Motor Cooling: Fin Housing vs Water Cooling

Electric motors are not only used as actuators for electric vehicle (EV) drive systems, they are now a major part of the development of other industrial automation systems and the application of mobile equipment. Therefore, as the use of electric motors by OEMs continues to grow, the thermal management of electric motors has become one of the most significant factors affecting the performance, reliability, and service life of electric motors.

Cooling an electric motor in an efficient manner not only allows a motor to operate consistently, but it also will enable the production of the highest output power from the motor, and maximize the efficiency of the motor's use of the available electrical energy. Fin-type cooling solutions (air cooling) and water-cooled solutions are among the most commonly utilized cooling methods. Both air-cooled and water-cooled cooling systems have specific characteristics and application benefits, and a thorough understanding of the differences will assist engineers and OEMs in selecting the best suited cooling solution for each of their individual use conditions.

Fin Cooling System: Simple, Reliable The cooling method used for fin-cooled electric motors includes natural and/or forced air circulation (convection) in order to remove heat generated by the operating electric motor. The external fins that protrude from the motor housing increase the amount of surface area available for heat dissipation. The natural and/or forced air circulation method of cooling allows for an efficient transfer of heat generated within the motor to the ambient air surrounding the motor.

Therefore, the primary advantage of fin-cooled motors is their relatively simple structure. The lack of a separate cooling circuit (and associated pumps and hoses) will greatly increase the reliability and maintainability of the air-cooled motors, making them best suited for applications where low complexity, minimal maintenance, and the ability to control the costs associated with manufacturing the devices are primary concerns. In addition, air-cooled motors perform effectively in environments where air movement is readily available, such as open industrial environments or mobile equipment with adequate natural ventilation. 

However, the heat dissipation capability of fin-cooled motors is very much dependent upon ambient conditions and airflow. In situations where a motor will be used in a confined space or under very high-load conditions, there may not be enough available ambient air to allow for the motor to operate continuously at the highest output power. Water-Cooled

Electric Motors: High Efficiency, and Thermal Stability The water-cooled electric motor utilizes a water-based cooling system integrated into the motor housing, and coolant is circulated through internal cooling channels within the motor to absorb heat from the motor core and transfer it to either a radiator or heat exchanger. The primary advantage of using water-cooling systems is that they provide improved heat removal capability compared to traditional air-cooling systems. In addition, water cooling provides more efficient and consistent thermal control for electrical motors, enabling electric motors to operate at greatly increased power densities without overheating.

Therefore, water-cooled electric motors are ideal candidates for high-performance applications requiring continuous operation, small form factor, and thermal stability. Additionally, water-cooled electric motors will provide reliable performance when used in either harsh operating environments or enclosed spaces, and their performance will be less impacted by ambient temperature than less efficient air-cooled motors. However, the installation and maintenance cost for water-cooled motors will be higher than that of fin-cooled motors due to increased complexity, required auxiliary components (pumps, seals, cooling lines), higher demands for installation quality, and higher demands for management of maintenance activities.

The motor's cooling method, as selected, affects the motor's design and layout/size. For example, due to lower cooling efficiency than water cooled designs, the manufacture of a fin (or air) cooled motor requires larger overall dimensions (to meet the rated operating power). Whereas water-cooling techniques allow for smaller motor housings and more compact size with respect to output. Additionally, since water-cooled motors are less susceptible to thermal expansion (compared to fin cooled), high-duty cycle motors are more likely to operate reliably for extended periods of time in high-temperature service conditions.

In selecting a cooling method, consider the following when using fin housing motors: low-cost alternatives, intermittent duty cycles, best airflow, and systems emphasizing power density and simplicity (and durability). Alternatively, water cooled motors are preferred for high power/long-duty cycle applications, smaller than available space applications, and sealed or extreme environment applications as well as for electric vehicles/heavy-duty mobile equipment.

Thus, there is no one preferred method for cooling motor machinery; the advantage of using fin housing cooling methods is low cost and simple design; however, the advantages of water cooling include superior thermal performance and higher power densities. The selection of the appropriate cooling method will vary based on application requirements, item/moderate service conditions, and item/moderate performance requirements. The proper selection of the appropriate cooling method will ensure the optimal performance of the motor and provide the manufacturer with the ability to produce high quality products with high efficiency motors operating over stable service conditions.