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What to Consider When Purchasing a Motor

Mar 04, 2017

There are several characteristics that you need pay attention to when selecting a motor but voltage, current, torque, and velocity (RPM) are most important. 

Current is what powers the motor and too much current will damage the motor. For DC motors, operating and stall current are important. Operating current is the average amount of current the motor is expected to draw under typical torque. Stall current applies enough torque for the motor to run at stall speed, or 0RPM. This is the maximum amount of current the motor should be able to draw, as well as the maximum power when multiplied by the rated voltage. Heat sinks are important are constantly running the motor or are running it at higher than the rated voltage in order to keep the coils from melting.

Voltage is used to keep net current flowing in one direction and to overcome back current. The higher the voltage, the higher the torque. The voltage rating of a DC motor indicates the most efficient voltage while running. Be sure to apply the recommended voltage. If you apply too few volts, the motor will not work, whereas too many volts can short windings resulting in power loss or complete destruction. 

Operating and stall values also need to be considered with torque. Operating torque is the amount of torque the motor was designed to give and stall torque is the amount of torque produced when power is applied from stall speed. You should always look at the required operating torque, but some applications will require you to know how far you can push the motor. For example, with a wheeled robot, good torque equals good acceleration but you must make sure the stall torque is strong enough to lift the weight of the robot. In this instance, torque is more important than speed.

Velocity, or speed (RPM), can be complex regarding motors. The general rule is that motors run most efficiently at the highest speeds but it is not always possible if gearing is required. Adding gears will reduce the efficiency of the motor, so take into account speed and torque reduction as well. 

These are the basics to consider while selecting a motor. Consider an application’s purpose and which current it uses to select the appropriate type of motor. An application’s specifications such as voltage, current, torque, and velocity will determine which motor is most appropriate so be sure to pay attention to its requirements.