Answer to Question #93756 in Electrical Engineering for Shawn Dickson

Question

DC series motor has 3.5 ohm resistance in starter, no load current of 0.3 amps and a full load current of 2 amps rotating at 1800 RPM find speed at full load?

Answer 1

The speed of the motor is directly proportional to its back EMF:

Here - supply voltage on the terminals of the motor.

For both cases (no-load and full-load) we have:

Divide one by another:

In this problem we assumed that "3.5 ohm resistance in starter" is the total resistance of stator and armature.