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 Power versus Torque


Understanding the relationship between electric motor power and torque is essential for designing, selecting, and optimizing motor-driven systems. In this article, we’ll explore the concepts of power and torque in electric motors, how they relate to each other, and their significance in various applications.

Electric Motor Power:

Power, in the context of electric motors, refers to the rate at which work is done or energy is transferred. It is typically measured in watts (W) or kilowatts (kW). In electric motors, power output determines the motor’s ability to perform work, such as rotating a shaft, driving a load, or generating mechanical motion. The power output of an electric motor is influenced by several factors, including voltage, current, and motor speed.

Electric Motor Torque:

Torque is a measure of rotational force or the tendency of a force to cause an object to rotate about an axis. In electric motors, torque represents the twisting force applied to the motor shaft, which results in rotational motion. Torque is typically measured in newton-meters (Nm) or pound-feet (lb-ft). The torque output of an electric motor is determined by the motor’s design, including factors such as the number of turns in the winding, the strength of the magnetic field, and the motor’s physical dimensions.

Relationship between Power and Torque:

The relationship between power and torque in electric motors is described by the following equation:

Power (W)=Torque (Nm)×Angular Speed (rad/s)Power (W)=Torque (Nm)×Angular Speed (rad/s)

In simpler terms, power is directly proportional to torque and motor speed. This means that to increase power output, you can either increase the torque applied to the motor shaft or increase the motor speed.

Understanding Power-Torque Characteristics:

Electric motors exhibit specific power-torque characteristics based on their design and operational parameters. Some key characteristics include:

  1. Constant Power Region: In this region, the power output remains constant even as the motor speed changes. This means that torque decreases as speed increases, and vice versa.
  2. Constant Torque Region: In this region, the torque output remains constant regardless of changes in motor speed. As a result, power output increases linearly with speed.
  3. Maximum Power Point: This is the operating point where the motor delivers its maximum power output. It occurs at the intersection of the constant power and constant torque regions.

Practical Applications:

Understanding the power-torque relationship is crucial for various applications, including:

  • Industrial Machinery: Selecting motors with appropriate power and torque ratings to drive conveyor belts, pumps, compressors, and other industrial equipment.
  • Electric Vehicles: Optimizing motor designs to balance power and torque requirements for efficient propulsion and acceleration.
  • HVAC Systems: Sizing motors to provide sufficient torque to drive fans, blowers, and pumps while minimizing energy consumption.


Electric motor power and torque are interconnected parameters that play a fundamental role in determining the motor’s performance characteristics. By understanding the relationship between power and torque, engineers can design and select motors that meet the specific requirements of various applications, ensuring optimal performance, efficiency, and reliability. Whether it’s powering industrial machinery, electric vehicles, or HVAC systems, the synergy between power and torque remains essential in the realm of electric motor technology.