The easy way of looking at
power factor is that the
phase alignment between when peak
current draw and peak
voltage do not match.
The best example is cheap
HID fixtures, such as the 70w HPS fixtures on sale at Home Depot and other places. They should be drawing 70 watts plus a few extra watts for what is wasted on the
ballast. About 0.58 amps at 120 volts, right? Nope! Try over an amp! These fixtures have a
power factor of 47 (or .47 depending on if real or %)
If you multiply the
current draw and the supply
voltage you come up with a figure MUCH higher than 70 watts. What is happening is that because of the reactor
ballast, the
current draw peaks -after- the
line voltage has peaked. As the
fixture is collecting it's energy at a
point lagging behind peak
voltage, it's
current draw is much higher than you would expect. This can be corrected with a
power factor correction
capacitor. (Required on all indoor type fixtures, or more specifically, low
power factor is not allowed.)
For the most part, movers, even the cheap ones, do include the PF cap.
Switch mode supplies also have a
bit of a problem, but no where nears as dramatic. The supplies do draw peak
current at peak
voltage, but draw almost no
current outside of the peak region! That is why in the computer world, battery backup systems are rated in VA. This gets confusing as one would think V time A = watts, right? Nope. In this case they are specing maximum
current times maximum
voltage, which is how a
switch mode supply draws
power. The maximum wattage output of the battery backups is actually derated from the VA
rating. (Note the use of the word "maximum", not peak)