How to Calculate Load Torque for a Small DC Motor

Written by thomas bourdin
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How to Calculate Load Torque for a Small DC Motor
DC motors are used in many different applications. (Jupiterimages/ Images)

A direct current (or DC) motor is an electric motor that operates using electricity from a direct current (as opposed to alternating current, or AC). DC motors find use in a number of applications, including automobiles. An important quantity in DC motors is the load torque (also called full-load torque), which is the torque required to produce the rated power of a motor when the motor is operating at full speed. Calculating the load torque can be done with knowledge of these quantities.

Skill level:


  1. 1

    Start the motor and determine the rated power of the motor (measured in horsepower, or hp) and the speed of the motor (in revolutions per minute, or rpm). In most motors, there will be a gauge built into the unit that will allow these measurements to be taken.

  2. 2

    Multiply the motor power by the number 5252. As an example, if the motor power is 30hp, then the product of these numbers is 157,560. Call this result A.

  3. 3

    Divide result A by the speed of the motor. Continuing the example, if the speed of the motor is 1725rpm, dividing result A by this number gives 91.34 pound feet. This is the load torque of the DC motor.

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