Temperature Control

Although temperature control is important in internal combustion engines, Lithium Ion cell temperature management is of vital importance in an EV, both for the safety and battery longevity. It is more complex and is tightly integrated with the cabin climate control system as described below, as it applies to the Model S.

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 the original cabin heat exchanger (16) and/or to cool the glycol loop using the coolant heat exchanger (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 the AC condenser (11) and the cabin air evaporator (16) but instead of air it cools glycol coolant passing through it. While the cabin air evaporator (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 the chiller activation valve (14). To keep the cabin air evaporator (16) functional (if user requested) the coolant redirection valve (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 the coolant heat exchanger (13) or not.

15. Cabin evaporator activation valve. Is an on-off valve that either blocks the refrigerant from expanding into the cabin air evaporator (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 cabin air heater (17).

17. Cabin air heater. Rated at 6kW maximum power, running 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.

• 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 the secondary coolant pump (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 the battery is below this value, heat that has been generated by the DC-DC converter (6), the onboard charger (8), and the drivetrain (9) will bypass the radiator (1) and will be absorbed by the battery.

• Active Cooling Target: this is the upper value for the battery temperature. If the radiator is not capable of providing enough cooling and trend is to go above that value, active cooling measures will increase. This means the chiller activation valve (14) activates the coolant heat exchanger (13) and the coolant redirection valve (4) selects a portion of coolant to be chilled. Depending on requirements the coolant heat exchanger (13) speeds up, as will fans on the AC condenser (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, using the coolant heater (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.

Images below are taken from an operational Model S in workshop mode, illustrating Parallel-Series loops and values.

The Tesla Model 3 uses a similar system, but is more highly integrated, and for this reason TeslaRR uses the "Super Bottle" from the Model 3 to simplify plumbing requirements. The video below describes how this is used in the Model 3.