Watch our short video on DC Motors.
DC motors are the most common type of motor for low voltage and/or high starting torque applications, most often seen in the automotive and agricultural industries.
DC Motor Construction and Operation
A DC motor is comprised of a wound armature, commutator, brushes and magnets—all within a totally-enclosed housing.
Rotation occurs when the magnetic field of the motor—created by the permanent magnets in the housing—interacts with the commutator through graphite or carbon brushes.
DC Motor Characteristics
- Runs on DC power or AC line voltage with a rectifier
- Operating speeds of 1,000 to 5,000 rpm
- 60-75% efficiency rate
- High starting torque
- Low no-load speeds
DC Motor Advantages & Disadvantages
Advantages | Disadvantages |
Operates on DC power supply without a control |
High maintenance due to low brush life (2,000 hrs max in continuous duty applications) |
Inexpensive controls for speed regulation |
Cogging at speeds of less than 300 rpm |
Generally a low-cost motor option |
Significant power loss on full wave rectified voltage |
Easily pairs with gear reducers |
High starting torque can damage reducers |
DC Motor Performance Curves
Here we have the typical speed-torque curve of the DC motor.
Looking closely, we can see an interesting phenomenon with the hot motor curve. As the motor temperature rises, the no-load speed also increases. This is due to the effect heat has on the magnets. As the motor cools down, the speed will return to normal. The same concept applies to the other end of the curve where stall torque is reduced for a “hot” motor. Notice the efficiency curve and how under ideal circumstances the motor’s peak efficiency will occur near the motor’s operating torque.
AC, Brushless DC, and DC Motors can be used with a control to adjust motor speed. Generally, fractional horsepower DC motors don’t need to rely on controls for optimal performance, unlike AC and BLDC motors. DC controls operate by varying the voltage sent to the motor.
DC Motor Wrap Up
To pull everything together, DC motors are great when needing a fairly inexpensive motor option with high starting torque capabilities. Their versatility with power supply gives them the ability to run in portable or remote locations.