I. Brushed DC Motor
A brushed DC motor is a type of DC motor. The stator of a brushed motor has fixed main magnetic poles and brushes, while the rotor has armature windings and a commutator. Electrical energy from a DC power supply enters the armature windings through the brushes and commutator, generating armature current. The magnetic field generated by this armature current interacts with the main magnetic field to produce electromagnetic torque, causing the motor to rotate and drive the load. Due to the presence of brushes and the commutator, brushed motors have a complex structure, poor reliability, frequent failures, high maintenance workload, short lifespan, and are prone to electromagnetic interference from commutation sparks.
II. Working Principle of Brushed DC Motors
The working principle diagram of a brushed DC motor is shown in the figure. The fixed part of the brushed DC motor contains magnets, referred to here as the main magnetic poles; the fixed part also contains brushes. The rotating part consists of a toroidal iron core and windings wound around the toroidal iron core.
A brushed DC motor has two poles. The stationary part (stator) of the motor has a pair of stationary main magnetic poles, N and S, with DC excitation. The rotating part (rotor) has an armature core. There is an air gap between the stator and rotor. An armature coil, consisting of two conductors A and X, is placed on the armature core. The beginning and end of the coil are connected to two arc-shaped copper segments called commutator segments. The commutator segments are insulated from each other, and the entire assembly of the commutator segments is called the commutator. The commutator is fixed to the shaft, and the commutator segments are also insulated from the shaft. A pair of fixed brushes, B1 and B2, are placed on the commutator segments. When the armature rotates, the armature coil is connected to the external circuit through the commutator segments and brushes.
III. Differences between brushless DC motors and brushed DC motors
(I) Characteristics of Brushless DC Motors (BLDC):
1. High efficiency: Brushless DC motors are more efficient than brushed DC motors, reaching over 90%.
2. High torque: The speed and torque characteristics of brushless DC motors are more stable than those of brushed DC motors, enabling high torque and low-speed operation.
3. Long lifespan: Brushless DC motors have a longer lifespan than brushed DC motors because brushless DC motors can avoid brush wear.
4. Low noise: The electronic speed controller of a brushless DC motor can control the speed and torque of the motor through PWM, avoiding the influence of the brush on the torque, thus resulting in low noise.
5. Convenient speed adjustment: The electronic speed controller of the brushless DC motor can be flexibly configured to realize multiple control modes, which is convenient for realizing special control needs such as automation and digitalization.
6. High cost performance: Brushless DC motors are relatively expensive, but considering their efficiency and lifespan over long-term use, their overall cost performance is still high.
(II) Characteristics of brushed DC motors:
1. Simple structure: Brushed DC motors have a relatively simple structure and are easy to maintain and repair.
2. Low cost: Brushed DC motors are relatively inexpensive, cheaper than brushless DC motors.
3. Convenient speed adjustment: The speed control system of a brushed DC motor is usually relatively simple, and speed adjustment can be achieved through simple control methods such as potentiometers.
4. High reliability: Brushed DC motors have relatively stable speed and torque characteristics, making them suitable for various industrial and household applications.
5. Relatively high noise: There is unstable mechanical contact between the rotor and stator of a brushed DC motor, which results in noise.
(III) Differences between brushless DC motors and brushed DC motors
Brushless DC motors and brushed DC motors are based on different transmission principles and structural designs. The following are the main differences between them:
1. Different structures: Brushed DC motors have a rotating rotor and a fixed stator inside the motor, with current transmitted between them through carbon brushes and ring slip rings. Brushless DC motors, on the other hand, have permanent magnets mounted on the rotor, and the electromagnetic field is switched through electronic components to drive the rotor to rotate. They do not have carbon brushes or slip rings.
2. Efficiency difference: Because brushless DC motors do not have carbon brushes and slip rings, the internal energy conversion efficiency of the motor is higher, the operation is more stable, and the service life is longer.
3. Different maintenance costs: Brushed DC motors require regular replacement of carbon brushes, while brushless DC motors do not, resulting in lower maintenance costs.
4. Different control methods: Brushless DC motors have a more advanced control method. They can adjust the speed and direction of the motor through an intelligent controller to achieve efficient dynamic control. Brushed DC motors, on the other hand, must use a traditional speed controller, which has relatively low control precision.
In summary, brushless DC motors are widely used in power tools, drones and other fields, while brushed DC motors still hold a certain market share in home appliances, automotive starters, motorcycles and other fields.
