What does 4000 VA mean?

I have traveled a large part of the world and only in the USA are generators and inverters badged with WATTS. Everywhere else they are badged in VA. I believe it is purely a marketing ploy to attach a bigger number.

Go with road-runner's answer, I see no error. No phase shift in DC, so no need to worry about pf on the DC side.

This thread is interesting but it gave me a headache. Still, I take away the following:

VA doesn't mean something with rated wattage will run on advertised/rated VA.

VA is advertised instead of the more useful Wattage spec because VA is a bigger number and bigger sells better.

I'll buy a bigger UPS than I thought I needed.

If GOD wanted me messing with Electrons, HE'd've made them big enough to see.

Road Runner,
Maybe it is because small UPS equipment is usually MSW inverters and larger ones like in server cabinets have PSW inverters. Lots of harmonic distortion in MSW inverters and that is wasted power.

Hi RCMAN46,

Well, my kill-a-watt meter says 723 watts running hard. I never see 40 amps from it (37 max), and I never see 14.4 until amperage drops considerably lower than the 37 amps.

I was trying to calculate input watts which is why I divided the 0.7 into the watts of output.

RCMAN46 wrote:

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

.



The correct answer is 40 X 14.4 X 0.7 = 403.2 watts.

Is this why my PD says 1300 watts but comes with a fancy schmancy 20amp plug? I have been puzzling over that one.

As opposed to my 1500 watt oil heater that plugs in with a lamp cord (which gets hot and is clearly undersized, but still...)

road-runner wrote:

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?

40 amps * 14.4 volts = 576 watts DC output
576 watts DC output / 0.8 converter efficiency = 720 watts AC input needed
720 watts / 0.7 PF = 1029 VA AC input needed

Wonder how many different answers you'll get? I'm certainly not beyond making errors.

actually pretty close to actual current draw from the line for this unit. I've measured it on mine with the kilowatt meter and at full output and came up with VA close to your calculation. IIRC it was slightly under 1000VA, but the PD delivers the 40A at nearer 13V or less and tapers as the voltage rises and in most cases won't be delivering 40A at 14V, by then it is down in the 10s of amps.

and in the rv world there are quite a few items with reactive loads that draw way more current than the power rating indicates. Microwave ovens, converters/chargers, are two big examples. AC and most induction motors typically has a PF around .9, then there are all the wall warts, and TV's. etc.

and most generators are really rated in VA not watts, even though they are advertized in watts, (honda's, yamaha's etc.) there are some generators that can handle pretty high reactive loads.

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?

40 amps * 14.4 volts = 576 watts DC output
576 watts DC output / 0.8 converter efficiency = 720 watts AC input needed
720 watts / 0.7 PF = 1029 VA AC input needed

Wonder how many different answers you'll get? I'm certainly not beyond making errors.

smkettner wrote:

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.

OK, I found a web site that says the standard for small UPSs is that the watt rating is 60% of the VA rating. I still think it's strange, but it is what it is. I've never noticed a generator or inverter rated like that, and I "assume" the UPS contains an inverter. Maybe it has something to do with the battery or heat dissipation. For larger UPSs (whatever "large" means), it says the the watt and VA ratings are generally the same.

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

.



The correct answer is 40 X 14.4 X 0.7 = 403.2 watts.