Why do fans and angle grinders use brushless and brushed one? The use of different motors for the two types of electrical appliances is mainly due to the difference in use. The angle grinder uses a brushed motor and a series-excited brushed motor. In addition to a certain power, the angle grinder also needs a relatively high speed; however, the electrical Compared with angle grinders, fans are light-loaded appliances and do not require high speeds. The motor used on the fan does not use a brush, but strictly speaking, it is different from the usual brushless motor, which uses an AC induction motor. The working principle of the fan motor Most of the fan motors used are AC induction motors, which use the frequency and waveform of the AC itself to generate a rotating magnetic field, which is rotated by eddy currents in the rotor. But this kind of motor needs a magnetic field with a phase difference to form a certain angle at the initial operation, so it needs an auxiliary winding as the starting winding, and the voltage formed between the starting winding and the running winding is formed by the phase-shifting effect of the capacitor, and the rotation is completed. initial start-up conditions.
For the single-phase motor used by the fan, in fact, the capacitor and the starting winding complete the task after the start after power-on. At this time, the motor can run normally even if the winding is disconnected. The speed regulation of the fan motor is generally realized by changing the voltage of the running winding. In order to make the speed regulation more convenient, the running winding is generally designed with multiple taps, and different speeds are controlled by connecting different taps. Although changing the voltage speed regulation will affect the power of the motor, there is no problem at all in the case of a small power load such as a fan. The working principle of the angle grinder motor The motor used on the angle grinder is a brush motor, which is a series motor. Both the rotor and the stator use electromagnetic coils to provide a magnetic field, and finally only two power supply wires are output, and the stator winding and the rotor winding are connected in series.
Since the stator winding of the motor itself has a certain connection and winding method, the motor will automatically change the magnetic field under the action of the brush and the commutator after power-on. Its working process is similar to that of the permanent magnet brush motor, except The permanent magnet brush motor can only work with direct current, while the series motor of the angle grinder works on alternating voltage, but it can actually work on both alternating and direct currents. In addition to angle grinders, many power tools use series motors, which generally do not require speed regulation when used on angle grinders. When used on other power tools, such as electric drills, speed regulation is required. The speed regulation of this kind of motor can also be carried out by voltage regulation, generally using a thyristor voltage regulation circuit to achieve speed regulation. Why the fan uses an induction motor and the angle grinder uses a series motor. The two types of electrical appliances use different motors mainly because of different work requirements.
The fan generally does not need too much rotation speed and high power, because its load is only the fan blade; and the angle grinder relies on high-speed operation to cut or grind the workpiece, and due to the problem of the load relationship, it needs a certain output power , Generally, the power of the angle grinder is less than a few hundred watts and more than one kilowatt, while the power of the fan motor generally only needs a few tens of watts. Therefore, due to the different working conditions of these two motors, the required parameters are also different. The speed of the induction motor is determined by the frequency of the alternating current. Its speed cannot be made too high, and the highest speed can only reach About 3000 rpm, but angle grinders, including many power tools, require high speed, and the maximum speed often reaches more than 10,000 rpm. The difference between a brushed motor and a brushless motor If a brushless motor is mentioned, it is actually an AC motor in the conventional sense. It drives the motor after converting the input DC voltage into pulsating DC or AC with a certain waveform through the controller. , the speed of this motor can be much higher than that of ordinary AC induction motors.
The biggest difference between the brushless motor and the brushed motor structure is the brush and the commutator. The brushed motor needs to transmit electric energy through the brush, and can automatically control the winding that needs to be energized through the commutator. The winding of the brushless motor is directly It is a structure that does not need brushes for external leads. Since the brushless motor does not have a commutator, its coil control cannot be automatically converted. It is necessary to detect the current position of the rotor through the sensor, and feedback it to the controller to determine which set of coils needs to be energized. There are generally two ways to detect the rotor position, one is through the Hall element, and the other is through the winding itself. Hall element is a kind of magnetic sensitive element. When the magnetic field is close, it will change the relationship of output level. Hall element, but the control logic of the controller is relatively complicated.
Compared with brushed motors, brushless motors require less maintenance because they do not use brushes. Because the brushed motor is working due to the friction between the brush and the commutator, there will be carbon powder deposited on the commutator, and the brush itself is also a loss element, the friction between the brush and the commutator is caused by the friction between the brush and the commutator The generated spark will also interfere with some control circuits, and it is also very dangerous to use in some flammable and explosive occasions. The difference in structure of the brushless motor solves the drawbacks of the brushed motor, but its manufacturing cost will increase.
