In modern industrial production, electric motors are indispensable core equipment. Whether in factory assembly lines, CNC machines, building HVAC systems, or transportation systems, motors play a vital role. However, during motor operation, a dangerous phenomenon may occur—stalling. Once a stall happens, it not only affects production efficiency but may also cause serious damage to the motor itself. Therefore, understanding the principles, causes, hazards, and protective measures of motor stall is crucial for enterprises and engineers.
Motor stall refers to the situation in which the rotor of a motor can no longer maintain normal rotation during operation, resulting in a sharp drop in speed or complete stoppage. In simple terms, the motor becomes "stuck and stops rotating."
The essence of stalling is that the electromagnetic torque output by the motor is insufficient to overcome the load torque. When the load demand exceeds the motor’s capability, the motor enters a stalled state.
The operating characteristics of a motor can be described using the torque-speed curve. Taking a typical three-phase asynchronous motor as an example:
At zero speed, the motor torque is at its maximum, known as the stall torque.
As speed increases, the torque gradually decreases.
Near synchronous speed, torque approaches zero.
If the load torque is always less than the motor’s electromagnetic torque, the motor can operate smoothly. However, when the load demand shifts the intersection point toward the low-speed region—or even exceeds the stall torque—the motor cannot maintain operation and stalls.
Excessive Load
When the external load suddenly increases or is inherently too heavy, the motor cannot provide sufficient torque and easily stalls.
Power Supply Issues
Low voltage
Phase loss or unbalanced voltage
These conditions directly reduce motor torque and may lead to stalling.
Abnormal Mechanical Resistance
Bearing seizure, rotor blockage by foreign objects, or excessive transmission resistance may prevent the motor from running normally.
Improper Control
In stepper and servo motors, unreasonable drive signal settings (e.g., overly high frequency or excessive acceleration) can also cause stall.
Current Surge
When a stall occurs, motor current rises sharply, approaching or even exceeding the locked-rotor current, which may burn the windings.
Rapid Temperature Rise
In stalled conditions, heat dissipation is minimal, and temperature increases rapidly, damaging the insulation.
Mechanical Damage
Prolonged stalling may twist the shaft or damage couplings, affecting the transmission system.
Production Downtime
Stall directly interrupts equipment operation, reduces efficiency, and may cause safety accidents.
Three-Phase Asynchronous Motor
Stall typically occurs under overload or abnormal power supply, characterized by current surges and rapid speed reduction.
Stepper Motor
Common under excessive acceleration or heavy loads. “Lost steps” or complete stoppage are typical signs of stall.
Servo Motor
Although closed-loop control is used, stall may still occur if overloaded or if control parameters are improperly set.
Proper Motor Selection
Choose a motor with sufficient torque margin to avoid operating at full capacity continuously.
Improve Power Supply Quality
Ensure stable supply and avoid undervoltage, phase loss, or unbalanced voltage.
Enhanced Protection
Add overload, overcurrent, and stall protection in motor control systems.
Regular Maintenance
Maintain proper bearing lubrication, reduce mechanical jamming, and check cooling systems.
Optimize Control Strategies
For servo and stepper motors, use reasonable acceleration and deceleration curves to avoid rapid starts and stops.
Motor stall is a dangerous yet common operating fault, usually caused by excessive load, abnormal power supply, or mechanical resistance. Once stalling occurs, it not only disrupts production but may also burn out the motor and pose safety risks. Therefore, in motor design and application, it is essential to consider stall risks and adopt reasonable selection, protection, and maintenance measures.
If you are looking for high-performance and reliable motor products, it is recommended to choose a professional manufacturer. Fuxing Motor specializes in the research and production of three-phase asynchronous motors. With high efficiency and comprehensive protection functions, Fuxing motors effectively reduce stall risks and ensure production safety and efficiency.
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