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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 19th Feb 2013, 17:01
  #741 (permalink)  
 
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@bubbers44
The 787 uses starter generators for engine start, not pneumatic starters like other Boeings.
Yes, twin 250KVA, and which are powered by twin APU 225KVA starter generators.

Only the APU is started from a battery, which IMHO will draw less than 7.5KW (300A x 25V).
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Old 19th Feb 2013, 17:20
  #742 (permalink)  
 
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No powered plane without fire

Aeroplanes have been living with fire (in their engines) for over 100 years. This COULD be a precedent for permitting (inadvertent) fires in another power source, the batteries, provided it was as well contained as the engine combustion???
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Old 19th Feb 2013, 17:40
  #743 (permalink)  
 
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FlightPathOBN:
meanwhile, production rate is about what, 40 a month? at least 120 ac stored somewhere waiting for the temp fix…
Current production is four frames at Everett and one at Charleston per month. The plan is/was to be at 10 per month across both FALs by End-Of-Year.

FlightPathOBN:
"No battery-related incidents occurred before January 2013, when the airplane experienced two events."

Replacing over 100 of them so far is certainly an issue with the design and viability of the design.
The 100 replacements were due to the battery shutting down due to being over-discharged. As over-discharging can induce thermal runway, the system is designed to shut the battery down when it reaches a specific level of charge. So in these cases, the battery safety systems were operating as designed.
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Old 19th Feb 2013, 19:20
  #744 (permalink)  
 
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No powered plane without fire*

Hi,

Dtype:

Aeroplanes have been living with fire (in their engines) for over 100 years. This COULD be a precedent for permitting (inadvertent) fires in another power source, the batteries, provided it was as well contained as the engine combustion???


You introduce an important point: We operate (and live with) machines with contained fires. What is not accepted is:

A company introduce a new design (under special "conditions") and in an interval of days two planes suffer incidents with HEAT, SMOKE and FIRE (BOS). The second (TAK) was bound to be much worse. A short circuit saved Boeing discharging the battery thus avoiding an in flight fire in a compartment with important electronics. (This is a model posted and commented earlier)

The technical answer is:

A dependable and safe battery (one that not is transformed suddenly in a dragon: heat, smoke and even fire) is absolutely required. A battery (that could caught fire) well contained with "normal" MTBF will be certified.

Problem now is not only technical. Became almost a "political" issue with not small technical challenges.

(*) No powered plane without fire. There are powered planes (electric motor) with these batteries.

saptzae:

IMHO will draw less than 7.5KW (300A x 25V).
Good estimate

These LiCoO2 cells are de-rated to 4.025V, and should not show any anomalies after a few months / a few hundred flight hours.
What really happened? Just random? Coincidence?

FlightPathOBN:

In the re-design, go back from 32V to 24V..
32 V was designed due BDM (diode module)

ITman:

I am sure that these issues were considered in Mr B's design,...
We detected errors so, we are not so confident on that.

Hi_Tech

2. Is it just a coincidence that we have 2 fire incidents in one month.
One fire incident in BOS (Logan) TAK had heat, smoke and hot chemical spray (battery lost 5 Kg)

3. Surely the battery would have gone through a rigorous testing before manufacture and it is difficult to imagine that there were no problems at all with this compact design of a highly volatile chemistry.
We donīt know. This is a Testability issue.

TURIN:

Someone at Boeing got their wires crossed.
The disconnection seems not just between engineers at Seattle and Chicago high rocks.

cockney steve:

Some bean-counter's being grossly overpaid for a stupendous level of incompetence!


green granite:

It then has the ability to recharge in a relatively short period of time so that it is available for the critical backup role that it plays during flight.
Logical question!

Last edited by Jetdriver; 19th Feb 2013 at 20:14.
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Old 19th Feb 2013, 19:27
  #745 (permalink)  
 
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cockney steve:

so the cumulative service life of these aircraft, (land and ground,-their figures) is 250,000 hours that means a total service-life of 1,000 hours per battery OR 16 dollars an HOUR ....32 DOLLARS an HOUR, EVERY hour per aircraft....
If my airline starts putting a battery surcharge on my ticket, I'm blaming you for giving them the idea.
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Old 19th Feb 2013, 19:32
  #746 (permalink)  
 
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Hi DType

I had thought of that, looked at the applicable rule, and see some room for something like what you say.

(a) In each area where flammable fluids or vapors might escape by leakage of a fluid system, there must be means to minimize the probability of ignition of the fluids and vapors, and the resultant hazards if ignition does occur.
Leakage of electrolyte is associated with expansion and heating of the battery case, causing a crack.

Leakage, in the rule, is not constrained, but addressed only in that it may ignite.
If the temperature of the interior of the battery and its enclosure can be kept below the fluid's ignition (flash) point, leakage, per se, is not prohibited.

That satisfies "minimize the probability of ignition." It does not say "Possibility", and minimizing a "probability" is less constraining (easier) to do. So in the case of the fluid and vapor leakage, "possible" leakage is allowed.

Now, "the resultant hazards if ignition does occur." That means the results of ignition must be "minimized". That does not mean "controlled", or even "mitigated". If the burning electrolyte is contained in the enclosure, that would satisfy the "minimize" part of the langauge.

BUT:
Electrolyte escaped from the Battery in the JAL accident, and it is assumed it continued to burn as it flowed along the EE Bay decking. This would likely NOT be allowed by the rule, so "containment" enters the controlling language.

(2) Flammability characteristics of fluids, including effects of any combustible or absorbing materials.
What if the electrolyte, alight, puddled in an area of CFRP? (Carbon Fiber Reinforced Plastic). This is potentially a show stopper.

CFRP ignites at 580 degrees Fahrenheit. By demonstration, CFRP must be proven not to ignite at the temperature of burning electrolyte. If it cannot, the CFRP is combustible, by rule, and leakage is prohibited. NEVER ALLOWED.

The fuselage is constructed of this material (CFRP). If it catches fire, it will burn on its own, in continuous fashion, until extinguished by an approved method. If it ignites in the Hold, extinguishment is not possible until landing. On board extinguishing is not provided, and would be in conflict with the rule making anyway, CFRP cannot ever be allowed to ignite, under any condition. What are the products of burning CFRP? If these combustion by-products entered the flight deck or cabin, is the air breathable?

Back to the drawing board. A box that cannot leak is required, by regulation. Any breach of the contents of the enclosure MUST be dumped overboard, if the contents are burning, the exterior of the Hull is at risk to ignite.

Last edited by Lyman; 19th Feb 2013 at 21:47.
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Old 19th Feb 2013, 19:50
  #747 (permalink)  
 
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Mac the Mechanic
Home - Boeing 787 Updates

Interesting link here.
Quote:- When the going gets tough, program teams get going
Another interesting quote, which indicates to me that the site was put together in a big hurry without proofreading by someone with a technical background:
On the ground, the 787 can be started without any ground power: The APU battery starts the APU generators, which start the APU to power the engine generators, which then start the engines.
There an excusable confusion between a generator and a motor-generator or starter-generator, but the idea of starting rather than powering a device "which then...." implies that it is running before the associated APU or engine starts to turn over.
I also believe that only one of the two APU generators at a time is involved in the APU start.
Details may not matter in publicity, but they matter when discussing the engineering.
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Old 19th Feb 2013, 20:06
  #748 (permalink)  
 
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Aeroplanes have been living with fire (in their engines) for over 100 years. This COULD be a precedent for permitting (inadvertent) fires in another power source, the batteries, provided it was as well contained as the engine combustion???
Aeroplanes have also been living with a means to cut off the fuel to a burning engine for over 100 years.

If the batteries in question were installed so that they could be isolated, then doused with large quantities of water (paddling pool volumes) and/or ejected from the airframe, then it might be worthy of consideration.

No pilot that I know would be happy with a piece of equipment in an inaccessible area that was a demonstrated fire risk, "contained" or not. What's the point of all the dangerous goods legislation if you carry something similar to a prohibited item around with you all the time?
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Old 19th Feb 2013, 20:30
  #749 (permalink)  
 
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32V

@RR_NDB
32 V was designed due BDM (diode module)
32.2V is end of charge voltage (4.025 x 8).

29.7V is rated voltage.

I'd go for 25V being available when battery low and at a high current load.

I estimate that BDM drops less than 1V (0.8V typ) at 150A if based on Schottky diodes and less than 0.5V (0.3V typ) if based on MOSFets.

NiCad rated bus voltage is about 24V and end of charge 29V for 20 cells. End of charge less 27-28V at elevated temperature.

What really happened? Just random? Coincidence?
My best bet, as outlined in earlier posts, Primary failure (short) due to gradual cell deterioration after one or more (in no particular order of preference) of :
  • Mismanagement by BMS.
  • Mishandling (assembly, rework, repair, maintenance, storage)
  • Mishandling deep discharge and reset BMU lockout
  • Mishandling external over voltage, such as bus over voltage, also during maintenance or storage (recharging - dunno they do that).
  • Tested to overstress - Boeing says they test a lot and hard (unlikely IMHO)
  • Bad cells (unlikely IMHO)
Edit: Apparently, current battery tests do not detect cell deterioration. I do not claim that tests possibly could detect it.

Last edited by saptzae; 19th Feb 2013 at 21:09. Reason: Edit
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Old 19th Feb 2013, 21:07
  #750 (permalink)  
 
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B787 battery

Redesign - remove all batteries & use super capacitors. End of story!!
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Old 19th Feb 2013, 21:13
  #751 (permalink)  
 
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Redesign - remove all batteries & use super capacitors. End of story!!
Cute idea, but the capacity and load capability would be too low.

And, anything that has the capacity, can make fireworks too, NiCad included.
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Old 19th Feb 2013, 21:35
  #752 (permalink)  
 
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The voltage might be slightly higher.MEL maintenance action after APU bat charger fault:
"Prior to each departure, verify on the ELECTRICAL maintenance page 1
that the APU battery voltage is 31 DC-V or greater"
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Old 19th Feb 2013, 22:09
  #753 (permalink)  
 
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Comments on many posts

Hi,

FullWings:

If the batteries in question were installed so that they could be isolated,

This comment triggered an idea will post on a Fault tolerant battery. Less risk of "uncontained thermal runaway" and capable to be "isolated". Will comment on that later.

No pilot that I know would be happy with a piece of equipment in an inaccessible area that was a demonstrated fire risk, "contained" or not. What's the point of all the dangerous goods legislation if you carry something similar to a prohibited item around with you all the time?


saptzae:

32.2V is end of charge voltage (4.025 x 8). 29.7V is rated voltage.
I'd go for 25V being available when battery low and at a high current load.

Perfect.

I estimate that BDM drops less than 1V (0.8V typ) at 150A if based on Schottky diodes and less than 0.5V (0.3V typ) if based on MOSFets.
Some days ago i read and saved a .pdf from Sandia Labs telling on a device for 787 program. IIRC MOSFet. Itīs lost in one HD


My best bet, as outlined in earlier posts, Primary failure (short) due to gradual cell deterioration after one or more (in no particular order of preference) of :
Mismanagement by BMS.
Mishandling (assembly, rework, repair, maintenance, storage)
Mishandling deep discharge and reset BMU lockout
Mishandling external over voltage, such as bus over voltage, also during maintenance or storage (recharging - dunno they do that).
Tested to overstress - Boeing says they test a lot and hard (unlikely IMHO)
Bad cells (unlikely IMHO)

Fully agree including sequence (hierarchy)

Apparently, current battery tests do not detect cell deterioration. I do not claim that tests possibly could detect it.
Thatīs another concern i have with these cells. Lack of knowledge. "uncharted waters"

bill good:

Redesign - remove all batteries & use super capacitors. End of story!!
Yes, end of history: payload of the redesigned plane will be zero.

saptzae:

can make fireworks too, NiCad included.


no-hoper:

...verify on the ELECTRICAL maintenance page 1
that the APU battery voltage is 31 DC-V or greater"
This is an interesting indication. Conservative approach. Tight tolerance on batt. charge condition. Pre flight

Makes me remember the laptops battery range (empty to full of just one Volts)
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Old 19th Feb 2013, 22:27
  #754 (permalink)  
 
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@RR_NDB

Yeah, the poor battery integrators and BMU/BMS guys feel the heat for sure.

Making a positive assumption in view of the fact that 150 batteries were replaced, according to Boeing mostly due to being discharged until lockout.....

Mishandling deep discharge and reset BMU lockout

It could explain why nothing happened for several years, and then two in a row...

Unfortiunately, that just being another easy answer, it still would leave the Secondary (multi-cell failure/runaway) and Tertiary failure (fire) to deal with.

Gosh, mis-drilled oil pipes leading to wing perforation and environmentally friendly coatings leading to fan mid shaft failure and torched grass seem to be so much easier to deal with.
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Old 19th Feb 2013, 22:44
  #755 (permalink)  
 
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Devil Management problems at ALL levels

Hi,

saptzae:

Yeah, the poor battery integrators and BMU/BMS guys feel the heat for sure.
High rocks always are the ultimate responsible. And management failed: BMU/BMS guys feel the heat

It could explain why nothing happened for several years, and then two in a row...
Good point!

Gosh, mis-drilled oil pipes leading to wing perforation and environmentally friendly coatings leading to fan mid shaft failure and torched grass seem to be so much easier to deal with.
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Old 19th Feb 2013, 23:22
  #756 (permalink)  
 
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Mishandling deep discharge and reset BMU lockout

It could explain why nothing happened for several years, and then two in a row
A long time ago, I suggested that a system which allowed a deep discharge,was a fundamentally flawed design....I was shouted-down on the basis that, under emergency conditions , every last amp might be needed.

The fact, apparently, is that under NORMAL usage-conditions, these batteries are being driven into an unsafe area....IMO they should load-shed/lock out with sufficient reserve to start the APU and then be able to safely recharge from on-board generation.

Under the present regime (grounding excepted), what happens if the fuel-flaps/nav.lights/whatever drain either or both batteries to lockout . the aircraft is presumably then held up until replacements can be sourced/fitted.
A far from ideal situation and entirely preventable with proper engineering.

@ EENG...I was trying to highlight just how ridiculously short the life currently is.

An average lead-acid battery for a diesel car would cost about 0.6 of a CENT per hour of it's life !!!
Oh, dear, I really must get out more.
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Old 20th Feb 2013, 00:03
  #757 (permalink)  
 
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Thumbs up The fact, apparently, is that under NORMAL usage-conditions...

Hi,

cockney steve:

these batteries are being driven into an unsafe area
So, letīs reduce this problem by half:

787 batt. redesign, K.I.S.S. version 1.0


Please, bombard this first version. Objective: Fast and safer return to the skies.
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Old 20th Feb 2013, 02:56
  #758 (permalink)  
 
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@cockney steve
A long time ago, I suggested that a system which allowed a deep discharge,was a fundamentally flawed design....I was shouted-down on the basis that, under emergency conditions , every last amp might be needed.
Yes, but it is needed, as much as the pilot, to "fly the plane to the end".

A far from ideal situation and entirely preventable with proper engineering
Yes, together with management.

Last edited by saptzae; 20th Feb 2013 at 02:57. Reason: Clarify
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Old 20th Feb 2013, 03:17
  #759 (permalink)  
 
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CFRP, the epoxy component, is full of over 90 chemicals and this is why it was banned by the FAA finally from A/C interiors due to FST (Fire, Smoke and Toxicity) hazards back in the 70's due to numerous aircrew and passenger deaths deaths from FST. I worked on the problem between 1960's and 1970's
A recent CFRP crash example was in Guam a few years ago involving the B-2A. The fuel fire was extinguished within less than 30 minutes, but the wreckage continued to burn for over two days in spite of the efforts of over 60 trained USAF fire personnel due to continuing hot spots and flare ups. This is fully documented by USAF in their incident report, but FAA and Boeing ignored my protests as they had my earlier inputs and protests concerning 787 crashworthiness proposed SC's.
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Old 20th Feb 2013, 11:28
  #760 (permalink)  
 
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An average lead-acid battery for a diesel car would cost about 0.6 of a CENT per hour of it's life !!!
Or in the case of the factory fitted Bosch battery in my Mercedes, now in its ninth year of service, 0.04 cents per hour.

And with 110Ah capacity and 1100amp cold cranking, it would almost certainly fire up a soft start APU. Don't know about the weight but is certainly smaller than the Li-on unit installed on the 787! ;-)

And, anything that has the capacity, can make fireworks too, NiCad included.
Exactly.

At the end of the day it is a box of energy and the more energy in that box the more potential for harm.
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