Many people are familar with DC motors. If you have ever had a electric
toy train or car as a child, you may know how a DC motor works. If you
were like me you probably took one apart and couldn't put it back together.
Usually the brush springs get lost.
The stator is the stationary outside part of a motor. The rotor
is the inner part which rotates. In the motor animations,
represents a magnet or winding with a north polarization, while
represents a magnet or winding with a south polariztion. Opposite, red
and green, polarities attract.
The stator of a permanent magnet dc motor is composed of two or more
permanent magnet pole peices. The rotor is composed of windings which
are connected to a mechanical commutator. In this case the rotor has three
pole pairs. The opposite polarities of the energized winding and the stator
magnet attract and the rotor will rotate until it is aligned with the
stator. Just as the rotor reaches alignment, the brushes move across the
commutator contacts and energize the next winding. In the animation the
commutator contacts are brown and the brushes are dark grey. A yellow
spark shows when the brushes switch to the next winding.
Notice that the comutator is staggered from the rotor poles. If the connections
of a dc motor are reversed the motor will change directions. Though it
will not always work as well in both directions.
This is a permanent magnet dc motor. Two other types of dc motors are
series wound and shunt wound dc motors. These motors also
use a similar rotor with brushes and a commutator. However, the stator
uses windings instead of permanent magnets. The basic principle is still
the same. A series wound dc motor has the stator windings in series with
the rotor. A shunt wound dc motor has the stator windings in parallel
with the rotor winding. The series wound motor is more common. A series
wound motor is also called a universal motor. It is universal
in the sense that it will run equally well using either an ac or a dc
voltage source. Reversing the polarity of both the stator and the rotor
cancel out. Thus the motor will always rotate the same direction irregardless
of the voltage polarity. A universal motor is in a sense an ac motor in
that it will operate from an ac power source. I prefer the term universal
motor to avoid confusion with ac induction motors.