the FAA design review. A mere change to Ni Cd could not be the only required change.

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Old 11th Feb 2013, 09:06
  #620 (permalink)  
 
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B787 battery

Cell failure - multi current paths involving metal cased cells & metal battery case all resulting in further cell failures currents via earth straps bonding, heat etc. If need to stay with the same cells. Answer redesign battery case for temps above 800 degs C without metal. Material- basalt internal with kevlar external safety outer. Basalt & kevlar dividers between cells. Good for over 1600 degs C. No shorts, no ground loops, light weight.

Most batteries changed because they had been discharged too far. (ground handling?) It is most likely to be found the underlying reason for the two major failures. State of charge indications as a percentage comes to mind. If it at the present displayed as a percentage, then the low end should be recalabrated. If it is voltage it is just wrong. ( don't have how it is displayed & could not find ref in the thread.) The voltage indication of Li-Ion batteries between good & bad are too close for voltage readings anyhow. (coulomb counting for short term indicating)


Regards

Last edited by bill good; 11th Feb 2013 at 10:30. Reason: ps
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