the Cynic in me hopes this is just a simple imperial to metric error.. eg batts sending temp out in celsius but the charger is expecting fahrenheit.

FYI The Seattle Times illustration claims the batteries have lithium cobalt oxide cathodes. This is what I thought initially as well, as it was the original spec for test/certification aircraft.

However it seems production aircraft may have been fitted with (more safe) lithium manganese oxide batteries, according to Turins anf Fargoos B787 training notes, and an article from 2008.

The sealed lead batteries on the B777 (particularly the main battery that seemed to have a higher failure rate) can go into thermal runaway and start smoking.

ScareBatt
 

Machinbird:

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As a betting man, I'll bet that the issue with the battery is actually with the charging system and insufficient feedback from the battery to the charging system regarding cell temperature. The charging system should not continue to charge a battery that is moving in the direction of thermal runaway.

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The closed loop System must use TEMPERATURE and VOLTAGE. Before thermal runaway the cell voltage becomes abnormal. Just a cell is actually critical. When arranging in series or series-parallel the issue becomes complex. And dangerous.

ScareBatt :mad:

My pilot son before the RTW flight made a lot of dangerous uses of LiPo in the RC models. :E Extra precautions were made here. We simulated how to proceed, just in case after youtube watching. :E

Number of cells
 

Diamond Bob:

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Looks like the battery had 8 cells, according to this graphic accompanying a story in the Seattle Times. In another forum someone who seemed to know says that both the APU start battery and the main battery are the same unit.

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Thanks bob, this points to another issue. They designed a non conventional circuitry (charger, ETC.) to manage the higher voltage (29,6 V nominal up to 33,6 V "floating" voltage). Aviation uses 24 ~28 V span. A battery replacement would require a redesign, etc. (time consuming) of critical circuitry. :{

I hope for charger issues. (best case scenario)

Batteries are "female". Some surprises are trouble.
 

Ngineer:

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The sealed lead batteries on the B777 (particularly the main battery that seemed to have a higher failure rate) can go into thermal runaway and start smoking.

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For sure! (bold mine)

Batteries are not a simple issue. I had problems with ALL types in my professional life. I remember in first year of academy i read a russian book on batteries. I was amazed how complex were. (1970). Today we need microprocessors to manage them. :mad:

While ANA was quoted on Wednesday saying they expected to by flying again within a few days, it seems they have now changed their mind. Until the wee hours of Friday morning (Japanese time), this is what their reservation change policy read:

"2. Waiver of Date change and Cancellation
Application period until January 23rd, 2013
(1) Date change
One time date change is possible without regardless of the fare rule. The date change is subject to space availability and the new departure date must be until March 31st, 2013. (including arriving Japan on April 1st,2013)
(2) Waiver of Cancellation and Refund charge
Cancellation charges or refund charges will be waived irrespective of the fare rules.
"

The application period has now been extended to March 31st.

...
 

Please define "best". I agree with "beautiful". We'll see about composite and "mature" ... I'm sure everybody thinks about the Comets and its nice large windows all the time ... damn shame that one. De Havilland was such a great company.

About the battery voltage, number of cells and such, Boeing might be using various power converters (DC-DC etc) between the batteries and electrical systems. It might well be more efficient to design the battery array at its optimal voltage/configuration, then convert to the optimal voltage for the electrical system. Having said that the burnt battery does look like 8 cells. But it wasn't the main battery was it?

With some of the power figures being talked about (1.4MW in one post -- can that really be right?), I'd expect conversion to high voltages for distribution. Otherwise they would be talking about the airplane being mostly copper rather than composite.



For that matter (just conjecture) it might be interesting to contemplate a "distributed" battery. Rather than co-locating many cells, place single cell (or low cell count) batteries at various places so one cell cannot heat another one. Each one can have an independent charger/controller and can convert its 4V output to 28V (or go 2 cell / 8V if 4V isn't enough headroom for the power converters).

But then maybe you'd have to duplicate the thermal protection / detection systems so perhaps inefficient.

Are there any photos of the top of the battery? The one I saw had the top missing but was it removed or ??

Edit: This looks like it might be it..

http://media.komonews.com/images/130..._battery_1.jpg

Not so. The battery voltage, under charge, sits at 33v quite often in the older "Boeing" jet I fly. ;)

That is the charging voltage being measured, not the battery voltage!

If you charge a 28V battery at 28V you will still be waiting for it to be charged next Xmas! ;-)

Jp Authorities release ANA 787 battery photos
 

See them here in the Yomiuri.
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I know that is supposed to be a joke but in fact they may eventually burn.

'Charging' at this rate will eventually lead the battery to become completely discharged where we get into another 'danger area' for the Lithium based high energy density system.

Too much charge =risk of thermal runaway.
Too little charge =risk of thermal runaway.
Too high temperature =risk of thermal runaway.
Cell short circuit. =risk of thermal runaway.
Loss of charging voltage regulation =risk of thermal runaway.
Excessive AC ripple =risk of thermal runaway.

To use these batteries in a safety critical situation they not only need to pass strict quality control and be installed correctly, but also require a reasonably complex system of monitoring voltages and temperatures to control charging.

If all this works as it should, then there is no reason for any Li-Ion battery to get anywhere near thermal runaway. Redundancy in this system is the way to go rather than ensuring enough distilled water is available to douse the fire when it does happen.

Boeing will be hoping that the two batteries involved turn out to be from a faulty batch at Yuasa. Redesigning an inherently inadequate charging system is likely to take some time. :-(

NiCd´s?
 

Capn Bloggs:

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The battery voltage, under charge, sits at 33v quite often in the older "Boeing" jet I fly.

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Could you check the number of cells (series) in this case?

You can (reducing batt life) keep them more charged. Until a certain point. Excessive gassing (lead acid) or higher temperature (NiCd). Both are NOT CRITICAL like the Lithium counterparts.

In lithium ones you need to monitor carefully temperature and even ea. cell voltage (early warning on impending problems)

Float current is what you need to keep an eye on with these 'systems'.

SoS

Hope not a dumb question. I was trained, in utilizing this type of battery, to isolate a cell from concurrent charge/discharge. The system prevented a battery from being used whilst charging. Is that what you mean by "Float"?

thanks

I wonder if the fault lies with the airlines (Only ANA/JAL aircraft involved) training and maintenance procedures OR with Boeing who may have rushed to deliver aircraft because of previous delays?
Whatever thank goodness we're not scrapping bodies off the tarmac - at least we know the alarm systems are working.

Lyman

I 'think' SoS is meaning the charging current would be adaptive to provide the correct optimal charging current for the batteries. Not too little - not too much :)

Would lifepo4 be a better choice
 

Just curious but does anyone have any idea why Boing have not chosen Lifepo4 batteries for their better safety. Ok the energy density is not quite as high but the better safety and longer life would surely outweigh this.

It seems possible to me that the design of the battery system is too focussed on having the new technology mimic the function of traditional batteries rather than making best use of the new technology. Traditional batteries are used to regulate the voltage on the busses. They are able to tolerate overcharging quite well. In my view best use of Lithium technology would involve having a separate voltage regulation system with the battery waiting in reserve, perhaps connected through a diode, to provide power in the event of a generation shortfall below demand. The battery only charged when monitoring deems necessary.