How to choose the frequency inverter for light load and heavy load?

In the process of inverter selection, light load and heavy load are two important concepts. Correctly understanding and distinguishing these two load types is crucial to choosing the right inverter.

What is light load?

In the electrical industry, light load means that the electrical control element can drag a load of equal power under the condition of rated power, but its output torque is small. Typical light-load equipment includes centrifugal fans, water pumps and oil pumps. The load characteristics of these equipment are usually proportional to the square of the speed, that is, the load torque is proportional to the square of the speed.

Characteristics of light-load equipment:

The load torque increases rapidly with the increase of speed.

During operation, the load torque is small.

Suitable for inverter light-load power selection.

The inverter current is small during operation.

Selection suggestions: For light-load equipment, when selecting an inverter, ensure that the inverter's light-load power is not less than the rated power of the motor; the overload capacity is required to be low.

What is heavy load?

Heavy load refers to equipment with relatively constant or small changes in load characteristics. Typical heavy-duty equipment includes conveyors, mixers, extruders, cranes, hoists, air compressors, ball mills, injection molding machines, and reciprocating piston pumps. The load characteristics of these equipment are usually independent of the speed, that is, the load torque is basically constant.

Characteristics of heavy-duty equipment:

The load torque remains basically unchanged throughout the operation.

Requires a larger starting torque.

Suitable for inverter heavy-duty (HO) power selection.

The inverter current is large during operation.

Selection suggestions: For heavy-duty equipment, when selecting an inverter, ensure that the inverter's heavy-duty power is not less than the rated power of the motor; relatively speaking, the overload capacity is higher, but there will be a higher temperature, so an inverter with a higher temperature working capacity should also be considered.

Selection example

Question: How to select a power module for a conveyor motor with a rated voltage of 380V, a power of 5.5kW, and a current of 11.6A without overload?

Answer: The conveyor belt is a constant torque load, and the inverter should be selected according to the heavy-duty power. You can choose the SW100 5R5G3B inverter to drive the motor.

Summary

In the inverter selection process, correctly distinguishing between light load and heavy load is the key to ensure the normal operation of the equipment. Light-load equipment such as centrifugal fans and water pumps should choose inverters with light load power, while heavy-load equipment such as conveyors and mixers should choose inverters with heavy load power. Through reasonable selection, the operating efficiency and reliability of the equipment can be improved.