Stalling is a condition at which a motor stops rotating even when there is sufficient voltage at it’s terminals. This condition occurs when the torque required by the load is more than the maximum torque (Breakdown torque) that can be generated by the motor. At this condition, the motor drains the maximum current and the speed comes zero.
DC Motor Torque speed Characteristics
Every motor is designed to spin a particular amount of load. When the load is further increased above its overload region, the speed of the motor gradually reduces and the motor stalls. The Slip during stalling of a motor is 100%. Since the motor is not rotating, there will be no back EMF and so the power consumption will be the maximum.
Reasons for stalling of motors:
1. Electrical reason: Missing out of one phase (two phasing) or single phasing of input supply
2. Mechanical reason: Rotor jam, overload or load unable to move.
Stall current is the current drawn by the motor at locked rotor condition. It is the highest current a motor can draw and is proportional to its rotor resistance. If stall current is drawn by a motor for a longer time, motor gets overheated causing damage of winding.
Stall torque is the load torque at which the motor shaft stops rotating. It is also known as locked rotor torque.