What Is a Brush Motor?
A brush motor is a motor with sliding contacts called brushes to conduct current to the rotating shaft. They are characterized by simple and inexpensive construction and easy torque control. However, brushes are worn by rotation and require periodic maintenance. The disadvantage of brush motors is that they are noisy when driven.
Although wound AC motors and other types of motors also use brushes, the term “brush motor” generally refers to DC brush motor.
Uses of Brush Motors
Brush motors are used in a wide range of applications, from consumer products to industrial applications. Typical examples are as follows
- Small office fans and PC cooling fans
- Industrial equipment such as boiler exhaust fans
- Running motors for commuter trains
- Elevator lifting motors
Because they are inexpensive among DC motors, they are used in cooling fans for DC office equipment. They have also long been used in moving equipment such as trains and elevators because of their easy torque and rotation speed control.
In recent years, inverter control, which requires no brushes and is easy to maintain, has become the mainstream for torque control in mobile equipment. Brushless motors are also becoming popular.
Principle of Brush Motors
Brush motors consist of a rotor, stator, and commutator. The stator may use a coil or a permanent magnet.
The stator generates a magnetic field at all times, and the current flowing in the coil wound around the rotor, and the stator’s magnetic field generates electromagnetic force to rotate the motor. It is important that the brushes are in contact with the commutator and that the direction of the coil current is in one direction.
Torque and speed can be controlled by changing the magnitude of the current.
Other Information on Brush Motors
1. Brush Motors Life
The brush life of brush motors is generally several hundred to several thousand hours. On the other hand, the life of the brush motors itself is determined by the life of the bearings and is generally tens of thousands to hundreds of thousands of hours.
Brush motors rotate by switching between repelling and attracting forces between the stator and rotor. For the rotor to rotate, the polarity of the magnetic force must be switched according to the angle of rotation, and the commutator plays this role.
While the drive is simple and easy to use by simply applying DC voltage, the brushes are mechanical contacts that wear out due to rotation, so if the brushes cannot be replaced, the life of the motor depends on the life of the brushes.
2. Difference from Brushless Motors
Brush motors are also called DC motors because they can be easily driven by a DC power supply. Brushless motors, on the other hand, are also called permanent magnet synchronous motors. Brush motors are easier to drive and less expensive than brushless motors, making them suitable for a wide range of applications.
Brush motors are used in many applications, but their short life span due to brush wear is a drawback. Brush replacement is necessary for long-term use. Brush motors can be controlled not only by DC voltage but also by PWM pulses.
Brushless motors, on the other hand, eliminate the commutator and brushes and use permanent magnets in the rotor. The absence of brushes gives brushless motors a longer life, and bearing life is the life of a brushless motor.
The brushless motor drive is classified into “square wave drive” (a method of driving with square wave voltage) and “sine wave drive” (driving with sine wave voltage). While square wave drive has a relatively simple drive circuit, it generates noise and vibration during rotation. Sine wave drive, on the other hand, has a more complex drive circuit but features lower noise and vibration during rotation.