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Adjusting the load to improve motor starting difficulties

Effective motor starting requires optimizing both the motor's capabilities as well as matching the load characteristics.

Motor Starting Performance and Load Matching

As a motor manufacturer with many years of experience, Lunyee has conducted research on some common problems with motors and has encountered many motor issues. Recently, we came across an experience shared by an online user. He mentioned that he had a 37kW motor, and recently encountered the following issue: when using a star-delta reduced voltage starting method to drive a water pump, the motor could not enter the running state when the water valve was fully open, and the pump could not operate. Later, he closed the water valve first, started the motor, and gradually opened the water valve until the motor entered normal operation, and the pump could work properly. The issue this user encountered is related to the rationality of matching the motor's starting performance with the load.

Motor Starting Performance

The starting process of the motor is itself a process of balancing the torque and resistance. On the one hand, we can improve the starting performance of the motor by appropriately improving the parameters of the motor itself, such as controlling the starting current to increase the starting torque; on the other hand, we can also achieve the starting purpose from the perspective of adjusting the load.

Adjusting the Load

When the equipment matched with the motor can be started in light load or even no-load conditions, the motor starting problem can be solved by adjusting the size of the load. From the analysis of the operation status of the motor rotor, the starting process is the change process of the motor rotor from static to dynamic and then to rated speed. From the perspective of changing the inertia of the object, the larger the load driven by the motor, the more difficult it is to start. On the contrary, if the load driven by the motor is appropriately reduced, the motor starting will be easier.

Motor Starting Torque

Starting from the design principles of the motor, the starting torque is greater than the rated torque, which is specifically stipulated in the technical conditions of the motor, generally around 2 times; the starting torque is the electromagnetic torque at the moment of motor start-up, which is equal to the static friction torque of the motor load, and is also the moment when the motor start-up current is at its maximum.

Optimizing Motor Starting

However, for motors that are directly started under constant load, more can only be done to optimize and improve the performance of the motor itself, such as taking measures on the squirrel-cage rotor slot shape, measures to reduce the rotor resistance of wound rotor motors, and measures such as variable frequency starting, which is currently widely used, are all effective measures to assist and improve motor starting.

Gradual Load Adjustment

From the enthusiastic comments of netizens, we can also find that for load-adjustable working conditions, during the motor starting process, the load size can also be gradually adjusted according to the actual starting situation of the motor. When the motor starts, the load also basically reaches the rated load state.


Effectively starting a motor requires adapting it to the corresponding load requirements.s. While improved designs enhance torque output, adjusting the load size and gradually increasing it aids the transition from static to dynamic operation. For constant loads, internal motor modifications assist starting. But for adjustable loads, gradual adjustment as the motor warms up allows the starting process to proceed smoothly by reducing initial inertia. This balanced approach considers both mechanical and electrical factors. At Lunyee, we strive to thoroughly understand application needs and provide customized solutions leveraging these principles. Please feel free to contact us if you need any technical recommendations on integrating motors while ensuring reliable starting under all operating conditions.

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