What is the maximum armature current in a series DC motor at starting condition?

In a series DC motor, the armature winding is connected in series with the field winding, which means that the same current flows through both. At startup, the rotor is stationary, and thus the back EMF (electromotive force) generated is negligible because back EMF is proportional to the speed of the motor.

In this condition, the armature current is limited primarily by the resistance of the armature winding and the supply voltage. Since there is little to no back EMF to oppose the applied voltage, the armature current can rise significantly. As a general rule, the starting current can reach two to three times the full load current; however, it is commonly accepted that at starting, the armature current can be approximately 150% to 200% of the full load current in a series DC motor.

Choosing the value of 150% as appropriate is based on common practice and can vary slightly depending on the specific motor design and application. Under normal operating conditions, motors will usually draw a high starting current due to low back EMF, and in this case, the current could reach 150% of the full load value when taking into account potential practical limits.

Thus, selecting 150% of the full load