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The difference between brush motor and brushless motor

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The difference between brush motor and brushless motor

First, the principle of brush motor

Brush motor adopts mechanical commutation, the magnetic pole does not move, the coil rotates. When the motor is working, the coil and commutator rotate, the magnetic steel and the carbon brush do not turn, and the alternating change of the coil current direction is completed by the commutator and the brush that rotate with the motor. In a brush motor, this process is to group the two power input end of the coil, in turn, arranged in a ring, separated with insulating materials between each other, forming a anything like cylinder, become an organic whole repeatedly with the motor shaft, the power supply through the two small pillar made of carbon (carbon brush), under the action of spring pressure, from the two specific fixed position, A set of coils is energized by pressing two points on the top coil power input ring cylinder. As the motor rotates, different poles of different coils or the same coil are energized at different times, so that the N-S pole of the magnetic field generated by the coil and the N-S pole of the closest permanent magnet stator have a suitable Angle difference. The opposite magnetic field attracts and the same repels each other, generating force and pushing the motor to rotate. The carbon electrode slides over the coil tip like a brush on a surface, hence the name carbon "brush". Sliding each other, will rub the carbon brush, resulting in loss, need to replace the carbon brush regularly; Alternating between the carbon brush and the coil connector, electrical spark will occur, produce electromagnetic break, interference with electronic equipment.


Two, brushless motor working principle

Brushless motor adopts electronic commutation, the coil does not move, the magnetic pole rotates. Brushless motor, is the use of a set of electronic equipment, through the Hall element, sense the position of the permanent magnet pole, according to this perception, the use of electronic circuit, timely switch the direction of the current in the coil, to ensure that the right direction of the magnetic force, to drive the motor. Eliminate the shortcomings of brush motor. These circuits are the motor controllers. The controller of the brushless motor can also realize some functions that the brushless motor cannot achieve, such as adjusting the power switch Angle, braking the motor, making the motor reverse, locking the motor, using the brake signal, stopping the power supply to the motor. Now the electric alarm lock of the battery car makes full use of these functions. Brushless DC motor is composed of motor body and driver. It is a typical mechatronics product. Because the brushless DC motor is operated by automatic control, so it will not be like the frequency conversion under the heavy load start synchronous motor in the rotor as another start winding, also will not produce vibration and out of step when the load mutation.

Three, the difference in speed regulation

In fact, the control of the two motors is voltage regulation, but because the brushless DC uses electronic commutation, so it can be achieved by digital control, while the brushless DC is commutated by carbon brush, and can be controlled by traditional analog circuits such as silicon controlled, which is relatively simple.

1, brush motor speed regulation process is to adjust the motor power supply voltage level. The adjusted voltage and current can change the magnetic field generated by the electrode through the commutator and brush-ground conversion to achieve the purpose of changing the speed. This process is known as variable voltage speed regulation. 

2. The speed regulation process of the brushless motor is that the voltage of the power supply of the motor remains unchanged, the control signal of the electric regulation is changed, and the switching rate of the high-power MOS tube is changed by the microprocessor to realize the change of the speed. This process is called variable frequency speed regulation.

Four, performance differences

1, brush motor structure is simple, long development time, mature technology as early as in the 19th century when the birth of the motor, the practical motor is brushless form, that is, AC squirrel cage asynchronous motor, this motor has been widely used after the generation of alternating current. However, asynchronous motor has many insurmountable defects, so that the development of motor technology is slow. In particular, brushless DC motor has been unable to be put into commercial operation. With the rapid development of electronic technology, it has been slowly put into commercial operation until recent years. In essence, it still belongs to the category of AC motor. Brushless motor was born soon, people invented the DC brush motor. Because the DC brush motor mechanism is simple, easy to produce and process, convenient maintenance, easy to control; Dc motor also has fast response, large starting torque, from zero speed to rated speed can provide rated torque performance, so it has been widely used as soon as it came out. 

2. Dc brush motor has fast response speed and large starting torque. Dc brush motor has fast starting response speed, large starting torque, stable speed change, and almost no vibration can be felt from zero to the maximum speed. Brushless motor has large starting resistance (inductive reactance), so the power factor is small, the starting torque is relatively small, there is a buzz when starting, accompanied by strong vibration, and the driving load is small when starting. 

3. The DC brush motor runs smoothly, and the starting and braking effects are good. The brush motor is regulated by voltage regulation, so the starting and braking are stable, and the constant speed is also stable. Brushless motor is usually digital frequency conversion control, the first AC into DC, DC and then into AC, through the frequency change control speed, so the brushless motor in the starting and braking operation is not stable, vibration, only when the speed is constant will be stable. 

4, DC brush motor control precision is high DC brush motor and reducer, decoder is usually used together, so that the output power of the motor is greater, higher control accuracy, control accuracy can reach 0.01 mm, almost can let the moving parts stop in any place you want. All precision machine tools are controlled by DC motors for precision. Brushless motor is not stable when starting and braking, so the moving parts will stop in a different position each time, must be through the positioning pin or limiter can stop in the desired position. 

5, DC brush motor use cost is low, convenient maintenance. Due to the simple structure, low production cost, many manufacturers, and mature technology of DC brush motor, it is widely used, such as factories, processing machines, precision instruments, etc., if the motor fails, only need to replace the carbon brush, each carbon brush only needs a few yuan, very cheap. Brushless motor technology is not mature, the price is high, the application range is limited, mainly should be in constant speed equipment, such as frequency conversion air conditioning, refrigerator, brushless motor damage can only be replaced. 

6, brushless, low interference brushless motor to remove the brush, the most direct change is that there is no brush motor when the electric spark, which greatly reduces the interference of electric spark on remote control radio equipment. 

7, low noise, smooth operation brushless motor without a brush, when the friction is greatly reduced, smooth operation, noise will be much lower, this advantage is a great support for the stability of the model operation. 8, long life, low maintenance cost less brush, brushless motor wear is mainly on the bearing, from the mechanical point of view, brushless motor is almost a maintenance free motor, when necessary, just do some dust removal maintenance.



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