Stalled rotor current: an important parameter for motor control

When the motor is prevented from rotating, the current consumed is the locked-rotor current. This is a special state that occurs when the motor is started or running and is crucial to the performance evaluation and design of the motor. This article will discuss the definition, causes, measurement methods, influencing factors, applications, and methods of effective management of stalled current.

Overview of locked rotor current
Locked rotor current refers to the current generated when the motor is unable to rotate due to external resistance. Normally, the motor's rotor rotates due to electromagnetic force, but when the motor cannot overcome external resistance, the rotor will stop rotating and generate a stalled current.

Causes of blocked rotor current
There are many reasons for stall current:

1. Overload: When the motor working load exceeds the rated load, the rotor may not be able to rotate and be blocked. In an attempt to overcome the external resistance, the motor draws more current, creating a stall current.

2. Mechanical failure: Mechanical failure may occur during motor operation, such as bearing damage or gear jamming. These problems will cause the motor to be unable to rotate and cause stall current.

3. Starting inertia: At the moment when the motor starts, due to the inertia of the rotor, a larger current is needed to overcome the static friction and initial resistance, so that the rotor starts to rotate. This inertia at start-up can also cause a short-term increase in stall current.

Measuring method of locked rotor current
To measure stall current, there are two common methods:

1. Direct measurement: This method requires connecting the current sensor to the motor's power line or motor driver to measure the current in real time. Although accurate stall current values are provided, proper equipment and technical support are required.

2. Indirect measurement: Indirect measurement of locked-rotor current is to estimate the size of the locked-rotor current by measuring the current and speed of the motor. An estimate of the stall current can be calculated from the current and speed data using parameters and algorithms provided by the motor driver or controller. This method is relatively simple and does not require additional sensors, but the accuracy may be limited.

Managing stall current is critical to motor performance and long equipment life. By monitoring and controlling the locked-rotor current, the risk of motor overload and mechanical failure can be reduced, and the reliability and efficiency of the equipment can be improved.