What does 4000 VA mean?

The term Volt-amps is used to take into consideration the demands of an inductive load. This is common in commercial/industrial line service.
For further info Google "The rule of ELI".

road-runner wrote:

VA does not always equal watts. I just bought an uninterruptible power supply for my computer equipment. It is rated 750 VA/450 watts.

I find that really strange. If you have a load that's 600 VA and also 600 watts, which limit applies?

The lower limit just like towing.

VA does not always equal watts. I just bought an uninterruptible power supply for my computer equipment. It is rated 750 VA/450 watts.

I find that really strange. If you have a load that's 600 VA and also 600 watts, which limit applies?

VA does not always equal watts. I just bought an uninterruptible power supply for my computer equipment. It is rated 750 VA/450 watts.

Technically, VA is the RMS voltage times the RMS amps. When the voltage and current are the same waveform and are perfectly in phase, the power factor is 1, and VA = watts. When the voltage and current waveforms aren't identical and in phase, the resistive losses in the generating and transmission apparatus are higher. Some of the power that would ideally go to the load instead goes up as heat. The inverter and generator manufacturers want you to think that their equipment is rated in watts, but when you get to the real specs, the power is rated in VA. The consuming device manufacturers want you to know how many watts the device consumes, and want to keep quiet about the VA. Power factor correction in motors is fairly easy with passive components. In a switching power supply, active circuitry is required for correction, which is probably why it's not more widespread as of yet. Don't know if it will help or not, here are a few reads that might help connect a dot or two before they go off into the highly technical weeds:

http://www.aptsources.com/resources/pdf/PFC.pdf
http://www.aptsources.com/resources/pdf/Power%20Factor%20V%20Crest%20Factor.pdf
http://www.aptsources.com/resources/pdf/True%20vs.%20Apparent%20Power.pdf

pianotuna wrote:


I do know the answer for the generator which in my case is 2800 VA.

Amps = 2800VA / 120V (assuming that the generator is 120V)
Amps = 23.33 ideally

pianotuna wrote:
In the case of my PD 40 amp converter PF is 0.7 so 40 amps x 14.4 volts / 0.7 = 823 watts.

Is that correct?

Mandalay Parr wrote:
Actually VA times the power factor(pf) = Watts.
For practical purposes you can consider that watts is basically = to VAs

Since you converted the number using PF I believe it would be 823VA.
Wattage might be lower but the available power must be 823.

Don't forget conversion losses.

Xantrex PF whitepaper

In the case of my PD 40 amp converter PF is 0.7 so 40 amps x 14.4 volts / 0.7 = 823 watts.

Is that correct?

Mandalay Parr wrote:
Actually VA times the power factor(pf) = Watts.
For practical purposes you can consider that watts is basically = to VAs

Hi 2oldman,

I did look it up. I don't understand the answer. Which is why I asked here.

I do know the answer for the generator which in my case is 2800 VA.

I guess I will have to break down and buy a kill-a-watt that does have a PF button. Mine is too early to have that feature.

2oldman wrote:
Ahh.. I'm sure I could look that up.

As Roger said, volt-amps, or "apparent power". It's the RMS voltage multiplied by the RMS current.

It's not quite exactly the same as watts (actual power), but much of the time the differences are not worth worrying about as a practical matter for the sorts of things RVers deal with. When the power factor is poor (less than one), the apparent power will be greater than the actual power. It cannot ever be less than the actual power, however.