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ScotCan
User Rank
Platinum
Re: Design Decisions
ScotCan   1/28/2013 9:43:13 AM
We're working at the grass roots level with lithium systems in E-Scooters and we're having our problems although not quite as dramatic as Boeings. The battery management system does what it's supposed to do where temperature increases beyond a certain level opens the circuits...somewhat inconveniently after about 3 blocks of hard acceleration. Troubleshooting indicates that by disconnecting the battery, pausing, then reconnecting resets the system, and as long as a reasonable acceleration is the input the system works continuously. As soon as a higher torque (hence amperage increase) is applied to the drive system over a certain length of time the system cuts out. Our solution to this irritation is in work consisting of a hybrid battery system using lead acid for acceleration and lithium for cruise, the controller being rigged to accomodate the changes. Boeing's solution may be the same in the long run...cooling systems are just another aggravation, but hybrid battery systems rigged through a reliable controller may be slightly heavier but likely not as heavy as a cooling system and have the advantage of no dead weight (all batteries being functional)

 

Battar
User Rank
Platinum
Re: Cooling System
Battar   1/28/2013 9:37:09 AM
NO RATINGS
Not so puzzling. Before you design in a cooling system, you ask how high can you go without it. For example, if a transistor is rated with a junction temperature of 150 degrees, I would let it heat up to 100 degrees before I put a fan in. Thats a 33% margin. Cooling at sea-level is not the same as cooling at 8000ft equivalent alitude in a pressuized airliner, though.

YJ77
User Rank
Silver
Re: Design Decisions
YJ77   1/28/2013 9:37:06 AM
Boeing will suffer politically, regardless of the decisions they make now.  Their best option is to have a replacement strategy defined and a timeline for implementation & FAA approval before the end of this week.  Any more delay will cripple their Dreamliner, giving the A380 a huge advantage. 

Ken E.
User Rank
Gold
Cooling 'built in'?
Ken E.   1/28/2013 9:32:06 AM
It's possible the cooling was 'built-in', i.e. the design current draw and subsiquent heat load was lower than the thermal capacity of the unit as installed. That's how zillions of the small and ubiquitous lithium batteries consumers use every day work.  It'll be interesting to see how this story plays out.  Certainly some mistake was made somewhere, but we seem to be jumping to conclusions

Greg M. Jung
User Rank
Platinum
Re: Design Decisions
Greg M. Jung   1/27/2013 11:48:44 AM
NO RATINGS
Good point William.  I wonder if the energy density of the lithium-ion battery system with an additional cooling system would now be less-favorable than the energy density of the traditional/proven battery technology (without the additonal cooling system).

williamlweaver
User Rank
Platinum
Design Decisions
williamlweaver   1/26/2013 8:57:06 AM
NO RATINGS
Chuck, do you get a sense that perhaps Boeing moved to the cobalt oxide cathode lithium-ion batteries to shed weight and then made a decision to not include a cooling system that would have added net weight? It is feasible that this type of failure is only found after the 787 is used in process and not in testing and that Boeing can find a safe fix. Gosh, I sure hope that it does not turn out to be known, debated cost-saving management decision that turns political...

Nancy Golden
User Rank
Platinum
Cooling System
Nancy Golden   1/25/2013 7:34:07 PM
NO RATINGS
The lack of a cooling system would be very puzzling. According to a friend of mine who is a battery guy, lithium ion batteries are the highest energy density and are one of the most volatile chemistries, so correct charging and cooling are of paramount importance.

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