Electronics Principles V11

Clive W. Humphris

ELECTRICAL MACHINES: A Simple AC EMF Generator.  


A simple generator can be constructed by rotating a coil of one turn between the poles of two permanent opposing magnets, alternatively this could be the ends of a horseshoe magnet. As the coil is rotated, (called an armature) around the X - X axis, an EMF will be induced which appears across the load resistor 'Rload'.

The example shows two conductors the active length is that which is under the influence of the magnetic flux. Note the connection to the slip rings which develop an AC waveform.

When the two conductors in the diagram are vertical the induced EMF is zero. As they are rotated clockwise a maximum positive EMF will result as the conductor cuts the magnetic flux. There is a sinusoidal fall in EMF as the second reversed vertical position is approached which then increases in the negative direction, thereby completing one revolution.

The output EMF and the frequency will depend largely on the speed of rotation (velocity) as the flux density and dimensions of the coil will remain fixed in a practical application.


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