Air cooled battery modules

[efxjim]

I think helium instead of air might be used as the cooling fluid. It has about 6 times the ability to transfer heat as air and about 1/4 the ability of water. Since the cell can be completely covered in flowing gas it has about the same efficiency as water. The battery pack could be helium tight with the use of a pressure compensating bladder. It is non conductive/corrosive. Has minimal cost in the volume needed. A purge system would be need to be utilized in manufacturing the sealed unit. Hydrogen is even more efficient and is used to cool large power plants. But we know one should never use hydrogen in a car!

 

[JeffK]

I think helium instead of air might be used as the cooling fluid. It has about 6 times the ability to transfer heat as air and about 1/4 the ability of water. Since the cell can be completely covered in flowing gas it has about the same efficiency as water. The battery pack could be helium tight with the use of a pressure compensating bladder. It is non conductive/corrosive. Has minimal cost in the volume needed. A purge system would be need to be utilized in manufacturing the sealed unit. Hydrogen is even more efficient and is used to cool large power plants. But we know one should never use hydrogen in a car!

Helium has a low vapor point which might cause issues...

 

[Swampgator]

Jeff,

I'm not sure I follow your logic. At the operating temps of an EV helium is always in a gaseous state correct?
You can get it to zero C and it's still a gas with superior thermal conductivity to air.
Although I think something like this is unlikely, I don't understand how the low vapor point comes into play here.

 

[JeffK]

Jeff,

I'm not sure I follow your logic. At the operating temps of an EV helium is always in a gaseous state correct?
You can get it to zero C and it's still a gas with superior thermal conductivity to air.
Although I think something like this is unlikely, I don't understand how the low vapor point comes into play here.

It only matters if using liquid helium. When using helium as a gas you'd need to have it under relatively high pressure to get the density where it needs to be.

 

[Frank99]

Using helium has one major problem: You have to have a leakproof, sealed cooling system. If you're going to build that, you might as well continue to use water.

The advantage of using cooled air is that you don't have to build a leakproof system - as long as its reasonably sealed (think the air ducts in your house), you get all the benefits much cheaper than you would by building a sealed system. You don't have to use precision fittings with O-Rings and clamps - you just have to slide some ductwork together.

 

[garsh]

You don't have to use precision fittings with O-Rings and clamps - you just have to slide some ductwork together.

Don't go crazy now. That battery pack has to also be designed to keep water out. You want to be able to drive on a flooded road without shorting everything.

 

[Frank99]

Don't go crazy now. That battery pack has to also be designed to keep water out. You want to be able to drive on a flooded road without shorting everything.

My initial response was going to be "I'm pretty sure that's not part of the requirements for the Model 3", and then thought, well, just maybe it is.
i'd certainly believe a certain level of sealing is necessary - you surely don't want salted slush making it's way into the battery pack. It's just not clear to me how sealed the pack has to be to prevent that. For example, closed-cell foam weatherstripping is probably plenty to prevent splash from making into the pack, but is unlikely to maintain a helium atmosphere inside the pack, or to make the pack submersible.
I wonder what Tesla designs for here - do they really want people to be able to drive though flooded streets?

 

[Yggdrasill]

I decided to look at how a cell cycling facility for 11 million cells would look like, and it doesn't seem too infeasible or expensive.

At the end of the cell production line, you could stack the cells into a 1 meter by 1 meter by 7.5 cm tray. I think you could stack something like 2000 cells into such a tray without great difficulty. This tray could be carried to a stack of cell testers. Basically 1.1 meter by 1.1 meter by 30 cm modules, stacked 5 meters high, with a slot for the cell tray, and robust pin connects at the top and bottom. After the tray is correctly positioned in the cell test module, the interface is raised from the bottom and lowered from the top, connecting all the cells to the testing module. All 2000 cells are connected to a circuit board, which cycles the cells correctly, then assesses the quality of each cell.

Each 5 meter high and 1.1 meter by 1.1 meter stack would hold approximately 30.000 cells. And you'd need about 370 such stacks, or about 5550 cell test modules. Assuming each module costs 5.000 USD, and each stack adds 50.000 USD, the cost would add up to approximately 46 million USD. And the required space would be somewhere in the region of 600 square meters or 6500 square feet (assuming a fully automated facility), with 5 meter high ceilings.

Interesting to see how they actually do the cell drying (at 27:00):

Looks like they use trays with 256 cells, not 2000 cells, but the total area dedicated to this purpose doesn't seem far off. (I can't tell if they do any cell cycling. They might not need it.)

 

[stopcrazypp]

Interesting to see how they actually do the cell drying (at 27:00):

Looks like they use trays with 256 cells, not 2000 cells, but the total area dedicated to this purpose doesn't seem far off. (I can't tell if they do any cell cycling. They might not need it.)

I thought the same to move back to this thread given the recent Gigafactory tour. It seems Tesla will use a traditional cell manufacturing process and use racks to do cell aging (not the in-module theory the author predicted).

Also:
"-The half centimeter height increase for the car packs would be offset with more efficient battery packaging which will make the packs actually the same thickness or less than current packs and obviously with a higher energy density.
-Musk noted that once the 21-70s were in mass production, they could find their way into existing Tesla car battery packs for the Model S and X as well as the Powerwall."
Tesla Gigafactory tour roundup and tidbits: ‘This is the coolest factory in the world’

This suggests that the packs will remain similar to the current design (not some kind of active balanced air cooled design). The pack height optimization also proved a point I made before that a thinner battery plate design does not require air cooling.

 

[apacheguy]

Tesla will always have liquid cooled batteries.