Generators
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Basic idea
• Let’s imagine we have our simple electric motor,
made from one rectangular loop of wire.
• Instead of putting electricity through the coil, we
rotate the coil.
• Applying the RH palm rule, we find that the
electrons in the loop experience a force.
• A current starts to flow in the loop and is used
to power an external circuit.
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AC generators
AC generators are the most simple type, they use
a slip ring commutator:
The slip ring commutator maintains a constant
connection between the loop and external circuit
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AC generators cont...
Because of the slip ring commutator, we get a
reversing current. Every time the coil rotates by
180º, the current changes direction, so we get an
alternating current (AC)
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DC generators
DC generators have one main difference to AC
generators, they use a split ring commutator:
The split ring commutator reverses the connection to
the external circuit every 180º (same as DC motor).
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DC generators cont...
The result is a current which is always positive, but
varies in strength:
Note that we could put lots of coils on the armature
at different angles, and then add them together.
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Solenoids
It is possible to look at a solenoid (electromagnet) and
determine which end is North and another is South.
One way is to consider the letters N and S.
N
S
The arrows indicate the direction of conventional
current when viewed from that end.
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Questions
1. What is the main difference between an AC
generator and a DC generator?
2. Can you see any differences between a DC motor
and a DC generator?
3. List components which you think are common to
both generators and motors (eg. armature).
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