Example of DC Motors:

If the overall load current of the motor mentioned previously is 50 amps, and it is desired to limit starting current to 125% of this value, find the required resistance that must be added in series with the armature.

R_s = E_t/I_s -R_a

R_s = 260 VDC/ 125 %( 50 amps) - 0.4?

R_s = 3.76?

The starting resistors are used in a DC motor through placing them in the beginning circuit of the motor controller which is used to begin the DC motor. Starting resistors are generally of variable resistances, along with the value of resistance within the circuit at any time being either manually or may be automatically controlled. A maximum amount of resistance will always be inserted when the motor is first started.  Since the speed of the motor increases, counter EMF will start to increase, decreasing armature current.  The starting resistors might then be cut out, in successive steps till the motor reaches full running speed.