A detailed webpage version of the video is given below.
Let’s first start with the simplest DC motor possible. It looks like as shown in the Fig.1. The stator is a permanent magnet and provides a constant magnetic field. The armature, which is the rotating part, is a simple coil.
Improving the Torque action
But if you observe the torque action on the coil closely, you will notice that, when the coil is nearly perpendicular to the magnetic flux, the torque action nears zero.
Use of ElectromagnetA permanent magnet stator pole is used only for very small DC motors. Most often an electromagnet is used; the field coil of the electromagnet is powered from the same DC source.
Shunt & Series Motors
The field coils can be connected to the rotor windings in 2 different ways; parallel or series. This results into 2 different kinds of DC motor constructions; a shunt and a series motors.
The shunt motor has a low starting torque, but it is able to run almost at a constant speed, irrespective of the load acting on the motor. This is an attractive operation characteristic of a shunt wound motor, the nature of the speed-torque variation is shown in the Fig. 10.
The concept of Back E.M.F
Unlike the other electrical machines D.C motors exhibit a unique characteristic; the production of back EMF . A rotating loop in magnetic field will produce an EMF according to the principle of electromagnetic induction.
One of the interesting variations of the DC motor is a universal motor, which is capable to run under both A.C and D.C power sources. We will go through its working and operational features in a separate article.