Model S - Batteries still liquid cooled?

[WarpedOne]

Roadster's battery pack is, as we all know by now, liquid cooled. Basic reason for this is that there is not enough exposed surface of the pack for air cooling to suffice. The pack is basically just a box, where only small amount of the cells lie directly to outer box walls, most of them have other cells for neighbors. Without circulating liquid there would be only other cells to transfer heat to.

Model S' battery pack is supposed to be completely flat and under the car. They will probably still use 18650 cells, so the pack will be only about 8 cm or 3 inch thick (cells are 6,5 cm high plus some housing) and every cell will have its own exposed surface through which it could dissipate its own heat.

Pack of 8000 cells in 18650 format would have at least 2,3 square meters of exposed surface under the car over which the outside air will blow. It is much harder (much more added wight) to liquid cool such a flat pack than it is for a more box-like one in the roadster. Another factor is that this pack is supposed to be easily swappable. If it is liquid cooled it would have to have its own reservoir, pump and heat exchanger or a pipe connected to a car. This pipe would then had to be easily pluggable.

All this brings me to the conclusion Model S' battery will be air-cooled. Maybe it will have some embedded heating, but no internal liquid cooling. This also means there will be no water pump to run 24/7 and lower total battery weight.

[efusco]

I hope you're right, that would be fantastic as far as I'm concerned. That said, having a liquid cooling system as a back-up in case temps get higher than some predetermined threshold (?100F), like the fan in the Prius does for it's pack, would make sense to prevent damage in case of some untoward high temps or a very hot local like Phoenix or Vegas.

[WarpedOne]

Liquid cooling by itself is only a HEAT TRANSFER system, it transfers heat from a dense space where heat is produced to more open space, where it can be more easily dissipated into environment. Roadster's battery is such a dense space, where liquid cooling makes sense and is effective. It transfers heat from the pack to the front radiator where it is dissipated into the incoming air. It cannot and does not cool the pack below the temps of outside air. Same holds for that Prius fan, it can only cool that pack down to the temperature of the outside air and not below it. If the air is 100F, the pack would be at at least 100F.

A large flat pack already has large area for dissipating that heat into the incoming air. Liquid could only help if its temperature was below the temperature of the outside air. For this you'd need special AC unit for actively cooling it which would consume at least a few kWs and as such drasticaly reduce range.

[efusco]

Liquid cooling by itself is only a HEAT TRANSFER system, it transfers heat from a dense space where heat is produced to more open space, where it can be more easily dissipated into environment. Roadster's battery is such a dense space, where liquid cooling makes sense and is effective. It transfers heat from the pack to the front radiator where it is dissipated into the incoming air. It cannot and does not cool the pack below the temps of outside air. Same holds for that Prius fan, it can only cool that pack down to the temperature of the outside air and not below it. If the air is 100F, the pack would be at at least 100F.

A large flat pack already has large area for dissipating that heat into the incoming air. Liquid could only help if its temperature was below the temperature of the outside air. For this you'd need special AC unit for actively cooling it which would consume at least a few kWs and as such drasticaly reduce range.

Liquid cooling CAN cool below ambient if there is also a cooling system inline. Just like the Prius, it uses the cabin air conditioned air to cool the battery pack below the outside ambient air temp (assuming the AC is turned on). In fact, it's possible to get better fuel efficiency in the Prius, at times, when the AC is turned on than when it's turned off if ambient temps are very high and the battery is in a high demand condition.

I'm not very knowledgable about the Roadster, I readily admit, but I thought that there was an air conditioner-like compressor that cooled down the battery coolant, not just a passive radiator system.

[Tdave]

I thought the Roadster uses the AC if needed to cool the battery pack.

[BBHighway]

My understanding was that the Model S is to use a liquid cooled motor, so I would be surprised if that same cooling system doesn't include the batteries as well.

[doug]

I would say the Model S battery pack is most certainly liquid cooled. It's necessary to maintain the pack temperature when the car is stationary, particularly while charging. The Roadster battery pack is actively cooled while charging. This is part of the reason it's less efficient to charge quickly; more heat is produced and the cooling system has to work harder.

It is much harder (much more added wight) to liquid cool such a flat pack than it is for a more box-like one in the roadster.

Actually eleven flat sheets comprise the Roadster battery pack. Each individual sheet has it's own set of hoses. (Of course the pack as a whole has a primary pair of supply and return hoses.) So in that sense, the Roadster pack isn't that different.





However, Tesla has said they've figured out how to pack the cells more efficiently for the Model S.

Another factor is that this pack is supposed to be easily swappable. If it is liquid cooled it would have to have its own reservoir, pump and heat exchanger or a pipe connected to a car. This pipe would then had to be easily pluggable.

Quick connect/disconnect fittings are not that uncommon. We sometimes use them in the lab with equipment that has to be water cooled. The fittings have a spring loaded valve in them that closes when the hose is disconnected, minimizing leakage. The valve is forced open when the hose is connected again. It's completely passive. Wouldn't take too much engineering for Tesla to use something like this.


Btw, here is the Smart EV battery pack by Tesla. It's a "flat" pack that sits under the floor and is liquid cooled.

[siry]

Basically if it is a Lithium Cobalt Oxide cell in an automotive application it needs to be liquid cooled. That's (part of) the price you pay for long range.

[TEG]

Basically if it is a Lithium Cobalt Oxide cell in an automotive application it needs to be liquid cooled. That's (part of) the price you pay for long range.

You can get long range with other chemistries too. To me the cooling is needed so you can use commodity laptop cells as a cost reduction/control method. How about $50K worth of A123 batteries?

[siry]

good luck fitting a pack of LiPO4 cells big enough to go 200+ miles in a car! They just don't have the energy density so the pack is too big.