As we continue our column-by-column review of the single-phase motor specifications on page 13 of the AIM Manual, this week we find ourselves at the column marked PF, or Power Factor. If you read the recent post, Most Missed Question, you’re already a step ahead.
In an AC (alternating current) system, voltage and current are not completely in phase. That is, their peaks and valleys don’t line up in perfect phase.This difference in phase between the voltage and the current is the power factor. As it turns out, the more in phase the voltage and current are, the higher the power factor. As a matter of fact, in the perfect world picture, the power factor is 100% (expressed as 1.0). In the real world picture, the power factor is around 75% (expressed as 0.75).
Note that because the voltage and current can never be more than 100% in phase, power factor can never be greater than 1.0. Conversely, it can also never be smaller than 0.
So what? Why does power factor matter?
Power factor is important because it affects our motor’s power consumption. Back in school, you probably learned that
Volts x Amps = Watts (Power)
While that is true in a DC (direct current) system, an AC system never gets quite as much power out of a system as is put into it. That lag between volts and amps we discussed above is the reason for that. Therefore, when calculating power consumption for an AC system, the equation looks like this:
Volts x Amps x Power Factor = Watts (Power)
By the way, you may also note that the more efficient the motor, the higher the power factor.
Hopefully by now you’ve realized that everything on this page works together. Next week we’ll move to the right to the Locked Rotor Amps column as we get closer to wrapping up the series.