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Beer & Power Factor – Short #144

Bryan describes the tricky concept of power factor and why we should care about it. He also compares power factor to a beer mug to make the topic easier to understand.

Power is often represented on a sine wave, which is a curvy line that marks the state of electrical energy at different points on a circle. Power gets stronger and weaker, and it goes above and below the neutral line depending on the excess or deficit of electrons.

Unity power factor refers to a power factor of 1, indicating that voltage and amperage are perfectly balanced; there is no lag. However, an inductance (a form of resistance) opposes the current and causes an imbalance between current and voltage. Power loss or quality refers to the difference between the input and output power that results.

Apparent power refers to volt-amps, which we’d traditionally consider to be the wattage; however, in an inductive load, the true or real power (wattage) accounts for that power loss and comes from volts x amps x power factor. We can imagine power factor as a mug of beer: apparent power (VA) is the entire mug, the foam is reactive power (wasted), and the beer itself is real power. The power company only charges for the real power, not the reactive power. However, a power factor closer to unity can help prevent motor windings or wires from overheating.

To get closer to unity power factor, we need to make sure we have a run capacitor of the correct size. You can measure power factor with a power quality meter.

Bryan also covers:

  • Voltage and current
  • Root mean square
  • Inductive reactance
  • Capacitance and how capacitors work
  • Transformer VA ratings

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Comments

Chris Mohalley - Regal Rexnord
Chris Mohalley - Regal Rexnord
8/28/22 at 08:49 AM

This is a great topic, and one that provides even more insight to the ECM motors that are now common place in residential HVAC equipment. I am often asked why an ECM that is supposed to be more efficient than a PSC draws equal to or even more amperage than a PSC. Power Factor (PF) is the reason why. ECM operate at a PF of approximately .6-.7 PF whereas PSC operate at a PF of approximately .9 PF. When you add PF to the equation (Volts x Amps x PF = Watts) it starts to make sense that ECM can be more efficient at the same or even higher amperage than a PSC.

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