UPS va/watt ratings

Status
Not open for further replies.

gman2003

Member
Location
Florida
I have noticed on smaller UPS systems (for computers, etc...)there are dual ratings, such as 600va/360watts. What does each rating represent on these systems. Isn't va another way of expressing watts? Thanks.
 

Ed MacLaren

Senior Member
Re: UPS va/watt ratings

You could also say that VA (apparent power) is the vector sum of the Watts (true power) and the Vars (reactive power) drawn by an inductive or capacitive load.

Power factor represents the percentage of the volt-amps that is watts (real power, or energy actually converted by the load).



Ed

[ May 17, 2003, 12:37 PM: Message edited by: Ed MacLaren ]
 

gman2003

Member
Location
Florida
Re: UPS va/watt ratings

Thanks for the info. Ron & Ed. So then the second number of the UPS rating is the maximum load that the UPS will supply (360 watts) and the first number is the total power that the UPS consumes including the load served by the UPS(600va). Is that correct? Thanks again.
 

ronaldrc

Senior Member
Location
Tennessee
Re: UPS va/watt ratings

Ed correct me here if I'm wrong but the 600 va would be 600 watt if it where only a resistive load. And I think 360 va wattage rating with the power factor being at its maximum.

The true wattage rating would be dependent on the true power.

Ronald :)
 

Ed MacLaren

Senior Member
Re: UPS va/watt ratings

So then the second number of the UPS rating is the maximum load that the UPS will supply (360 watts) and the first number is the total power that the UPS consumes including the load served by the UPS(600va). Is that correct?
Not exactly. Both the 600 va and 360 w are output ratings, in other words, the load that the UPS will handle.

Most UPS units are designed to operate electronic equipment that usually includes a switch-mode power supply.

The switch-mode power supply, when viewed as a load, is neither capacitive nor inductive, but non-linear. A switch-mode power supply draws current in short pulses that are not in phase with the line voltage.
This can cause the Power Factor to be less than 100% in the same way that an inductive (motor) load can.
The volt-amps (product of RMS volts x RMS amps) is considerable higher than the watts (real power consumed), and thus the Power Factor is less than 100%, typically around 60 to 70%.

Many UPS manufacturers assume the load Power Factor to be 60% for lower rated units, and 80% for their larger rated units.

600 va X .6 = 360 watts

This is a difficult subject to try to explain in a forum such as this. It takes my students a week to understand it. :)

Ed
 

brian john

Senior Member
Location
Leesburg, VA
Re: UPS va/watt ratings

What this rating means that the UPS can supply a load with a power factor (pf) of 1 (pure resistive load of 600 VA or at 120 volts the UPS will support 5 amp load. Or the UPS can support an inductive load of 360 watts with a pf of .6 (low pf) or a 3-amp load.
 

Ed MacLaren

Senior Member
Re: UPS va/watt ratings

Or the UPS can support an inductive load of 360 watts with a pf of .6 (low pf) or a 3-amp load.
A 120 volt, 360 watt load with a power factor of .6 (60%) will still draw 5 amps.

W = ExIxPF I = W/ExPF I = 360/120x.6


Ed
 
Status
Not open for further replies.
Top