PPRuNe Forums - View Single Post - 787 Batteries and Chargers - Part 1
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Old 15th Mar 2013, 13:38
  #986 (permalink)  
cockney steve
 
Join Date: Jan 2008
Location: lancs.UK
Age: 73
Posts: 1,196
@ Machinbird...
yes, but we're not talking huge earthenware jugs here,- lightweight modern ceramics can do the job and minimise the possibility of a short-circuit to the firebox as well as containing the heat.

We're talking a posh kludge here. Given that Boeing refuse to admit they rushed ahead with a novel emergency-supply system and no backup plan,that they refuse to abandon the current Lithium Ion technology, we have to think how this may be made safe and reliable-enough that you or I would venture forth across a wide pond in the aircraft.
Every cell insulated/isolated....thermal runaway is minimised
every cell monitored.....we've already discussed this....electronic components are cheap as chips, there are plenty of multipole Mil-spec plugs of the type currently used, which would accomodate the extra harness needed to monitor and balance every sub-cell (24 per battery in current design)
fusible connections would not be significantly bulkier than the present arrangements. "crowbaring" would add 8 contactors under your proposal and it would also reduce both the voltage and capacity of the battery.....assuming only ONE cell popped and self-isolated, you'd still have full voltage AND 66% capacity available from that cell better than being 12.5% down on both capacity and volts when in dire need!....remember, these batteries are "supposed" to be a last-resort backup...(they're not!)
the APU battery is routinely used for nav-lights at pushback, as well as APU start when main engines aren't turning.
the essential instrument and braking battery is routinely used to power a refuelling valve /flap!

Latest news seems to confirm what I said very early on.... these batteries CAN be used for high-rate applications , but both charge and discharge must be monitored and controlled rigorously.
In a situation where these batteries are used in anger, I'd think the destruction and fire risk would be pretty low on the list of worries
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