Why starter is needed in DC motor?

Why a starter is needed in DC motor?

In a dc motor, there are two winding which acts simultaneously. The rotor winding is energized from a voltage source and the field winding provides the necessary magnetic field. But due to the interaction, another electromotive force is also generated which is opposing the main electromotive force given to the rotor winding. Actually, the effective resistance of a typical armature winding is in few ohms.

Ohm’s law states that, V = IR. If we think deeply we can visualize the necessity of a starter.

Initially, the entire voltage (suppose 230 volts) is applied to the armature. But the armature resistance is very small, suppose 2 ohms. Therefore, I = V/R that is the current through the armature is 230 / 2 ampere that is 115 ampere. Initially, no such electromotive force is generated which can oppose the main voltage. So, this huge amount of current can destroy the armature winding as well as it is also harmful to the other sophisticated parts of that dc motor. To protect the machine from this huge initial current we need to attach a starter with a dc motor. A starter is nothing but a series resistance arrangement with some special security arrangements like low voltage protection and over-voltage protection.

The huge initial current is controlled by the starter itself and after some time the resistance is reduced by changing the starter taps and in the meantime, the main electromotive force is already opposed. In this way, the implementation of a starter can reduce the very high starting current. Especially, in the larger motor, the high starting current can damage the commutator or the windings. So, a starter is needed to insert a current limiting resistor until the motor gets up to a specific speed.