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UPS Wattage? - Page 2

post #11 of 14
Quote:
Originally Posted by this n00b again;14475932 
VA is what we call apparent power.
Watts is what we call True Power.
The ratio of watt to VA is what we call PF.

Generally in the US Most manufacturers assume the PF is 60% in other words .6

This explains why a 1000VA UPS is normally rated around 600 watts.
Of course this varies according to manufacturer.

So lets say you have a Computer that draws 10 Amps from the Mains of 120 Volts.

The input power for the PSU is 120V * 10A = 1200 VA with 1200 *.6= 720 Watts.

Meaning you need to get a UPS that's rated for AT LEAST 1200VA 720 watts.

You want to measure the Computer while it's under load.
And remember a ups at FULL Load will only last around 2-3 Minutes.
So if you needed 1200VA / 720- Watts and had exactly that UPS it would probably provide about 2 minutes of backup time.
If you had a UPS rated at 2400VA / 1440 watts it would last around 6-10 Minutes.

^ of course the above are just rough numbers, actual performance will vary.

Also avoid Cheap UPS as they will not output a PURE sine wave. A PSU with Active PFC looks for a pure sine wave, and cheap consumer marketed UPS' either have a squared or stepped up wave.

So is there any harm in going by max load of your system in wattage, and comparing it to the wattage value listed on these UPS? Essentially skipping this math, or is that faulty thinking? I don't really see a situation where it wouldn't work, if I'm understanding what you wrote right.

If the UPS is rated up to 600w and your max load you put on it is 580w, then it should be a capable UPS by just using those 2 numbers right? Of course the higher the load, or less headroom will generally give you less battery time.

Didn't mean to go OT, but I wanted to know what the VA was all about, also good to know in general tongue.gif
post #12 of 14
In theory you're okay.

If you have a 600 watts PSU and buy a good brand UPS rated at 600 Watts, it will work. But remember to incorporate the monitor and other accessories you may need powered.

Some cheap manufacturers will over market their ratings and the unit won't be able to provide those ratings. So avoid cheap no name brands. Generally If you stick with APC, cyberpower, Tripplite, or such you should be okay.
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post #13 of 14
Quote:
Originally Posted by this n00b again View Post
In theory you're okay.

If you have a 600 watts PSU and buy a good brand UPS rated at 600 Watts, it will work. But remember to incorporate the monitor and other accessories you may need powered.

Some cheap manufacturers will over market their ratings and the unit won't be able to provide those ratings. So avoid cheap no name brands. Generally If you stick with APC, cyberpower, Tripplite, or such you should be okay.
Right, so cheaper brands might fudge the ratio a bit, and have a lower VA:watt to make it seem like they are better, that's about the only time you could miss your mark then?

Also I like to keep headroom with my UPS, so if I determine my entire setup, screen/pc/speakers will draw 500w, then shoot for a 650/700w UPS so there is that ~30% buffer, may allow for upgrade or different components, and also increased battery time during an outage.
post #14 of 14
I will add my self with almost the same doubt, I got my RIG in the sign, and + printer + router + modem + monitor + audio system.

I got all of that in a 0.5 KVA stabilizer could be 1 of the main reasons that make it died?

And now that I need a replacement, how big should it be? 1000 VA would be ok?
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