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Question: What is the difference between full wave and half wave rectifier? Is 18 volts AC - 60 cycles, still 60 cycles?

Answer: It is still 60 cycle power because the width of the pulses are still from the 60 cycle source.  The difference between 60 cycle full wave power and 60 cycle half wave power is half the pulses are missing.
The frequency is measured from the 'zero crossings'.  AC power, when viewed on an oscilloscope is a sine wave.

This goes on forever.

See how it goes up and down?  See how it crosses the zero volts line?
Lets look at the two that go up.  (Near the letters A and B)  If you measure from A to B on 60 cycle power you will find it is 1/60th of a second.  Or 60 cycles per second or 60 Hertz (Hz).

If you rectify this power with a bridge rectifier you get this picture..

Notice how the bottom half of the sine wave got moved into the upper half.
This is full wave DC power.  (And points A and B are still 1/60th of a second apart.)

Half wave has the following picture..

See how every other hump is missing?  Yet if you measure from A to B, you once again get 1/60th of a second.  So this is not 30 cycle power -- it is half wave 60 cycle power.

Of course, all of this discussion assumes you are starting with 60 cycle AC power.

Thorin (First name)
Marty  (Last  name)