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Question about UPS max wattage

T

The111

n00b
Joined
May 4, 2009
Messages
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I have never owned a UPS and I am thinking about getting one, not so much for the traditional reasons of "saving my work" if the power goes out... but more because I have been doing a lot of firmware flashing lately... both my BIOS and my SSD as they keep releasing revisions, and I thought to myself how much it would suck if the power went out for a minute while doing either of these things.

So, my PC idles at around 200W and CAN max out at 600W but usually doesn't go above 400W in normal operations. So if I get a UPS that is rated for 300W or so... does that 300W number matter at all times, even when the house power is not out? I.e. a "300W UPS" can't transmit 600W, even when plugged into the wall? Or does it only apply when running off of the battery? Does this Q make sense?

Thanks!
 
The power rating generally matters only when running off the battery, although line interactive UPSes do perform some of their own voltage regulation a lot of the time and exceeding the power rating would place the components in charge of that under more of a load than they would normally be under. However, you should be good with a UPS rated for lower than the max consumption of your PC as long as you aren't so unlucky that the power goes out while you're in the middle of a gaming session.
 
i would never buy a UPS thats smaller than the power supply. it doesnt cost that much more for a decently sized one.
 
If your PC components use 600W, the UPS must provide more than 600W to your PC due to the less-than-100% efficiency of your PSU. Let's say your PSU has an 85% efficiency. Then, the UPS must provide 706W.

A power of 706W corresponds to a current of 706W / 120V = 5.8A (I am assuming your power line is at 120V).
This 5.8A current must pass through a switch in a stand-by UPS.

The manufacturer of a 300W UPS does anything possible to minimize cost. A switch that can carry 5.8A is more expensive than a switch that can only carry 3A.

I would never use a 300W UPS if my load is more than 300W even if I never lose power.
 
It gets worse when you consider power factor as well, since the UPS must be able to handle the apparent power, not the real power. Most PC PSUs w/o active PFC, and lightly loaded PFC supplies will probably have a power factor of 0.75 or worse.

I would not recommend using an under-rated UPS. At best it will annoy you with an overload alarm periodically (most will alarm based on overload even when running on line power). At worst it will shut off the load periodically, or when on battery power, and you've just wasted your money.

Are you really pulling 600W from the wall? That seems excessive, even for an enthusiast rig, but if you're including monitors as well I guess it could be reasonable. I'd get a 1000VA unit if that's the case.
 
Why not build your own? Ill get pics up later.

But why not get something better for less money. Go to walmart and buy a deep cycle battery then go to a local truck stop and buy a large inverter I personally bought a 1800W inverter and wire it to that battery and with my laptop "theoretically" i get 13hrs. of life.

Heres where your choice comes in you can either by a cheap trickle charger or go high tech and buy a small solar array for 249$ PM me if you want full directions and/or all the links for mine.
 
keenan said:
Are you really pulling 600W from the wall? That seems excessive, even for an enthusiast rig, but if you're including monitors as well I guess it could be reasonable. I'd get a 1000VA unit if that's the case.
Click to expand...

In normal conditions, no I never pull that much. But using OCCT PSU tester (which puts CPU and GPU to 100%) I managed to reach 570W.

920 @ 3.8GHz
ATI 4890
4 HDD's
8 LED fans

I idle at 220W... in my normal use I never break 400W. But the OCCT app showed that I CAN approach 600W.

And no, none of that is including monitors.

Thanks for all the input, everybody.
 
Cory70 said:
Why not build your own? Ill get pics up later.

But why not get something better for less money. Go to walmart and buy a deep cycle battery then go to a local truck stop and buy a large inverter I personally bought a 1800W inverter and wire it to that battery and with my laptop "theoretically" i get 13hrs. of life.

Heres where your choice comes in you can either by a cheap trickle charger or go high tech and buy a small solar array for 249$ PM me if you want full directions and/or all the links for mine.
Click to expand...

Sounds interesting, but I build too much stuff myself. See example:

http://www.matthoover.com/gallery/skydiving-videos/Phyxius_Project-HQ.html

I think for this one I'll just pay the pros.
 
The111 said:
Sounds interesting, but I build too much stuff myself. See example:

http://www.matthoover.com/gallery/skydiving-videos/Phyxius_Project-HQ.html

I think for this one I'll just pay the pros.
Click to expand...

Pretty impressive I must say just offering the thought. It is very easy once you get down to it i think i still have all the links from when i built mine and its mindblowing the money you can save from it. However when i got into the solar recharging thats when the price/usabilty thing became an issue but overall i must say i am very pleased
 
keenan said:
It gets worse when you consider power factor as well, since the UPS must be able to handle the apparent power, not the real power. Most PC PSUs w/o active PFC, and lightly loaded PFC supplies will probably have a power factor of 0.75 or worse.

I would not recommend using an under-rated UPS. At best it will annoy you with an overload alarm periodically (most will alarm based on overload even when running on line power). At worst it will shut off the load periodically, or when on battery power, and you've just wasted your money.

Are you really pulling 600W from the wall? That seems excessive, even for an enthusiast rig, but if you're including monitors as well I guess it could be reasonable. I'd get a 1000VA unit if that's the case.
Click to expand...

I would almost agree with you, but every UPS I've ever seen has the wattage rating based on an assumed load power factor of 0.6-0.7, so a 600W UPS for a PC consuming 600W max would actually leave significant margin.
 
PM650 said:
I would almost agree with you, but every UPS I've ever seen has the wattage rating based on an assumed load power factor of 0.6-0.7, so a 600W UPS for a PC consuming 600W max would actually leave significant margin.
Click to expand...

Yeah, that's true, I was just assuming (perhaps incorrectly), that the OP was confusing W and VA, since UPS watt ratings are rarely obvious, and sometimes not quoted at all (since it's basically just VA * some random power factor).
 
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