The transition from Internal Combustion Engine (ICE) vehicles to electric vehicles (EV) comes with a lot of opportunities and challenges. It is crucial for automakers to make EV subsystems and end vehicles that are efficient and cost-competitive to ICEs if they want mass adoption of their product. Increasing overall subsystem efficiency helps maximize drive range, and optimizing costs throughout the supply chain makes EVs attractive to the end user. A system that automakers must learn how to make more efficient and cost-effective is the thermal management system of the EV. In an EV, the cooling process is similar to the that of an ICE or residential systems via using a compressor to blow cold air through the coolant. However, when it comes to heating, a different approach must be used. ICEs can capture and use heat from the engine to pass through the coolant or directly through the cabin. But when it comes to EVs, there is no engine. And, the traction motor is too efficient to generate enough residual heat fast enough to capture for heating the coolant or cabin. So, one method commonly used to either supply additional heat or take full responsibly of heating the coolant/cabin in EVs is via positive temperature coefficient (PTC) heaters.
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PTC heaters generate heat via resistive heating. Current flows through the PTC heating element (thermistor) and generates instantaneous heat to either heat the coolant or the cabin directly, with the heat increasing as more current flows through. Once a specified temperature is achieved, the resistance in the heating element rises significantly. This limits the chance of overheating. This application has the advantage of simplicity of use and system design. The control for this application is responsible for supplying current within the rating of the PTC load over a period of time and shutting off that current once heating is completed. The drawback to PTC heaters is that their Coefficient of Performance (CoP), the ratio of useful heat or cooling to energy needed for said system, can be at most 1:1, as opposed to heat pumps which can achieve a much higher CoP. This is accomplished by the heat pump using the power it gets from the battery to move hot air to and from the outside environment instead of generating the heat like the PTC heater does. So, more heat energy is transferred into the cabin than electrical energy is used to operate the system. The higher CoP results in a longer driving range for the EV, making this system attractive to automakers. However, a designer may still want to use a PTC heater solution instead of/in addition to a heat pump due to its simplicity and cost advantage over a heat pump system. The designer may also deem the PTC heater as a more practical heating system than the heat pump if the EV end user is in a very cold climate. The heat may have to be generated if it is not available in the outside environment of the car.