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DC generators

 DC generators

A simple DC motor consists of a very similar arrangement

to that of the DC generator that we met earlier.

magnetic field. Also, from the relationship F _ BIl it can be seen that the force used to provide the torque

in a motor is directly proportional to the size of the magnetic flux, B .

  Instead of using a permanent magnet to produce this flux, in a real motor, an electromagnet

is used. Here an electromagnetic field is set up using the solenoid principle


 A long length of conductor is wound into a coil consisting of many turns and a current passed through it. This

arrangement constitutes a field winding and each of the turns in the field winding assists each of the other

turns in order to produce a strong magnetic field.

  As in the case of the DC generator, this field may be intensified by inserting a ferromagnetic core

inside the coil.

 Once the current is applied to the conducting coil, the core is magnetized and all the time the current is on it acts in combination with the coil to produce a permanent magnet, having its own N–S poles.


Now returning to the simple motor, we know that when current is supplied to the rotating armature ( rotor ) a torque is produced.

In order to produce continuous rotary motion, this torque (turning moment) must always act in the same



Therefore, the current in each of the armature conductors must be reversed as the conductor passes

between the north and south magnetic field poles.


The commutator acts as a rotating switch, reversing the current in each armature conductor at the appropriate

time to achieve this continuous rotary motion.

Without the presence of a commutator in a DC motor, only a half turn of movement is possible!

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