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Model S - Batteries still liquid cooled?

Discussion in 'Model S: Battery & Charging' started by WarpedOne, Apr 26, 2009.

  1. WarpedOne

    WarpedOne Supreme Premier

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    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.
     
  2. efusco

    efusco Moderator - Model S & X forums

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    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.
     
  3. WarpedOne

    WarpedOne Supreme Premier

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    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.
     
  4. efusco

    efusco Moderator - Model S & X forums

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    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.
     
  5. Tdave

    Tdave Member

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

    BBHighway Member

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    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.
     
  7. doug

    doug Administrator / Head Moderator

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    #7 doug, Apr 26, 2009
    Last edited: Apr 26, 2009
    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.

    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.

    2394600449_1d0fa71f47.jpg

    _MG_8032.jpg

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

    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.
    3389747574_3f030c1d49.jpg
     
  8. siry

    siry Member

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    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.
     
  9. TEG

    TEG TMC Moderator

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    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?
     
  10. siry

    siry Member

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    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.
     
  11. TEG

    TEG TMC Moderator

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    Maybe not LiPO4, but some other chemistry that doesn't need so much safety technology.

    Tesla ESS is something like 53kWh / 450kg so about 120W/kg (including coolant lines, pump, monitoring computers, etc.)

    Toshiba Lithium Titanate claims 100W/kg which seems in the ballpark at least.
     
  12. fred Huang

    fred Huang New Member

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    Tesla Model S uses liquid cooling system but it doesn't have pump or heat exchangers. The grycol inside snake tube flows naturely
     
  13. jaguar36

    jaguar36 Member

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    Umm, this thread is 7 years old and was speculating before the Model S even existed.

    In addition the Model S has 2 or 3 coolant pumps (depending on VIN) and some heat exchangers.
     
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  14. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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  15. Rocky_H

    Rocky_H Member

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    Yeah, I was really confused reading the first half of the first comment and then saw that it was from 2009. What the heck?
     
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