Boeing 787 Dreamliner & Battery Issues

[Doug_G]

Remember at higher altitudes there is less air available for cooling. Even though the air is cooler at the high altitudes that these airplanes fly, there may not be enough exchange to passivly cool the pack. IMO liquid cooling and temperature management will help. Airplanes with turbochargers have this problem at higher altitudes.

Oddly enough, apparently with this aircraft the reverse is true. They bleed off cabin air to cool/purge the batteries, so at altitude there's lots of air flow, and at ground level there's nada.

 

[GSP]

I'm sorry but this battery should not be getting hot enough to need active cooling, if it is then it's not sized properly and/or it's not the right chemistry. This is not an EV pack that needs to put out a lot of power for a long time, it's a starter battery for the APU, (generator). From the beginning I've thought this could be a charge/discharge issue that wasn't properly controlled by the BMS and/or the charger, and in the latest EVTV episode Jack Rickard points out a possible flaw in the design. The specs show a max operating voltage of 32.2V or 4.025V per cell. If the generator is run for a long period and charging is never completely shut off then 4.025V is above the full resting voltage of the cell, so that means the cell could be consistently over charged every time the APU is running. Over time this could lead to swelling, shorting, and eventually burning of the cell, especially after one cell goes dead and the charger tries to bring the voltage back up by increasing current.

Good info JRP3. Thanks.

Chevy Volt engineers say that the liquid cooling is only for life, not safety. I agree, and think Cairns is wrong to suggest liquid cooling is needed for safety.

The symptoms do point toward overcharging, and to a need for better BMS oversight of the voltage and temperature of every cell.

Boeing also needs to insure soft shorts due to cell defects will not cause fires, and if they do it will not propagate to the adjacent cells.

GSP

 

[JRP3]

Remember at higher altitudes there is less air available for cooling. Even though the air is cooler at the high altitudes that these airplanes fly, there may not be enough exchange to passivly cool the pack. IMO liquid cooling and temperature management will help.

My point is there should not be any heat generated that needs to be removed, not enough to worry about. If there is these packs are not sized properly. I'm afraid that Boeing is just building a better vault for the inevitable fires that will continue to happen unless they change the operating parameters or the battery, preferably both. Lower the peak operating voltage for the pack or add a cell to lower the peak voltage per cell, increase the size of the cells to lower the relative current demand, or change the battery chemistry, or do all of that.

 

[stopcrazypp]

I'm sorry but this battery should not be getting hot enough to need active cooling, if it is then it's not sized properly and/or it's not the right chemistry.

Good point. Elon suggested better spaced cells so that in case a thermal event happens it does not spread to other cells. It was not about better cooling during normal operation.

 

[JRP3]

I guess someone at Boeing has been listening to me :wink: http://www.greencarcongress.com/2013/03/boeing-20130315.html

Boeing, Thales and GS Yuasa have also decided to narrow the acceptable level of charge for the battery, both by dropping the charging ceiling to reduce the potential energy of the battery and also raising the voltage floor to better protect against effects from deep discharge.

I'd like to know the voltage parameters before I give it my stamp of approval but at least they are addressing what I think is the main issue.

 

[GSP]

Boeing presentation on the fixes. I would feel a lot better if they had identified the cause of the cell swelling, failures and venting. Their claim of no overcharging makes me nervous. If no overcharging, then what the heck is causing the problems?! :cursing:

http://assets.sbnation.com/assets/2321443/Boeing-787-solution-presentation-English.pdf

GSP

PS. JRP3's green car congress link has some interesting details, such as the enclosure preventing fires by eliminating oxygen. How can that possibly work? Li-ion cells have built in oxidizer.

 

[JRP3]

The only possible cause for thermal runaway at an airplane level is overcharging

Following detailed review no evidence of overcharging was found in either event.

Yet they had thermal runaway, so if the first statement is true the second must be false. Since they don't seem to know what went wrong they can't claim to have fixed it. They basically threw every possible fix they could think of at it and are hoping one of them hits the target. Maybe they got it right, but we won't know until it's in use. At least they improved the containment so if it does fail it should do little to no damage.

 

[vfx]

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http://evworld.com/news.cfm?newsid=30080

 

[vfx]

Video

http://www.bbc.co.uk/news/business-22319537

New batteries give Dreamliner clearance for take-off

 

[JRP3]

"This is it, this is our final solution, and it's going to work for the life of the airplane" I hope he's right. At least they put it all in a vault :scared: So much for energy density and weight savings.

 

[stevezzzz]

More text on the return to service...

BBC News - Boeing 787 Dreamliner returns to service in Ethiopia flight

If, as reported, Boeing invested 200,000 engineer-hours on the fix, and estimating a burdened cost per engineer hour of, say $200, Boeing's labor cost alone for the fix is around $40M. Ouch.

And that figure is probably much less than the lost revenue to the carriers who operate the 50 grounded Dreamliners, not to mention all the airplanes whose entry into service was delayed. Double ouch.