Power factors

Interestingly-- VA (AC RMS voltage and current measurements) is important for sizing wiring, transformers, AC Inverter, Generator "Head" (the alternator), and circuit breakers+fuses.

VA is not really important for sizing the battery bank. The actual power draw from the DC Battery bus really is driven (for the most part) by AC Watts (VA*PF=Watts).

VA combines both "True Power" (Watts) and purely "Reactive" Power (VA-Reactive) into something called Apparent Power (VA).

http://www.allaboutcircuits.com/vol_2/chpt_11/2.html

• REVIEW:
• Power dissipated by a load is referred to as true power. True power is symbolized by the letter P and is measured in the unit of Watts (W).
• Power merely absorbed and returned in load due to its reactive properties is referred to as reactive power. Reactive power is symbolized by the letter Q and is measured in the unit of Volt-Amps-Reactive (VAR).
• Total power in an AC circuit, both dissipated and absorbed/returned is referred to as apparent power. Apparent power is symbolized by the letter S and is measured in the unit of Volt-Amps (VA).
• These three types of power are trigonometrically related to one another. In a right triangle, P = adjacent length, Q = opposite length, and S = hypotenuse length. The opposite angle is equal to the circuit's impedance (Z) phase angle.

All of the "math" associated with AC Power is actually a very complex subject. It turns out that the "Reactive Power" does no "work", therefore does not draw any energy from the battery bank (other than various "losses" in the circuitry). Sort of like a swinging pendulum, you see it moving back and forth, but it does not take any energy to make the motion once you get it started (other than friction losses).

Connect the pendulum to a spoon to mix some liquid--Then you have to add energy to the pendulum to mix the liquid--Or it will quickly stop. That energy to mix the liquid is the "power" from the battery bank.

-Bill