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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 27th Jan 2013, 03:45
  #181 (permalink)  
 
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Main bat is connected to the hot bat bus through a diode module to ensure the bat only gets charged through its charger. APU bat has no such protection as it is only connected to the APU start circuit (and nav lights when towing without APU.)


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Old 27th Jan 2013, 05:00
  #182 (permalink)  
 
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@TacomaSailor

Thank you for the great report. It analyzes pretty much all single cell failure scenarios.

Here is what I am using, covering multi cells:
http://focus.ti.com/download/trng/do...0and%20How.pdf

@RR_NDB
Did you see this approach used before? How many amps to be shunted? Voltage control loading a charging (or charged cell) through by pass?
Common practice with larger (Pb) batteries and also Li batteries. Not encountered it with NiCd due to negative cell voltage temperature coefficient.

See above application note by TI.

The ANA main batt. geometry mismatch was likely due what kind of abuse? During charging cycles?
Picture is post event, can't tell pre-event, but there are some clues.

The event:
Labeling cells left to right, top to bottom.

  1. Cell #3 failed first, in a manner as outlined earlier, it shows "burned out" plates and also greater warping (thermal distress) around it
  2. cells #2, #6 and #8 show substantial signs of thermal runaway
  3. Cells #1, #5 and #7 show variations between plates and lesser thermal distress and over pressure. **
  4. Cells #1, #5 and #4 closest to #3 show less damage than #2, #6 and #8 **
  5. Conclude cell #3 has not thermally triggered thermal runaway of many/any?? other cells. **
  6. Conclude cells except #3 failed by electrically induced thermal runaway, triggered by over voltage after failure (short) of #3 and remaining powered by the bus
  7. Conclusion: Battery was kept at near 32V after #3 failed.
** But, it could be opposite, less bulging due to valves opening earlier.

Again, there are two independent failures, 1. and 7. Both have to be fixed.
7. seems to be the greater concern though, as it failed seven (7) very likely functional cells and multiplied the violence of the event.

Where is the source of information that the the battery is charged by the bus. Ive heard of a diode.

The direct connection of a Li Ion stack of cells to a bus seems very dangerous. A much safer approach would be:
Battery is connected to and will be charged via the bus. There is no 60A charger on those PCB's. There is also no 150A+ diode handling APU starter. Thus, the bus voltage must vary with battery voltage.

And, bus voltage must listen to charger, how that works together with bus tying I don't know. On failure (of #3) the charger should disconnect the battery from bus.

How the battery is protected from bus is the golden question. It seems it was not. If it was not, pre-event cell deterioration may also be caused by it.

With these thin wires seems just impossible to control cell voltages during the charging. A likely scenario (during charging) JAL BOS fire.
No, that's just fine. The bypass current would cover only differences in leakage and possibly capacity and be up to only 1-5 % of charging current. Less than 3A. 10s of mA typical. Once leakage, or imbalance goes beyond a few %, cell has to be replaced.

@ Turin
Thanks for info. One main and one APU battery failed. If not caused by bus, it is must be the charger continuing to power the battery.

@ Turin
Any info on bus tying. Can APU bus connect to main bus?

Edit:I keep wondering about why the four cells on the left show a pattern different from the four cells on the right. It seems like that plates have slightly moved apart, or have changed their properties somehow.

Why only these four, and could this change be pre-event, and be related to the failure of #3?

Can this pattern be observed on other in-service batteries?

Edit2:
Wiring errors would be a very convenient explanation of 1.
Without being aware of bypass facility, I discounted wiring errors earlier. Now, wiring errors could lead to the wrong cells being bypassed and to over voltage on the others.

Wiring errors could explain the pattern (if it is deterioration) in the cells on the left and failure of #3. Did they swap left and right monitoring or bypass wiring?

Or, is there another problem managing half the cells?

But, it still would leave 7. to explain and fix. My analysis of 7. could be wrong like everything else. While I doubt it, and stick to electrically induced thermal runaway, all other cells could also have been destroyed by thermally induced thermal runaway.

Last edited by saptzae; 27th Jan 2013 at 07:25. Reason: Typo, Add @Turin
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Old 27th Jan 2013, 06:54
  #183 (permalink)  
 
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The below is a screen grab from the NTSB briefing on the Boston battery failure:



The circle marks the location of an electrical short that they discovered in one of the cells.

The only thing I can conclude from this picture is that this particular short probably resulted from cell over-temperature.

I make this statement because the short is located along the centerline of the electrode plates where the least heat dissipation occurs. It would also seem that any physical manufacturing defect would be found along the edges of the plates.

It should be pointed out that there may also be other shorts that were not pictured and if they exist, they may have a different characteristic than this one.

Last edited by Machinbird; 27th Jan 2013 at 06:55.
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Old 27th Jan 2013, 08:50
  #184 (permalink)  
 
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Cell #3

On page 19 of http://www.ntsb.gov/investigations/2...87_1-24-13.pdf is a CT scan of #3.

They call it 6 as their picture on page 20 is inverted from the one posted here. It is implied that this is the electrically shorted cell.

I eagerly await a CT scan of the ANA battery.
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Old 27th Jan 2013, 14:16
  #185 (permalink)  
 
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Saptzae.
The APU AC BUS can be tied to the L and R AC busses.
From what I can see the only connection from the APU Battery is through the Start Power Unit (SPU) this converts 28vDC to 115vAC this then goes to the ATRU which converts to +/-130vDC which via the CMSC (Common Motor/Start Controller) is routed to the APU starters (VFSG). The APU hot bat bus doesn't connect to anything else from what I can see except if the Towing Switch is selected 'on'. In which case it powers the Position lights.
The APU charger receives it's power from the FO's Instrument Bus.


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Old 27th Jan 2013, 14:33
  #186 (permalink)  
 
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Temp rise during fast charging after being heated during APU start

Hi,

Machinbird (#183):

"Temperature as trigger of cell short circuit."

This matches the model of the battery being "abused" by a fast charging (operating near or within its temp. limits)

The charging regime (APU batt.) could be the main BOS JAL factor. With cells probably degraded before? How many hours operated before?

Likely it was being recharged when started to fail. Or
(imo, less probable) started to runaway during or just after delivering high current to APU starter.
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Old 27th Jan 2013, 14:46
  #187 (permalink)  
 
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Over in rumours and news, #273, re-checked posted a link to the ntsb
press briefing video:

Chairman Deborah A.P. Hersman briefs the media on the JAL Boeing 787 battery fire investigation. - YouTube

How to say very little over a long period, is the first thing that strikes
me and looks like the event is being carefully stage managed.

More interesting are the areas discussed, where the battery analysis takes
centre stage. Seems a bit odd to me, since any battery that suffered such
catastrophic failure would be expected to have cell deformation and evidence
of internal short circuits, yet the images are presented as though something
profound.

Possibly more important and not being discussed as yet is the intelligent
charger. A charger of that would be expected to have internal non volatile
storage and software to log both normal and abnormal conditions. For example,
the number of charge cycles and the voltage, currents and timescales involved.
There should be a log of the events and conditions that led up to the failure
which would be downloadable for analysis. Perhaps they are doing this already,
but no reports as yet...

Regards,

Chris
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Old 27th Jan 2013, 14:50
  #188 (permalink)  
 
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ANA main battery smoke

TURIN (# 181)

A failure in the diode module (typical is short circuit) may explain the smoke ATC saw.

APU circuitry doesnt require the diode as you understand (APU batt. never is directly connected to a supply. Just to loads: APU starter, through the modules you mentioned or to the lights when towing with APU ON). The charging of APU battery is not normally made during her only two above mentioned uses as we can imagine.

Last edited by RR_NDB; 27th Jan 2013 at 14:58. Reason: Typo and text impvmt
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Old 27th Jan 2013, 15:12
  #189 (permalink)  
 
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Typical DC bus operating voltage

TURIN,

With a diode module between the battery and the DC bus you have an automatic switching that inserts the main battery in the bus WHEN THE BUS VOLTAGE IS BELOW BATTERY MINUS DIODE VOLTAGE DROP. To keep the 32 V battery "disconnected" the bus voltage must be operating above 33,5 V or so.

What is the typical Voltage in the bus?

Mac

Last edited by RR_NDB; 27th Jan 2013 at 15:16. Reason: Typo
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Old 27th Jan 2013, 15:16
  #190 (permalink)  
 
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Short circuit would degrade the poly over time, due heat, so I am interested in the end cap integrity. Also, wouldn't Li metal tend to aggregate at the 'top'' of the cell, across the plate(s)? Are these cells three wound plates, or one continuous? The NTSB lab table appeared to have several 'unrolled' plates on it.

The NTSB briefing definitely looked scripted, the questions most definitely so. Nothing asked that wasn't covered in PPRuNe by the third day of grounding, imo.

This is a once in a lifetime opportunity to see how things work at this level of government, commerce....Boeing finally figured out the advisability of staying quiet. They may be minus a few people, those who spewed like electolyte...

I am annoyed at the unprofessional use of the language. Not even Hersman seems to know the difference between "How" and "Why"....

It is what it is....
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Old 27th Jan 2013, 15:28
  #191 (permalink)  
 
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Politicians short circuit

Bear,

I will love to see politicians being short circuited.

The best would see being grilled by the bouncing of what they say.

A lot of electricity in the air (augmented by comments not backed by good technicians)

Indeed, a lifetime oportunity.

Last edited by RR_NDB; 27th Jan 2013 at 15:34. Reason: Text tweak
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Old 27th Jan 2013, 15:47
  #192 (permalink)  
 
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RR_NDB

Question: How many amps the thin white wires could carry without being transformed in fuses? 1 amp? By pass?
From the image, it looks like those cables are 2-5A rated, but difficult to say
for sure.

There's no sign of power semiconductors and heatsinks on the pcb's though, which
mitigates against the idea of cell balancing electronically. Power dissapation is related
to voltage and current. Consider the following:

Fast charge rate: 65Ah / 1.5hours = 43 Amps + say 10% for losses = 47 Amps,
Say 50Amps absolute max.

Balance current 5% of charge current worst case (from saptzae) = 2.5Amps

Cell voltage = 4.2V max

So, worst case power dissapation in the bypass circuitry would be: 4.2 x 2.5 = 10.5W, per cell.

You would need 8 power semiconductors for the whole battery, together with associated heat sinks and there's no evidence of this on the pcb's...

Just to complete the loop on voltage sensing, you would need 2 sensing wires
per cell, or 16 wires total for 8 cells...

Regards,

Chris
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Old 27th Jan 2013, 15:54
  #193 (permalink)  
 
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FAA made a mistake with Lithium, and they know it. It is such a seductive technology, who wouldn't want it integrated with such a groundbreaking airplane (787)....

In reading the considerations, the motive for allowing the LiIon battery is clear, Economics, not airworthiness, or safety.

It reads like a waiver without a safe foundation, written to ennable an experiment in commercial carriage

That is not the FAA's purpose. The purpose of the FAA is to say NO....until safety is satisfied...

How do we know? Because the AD makes it plain that their mission was avoided.

They were not satisfied with Lithium safety from the beginning, all the considerations are written to prevent fire.....or to mitigate one that starts

Which makes perfectly obvious they are allowing the possibility of fire for a system that is not critical to safety, to flight, or to their mission, only to money

Now that the horses have bolted the corral, they command Boeing to "demonstrate the safety of the system" while allowing, in their initial approval, for unsafe conditions they now say are insufficient?

Hersman is correct, fire is not expected. She must not have got the memo from FAA....
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Old 27th Jan 2013, 16:45
  #194 (permalink)  
 
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"Seductive batteries" for an electric plane

Bear,

I was also in love with her, until my son started to use the dangerous units in his RC models. He was not allowed to recharge it inside our home.

(These batteries reminds the joke on why hurricanes were named with female names.)

Chris,

FAA authorizes, Thales offers the "seductive" batteries to Boeing, Securaplane design solutions, Yuasa offers the cells, PCBs are manufacture (OEM) and the mix is integrated in 787 with algorithms, protections, etc.

The mess starts. The politicians go to the stage (visibility)

Who is the ultimate responsible for the losses?

No problem...you can socialize (the losses). This was made since 2009 crisis.

Irony: A backup part (main battery) and the other to start an AUXILIARY power unit.

In a highly redundant (seems truly a dream in this respect)
(innovative electric plane-even bleed air app., windmill gennies in engines, etc.)

Batteries power is just 2/1000 of A/C power)

Sad
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Old 27th Jan 2013, 17:07
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My issue is with the regulation, not the technology. The ironic part is the steps needed to mitigate risk in a system that is required to provide safety in an emergency. Once (re)Airborne, the fleet could fly fifty years without primary power system fault that requires interruption with a system that has grounded the fleet due its own failures. In its first year of service.

Short sighted, sloppy, weak, ignorant.

It is patently clear the original rules were woefully lacking, even permissive instead of restrictive....

There is a warning label in Commerce: "Cannot be made SAFE".... By the time Boeing demonstrates a hefty ceramic battery vault with poured in place conductors, pressure sensing exhaust that dumps into the airstream, and cooling systems that have to work nonstop, with controllers and motors that are shielded from electrolyte, ad nausea, small nuclear reactors will power us about the heavens.
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Old 27th Jan 2013, 17:38
  #196 (permalink)  
 
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Stalemate?

Bear,

Remembering the "wise" words on 999% or similar. (Boeing could need US Treasury funding). Better to "fire" Li Ion and revert to Ni Cds...

I am curious to learn on the conditions of the other 94 batteries in the other (47) planes. This may solve more easily the puzzle. Just CT can show a lot. And the surviving ones could be used again. For APU.

Technical point:

Why not have a mix of Li Ion and Ni Cds:

If a EFFECTIVELY PROTECTED Li Ion fails a smaller Ni Cd enters in the circuit. This can be easily made in the A/C main battery section.

For APU it could be adequate the Li Ion (after the review)

Last edited by RR_NDB; 27th Jan 2013 at 17:44. Reason: Text impvmt
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Old 27th Jan 2013, 17:41
  #197 (permalink)  
 
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Originally Posted by Lyman
Hersman is correct, fire is not expected. She must not have got the memo from FAA....
Lyman
If you will recall, NTSB is independent of FAA, and makes recommendations as they see fit on incidents that are within their purview. These also include rail, highway and pipeline incidents.

FAA is the agency that is responsible for safety of flight. Sometimes those areas of responsibility conflict.

Hersman's statements were a careful summary of what they actually knew to date (which is not all that much), and how they intended to proceed.
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Old 27th Jan 2013, 18:06
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I am interested in the point you are making. What is it?

Hersman is being exceedingly kind to the FAA and their huge problem.

Hersman cannot say: "Fire is not allowed". Yet in a piece of non critical kit that has a history of spontaneous combustion FAA are allowing an expectation of fire. In their poorly worded 'release to service' of this problematic technology, my favorite is that any combustion/damage may not exceed a sphere of 56 inches. Not "Contained" but exceed

As if a fire is somehow self limiting to a certain volume, excluding flame from other, more critical, systems'.

This is a BACKUP BATTERY, not a generator (of which there are six), or a brake system, or......

Boeing demonstrated no need for the Lithium Battery, none, not even an honest statement that it would be light, energetic, and sexy in a brochure.....

The goat in my post is FAA....not Hersman.
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Old 27th Jan 2013, 18:14
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With a diode module between the battery and the DC bus you have an automatic switching that inserts the main battery in the bus WHEN THE BUS VOLTAGE IS BELOW BATTERY MINUS DIODE VOLTAGE DROP. To keep the 32 V battery "disconnected" the bus voltage must be operating above 33,5 V or so.
Interesting point. Is is just a diode? Lithium cells can be damaged by over discharging. I would hope there was something that protected the battery from feeding the bus via the diode if the bus voltage was too low for some reason. eg I would hope it's not a simple diode but a diode and an electronic switch with under voltage detection.

You have to be quite careful about recharging a lithium battery that has been allowed to go too flat.
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Old 27th Jan 2013, 18:16
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It is a backup system, please tell me it must be selected, and is not "inadvertent" or "automatic"?

Also, Why only two Batteries? If both are "back up" what starts the show?

Back up batteries are used casually in line-service? Come on......

The reason we know? FAA requires a minimum charge for dispatch.

That is a sign that this battery needs to maintain a minimum energy for definition of its role. I don't think they are saying "Charge it before Launch".

"EMERGENCY USE ONLY" comes to mind....

Last edited by Lyman; 27th Jan 2013 at 18:24.
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