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Tesla Thermal Management System - explanation

Discussion in 'Technical' started by arnis, Mar 25, 2017.

  1. arnis

    arnis Member

    Apr 13, 2015
    So I would like to explain everything I understand about Model S (very likely Model X is similar) thermal
    management system.
    Number in yellow is slightly to the left of the object it refers to.
    It's easier to open the picture in different window, drag it to the left screen portion while keeping text to the right.

    Tesla Thermal Screen.jpg
    1. Main coolant radiator. Does not have a fan apparently. When vehicle is in motion air passes through the fins cooling the liquid. Coolant enters from the right side. This radiator can be bypassed with device #10.
    2. Coolant circulation mode selector. A device that switches between two modes: Series and Parallel. If series, coolant passes from #1 to #3 and then from B to #7. If is parallel, one loop passes from #1 to #7 and other loop from B to #3.
    3. 12V coolant pump. Percents indicate pump running speed. Slower speed consumes less energy, prolongs pump life and slows the coolant flow.
    4. Adjustable coolant redirection valve. Sends 100% of coolant from #3 to #5, 100% form #3 to #13 or anything in between.
    5. Coolant heater. Apparently is rated for 6kW. Runs on high voltage. If activated, coolant will be heated up. This is used to heat the Battery fast. Heat generated by #6 #8 #9# can also be used to for pack heating. Cold pack will also cool down those devices.
    6. DC-DC converter. Takes energy from high voltage pack, keeps 12V battery charged and all 12V devices powered up. Small part of coolant is directed into this device as heat generation is small.
    7. 12V coolant pump. This pump is required to keep second loop of coolant flowing if #2 is in parallel mode. Acts as a backup to #3. In series mode both pumps run at equal speed.
    8. On-board charger. Is used for vehicle charging. Converts AC grid electricity to suitable DC for main battery. Second charger is not available any more. There is a coolant bypass. Likely required due to single charger has up to half the coolant throughput. Number on the left indicates temperature of the electronics inside.
    9. Drivetrain. Coolant enters the motor. Circulates in the stator. Also circulates in inverter (power electronics) and then exits (with temperature value shown). Transmission (reduction gear and differential) doesn't require cooling though it gets some heat as it is between warm motor and inverter. Which raises the temperature of the oil and makes vehicle slightly more efficient. Also rotor temperature is shown (most likely calculated estimation) and Inverter electronics temperature (PCB).
    10. Adjustable coolant redirection valve. Same as #4. Either sends 100% of coolant through the radiator, bypasses 100% or anything in between. If coolant is not directed to the radiator it can be used to heat the Battery.
    11. AC condenser. Required to cool down refrigerant. Does have a fan. Fan speed indicated in percents. There are two condensers each having a 12V fan. Are between fog lights and front wheel arches. Air enters through louvers and exits to the wheel arc. Louvers can be closed for better drag coefficient.
    12. Electric Air Conditioner Compressor. Runs on high voltage. It is used for two purposes. To cool the air for the cabin using #16 and/or to cool the glycol loop using #13. Percents indicate compressor running speed. If cooling requirements are very small compressor will be temporarily stopped to allow cabin air evaporator to stay above freezing point. Sensors before and after indicate temperature and pressure of the refrigerant before and after the compressor.
    13. Refrigerant-coolant heat exchanger. Functions the same way as #11 #16 but instead of air it cools glycol coolant passing through it. While #16 is not allowed to get below 0*C/32*F chiller can go colder as coolant will freeze at much lower temperatures. Though it's more efficient to pass as much of coolant as possible. Chiller can be disabled with #14. To keep #16 functional (if user requested) #4 can redirect only some of the coolant.
    14. Chiller activation valve. Is an on-off valve that either blocks the refrigerant from expanding into #13 or not.
    15. Cabin evaporator activation valve. Is an on-off valve that either blocks the refrigerant from expanding into #16 or not.
    16. Cabin air evaporator. Radiator inside HVAC system that cools the air that passes through. If climate control AC setting is "ON" or precooling is activated remotely this will cool and dry the air that passes it. Air gets here through cabin air filter and continues to #17.
    17. Cabin air PTC heater element. Apparently is rated for 6kW maximum power. Runs on high voltage. Due to it being Positive Thermal Coefficient device, it can generate 6kW of heat only if air that enters is very cold and is moving very fast. If the element gets hot, it will reduce its draw even if it is activated to 100%. Usually air that exits doesn't get scalding hot no matter what. Temperatures between 55*C - 80*C can be expected at full requested power.

    B. Main traction high voltage battery. Some data is shown on the picture.
    Trend - Temp - Trend is coolant temperature that enters the battery. If it is hotter, battery will heat up. If is colder, it will cool the pack. Coolant temperature after the pack is to the left, below #7.
    Max/Min Cell Temp: extreme values of the sensors in the pack. There are lots of those all mostly being very close to each other.
    Passive Cooling Target: this is the value system tries to bring the pack to passively. If B is below this value, heat that has been generated by #6 #8 #9 will bypass #1 and will be absorbed by the B.
    Active Cooling Target: this is the upper value for B temperature. If #1 is not capable to cool enough and trend is to go above that value, active cooling measures will increase. This means: #14 activates #13 and #4 selects a portion of coolant to be chilled. Depending on requirements #13 speeds up, as will fans on #11. At some point if cooling is not capable to cope other parameters can be limited (charging speed, vehicle power/regen limits).
    Active Heating Target: This is the lower value for B. Anything below that and vehicle will use active measures to heat the pack. Apparently #5. It appears that active heating to that limit can be disabled with range mode. This will compromise battery charging capability/regen a lot and also some of the power output.

    There are some more pictures that help to understand Parallel-Series loops and values.
    tesla termoregskeem.jpg
    • Informative x 17
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  2. Hans Allis

    Hans Allis Member

    Sep 21, 2016
    Leersum, Netherlands
    Oh how I would love to have access to diag mode :D Thanks for sharing.
  3. Buster1

    Buster1 Member

    Oct 13, 2016
    Las Vegas
    This is awesome. Thanks!
  4. sreehyd

    sreehyd Member

    Jul 10, 2012
    Hayward Hills, CA
    Good info ..

    thank you
  5. TonyWilliams

    TonyWilliams Active Member

    Jun 11, 2012
    San Diego - Tesla powered Rav4 EV
    Some folks have wondered how similar this is to the 2012-2014 Toyota RAV4 EV, and the only significant difference I can find is that the radiator has cooling fans, and the Denso PTC 6kW heating element is a liquid heater for cabin heating... not air.

    Also, because this car was a failed marriage between Toyota and Tesla, they have separate heaters / coolant for the cabin heater and the Tesla battery heater (made by a Canadian company that begins with "Sub", but I can't remember the name).
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