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On Sun, 27 Jan 2013 19:19:51 +0000 (UTC), (Bradley K.
Sherman) wrote:

wrote:
...
When you look at the complexity of the APU unit, it WILL be a
relatively minor tweek.
...

I don't think replacing the batteries with a safer, heavier
technology and redesigning/recertifying the electrical systems
of the plane can even be called a "tweak," let alone a "minor
tweak."

You can be fairly safe to bet that the batteries will not be replaced
with heavier old tech batteries. The charging system will be fixed -
and you will be safe to bet it will be a "relatively minor tweek" to
the system. It will not be a total re-design of the APU system. The
batteries do not overheat if they are not abused. The charge control
system is abusing the battery, causing it to overheat. They may need
to redisign the battery pack to add cooling to prevent damage IF they
overheat - but the first thing is to fix the charging system so they
do NOT overheat.

I also question why they used lithium Cobalt batteries - slightly
higher energy density than the safer Lithium Iron Phosphate or Lithium
Nickel Manganese Cobalt Oxide batteries, at the expense of a higher
danger of thermal run-away. Perhaps a change to one or the other of
these chemistries instead of the Lithium Cobalts will be required as
well.
|
| MIT Professor: Battery Fix Could Ground 787 Until 2014
| ...
| In a nutshell, Sadoway thinks that Boeing needs to monitor
| the temperature and cool each of the eight cells of the
| 787's lithium-ion battery or switch to an older battery
| technology that has a far better safety record -- nickel
| metal-hydride (NiMH).

Anything with a potassium Hydroxide electrolyte is a poor choice in
aircraft with aluminum structure. The 787 has a lot of high strength
composite, but aluminum is still a structural component. The 2
materials do not peaceably co-exist - in case of a leak there are
risks - which have been managed so far with Ni-Cads in aircraft use -
but they are NOT benign. NiCad and NimH both ose pottassium Hydroxide.

They are also not immune to overheating - they just boil the
Pottassium Hydroxide out, damaging the plane instead of burning. Not
quite as serious, in the short term - but perhaps just as damaging in
the long term?

In my opinion, going back to NiCad or Nimh would be a big step
backwards - as well as requiring a complete recertification of the
system.
|
| If Boeing opts to substitute NiMH for lithium-ion,
| certification could result in delays of up to a year --
| effectively grounding the 787 until 2014.
| ...
| When Sadoway got a look at the lithium-ion battery used in
| the 787, he was surprised by "the seeming absence of a
| cooling apparatus."
| ...
http://www.forbes.com/sites/petercohan/2013/01/27/mit-professor-battery-fix-could-ground-787-until-2014/

--bks