Tech:Electrical/Starter Motor/Principles

Principles

When current flows in a conductor, A magnetic field is generated in the direction shown in the illustration below in accordance with Ampere's rule of the right-hand screw.

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If the conductor is placed between the North and South poles of a permanent magnet, The lines of magnetic force generated by electric current in the conductor and lines of magnetic force from the permanent magnet interfere with each other, Causing the magnetic flux to increase in the bottom of the conductor and to decrease in the top of the conductor. We can think of magnetic flux as a rubber band that has been stretched. Thus, The magnetic flux, The force which is tending to pull in a straight line, Is stronger at the bottom the conductor. The effect of this is that the conductor is subjected to a force which tends to push it upward (Flemming's left-hand rule).

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A loop of wire placed between the poles of a permanent magnet will start to rotate when current is applied. This is because the current flows in the opposite directions on each side of the loop, So equal and opposite forces will be generated by the intersection of the lines of magnetic force of the wire with those of the magnet. As a result, The wire loop will rotate clockwise.

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With the correct timing, Alternately reversing the direction of current flow using a commutator will force the loop to continue rotating in the same direction. The figure below illustrates this, The simplest model of motor operation.