FLAGSTAFF, Ariz.--Investigators from the U.S. National Transportation Safety Board
(NTSB) arrived in Tucson, Ariz., Tuesday (Jan. 22) as the focus of
electronics problems that have grounded Boeing's 787 Dreamliner
shifted to battery-charging electronics.
The NTSB team is visiting Securaplane
Technologies, an avionics unit of U.K.-based Meggitt, to
test the company's battery-charging devices as well as wire bundles
and battery-management circuit boards. Japanese and U.S. airlines
grounded their 787s on Jan. 16 while investigators in both nations
looked into battery and other problems that have plagued the
airliner in recent weeks.
The Dreamliner, a huge business and
technology bet for Boeing, leverages advanced electronics, millions
of lines of software code and lithium ion battery technology to
claim 20 percent better fuel efficiency than the Boeing 767 it's
intended to replace.
Investigators said they examined the 32V battery using X-ray and CT
scans, disassembled the APU battery into its eight cells for
detailed examination and documentation. Three of the cells were
selected for more detailed radiographic examination to view the
interior of the cells prior to their disassembly, the NTSB said in a
statement. The agency added that an examination of the
flight recorder data from the JAL B-787 airplane indicate that the
APU battery did not exceed its designed voltage of 32 volts.
Securaplane, acquired by Meggitt in 2011, has been in business since
1986and offers a variety of avionics including aircraft
security systems, LiOn batteries and chargers and inverters--the
last leveraging Vienna rectifiers, power MOSFETs/IGBTs, planar
transformers, ultracapacitors, and advanced pulse width modulation
techniques, according to the company's web site.
The charger in question, the Boeing
787 BCU (schematic pictured above), uses advanced DC to DC conversion technology,
patented charging algorithms, comprehensive diagnostics and fault
isolation to charge the APU battery, according to company
Measuring 14.7 x 5.0 x 7.7 inches and weighing 11 pounds, the
rack-mounted system features 23VDC minimum and 80 Amps maximum input
power and 1500W max output power.
I don't understand the comment about exceeding the design voltage. You wouldn't expect an overcharge to result in higher battery voltage, unless they're talking about the charging voltage being higher than spec.
Overcharging LiOn cells is manifested by continuing to run too much current through them after the charging current has dropped to a low level, like 3 percent of the cell's rated current capacity. But the voltage, at that point in the charging cycle, has been at a constant level for most of the charging period. It quickly ramps up in the initial charging period, then settles as the reverse current through the battery drops steadily.
Perhaps they meant exceeding the charging voltage, during the charging cycle?
Overcharging a battery is not the same as overfilling a gasoline tank, if you are equating voltage with gallons of gasoline.
Except for the words "lithium" and "fire" there is no similarity to the single Volt issue last year. In that case the battery pack was intentionally damaged by smashing it into a steel beam and leaving it for a week. They speculate that current through the leaked coolant caused the fire.
If you want to make a comparison without facts a better one is the lithium laptop batteries that were spontaneously catching fire and exploding a couple years ago.
I work with two way radios,all use now Li batteries,I do not think there is an overcharging problem, all this batteries, have a small protection PCB inside, that drains 4 uA. This PCB limits the charging and discharge current to safe limits, and it also controls the voltage allowed to reach the battery. But I did received once a radio case with a burned battery that was not in use. The only explanation is the failure of internal parts, that shorted BOTH sides of the battery. To limit this problem, all shipments by plane today limit the battery capacity to a safe 30% level. This is new technology, and those who lead, take a risk.
The latest public statement from the Japan Transport Safety Board says the battery did not experience overvoltage, but rather, a sharp and unexpected drop in voltage. So no evidence of overcharging, but perhaps over-discharging into a hard short for a period of time. Hopefully they can quickly get to the root cause.
I have a friend that worked at Securaplane and he witnessed one of these battery systems catch fire and burn down the building he was working in. Seems nothing was reported on the incident - perhaps a cover-up?
If this is designed improperly or to close to the margins...not good
If the power cycle confuses the algorithm for the timer...not good
If Boeing took at a ground wire out to save weight and lightning strikes create 100's to 100's of differential voltage across the fuslage reverse biasing FETS in contol paths (that are grounded at differennt points than the battery, this can reverse feedcurrent into battery without any way to control it...Not good
There is something fishy about the details in this story. According to the NTSB's own website, there are two pictures of the damaged battery and one picture of an undamaged battery (see here):
If you zoom into the undamaged battery picture, you can clearly see that it was manufactured by a French company called Thales (where they boast about being the first to deploy this technology on the B787):
Both undamaged and damaged battery appear to be identical in dimensions, color, and decal location.
According to the story above, the battery system is provided by a company called Meggitt/Securaplane and the battery charger schematic (shown above) looks completely different than the one shown on the NTSB website. Why the discrepancy about the real battery manufacturer?