What factors are related to the no-load current?

The no-load current depends on the structure and parameters of the motor. The more important factors are as follows:

1. Characteristics of the motor core: The magnetic permeability and hysteresis characteristics of the core will affect the excitation current of the motor. Therefore, the no-load current of motors with different core materials and designs will also be different.

2. Parameters of the excitation coil: Parameters such as the resistance, inductance and position of the coil will affect the excitation current, and thus affect the no-load current.

3. Friction and elastic properties of the brush: The contact resistance between the brush and the electrode and the elastic properties of the brush will also affect the size of the no-load current.

4. Characteristics of the magnetic field: The strength and distribution of the motor's excitation magnetic field, as well as the magnetic circuit design of the rotor and stator will affect the no-load current.

5. Characteristics of the monitoring and control system: The response speed and accuracy of the motor control system will also have a certain impact on the size of the no-load current.

It should be noted that although the no-load current is usually small, in some cases, it may still have a negative impact on the operation of the device. Therefore, when designing and applying the motor, it is necessary to fully consider the no-load current and optimize the structure and parameters of the motor to reduce the no-load current as much as possible to improve the working efficiency and stability of the equipment.

It is mainly related to the power supply voltage. Because the power supply voltage is high, the magnetic flux in the iron core increases and the magnetic resistance will increase. When the power supply voltage reaches a certain value, the magnetic resistance in the iron core increases sharply and the winding inductance decreases sharply. At this time, a slight increase in the power supply voltage will cause a lot of increase in the no-load current.

The reasons for the excessive no-load current of the motor are:

1. The power supply voltage is too high. When the power supply voltage is too high, the motor core will produce magnetic saturation, resulting in excessive no-load current.

2. The motor is improperly assembled after repair or the gap is too large.

3. The number of stator winding turns is insufficient or the star connection is mistakenly connected to a triangle connection. For some old motors, the magnetic field strength is weakened or the insulation between the sheets is damaged due to corrosion or aging of the silicon steel sheets, resulting in excessive no-load current. For small motors, the no-load current can continue to be used as long as it does not exceed 50% of the rated current.

Generally, the no-load current of large and medium-sized motors is 20%~30% of the rated current, and the no-load current of small motors is about 35%~50% of the rated current.