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Please Help Me Choose a UPS for New PC

Last response: in Components
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July 5, 2011 2:37:54 PM

I just ordered parts for my new computer and I'm looking to get a UPS to help out with brown outs and to give me a few minutes to save what I'm working on during a black out.

At first I was ready to just get one of the top-rated ones on Newegg or Amazon (like this one), but then I started reading about all these other concerns: For example, apparently you can't get a normal UPS if your PSU uses Active PFC? I've read that you need something like this, at the minimum?

I'm very confused about all this pure sine wave stuff and about how many VAs and Ws I actually need.

Here are my relevant computer specs: SeaSonic 620W PSU, i5-2500K, Radeon 6850, 2 hard drives, 8GB RAM, and a 24" LCD.

So here are my questions:

1) How many VA/W would you recommend for my system? I only need 5-10 minutes of power, and I'll only be plugging in my computer and one LCD. Is it sufficient to just take 620W (my PSU) and add 75W (my monitor) = 695W?
2) Do I need a Pure Sine Wave UPS since my PSU uses Active PFC?

My new computer is only $900, so it seems like a lot to spend nearly $200 on a UPS just to give me a few minutes to save my documents, so I'd love to know if such a high end model is really necessary.

Thanks very much for any help you can offer!

More about : choose ups

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a c 1184 ) Power supply
July 5, 2011 10:21:01 PM

The Seasonic 620 Watt PSU has a DC output of 620 Watts. Since your power supply is not 100% efficient, it's 80Plus Bronze rated, the AC power input will be 746 Watts with a full 620 Watts DC power draw using 83% efficiency (from reviews I've read).

You won't be drawing the maximum power from your power supply so a more realistic system wattage with the GPU in FULL Stress is 220 Watts AC.

So 220 Watts (system) + 75 Watts (monitor) = 295 Watts. Just round that to 300 Watts AC to determine the battery run time that you need/want.

You should be using a pure sine wave UPS with PSUs that use Active PFC. Modified sine wave (e.g. stepped sine wave, filtered square wave, etc) UPS usage has been known to shorten the life of some PSUs that use Active PFC or for some the PSU just fails to operate properly.
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July 6, 2011 2:37:46 AM

Best answer selected by natharch.
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July 6, 2011 2:45:32 AM

Wow, thanks for the very informative answer!

It's amazing how hard it is to find easy to understand information about this stuff.

Just out of curiosity, how did you go from the 746 watts to 220? Or was 220 just an educated guess?

I've looked around on Newegg and Amazon, and it seems like the cheapest pure sine wave one would be the CyberPower 510W. It's $115, but it seems to be the lowest wattage of the pure sine type.

Thanks again!
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a c 1184 ) Power supply
July 6, 2011 2:57:30 AM

I googled and found a website that had measured the power consumption at the wall outlet for an i5-2500K system using a Radeon HD 6850 graphics card under full CPU and GPU load.

Before I googled I already had an educated guess of what your system power consumption was. Google just confirmed it.
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July 6, 2011 3:01:41 AM

I see - thanks very much!
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