Which type of DC motor is primarily used when a high torque is needed at startup?

The series motor is the ideal choice when high torque is needed at startup due to its unique characteristics. In a series motor, the field winding is connected in series with the armature winding, meaning that the current flowing through the armature also flows through the field. At startup, the motor draws a large amount of current to overcome inertia, which causes a strong magnetic field to be generated. This strong magnetic field produces a high torque output.

As the motor speeds up and the back EMF increases, the current through the motor decreases, which in turn reduces the magnetic field strength and the torque. However, during the initial startup phase, the high current allows for substantial torque generation, making this type of motor particularly suited for applications that require significant starting torque.

In contrast, shunt motors have a relatively constant field strength and provide lower torque at startup compared to series motors. Hybrid motors and stepper motors have different applications that do not prioritize high startup torque in the same way that series motors are designed to do, further supporting the reasoning behind selecting the series motor for situations where high startup torque is essential.