Questions and answers about basic motor knowledge(Three)

01/07/2019

★Why do general DC brushless motors have three Halls?
A: In short, in order to be able to rotate, the brushless DC motor must have a certain angle between the magnetic field of the stator coil and the magnetic field of the permanent magnet of the rotor. The process of rotating the rotor is also the process of changing the direction of the magnetic field of the rotor. In order to make the magnetic field of the two have an angle, the magnetic field direction of the stator coil must be changed to a certain extent. So how do you know the direction of the stator magnetic field? Then rely on those three halls. It can be thought that the three Halls shoulder the task of telling the controller when to change the direction of the current.

★ What is the approximate range of power consumption of the brushless motor Hall?
A: The power consumption of the brushless motor Hall is roughly in the range of 6m A-20m A.

★ How high can the normal motor work at high temperatures? How high can the motor withstand?
A: If the temperature of the motor cover is more than 25 degrees above the ambient temperature, it indicates that the temperature rise of the motor has exceeded the normal range. Generally, the temperature rise of the motor should be below 20 degrees. Generally, the motor coil is wound by an enameled wire, and when the temperature of the enameled wire is higher than 150 degrees, the paint film will fall off due to excessive temperature, causing the coil to be short-circuited. When the coil temperature is above 150 degrees, the motor housing exhibits a temperature of about 100 degrees, so the maximum temperature that the motor can withstand is 100 degrees based on its case temperature.

★The temperature of the motor should be below 20 degrees Celsius, that is, the temperature of the motor cover should exceed 20 degrees Celsius, but what is the reason why the motor heats up to 20 degrees Celsius?
A: The direct cause of motor heating is caused by large current. Generally, it may be caused by short circuit or open circuit of coil, demagnetization of magnetic steel or low efficiency of motor. Normally, the motor runs for a long time and high current.

★ What causes the motor to heat up? What kind of process is this?
Answer: When the motor load is running, there is power loss in the motor, which will eventually become heat energy, which will increase the temperature of the motor and exceed the ambient temperature. The value at which the motor temperature is higher than the ambient temperature is called temperature rise. Once there is temperature rise, the motor will dissipate heat to the surroundings; the higher the temperature, the faster the heat dissipation. When the heat emitted by the motor per unit time is equal to the amount of heat dissipated, the temperature of the motor no longer increases, but maintains a constant temperature, that is, a state of heat and heat balance.

★What is the general temperature increase allowed by click? Which part of the motor is most affected by the temperature rise of the motor? How is it defined?
Answer: When the motor load is running, it is better to use the load as much as possible (if mechanical strength is not considered). However, the greater the output power, the greater the power loss and the higher the temperature. We know that the weakest temperature resistance in a motor is an insulating material, such as an enameled wire. There is a limit to the temperature resistance of insulating materials. Within this limit, the physical, chemical, mechanical, electrical and other aspects of insulating materials are stable, and their working life is generally about 20 years. Beyond this limit, the life of the insulating material is drastically shortened and even burned. This temperature limit is called the allowable temperature of the insulating material. The allowable temperature of the insulating material is the allowable temperature of the motor; the life of the insulating material is generally the life of the motor.
The ambient temperature varies with time and location. When designing the motor, it is required to take 40 degrees Celsius as the standard ambient temperature in China. Therefore, the allowable temperature of the insulating material or the motor minus 40 degrees Celsius is the allowable temperature rise. The allowable temperature of different insulating materials is different. According to the allowable temperature, the common insulating materials for the motor are A, E, B, F, H. Five kinds. Calculated according to the ambient temperature of 40 degrees Celsius, the five insulating materials and their allowable temperature and allowable temperature rise are shown in the following table:
Grade Insulation Material Allowable Temperature Allowable Temperature Rise
A immersed cotton, silk, cardboard, wood, etc., ordinary insulating varnish 105 65
E Epoxy resin, polyester film, green paper, tri-acid fiber, highly insulating paint 120 80
B Mica, asbestos, and fiberglass compositions using an organic paint with improved heat resistance as a binder 130 90
F Mica, asbestos and glass fiber compositions bonded or impregnated with heat-resistant epoxy resin 155 115
H Mica, asbestos or fiberglass composition bonded or impregnated with silicon resin, silicone with rubber 180 140

★How to measure the phase angle of the brushless motor?
Answer: Turn on the controller power supply, and the controller supplies the Hall element to detect the phase angle of the brushless motor. The method is as follows: use the +20V DC voltage file of the universal meter, and connect the red test lead to the +5V line. The black pen measures the high and low voltages of the three leads respectively, and can be compared with the commutation table of the 60 degree and 120 degree motor.

★Why can any DC brushless controller and DC brushless motor be able to rotate normally without being connected? Why does DC brushless have a reverse phase?
A: Generally speaking, the brushless DC motor is a process in actual motion: the rotation of the motor---the direction of the rotor magnetic field changes---- when the angle between the direction of the stator magnetic field and the direction of the rotor magnetic field reaches 60 degrees of electrical angle - --- Hall signal change ---- phase line current direction change --- stator magnetic field forward 60 degrees electrical angle --- the angle between the stator magnetic field and the rotor magnetic field is 120 degrees electrical angle --- - The motor continues to rotate. So we understand that Hall has six correct states. When a particular Hall tells the controller, the controller has a specific phase output state. Therefore, the reverse phase sequence is to accomplish such a task, that is, the electrical angle of the stator is always stepped at an electrical angle of 60 degrees in one direction.