When high starting torque is desired, which type of DC motor is best to use?

The choice of a series DC motor for applications requiring high starting torque is well-founded due to its unique operational characteristics. In a series DC motor, the field windings are connected in series with the armature windings. This configuration means that when the motor starts and the armature current is low, the resulting field strength is also low. However, as the motor accelerates and the armature current increases, the field strength increases correspondingly because they are in series. This results in a significant increase in torque as the motor speeds up.

The torque produced by a series motor is proportional to the product of the armature current and the field current; thus, the motor can develop very high starting torque, necessary for applications like cranes or elevators where heavy loads are involved at start-up.

In contrast, other motor types like shunt motors typically exhibit lower starting torque, as they maintain constant field strength regardless of load, which limits their torque response to increasing armature current. Compound motors can provide better starting torque than shunt models, but series motors still outperform them in applications that demand high starting torque. Permanent magnet motors are often less effective in producing high starting torque compared to series motors since their field strength does not vary with the load in the