Crushers, stamping machines, vibrating equipment, and heavy-duty conveyor systems with frequent start-stop operations in industrial production are typical examples of impact loads. The key characteristics of such loads include significant torque fluctuations and strong instantaneous shock loads during operation. Under certain conditions, peak torque can reach 2 to 3 times the rated torque, often accompanied by frequent starting and braking cycles. These factors easily lead to high motor current surges, increased losses, and excessive temperature rise—issues that closely align with motor overheating and improper sizing under high-frequency switching conditions. Therefore, impact loads cannot be handled using conventional selection methods designed for steady loads. Instead, motors must be carefully matched based on overload capacity, thermal performance, duty cycle factors, and structural characteristics to ensure stable and reliable equipment operation.
First, the practice of selecting motors solely based on steady-state power should be abandoned. Instead, peak torque and overload capacity verification must be prioritized. Conventional motor selection typically matches only the average load power, whereas instantaneous peak loads caused by impact loading are the primary cause of motor damage. During selection, an appropriate service factor should be applied according to the severity of the impact: 1.4–1.6 for moderate impact loads and 1.5–2.5 for severe impact loads. This ensures that the calculated required output torque exceeds the peak load torque, preventing stalling or overload tripping during impact events. Additionally, squirrel-cage induction motors with high overload multiples should be preferred to accommodate transient load shocks, thereby eliminating the common issue of insufficient overload capability in standard motors.
Second, motor heating and allowable switching frequency must be strictly verified to suit frequent start-stop operations under impact loads. Impact loads often involve high-frequency starting and braking cycles, during which significant copper and iron losses occur in both the stator and rotor within a single impact event. The accumulated losses far exceed those under steady-state operation, making overheating and insulation aging highly likely. Motor temperature rise should be accurately calculated using the average loss method described above, and the use of inaccurate equivalent selection methods must be avoided. Furthermore, the maximum number of allowed switch-on cycles per hour (N) should be verified to ensure that actual operating cycle counts remain below the motor’s thermal limits. It is particularly important to note that simply increasing the motor’s rated power does not improve adaptability to impact conditions. In fact, higher power ratings lead to proportionally greater energy consumption during starting and stopping, failing to address the overheating risks associated with high-frequency impacts.
Furthermore, the matching of the motor’s operating mode and structural type should be considered. The impact load belongs to a variable load intermittent operation condition, and it is not suitable to choose a motor with the long-term continuous S1 operating mode. Instead, a motor with the S3 intermittent cycle operating mode should be preferred. Such a motor is specifically designed for frequent start-stop and load fluctuation conditions and has a stronger ability to withstand impact losses and temperature rise fluctuations. For heavily impacted equipment, a dedicated cage-type motor with high rigidity and rotor strength can be selected to enhance the rotor’s resistance to impact fatigue and avoid rotor structural damage and abnormal operating sounds caused by long-term impact.
Finally, the transmission and control systems can be relied on to assist in optimizing the matching effect. The impact load can be reduced by using a reducer to achieve deceleration and torque increase, thereby reducing the instantaneous load pressure of the motor and buffering the peak impact. At the same time, an appropriate variable frequency control system should be matched to stabilize the motor’s output torque, suppress the sudden increase in current during the impact moment, and reduce the motor’s loss and temperature rise fluctuations. For frequent emergency stops and heavy impact conditions, braking resistors and buffering devices can be installed to further weaken the impact damage of the load on the motor and extend the motor’s service life.
In summary, the core of motor matching for impact loads is “centered on torque verification, based on heat verification, and supplemented by working condition adaptation”. Abandoning the single power selection thinking, comprehensively matching based on overload capacity, temperature rise characteristics, operating mode, and auxiliary configurations can completely avoid problems such as overheating, overload damage, and selection failure of the motor under impact conditions.
Post time: Oct-28-2026