Answer
Oct 01, 2025 - 01:44 PM
VA and Watts are only the same if you have a resistive load like a heater. Loads like motors are inductive loads. With inductive loads the load itself reacts with the power source. With each cycle of current a magnetic field is set up within the motor coil windings. As the magnetic field starts up there is an inrush of current, once the field is established nothing much happens, and then at the end of the cycle there is an outrush of current. The effect has a time lag and the outrush of current fights the incoming current for the next cycle and thus reduces the total amount of power available to do the work. This effect is called Power Factor and can be defined as the ratio of the real power absorbed by the load and available to do work to the apparent power flowing in the circuit. With a typical inductive load the Power Factor might be in the region of 0.8
The Power Factor effect means that with resistive loads the formula Watts = Volts x Amps is true but with inductive loads the Watts is a lesser amount, Volts x Amps x Power Factor. That's why you will see inverter manufacturers quote their rated output in VA - its because it is the higher number and so looks better on the spec sheet.
The rated output for our most popular inverter charger, the Victron MultiPlus-II 12/3000 is 3000 VA but for inductive loads it is rated at 2400 Watts. This represents a Power Factor of 0.8 since 3000 VA x 0.8 = 2400 Watts
The Power Factor effect means that with resistive loads the formula Watts = Volts x Amps is true but with inductive loads the Watts is a lesser amount, Volts x Amps x Power Factor. That's why you will see inverter manufacturers quote their rated output in VA - its because it is the higher number and so looks better on the spec sheet.
The rated output for our most popular inverter charger, the Victron MultiPlus-II 12/3000 is 3000 VA but for inductive loads it is rated at 2400 Watts. This represents a Power Factor of 0.8 since 3000 VA x 0.8 = 2400 Watts
