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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 7th Mar 2013, 16:39
  #841 (permalink)  
 
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In most cases, the 12V battery will be of the lead-acid type, consisting of eight 1.5V cells in series.
In a car the battery is six 2V cells ie 12 V
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Old 7th Mar 2013, 16:41
  #842 (permalink)  
 
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Hi Chris...

I use the concept "eight batteries" and have from the OP.

A cell, is "wet", a "component" of a battery. A battery is an enclosed, individual unit capable of installation as a self contained power storage system, in connection with other similar components, or solitary.

Simply, a "Battery" means "collection of".

Each battery in the Yuasa container is capable of being isolated, and performing a storage function, sealed from the others.

So I consider each battery as composed of three separate electrodes, or cells, producing a typical voltage when discharging.

Boeing used the experience of each separate battery in its claim of fleet hours....

As they should, but they also did not rely on that description in the Press.

In the Yuasa application, any battery failure fails all eight.... The series is broken.

That is why it was important for Boeing to allow both descriptions in the Press (imo). They could refer to a cell failure, when in fact, a cell failure meant the entire system was failing. They did not want to portray the whole battery system as that vulnerable to failure, it trashed their predictability....

Your car battery has six cells. It is a battery, unto itself.

The blue box in the Boeing contains eight three cell batteries, in series.

Last edited by Lyman; 7th Mar 2013 at 16:52.
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Old 7th Mar 2013, 18:09
  #843 (permalink)  
 
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NTSB - Boeing 787 - Interim Report - March 7, 2013

Detailed Analysis.
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Old 7th Mar 2013, 18:31
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From Boeing Land...wow...

Boston airport firefighters encountered sizzling liquid and a hissing, “exploding” battery when they entered the 787 at the center of a two-month-long National Transportation Safety Board investigation, according to documents released Thursday.

The NTSB said Thursday it plans two public hearings next month, one to explore lithium-ion battery technology in general and another to discuss the design and certification of the Boeing 787 battery system. (Emphasis added...at least another month before hearings)

The safety agency announced the hearings as it released an interim factual report and 499 pages of related documents on its investigation of the Japan Airlines 787 fire at the Boston airport on January 7.

Among the findings in the documents released Thursday:

• On the day of the Boston fire, the battery did not behave as Boeing or subcontractor Thales predicted.

The battery’s power discharge was “not at the constant rate described by the Boeing or Thales documents and included large changes and reversals of power within short periods of time,” according to the Airworthiness Group Chairman Report.

• Sitting on a rack above the battery that burned was a smaller lithium ion battery, also supplied by Japanese manufacturer GS Yuasa, that is used to provide emergency power for the jet’s flight controls “for a minimum of 10 minutes when no other electrical power is available.”

Investigators found the exterior of this battery had been “lightly scorched” by the fire below and noted that its case had openings at the corners.

• No heat damage was found to any primary airplane structure.

However, the floor panel and carbon fiber floor support material, which are considered to be secondary structure, “were found to be heat damaged beneath where the APU battery had been installed.”

• The firefighters who were called to put out the fire did not know they were dealing with a lithium-ion battery, and had great difficulty putting out the intense fire.

When Capt. Mark Munroe of the airport’s aircraft rescue and firefighting (ARFF) unit entered the plane, he “saw heavy white smoke billowing through the floor” of the passenger cabin.

After locating the fire inside the electronics bay in the belly of the airplane, firefighters entered the compartment through dense smoke and applied shots of Halotron fire extinguisher to the battery.

Lt. David Hoadley of the ARFF unit reported that “It seemed like the fire did not want to go out, it kept rekindling.”

Then the battery “exploded,” according to Capt. Monroe.

“Capt. Munroe heard the battery hissing still and pushing white smoke or steam. There was liquid sizzling over the sides of the battery and still heavy smoke conditions. ... The battery continued to hiss before exploding.”

Monroe related that “he felt something hit him in the neck while he was in the airplane,” and he was sent out for medical treatment. “Something had burned his neck.”

Firefighters attempted to remove the battery from the jet, but found that the “quick disconnect” mechanism Boeing had included to allow mechanics to take out the battery for maintenance was “melted and un-recognizable” and a metal plate was preventing access.

The battery had to be cut out from the rack where it sat.

“With a hot battery and a gloved hand (Lt. Hoadley) could not access the bolts on the lower rails with tools. They attempted with pliers to remove the bolts for maybe 20 minutes. What looked like Teflon slides were burnt away and the battery would not move. There were 3 more screws that could not be removed.”

Firefighters cut away the metal plate, severed the battery wire, then “pried the battery loose with hydraulic spreaders and removed it.”

The battery was passed down to a firefighter and placed on the tarmac about 50 feet from the airplane.

The fire was declared under control an hour and forty minutes after the initial notification.

Boeing’s entire fleet of 787s has been unable to fly since two battery incidents in January prompted a Federal Aviation Administration order grounding the planes.

The company’s proposed tests of improvements to its battery system are currently under review by the FAA, which is expected to make an initial recommendation on those plans next week.


NTSB describes sizzling, hissing 787 battery in Boston fire | Business & Technology | The Seattle Times

Last edited by FlightPathOBN; 7th Mar 2013 at 18:34.
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Old 7th Mar 2013, 18:50
  #845 (permalink)  
 
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rogerg,

Thanks for spotting my "deliberate" (!) mistake.

Hi Lyman,

I now understand the thrust of your argument - thanks. Don't accept all of it, however. It's true that the six 2V cells in a 12V lead-acid car battery can't be separated without destroying the battery (AFAIK).

You are also right to point out the cascade effect from one short-circuited cell to its neighbours, which doesn't seem to happen in lead-acid batteries (and perhaps not in NiCds, but I'm not sure).

I infer you are saying that Boeing has claimed that an hour of battery time represents eight hours' experience. If so, can you direct me to a quote?

You argue that, because each 3.7V LVP-65 cell (which you refer to as a "battery") has three electrodes, that equates to having 3 cells within each. That seems a non-sequitur to me, and the Yuasu LVP-65 data sheet suggests otherwise. The LI-Ion battery in my mobile phone also has a nominal voltage of 3.7V, so does it have three cells? Or are your three cells wired in parallel?
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Old 7th Mar 2013, 19:02
  #846 (permalink)  
 
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Today's NTSB Interim Factual Report indeed makes interesting reading.

APU started at 1004 EST, battery failed at 1021 (only 1 minute after the flight crew had disembarked).

So the failure occurred about 16 mins after the recharge cycle had begun. Must admit I had expected a longer time-frame. I wonder what the temperature of the battery was before and after APU start.
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Old 7th Mar 2013, 19:13
  #847 (permalink)  
 
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Hi Chris.

Didn't APU start off one of the donks?

Time
Event
1000:24
Airplane touched down.
1004:10
APU started.
1006:15
Airplane completed turn into parking location.

1006:48
Parking brake set.

1006:52
Engine 1 shut down.
1006:54
Engine 2 shut down.

1021:01
APU battery bus voltage decreased from 32 to 31 volts.

1021:04
APU battery current increased to between 44 and 45 amperes for 4 seconds, indicating current flowing into the battery.

1021:07
APU battery bus voltage decreased to 30 volts.

1021:09
APU battery bus voltage decreased to 29 volts.

1021:10
APU battery bus voltage increased to 31 volts.

I am certain of Boeings claim to have an hours experience for each "Cell". I could look, but am not good in that sort of thing, I am computer marginal.

Put it on hold, I'll try.

Last edited by Lyman; 7th Mar 2013 at 19:22.
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Old 7th Mar 2013, 21:04
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Materials lab report

The March 7 released materials lab report has considerable detail on the battery covering some points which have been considered open on this form.

It can currently be found at:

http://dms.ntsb.gov/pubdms/search/do...251&mkey=85973

On my browser (firefox), clicking the download button five minutes ago generated an exception, but clicking the view button downloaded the pdf to my browser, from whence I was able to download the full pdf to my disc.

Among other interesting points, the "Description of the battery" section covers in more detail than I've previously seen the temperature monitoring technique, and responses, and other battery management details. Also mentioned are the container material and thickness, cell manufacturing dates and serial numbers, and so on.

All this in addition to considerable additional detailed observations from the event battery itself.

I think the materials lab report may contain more material of interest to participants in this thread than does the interim factual report also released today. However the NTSB server is currently responding very slowly, so some patience or retries may be needed.
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Old 7th Mar 2013, 21:32
  #849 (permalink)  
 
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archae86:

I get a few lines of javascript from the link, which says access denied.
Have tried using firefox and IE with the same result, do you have a link
that works ?.

Was able to find the other report from the NTSB website and some things
I did notice from an initial scan are that there are only two temp sensors,
but also that the isolation contactor in the battery case has normally
closed contacts. It's driven by logic on the BMU boards, also inside the case,
so if they fail for whatever reason, there is no way that the battery can be
disconnected from load or charger.

It would be much safer to make the contacts normally open, so if the power
or system fails for any reason, the battery is automatically disconnected...

Last edited by syseng68k; 7th Mar 2013 at 21:34.
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Old 7th Mar 2013, 22:33
  #850 (permalink)  
 
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docket link

The PPRuNe site inserts considerable overhead on links, presumably as part of a scheme to get paid for forwarding traffic in some cases.

If you can get to the NTSB site, you may find it helpful that the docket ID for this matter is 54251.

Before PPRuNe tampers with it, the following is a direct link to the docket page, and this time I've asked PPRuNe not to "automatically parse links in text". Possibly it will work better for some.

http://dms.ntsb.gov/pubdms/search/hitlist.cfm?docketID=54251&CFID=2871&CFTOKEN=67900912

I did test the previous one before posting--and aside from the mentioned long delays an intermittency, it did work in both FireFox and Chrome. For this one, you would need to copy and paste the URL I provided directly to a browser address bar, then wait a while, then click on the March 7 Materials lab report link, wait some more, then click on the "View" button. This all worked in both Firefox and Chrome for my own testing just a few minutes before finalizing this post.

A more direct link to the actual March 7 materials lab report page, if it works for you, should only require an initial wait, then clicking the View button, then a download wait--but won't work well if your browser is not configured for convenient pdf viewing.

http://dms.ntsb.gov/pubdms/search/document.cfm?docID=388418&docketID=54251&mkey=85973

That last link I tested in Internet Explorer as well. Assuming the PPRuNe site does not hide these (they were plainly visible and able to be copied in the preview I could see) they should work.
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Old 7th Mar 2013, 22:48
  #851 (permalink)  
 
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arch,

What are you talking about, the direct link has been posted several time in this thread and others...
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Old 7th Mar 2013, 23:09
  #852 (permalink)  
 
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Lyman:
Your car battery has six cells. It is a battery, unto itself.
The blue box in the Boeing contains eight three cell batteries, in series.
If you look inside a lead-acid battery, you find that there are often multiple positive and negative plates, with individual separators, layered inside a single electrolyte-containing envelope constituting one cell. The same appears to apply to the Boeing "cells", although the physical separation of the sets of electrodes is admittedly a lot greater.
So, I am willing to consider that some aspects of the cell can be interpreted more easily by thinking of them as three unit cells in parallel, I am not willing to go all the way and say that they should be categorized that way.
I will accept the description of the blue box as a battery bank rather than a battery because it does have individually removable components.

Last edited by inetdog; 7th Mar 2013 at 23:12.
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Old 7th Mar 2013, 23:37
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stream of consciousness -- shock and awe version

I hope you do not mind "reprints", for this is based on my comments from a thread on the same topic in another forum:

From the Interim Report:
The APU controller (discussed in section 1.6.5) monitors the parameters that are needed to operate the APU. The APU controller is powered by the APU battery bus, which receives its power from the APU battery. If the APU battery fails, then the APU battery bus will no longer receive power, and the APU will shut down.
And the ventilation fans which will remove any smoke resulting from the event will shut down too.
The ventilation fans in question are probably powered by multiple sources, including the total of 4 engine driven generators, and during flight the fans would therefore likely work OK.
The problem here is definitely that when the battery is both the only power source for the fans and the battery is also the source of the smoke (or perhaps there is NO battery power for the fans) you have an unsurmountable logical problem.
It is much less likely that the ventilation would have failed had the plane been in flight, especially as there would, at least in the new design, have been some ventilation from cabin pressurization and low pressure on the outside of the flame thrower -- I mean vent duct.

This seems even worse design to me though:
Firefighters reported that removing the battery was difficult because a metal kick shield installed in front of the battery prevented them from accessing the battery’s quarter-turn quick disconnect knob. Also, the quick disconnect knob could not be turned because it was charred and melted.
!!!:
The stainless steel sleeve and signal wires had damage consistent with excessive electrical current where they attached to the connectors at each end; at the battery case, the damage was also consistent with fire.
Excessive current on the signaling wires to the battery charger? Maybe just ground current in the signal grounds and the shield because of internal short circuit inside the battery case? At any rate, it does not appear to have damaged the charger.

Only two temperature sensors in the box (thermistors), possibly one for each of two BMU card? The 8 wires from each BMU card were described as voltage sensing wires, but probably doubled as balancing current conductors. The two cards did not contain two independent Battery Management Systems (BMSs) but were rather parts of one unit Battery Management System.

FDR data showed that, at 1021:01, a 1-volt decrease from the designed voltage of the APU battery (32 volts) was recorded. Three seconds later, the data showed a change
in current flow to 44 to 45 amperes into the battery. The battery voltage continued to decrease, and, at 1021:08, the current flow returned to 3 amperes out of the battery. At 1021:30, the battery voltage decreased to 28 volts, and the APU shut down 7 seconds later.30 Table 2 shows selected events recorded before and after the APU shutdown. The FDR did not record any data indicating that the APU battery voltage had exceeded 32 volts.
Not that it necessarily contributed to the event, but the initial sudden 1 volt anomaly did not cause the charger to shut down! This continued for 29 seconds. The steady decrease in battery voltage while charging also was not seen as significant!! The charge rate indicates that for whatever reason (probably the routine APU startup 15 minutes earlier) the battery was still substantially discharged at the time of the event. It was also being rapidly recharged after the substantial load of the APU start. No temperature information seems to have been recorded (?). I am also open to speculation that if the original voltage drop represented an internal short circuit in one cell, then the remaining cells could easily have been overcharged without the charger realizing it from the series voltage. Have to look at the BMU data to be sure.

OOPS:
The BMU main circuit card and sub-circuit card do not contain nonvolatile memory (NVM), and none of the BMU data are recorded on the FDR.
I think that the current flow reported is from the hall effect sensor, positioned like a shunt, in the battery itself and so represents net charging current to the battery independent of what the charge controller may have been delivering to the bus at the same time.

Aft EAFR stopped recording. Forward EAFR continued recording for about 9 minutes
58 seconds.
When the battery went offline and the APU spun down, there was no longer a source of power to the rear EAFR.



And, the last of my stream of consciousness commentary for now:
The battery shall be designed to prevent spilling flammable fluid, a hazardous event with occurrence with a probability of less than 10-9.
Much has been made in the press with the fact that two battery events have occurred within the first 50,000 flight hours that should have had a probability of 1 in 10,000,000 hours or less. If you think that the evidence of either of the two events supports that flaming electrolyte was in fact discharged, we have now hit the 1 in 1,000,000,000 condition too! Note that it was not just flammable but actually burning fluid. Maybe that's safer?

Last edited by inetdog; 8th Mar 2013 at 00:22. Reason: typos...
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Old 8th Mar 2013, 00:05
  #854 (permalink)  
 
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NTSB Interim Factual Report

Been out all evening since downloading it, but now see some have been struggling to locate it. Seems to be slightly different from the one posted above by archae86, but If his or others don't work, readers might like to try this one for the
NTSB Docket Management System:

Document 7 Airports/ARFF 16 - Attachment 3: BOS ARFF Incident Report Filing Date February 12, 2013 5 page(s) of Image (PDF or TIFF) 0 Photos

I commented earlier:
"So the failure occurred about 16 mins after the recharge cycle had begun. Must admit I had expected a longer time-frame. I wonder what the temperature of the battery was before and after APU start."

Quote from Lyman:
"Didn't APU start off one of the donks?"

Yes and (maybe) no. I'm not sure our experts in PPRuNe know enough about the system to establish what proportion of the APU starter-generator load is taken by the main electrical system (when available, as in this case), and how much (if any) is taken by the APU battery. On my last a/c type, the battery is used to supplement the main-system TRs in supplying the 700-1000 amps initial load. However, that system architecture may not be necessary or applicable on the B787.

If the APU battery took no significant part in the APU start, it seems an odd coincidence that the failure should have taken place so soon after APU start, at the end of a 12-hour flight.

To indulge in speculation, the only other possible triggers that spring to mind might be the changes in pressure associated with the recent descent and landing, or the very recent temperature changes caused by the opening of the rear cargo doors adjacent to the Aft E&E Bay. Does anyone know the temp at BOS?

PS
The link I posted above doesn't work for me right now, and neither does the manual one posted by archae86. Part of the problem may be at the NTSB end, I guess.

Last edited by Chris Scott; 8th Mar 2013 at 00:24. Reason: PS added.
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Old 8th Mar 2013, 00:14
  #855 (permalink)  
 
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Chris Scott:
If the APU battery took no significant part in the APU start, it seems an odd coincidence that the failure should have taken place so soon after APU start, at the end of a 12-hour flight.
For whatever reason, the battery was still being charged a rate of ~45 amps 15 minutes after the APU start. Since there should be no other loads in flight (unless the BOS plane had the same cross-wiring problem as the other), we can safely assume that it at least contributed to the APU starting current.
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Old 8th Mar 2013, 01:56
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Boeing cited "cell hours"

Lyman,
I don't know if this is what you saw, but there's a reference here to the 787's "cell hours".
Inside the 787

"The 787 main and APU batteries, each with eight cells, have logged more than 2.2 million cell-hours on the ground and in the air since the airplane entered revenue service, including more than 50,000 revenue service flight hours."

This inflates experience IMO.
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Old 8th Mar 2013, 02:44
  #857 (permalink)  
 
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Confirmed no NVM / no logging of details.

Scenario:
  • 10:21:01 Primary failure - cell short of #3
  • 10:21:04 Secondary failure - Large current (45A) for 3 seconds overcharging and damaging remaining 7 cells and driving them into _electrically_ induced runaway. TBD whether this is due to charger not shutting down or parasitic connection to a power source (Main Bat).
  • 10:21:27 Tertiary failure commences. Electrically induced runaway of #1, #2, #4, short of cell #6 along the way feeding more heat into #5, #7, #8. Smoke and fire.
TBD what caused Primary failure.

I suspect that NTSB schematic is simplified. It appears that there is no cell balancing. This would be ridiculous because it would lead to cell overvoltage and to Primary failure.

Last edited by saptzae; 8th Mar 2013 at 03:27. Reason: Expand
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Old 8th Mar 2013, 03:32
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they mention balancing

Originally Posted by saptzae
I suspect that NTSB schematic is simplified. It appears that there is no cell balancing. This would be ridiculous because it would lead to Primary failure.
I agree that the schematic obviously does not show all connections or components. Regarding balancing, there is a small explicit reference in the Materials Laboratory Factual Report released on March 7.
Page 4 of the lab report includes the text "The BMU performs cell balancing on cells over 4.00 V and monitors overall battery voltage for under-voltage conditions."
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Old 8th Mar 2013, 09:23
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The charge rate indicates that for whatever reason (probably the routine APU startup 15 minutes earlier) the battery was still substantially discharged at the time of the event. It was also being rapidly recharged after the substantial load of the APU start.
And...

Quote from Lyman:
"Didn't APU start off one of the donks?"

Yes and (maybe) no. I'm not sure our experts in PPRuNe know enough about the system to establish what proportion of the APU starter-generator load is taken by the main electrical system (when available, as in this case), and how much (if any) is taken by the APU battery. On my last a/c type, the battery is used to supplement the main-system TRs in supplying the 700-1000 amps initial load. However, that system architecture may not be necessary or applicable on the B787.

If the APU battery took no significant part in the APU start, it seems an odd coincidence that the failure should have taken place so soon after APU start, at the end of a 12-hour flight.

My understanding of the APU start system is that one Starter/Gen is powered from the main electrical busses and one from the APU battery bus.

It is an either/or scenario. Not both.

If main busses are powered then that's what is used, if not, it's over to the battery.

This concept of the APUC being powered by the APU battery however, regardless of main bus power does seem odd.
I'm not sure if this is the case on other a/c types. Research required methinks.
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Old 8th Mar 2013, 09:59
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Cell balancing in serial connection ?

From the Factual Report:

"These features included thermal protection devices, circuitry to monitor cell and battery voltages and temperatures, circuits to ensure that all cells in a battery are charged equally and within safe voltage limits, and components and circuitry that discontinue charging of the battery when conditions warrant this action."

I wonder how the cell balancing works, if only cell measurements are possible, but no other reaction than stop charging at overall battery level (via message from BMU to BCU or opening the contactor by BMU4).

I see no possibility to charge the cells separately, only in series connection. So I am really curious how they "ensure that the cells ... are charged equally".

Assuming a cell short circuit as primary event, it seems, the BCU manufacturer's patented "voltage monitoring only" cell diagnostics failed to detect or failed to report (to BCU) or failed to open the contactor (as a redundant charge-shutdown path, I guess).

Individual cell temperature measurement at the cost of some cents would have given a higher confidence in cell failure detection, instead of the shaky voltage monitoring, that Securaplane is so proud of.
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