does this AVR allow 1200w or 600w?

thecoolnessrune

Diamond Member
Jun 8, 2005
9,673
583
126
This is the difference between Apparent Power (VA) and Real Power (Watts). It has to do with the fact that systems with power supplies lacking power factor correction put a higher "apparent power" load on a system. For systems with good power factor correction, the difference is often of little significance. A modern Active PFC PSU in a computer will have a Power Factor from about 0.94 at low load, to 0.99x to full load, so the apparent power might be 20-25 watts higher in a system at full load vs. its real power.

Many modern UPS designs provide a large amount of overhead for apparent power, and as such, they get rated that way. The UPS you noted indeed is only rated for 500 Watts of real power, but it has a lot of overhead for Apparent Power.

That large difference between RP and VA is indicative of your standard budget UPS producing a square (or quasi-square wave) output. You'll notice as you get to Line Interactive or Online UPS systems with a Pure Sine Wave output, the numbers start to get very close to each other. You'll also notice they cost many times more.
 

PontiacGTX

Senior member
Oct 16, 2013
383
25
91
This is the difference between Apparent Power (VA) and Real Power (Watts). It has to do with the fact that systems with power supplies lacking power factor correction put a higher "apparent power" load on a system. For systems with good power factor correction, the difference is often of little significance. A modern Active PFC PSU in a computer will have a Power Factor from about 0.94 at low load, to 0.99x to full load, so the apparent power might be 20-25 watts higher in a system at full load vs. its real power.

Many modern UPS designs provide a large amount of overhead for apparent power, and as such, they get rated that way. The UPS you noted indeed is only rated for 500 Watts of real power, but it has a lot of overhead for Apparent Power.

That large difference between RP and VA is indicative of your standard budget UPS producing a square (or quasi-square wave) output. You'll notice as you get to Line Interactive or Online UPS systems with a Pure Sine Wave output, the numbers start to get very close to each other. You'll also notice they cost many times more.
How did you find out that it was 500w?

there is no specification of Curent for 120V unlike others

always is the PFC which shows the difference between the (V)AC and DC(W)?
 
Last edited:

thecoolnessrune

Diamond Member
Jun 8, 2005
9,673
583
126
How did you find out that it was 500w?

there is no specification of Curent for 120V unlike others

There was a link indicating 500 watts from @SKORPI0:


also the Apparent power wouldnt be affected more for the Efficiency of the PSU rather than the PFC? since a 89% efficiency gives a 112% power consumption from wall(AC)

No, not in this case :) PFC is "Power Factor Correction". PF is Power Factor. Power Factor is a measurement ratio between Real, and Apparent Power. Capacitive loads (and PC power supplies often have a lot of capacitors) bring the voltage and current sine waves more and more out of phase with each other. The more out of phase, the more this gap forms a degree of reactive load, which is the out-of-phase area where energy flowing back out approaches the amount of energy flowing back in. This area still consumes energy, but performs no work. That is the apparent power that a UPS must be able to cope with.

When you talk about Efficiency, you're talking about an extension of the resistive load. Your PSU produces 500 watts of DC power, but in exchange, at 90% efficiency it wastes about 50 watts of power. That brings the total resistive power need by your AC supply to 550 Watts. That stacks *onto* the Apparent Power as well. If you're using a net total of 550 watts from your PSU, and it's PFC at that wattage is .99, then your Apparent Power is 555 watts. So to run a 500 Watt PSU full-tilt, you need a UPS that can handle 550 Watts (Real Power), and 555 VA (Apparent Power). As you can see the situation is much better with Active PFC. In the 90s, when PSUs without any sort of PFC were common, you would see Power Factors as low as .6. That means that the above 500 Watt Power Supply, even if we consider it's magical modern efficiency (they weren't back then, they were often 65-70% efficient), that 550 Watt Real Power becomes almost 900 Watts of Apparent Power to a UPS. That's why PFC becomes much more important when using UPS's.
 
  • Like
Reactions: PontiacGTX