need help calculating VA for my UPS

[Rebirthoftheundead]

hi all i was wondering if you guys can enlighten me about calculating the VA for ups. I'd like to buy one for my new system but i have no idea where to begin with choosing a UPS as im on a tight budget too

[Arcmanov]

Use your power-supply's maximum power output as a guide.  Compare that to the maximum power capacity of tbe UPS you're looking at.

For example... I use a 1000 Watt PSU.  So when I'm looking for a UPS, I look for one that can at least sustain a 1000 Watt load.  The models that satisfy that particular criteria usually reside in the 1000 - 1500 VA range.  The one I'm currently using is a 1500 VA.  It cost a bundle, but it's worth every penny, and then some. 

You also have to consider the maximum load of the other devices that you're going to connect to it.  The power draw of a LCD is almost negligible now.  Speaker systems on the other hand, are not.  At max power draw, they will quickly overload a 1000 VA UPS.  For that reason, I don't ever connect speakers to my UPS.

My best advice... don't skimp on this.  Think of it as a long-term investment.  You want solid, uninterrupted power. 

Another point of note: make sure the UPS you choose can at least support monitoring via USB interface.  Those models usually include software that can monitor AC voltage levels and the health of the battery.  It might also even monitor the actual power usage of your system as you're using it... particularly useful in determining how much more devices you can safely connect to it.  It also uses this value to estimate your runtime on battery should 'korrent go'


I hope I've answered at least some of your questions here.  I'm sure the other tech-heads will chime in with some other equally important suggestions.



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[shivanandrs]

The VA rating of a UPS is basically the amount of Current (voltage x amperage) it can deliver. This is no to be mistaken for the Power (voltage x amperage) that can be delivered to/from a D.C. System. There are losses that take place during this conversion and it depends on the quality of the UPS's D.C. to A.C. converter when power is switched to battery backup.

On higher end products, you would usually find both VA and output power (in watts) of the UPS. I've noticed on the lower end products or where an output power was not supplied, you can count on it being around 50% - 60% of the VA rating at best. For example, a UPS rated at 1000 VA would give you an output power of 500-600W at best when running off battery power.

Now simply get a UPS that can output the maximum output of your system power supply...or if you have equipment to measure the wattage drawn from your system you can use those figures to determine what size of ups you need.

Another probably more simple way of calculating the UPS requirement is the old fashioned way of dividing the power consumption in watts of the system by the power factor of 0.6. This is always a safe bet.

A system that needs 600w of power would need a ups putting out

600/0.6 = 1000VA

** the power factor is determined by the UPS's Total VA/Output Power (watts)

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[Rebirthoftheundead]

i get it except for where you use the formula 600 * 0.6 = 1000VA. cause i get 360 from using this

[shivanandrs]

i get it except for where you use the formula 600 * 0.6 = 1000VA. cause i get 360 from using this

Ahh yes...I see what you mean. I'm an idiot, the above makes no sense. Maybe I should read over before I post. Lol! It's been some years since I used this kind of stuff, tryin to figure out which way it was.

Formula should be  wattage/power factor.

I'll edit above and double check with my text books when I get home...had a tonne of notes I made on this stuff some time ago.

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[Arcmanov]

Ok,  it was corrected.  I was now about to post about the power-factor issue.  Completely forgot about that.  Good looking out Shiv.

According to the monitoring software that came with my UPS, I see power levels exceeding 630 Watts at full load (overclocked),  and about 420 Watts at idle.

I'm pretty sure your system won't approach anywhere NEAR that, so I think it's safe to say you will be good with a 750-1000 VA model.  Just make sure that the battery is easily replaceable.  Most APC models' batteries can be purchased on eBay.



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[Saxito Pau]

Ok,  it was corrected.  I was now about to post about the power-factor issue.  Completely forgot about that.  Good looking out Shiv.

According to the monitoring software that came with my UPS, I see power levels exceeding 630 Watts at full load (overclocked),  and about 420 Watts at idle.

I'm pretty sure your system won't approach anywhere NEAR that, so I think it's safe to say you will be good with a 750-1000 VA model.  Just make sure that the battery is easily replaceable.  Most APC models' batteries can be purchased on eBay.



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Actully APC UPSes and batteries can be bought on Caroni Savannah Rd. from Informatics Engineering

[shivanandrs]

Actully APC UPSes and batteries can be bought on Caroni Savannah Rd. from Informatics Engineering

And for those in South, you can get replacement batteries from R & N Electronics on Cipero St. San Fernando.

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[Rebirthoftheundead]

i'm a idiot too i should hav posted my specs before hand but this knowledge is really good to have in the future. Im lookin at -
Meme:4gigs x 2 Corsair vengeance 1600MHz
GPU: 570 GTX super-overclocked edition 1.2gigs
CPU: i5 2600k intel (Looking to overclock this btw)
and about a 800watt powersupply
Do you still think im safe with 750 VA - 1000?

[Spazosaurus]

i'm a idiot too i should hav posted my specs before hand but this knowledge is really good to have in the future. Im lookin at -
Meme:4gigs x 2 Corsair vengeance 1600MHz
GPU: 570 GTX super-overclocked edition 1.2gigs
CPU: i5 2600k intel (Looking to overclock this btw)
and about a 800watt powersupply
Do you still think im safe with 750 VA - 1000?

I highly recommend that you get yourself a Kill a Watt, available relatively cheaply on Amazon. Once your system is connected to it, you can find out how many watts/volts/va's etc your system is pulling at any one time without the need to do any sort of calculations, plus it is very handy for any other device!! With my specs ( see under avatar), my system pulls 185 watts idle and just about 450w under bf3 gaming load.

I'd put the system under the heaviest load I can find, gaming, stress test and determine the maximum draw. From there, I would look for a ups with a corresponding max output (taking into account Shiv's explanation about ineffeciency of some ups'dc/ac converter, thanks for that).

Also keep in mind that you do not want to get a ups that is too much in excess of what you need as efficiency of these things, like power supplies, the less disparity that exists between your actual draw and the output, the more efficiently it operates. (Dont buy a 1200w psu when your system, at its most stressed uses half of that, efficiency will drop like a stone.


Arc, 420w @ idle son? Our systems are almost identical minus your extra fans! Gaddamn no wonder you cant leave your system on for long before u hadda decide between feeding the system or the baby!!!

[Arcmanov]

Even with overclocking, your system's max power draw still won't match mine.  Still, you do have to consider room for expansion, so I'll say go with the 1000 VA if you could afford it.  If not,  then the 750 should do nicely.  Check the specs closely though.



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[Spazosaurus]

Even with overclocking, your system's max power draw still won't match mine.

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Of course with a small army of fans and that H100 extra, id definitely expect more draw from your system but over TWICE the amount? Them 6950s related to Calder Hart or wa?

[Arcmanov]

LOL @ Calder Hart.

I should have clarified that's with HT enabled at 4 GHz.  With HT off, the idle power draw is currently 366 Watts.
I do have the 6950s slightly overclocked as well.

Remeber, these 920 CPUs draw over 130 Watts overclocked all by themselves, and each video-card draws about 180 Watts at full load.
So yeah, throw in fans and drives, and it quickly adds up.

[Spazosaurus]

Not trying to be a d!ck or anything, but I too have HT enabled, 3 mech hdds plus a ssd, a total of 12 fans, 2 video cards highly oc as well. The delta really shouldnt be that much.

Sounds like you need a kill a watt in your life, see what is really going on behind that plexy and steel.

[shivanandrs]

Im lookin at -
Meme:4gigs x 2 Corsair vengeance 1600MHz
GPU: 570 GTX super-overclocked edition 1.2gigs
CPU: i5 2600k intel (Looking to overclock this btw)
and about a 800watt powersupply
Do you still think im safe with 750 VA - 1000?

My system is similar to yours, see spec to the left. Except at the moment nothing in my system is overclocked. I'm currently running it off a 3 year old APC 550 VA ups. It isn't in any way capable of powering my system while gaming. If the power dips for any reason my system cuts off. It is however, able to keep my system running for around 4-5 mins or probably a little more when under light load. It's more than enough to save what I'm doing and shut down the system.

As Captain Awesome said, the kill a watt is a bess buy. Use it to measure power consumption, or if you have a capable multimeter better yet. From there you would be able to work out exactly what you need.

 As you are planning on overclocking your system, I would recommend nothing less than a 1000 VA and the APC brand. The other guys running SLI and more powerful UPS's would be better able to give you estimated runtimes of the units. I can only give you mathematics at this point :-P

I do own a "forza" (or something like that) branded ups rated at 750 VA. It was the most $hit I ever owned. It wasn't even capable of keeping my old q6600 system running longer than 10 seconds when the APC 550 had no problem. I avoid them at all costs.

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[Arcmanov]

Cap, nothing is wrong.  My CPU is a power hoe.  I will be the 1st to admit that.  It requires more voltage than normal to retain stability at 4 GHz, so
what I'm seeing is pretty normal for my current setup.  I have all my comms equipment, headset, and monitor plugged into it too eh.

As for runtime, PowerChute says I can get a max runtime of 15 mins at current power draw (idle).
I suppose that number will drop to about 5 or 6 minutes while gaming. 

[Rebirthoftheundead]

tyvm guys i think i'll get a 750 VA

[Netizen1]

So what size UPS would one use for a PS3 and a 40" LCD TV?

My 550VA APC doesn't seem to be able to carry the load while gaming at all. (see post in WTMC thread)