Brushless and brushed DC motors essentially perform the same function of converting electric current into rotational motion. However, there are still several differences between the two types of motors. Working principles will be explained before we talk about their differences.
Working principle of a brushed DC motor
When the motor works, the coil and commutator rotate, the magnet and carbon brush do not rotate, and the alternate change of coil current direction is achieved by the commutator and brush that rotate with the motor. Brushed motors are divided into high speed brushed motor and low speed brushed motor in the electric vehicle industry.
A brushed DC motor consists of two main parts: stator and rotor. The stator has magnetic poles (winding type or permanent magnet type) and the rotor has winding, and when energized, the rotor also forms a magnetic field (magnetic poles), and there is an angle between the magnetic poles of the stator and rotor. By changing the position of the brushes, the direction of the stator-rotor pole angle can be changed, thus changing the direction of rotation of the motor.
Working principle of a brushless DC Motor
An electric brushless bldc motor takes electronic commutation, where the coil does not move and the magnetic poles rotate. It uses a set of electronic device to sense the position of the magnetic poles of the permanent magnets through Hall elements. Electronic circuits are used to switch the direction of the current in the coils at the right time to ensure that the correct direction of magnetic force is generated to drive the motor.
These circuits are the motor controllers. The controller of a brushless motor can also realize some functions that cannot be realized by a brushed motor, such as adjusting the power switching angle, braking the motor, reversing the motor, locking the motor, and stopping supplying power to the motor by using the brake signal.
A brushless DC motor consists of motor body and driver, which is a typical mechatronic product. Since the brushless DC motor operates in a self-controlled manner, it does not add another starting winding to the rotor like a synchronous motor that starts under heavy load under frequency regulation.
Differences between brushed DC motors and brushless DC motors
1. Mode of speed regulation
The speed regulation process of brushed DC motors is to adjust the motor power supply voltage level. The adjusted voltage and current are converted through the rectifier and brushes to change the strength of the magnetic field generated by the electrodes, thus changing the speed. This process is called variable voltage speed regulation.
The speed control process of a brushless DC motor is to keep the voltage of motor power supply unchanged, change the control signal of ESC, and then change the switching rate of high power MOS tube through microprocessor to realize the change of speed. This process is called variable frequency speed regulation.
2. Simple structure and long development history of the brushed DC motor
A brushed DC motor is a traditional product with more stable performance, and a brushless DC motor is an upgraded product with better life performance than brushed motor. However, the brushless motor has complicated control circuit, so has more strict aging screening requirement for components.
Soon after the brushless motor was born, people invented the brushed DC motor. The brushed DC motor has been widely used once it was launched on the market due to its features: simple mechanism; easy to produce, process, maintain, and control; fast response; large starting torque; rated torque is available from zero speed to rated speed.
3. Fast response and large starting torque of the brushed DC motor
The brushed DC motor has fast starting response, high starting torque, and smooth variable speed, so vibration can hardly be felt when the speed changes from zero to maximum, and a larger load can be driven when starting.
The electric brushless bldc motor has large starting resistance (inductive resistance), so the power factor is small, the starting torque is relatively small, there is a humming sound accompanied by strong vibration when starting, and the starting drive load is smaller.
4. The brushed DC motor runs smoothly and has perfect starting and braking effect
The speed of the brushed DC motor is regulated by voltage regulation, so it starts and brakes smoothly, and runs smoothly at constant speed.
The brushless DC motor is usually digital frequency conversion control that converts AC into DC, then DC into AC again, and controls speed through frequency change, so the brushless motor cannot run smoothly and vibrates strongly.
5. High precision control of brushed DC motors
Brushed DC motors are usually used together with gearboxes and decoders to make the motors have more output power and higher control accuracy, thus allowing the moving parts to stop almost anywhere. All precision machine tools use DC motors to control accuracy. Brushless motors are not smooth in starting and braking, so the moving parts will stop at different positions every time, and must be stopped at the desired position by means of positioning pins or limiters.
6. Brushed DC motors have low cost and are easy to maintain
Its simple structure, low production cost, many manufacturers, and mature technologies enable the brushed DC motor to have more widespread applications, such as factories, processing machine tools, and precision instruments, etc. In case of motor failure, you should only replace the carbon brush. Brushless DC motor has immature technology and expensive price, so it has limited applications, such as inverter air conditioners, refrigerators and other constant speed equipment.
7. The brushless DC motor has low interference
According to brushless motor factory, the most immediate change of a brushless DC motor is the absence of electric sparks generated by the brushed motor operation, which greatly reduces the interference of electric sparks to remote control radio equipment.
8. Low noise and smooth running
Without brushes, brushless motors run smoothly with much less friction and much lower noise, which provides huge support for the stability of the motor operation.
Post time: Jul-08-2022