The frequency of an alternator is the number of cycles of AC produced per second. The frequency is determined by the number of poles and the speed of rotation.

The formula for calculating the frequency of an alternator is:

Frequency = PN / 120`

Where:

P = Number of poles

N = Speed of rotation in revolutions per second

120 = Constant

For example, an alternator with 4 poles rotating at 1000 revolutions per minute (rpm) will have a frequency of: