Why do most products use brushed DC motors?
The application of micro motors is very wide, and various electric products cannot do without micro motors. Among micro motors, we have brushless and brushed DC motors, and the speed and service life of brushless motors exceed those of brushed DC motors.
In the application of micro motors, most products still use micro brushed DC motors, such as angle grinders and electric screwdrivers in power tools, which use brushed DC motors and have high operating noise and easy wear of brushes. Why not use better brushless motors?
For electric tools, the source of noise comes from work noise, not from the motor. Brushless motors are expensive, have complex controllers, and are difficult to troubleshoot when faults occur. Therefore, it is still advisable to choose brushed DC motors, which have lower costs. Brushed DC motors have simpler control and are much cheaper than brushless motors, so most manufacturers still choose brushed DC motors.
Don't ignore micro brushed DC motors
With the emergence of brushless DC motors, brushed DC motors began to decline, but brushed DC motors have always been a low-cost and reliable choice. The magnetic pole direction jump of brushed DC motors is achieved through a fixed contact point, which is connected to the electrical contact point on the rotor of the micro motor. Fixed contacts are usually made of graphite. Compared with other metal materials, graphite does not melt or weld with rotating contacts. Moreover, this contact is spring-loaded and can continuously obtain contact pressure.
Decades ago, the advantages of brushed DC motors began to decline, and more products began to use brushless motors, such as disk drives, printers, etc. Brushless motors do not have brush wear, so they do not cause electromagnetic interference, resulting in a sharp decline in the use of brushed DC motors. Even though there have been significant changes from brushed DC motors to brushless motors, the cost of brushless motors is too high. On the premise of meeting the necessary performance and sufficient reliability, micro brushed DC motors are still a good choice, such as toy cars, massage products, beauty products, and so on.
Basically, brushed DC motors do not require electronic control devices, as long as two cable switches are connected between the brushed DC motor and the power supply, which can significantly reduce costs.
The operation of brushed DC motors relies on the interaction between the electromagnetic fields of the stator and rotor, which are controlled to periodically generate attractive and repulsive forces between the stator and rotor, resulting in rotation (this is true for all motors)
A brushed DC motor has a large number of coils wound around its armature, generating a strong magnetic field that interacts with an external magnetic field to produce rotational motion.
Brushed DC motor control is very simple. Connect the DC power supply, and the micro motor will rotate after starting, without the need for other electronic devices to participate; To rotate in reverse, simply swap the DC power cord; To adjust the speed, simply increase or decrease the voltage.
A brushed DC motor has a pair of brushes in the casing, which direct the applied current to the armature coil through the commutator contacts. Each metal plate covers nearly 180 ° of the armature. When the micro motor operates, the current, brushes, commutator metal plates, and the current circuit between the two micro motor windings automatically switches every half turn. Therefore, brushed motors do not require an external controller and can generate the rotating magnetic field required for armature rotation on their own.
The interaction between armature magnetic field and rotor magnetic field of brushed DC micro motor
The rotor magnetic field of a micro motor can be generated by the fixed coils of the micro motor itself or by permanent magnets. When the rotor rotates, the direction of the magnetic field also needs to be reversed to keep the micro motor rotating. The direction of the magnetic field generated by the coils is constantly switching and is attracted or repelled by the magnetic field generated by external coils or permanent magnets. The use of permanent magnets is limited to micro motors, such as electric toys, where the strength of the magnet is not sufficient when the size and weight are reasonable. But the use of rare earth materials for permanent magnets has changed this situation, as the design of both micro motors and excitation coils requires a balance of size, weight, and control factors.
This is a simple version of a brushed DC motor that uses permanent magnets to generate a stator magnetic field, paper clips as brushes, and small coils as armature winding coils. Once powered on, it can operate. The structure of all brushed DC motors is simple and basic.
▍ Excitation coil configuration of stator
There are various configurations for the excitation coil of the stator, with the most common being series winding, shunt winding, and composite winding (a combination of series and shunt). In a series wound motor, the excitation coil is connected in series with the armature coil (through an electric brush); In a shunt winding motor, the excitation coil is connected in parallel with the armature coil ("shunt" is another way of describing "parallel").
In the series winding structure, the excitation coils S1-S2 are connected in series with the armature coils A1-A2; For the shunt winding, the excitation coils F1-F2 are connected in parallel with the armature coils A1-A2; For the composite method, the excitation coils S1-S2 are connected in series, and F1-F2 are connected in parallel with the armature coils A1-A2.
Each wiring method provides different control, speed performance, torque, starting and running torque, and the ability to handle load changes. Some advanced designs use independent excitation control for the stator excitation winding and rotor armature winding to achieve greater flexibility and stricter control.
Although brushless motors have many advantages, the cost issue has not been solved. Nowadays, the performance of brushed DC motors is gradually improving. Although the design of micro motors has not changed in many aspects, there are still two important developments: first, permanent magnets have been widely used; Secondly, ICs and electronic switches are used for coil driving and functional feedback.
