UPS, which one?

I wouldn't worry about calculating power factor (it's never 1, more properly called unity, even on resistive loads, since some reactance always manages to get introduced); it's rarely enough of an issue to be of concern for anyone other than the power company (I've handled the capacitor banks used by power companies to correct power factor; some of those puppies are freaking huge). The VA rating of a UPS is normally used only to specify how much power is drawn at the outlet the UPS is plugged into and that will always be the same, no matter what power factor the UPS is rated at. That's why I didn't want to confuse the OP with it. Also, UPS manufacturers love to tout the input VA since it makes the UPS look more powerful than the output wattage would. Dividing the VA by the input voltage (normally, 120v in the U.S.) to get the amperage needed at the wall outlet is simple enough without having to mess around with charts.

That quote from Tripp-Lite must have been for industrial UPSes since I've never seen a consumer UPS that was rated in VA for both the input and the output (btw, when quoting something like that, it's standard practice to link the source). As you sorta pointed out, power factor is not a concern for computer gear so why worry about? It's always a good idea to slightly oversize equipment (say, 5-10%) to provide a safety margin and it doesn't hurt to oversize even more to allow for future expansion (such as I did with my UPS; I just pulled the trigger on three monitors that will use 50% more juice than my present single monitor). Of course, oversizing also allows for more runtime during an outage.

One more exception I take to the Tripp-Lite directions I already pointed out earlier; just because a computer PSU is rated for a certain wattage doesn't mean it will ever draw that much. If one has a PSU that will never draw more than a fraction of its rating, there is no need to shell out shekels for a UPS any bigger than will actually be needed.

@Lady Fitzgerald,

I have to try to work-out what you wrote. So you say pure sine wave is needed? What is this PFC thing? These are the models recommended to me http://www.cyberpowersystems.com/products/ups-systems/pfc-sinewave-series/CP1500PFCLCD.html APC Power-Saving Back-UPS Pro 1300. Is it true APC does not support pure sine wave?
TY for all the info :)

@Anak,

Actually I was hoping to order through newegg as soon as I calculate what I need.

TY :)

Been researching a bit in the last couple of hours and saw several references to the "pure sine wave" versus "stepped" or "simulated" sine wave outputs.

Seems the possible incompatibility issue is related to the "Active PFC" feature of most modern power supplies.


I did find a test of my Seasonic KM-560 Gold PSU at Xbit Labs, saying that a mid-level ($170) APC Smart UPS SC 620 UPS would shut down when switching to batteries when the Seasonic was loaded to 300 watts, even though its slightly higher wattage sister Seasonic models had no such problems. This UPS does NOT output a pure sine wave. The review did not say how the KM-560 behaved at loads below 300 watts. My PC cannot use more than about 170 watts, so I dunno if that would be a problem for me.

Here's a quote I found from Cyberpower tech support, from March of this year. A Cyberpower user had contacted them regarding a 825 AVR Cyberpower unit that would not transition to battery power at loads above a 125 watt idle. The PC in question typically used 200 plus under a normal load.

Here's the quote. Not sure what to make of it as I don't use a UPS at all. It seems few UPS under $200 output a pure sine wave.

"Your computer uses a power supply that utilizes Active Power Factor Correction (Active PFC) to improve efficiency. Power supplies with active PFC may experience incompatibility problems with a UPS that does not provide pure sine wave power output when the power supply switches from AC power to UPS battery power. As a result, when a computer system using a power supply with active PFC is attached to a non-sine wave UPS, the system may shut down when it switches to battery power. Also, if the power supply continues to operate, it may produce a humming or high pitch noise while running on battery. This humming indicates the power supply is operating beyond specified tolerances and may damage the power supply.

For computer systems using power supplies with Active PFC, we recommend that you protect your equipment with a UPS that provides sine wave output. We make a full line of Pure Sine UPS models that meet most technical and pricing requirements.

You can view our Pure Sinewave models on our site via the following links for more information:"
PFC Sinewave Series
Smart App Sinewave
Smart App Online

Here is a quote from APC on this issue:

"A computer’s power supply may also be subjected to a period of inrush, while the UPS is changing state (switching from utility power to battery power and back). Back-UPS and Smart-UPS SCs may experience up to an 8ms transfer time during this period.

This is just long enough to remove power from the PFC power supply, resulting in a momentary inrush of the PFC. Once the UPS changes states from "Online" (passing utility power) to "Onbattery" (passing power from the UPS's internal battery), the momentary inrush from the attached equipment subjects the UPS to the On battery power supply’s maximum power draw, resulting in a potential Overload condition or dropped load.

An Energy Star 4.0 compliant power supply has to be more than 80% efficient. For example, if a attached power supply is delivering 600W output power, its ‘input’ power can be as high as 750W.

This ‘input’ power should be the basis for sizing the UPS, so as not to Overload the UPS. This can be calculated by taking the PFC power supply’s rated output power and multiplying it by 1.25."

Again, I have no idea if any of this is true. This is just some of what I have found in the last couple of hours.

GRB70 said:

@Lady Fitzgerald,

I have to try to work-out what you wrote. So you say pure sine wave is needed? What is this PFC thing? These are the models recommended to me http://www.cyberpowersystems.com/products/ups-systems/pfc-sinewave-series/CP1500PFCLCD.html APC Power-Saving Back-UPS Pro 1300. Is it true APC does not support pure sine wave?
TY for all the info :)

@Anak,

Actually I was hoping to order through newegg as soon as I calculate what I need.

TY :)

The Cyberpower unit you linked appears to be a nice one. The only question is if it is big enough for your needs or not and only you can determine that. From looking at your specs, my guess is it should be fine. The UPS is rated for 11 minutes runtime at a 450W load. Unless you are running umpteen monitors and max out your rig with hard core gaming, you should easily be well below 450W. NewEgg has it for just $195 (Amazon also has it for the same price). Personally, I would get it.

Keep in mind that a UPS has to recharge its batteries after a power outage, which can take as much as 24 hours. Having extra capacity will allow you to survive multiple power outages in a short period of time and will allow you to extend your running time longer should you be in the middle of a project you want to finish, then manually shut down instead of letting the UPS hibernate the computer mid-project. Extra capacity would also mean your batteries can be more worn out before being forced to replace them and you can upgrade your system without having to replace or supplement the UPS.

I looked at several APC models and, apparently, none of them output a sine wave AC, which is a pity because the APCs have some nice features. I firmly believe a sine wave output trumps other features, even if one's present rig doesn't require it, if only to future proof the UPS.

@Lady Fitzgerald,

I understand only the monitor & CPU are to be plugged in, I'm lost on how to get the wattage of peripherals going into the PC. However, you also said

To determine the wattage needed, you will need to find out how much the devices
you will plug into the UPS will actually use

, which leads me to believe USB peripherals I use are not counted, did I understand correctly? Is kill-a-Watt a program or hardware? I think I'm lost, all in all I'm still not sure.

Keep in mind that a UPS has to recharge its batteries after a power outage,
which can take as much as 24 hours. Having extra capacity will allow you to
survive multiple power outages in a short period of time and will allow you to
extend your running time longer should you be in the middle of a project you
want to finish, then manually shut down instead of letting the UPS hibernate the
computer mid-project. Extra capacity would also mean your batteries can be more
worn out before being forced to replace them and you can upgrade your system
without having to replace or supplement the UPS

This is a good arguement for higher capacity, makes sense.

Thx again :)

GRB70 said:

I think I'm lost, all in all I'm still not sure.

A Killawatt is a hardware device, about $20 from Newegg or Costco. Plug anything into it and it will tell you how much power it uses. PC, TV, lamp, stereo equipment, whatever.

You don't have to plug all of your peripherals into the "battery" side of the UPS. Some you could just connect to the "surge protection" side. For instance, you probably would NOT connect your printer to the battery side.

The relatively high wattage stuff is the graphics card and processor. That's probably 70 percent of the total in a typical setup. Hard drives are under 10 watts. RAM is even lower. A recent 23 inch LED monitor might use 20 or 30 watts.

Not sure about your liquid cooler. Ask Corsair.

As near as I can find out, the cheapest APC brand pure sine wave UPS is the Smart-UPS C 1000VA LCD 120V model, which weighs 38 pounds and is around $300. It's 17 inches deep and 9 high.

So, looks like Cyberpower is a better option. They have pure sine wave models down to about $120.

http://www.newegg.com/Product/Produc...82E16842102131

TY for that, I didn't know everything inside mattered. :)

If you look at slightly larger units they all take a big price jump I think the 1500VA is the biggest without getting into really big money and the 1000VA is maybe mid-tower sized and below.......my take on things! Yes just like a PSU more watts and VA is better.

Kill-a Watt. More expensive models are available but you shouldn't need it.

Just because a component is rated at so much wattage doesn't mean it will use all that; the actual amount would depend on your usage. If you decide to get the Kill-a Watt, just plug in the computer and uses it for a day or two to find out what its peak draw is; same for your monitor. As Ignatz mentioned, you don't need to include peripherals, such as the printer in your calculations.

Or, you could just take a shortcut, forget the Kill-a-Watt and apply the money you would have spent to the UPS you linked earlier (assuming it's not out of your budget). Compare my rigs specs to yours and you will see it is "thirstier" than yours. My UPS is rated at 2200VA. The software shows my computer and monitor are drawing only 180W right now; the most I've ever seen it draw is less than 250W. At 180W draw, I have 116 minutes of runtime; that's nearly two hours (I oversized it for future expansion, such as the three 24" monitors I have on the way to replace my old 22")! If I had the 1500VA model you linked, I would still have around an hour of runtime available, even with the new monitors.

My huge full tower, two monitors and everything under the sun running off it will go 28 minutes off my new 1500va. When major events hit it gives me all the time to finish and power down, plus stabilizes power and absorbs surges...it's worth its weight in gold, your currency may vary.