Dreamliner: Boeing 787 Aircraft Battery "Not Faulty"

SternisheFan writes "Airline safety inspectors have found no faults with the battery used on Boeing's 787 Dreamliner, Japan's transport ministry has said. The battery was initially considered the likely source of problems on 787s owned by two Japanese airlines. The world's entire fleet of 50 787s has been grounded while inspections are carried out. Attention has now shifted to the electrical system that monitors battery voltage, charging and temperature. Transport ministry official Shigeru Takano said 'we have found no major quality or technical problem' with the lithium-ion batteries. Shares in GS Yuasa, which makes the batteries, jumped 5% on the news. 'We are looking into affiliated parts makers,' he said. 'We are looking into possibilities.'"

Comments

Re:Japanese covering their butts?

[anubi]

The charge management circuit is what has me concerned. I have messed with plenty of failed power tool batteries, dissecting each, and finding common points of what caused the whole assembly to fail, and every time it has been the concept of cells in series.

The cells do not have identical leakage, so some cells tend to overcharge to compensate for the other cell in the stack which leaked its charge away.

This phenomena shows up after the cells have been in service for months to years.

The older chemistries I have worked with have been relatively tolerant of overcharge, converting the excess energy either to heat or hydrogen gas, which was silently vented. Lithium ion cells are not nearly as tolerant to overcharge as NiCd, LiMH, or Lead-Acid cells. Overfilling a lithium ion cell seems like overfilling a propane tank. Once it tops off, there is nowhere for the excess energy to go and POP goes the weasel.

If you are charging based on stack voltage, you will overcharge the hell out of a good cell as you try to bring the terminal voltage of a weak cell up. You will detonate your good cell in the process.

I am currently playing around with a lithium battery pack monitor with which I have individual chargers for each cell. There is no way I would consider charging all cells in series as is commonly done in the earlier packs. With the DC isolation I can easily get from high frequency inverters, it is quite easy for me to get matched voltages from multiple windings. I use supplemental converters to additionally charge individual cells that leak a bit more than others in the pack. I also have switched cell monitors which rapidly switch each cell onto a measurement buss along with three tightly controlled reference voltage sources. This results in a signal stream which indicates terminal voltage of every cell in the pack, cell by cell. This feeds a digitizer which constantly tracks each cell voltage and is instructed to terminate battery function if any cell shows over or under charge. If a cell simply needs a little help, the individual cell inverters kick in to boost the weaker cell and such activity logged.

A supplemental benefit of the serial analog data stream is that I can use any oscilloscope to see all the cells at once... I can sync to cell 0 which is the reference voltage. ( three references because this is so critical that if I have a reference drift I will have two others that hopefully are providing reliable data. Bad data = explosion; false trip=expensive downtime ).

Lithium batteries have a lot to offer, but they are also quite a bit more volatile than other chemistries I have worked with. Even YouTube has quite an assortment of videos of overcharged lithium cells igniting. Like a propane tank, they are quite useful if not mistreated, but can really take you to the cleaners if you do.