UPS Power Rating Calculation Help Required

[KamalS]

1. I need to decide on what UPS to buy for my system.

2. But first I need to decide how beefy it needs to be - this is where I need your help.

My SMPS is a 650W Active PFC, 80+. Details : http://www.newegg.com/Product/Produc...82E16817371015
Brought it because it was cheap.

3. Here are my system details:

CPU : Q8400, TDP 95W. Details : http://www.newegg.com/Product/Produc...82E16819115057
MB : GA-EP45-UD3P, Max draw 196W. Details : http://www.newegg.com/Product/Produc...px?i=3508&p=11 ( this posts 242W at full load )

I don't have a clue what these consume ( any ideas? links? )

RAM : TWIN2X4096-6400C5. Details : http://www.newegg.com/Product/Produc...82E16820145184
GPU : GeForce 9800 GT 1GB. Details : http://www.newegg.com/Product/Produc...82E16814133304

To these I will hookup an externally powered HDD, internal SATA HDD, DVD Writer, mouse, keyboard - standard stuff.

The monitors will be externally powered, and NOT hooked to the UPS.

Taking all these things into consideration, I just pulled a number outta my a*s - 350W would be my system draw at peak load.

What do you guys think?

4. That means, the load to my SMPS would not be more than ~350W at peak load?

In that case, my UPS needs to supply this much juice:

sqrt ( 2 ) * 1.25 * 350W = 1.8 * 350VA = 630VA

( sqrt ( 2 ) -> power factor, 1.25 -> 80% efficient SMPS )

5. So I believe a 750VA UPS should be good enough?

My calculations get totally screwed if my system consumes more than 350W and this is what I want to confirm with you guys - to help me figure this out.

6. As the SMPS is APFC, I can play a game by buying a UPS without pure sinewave output - would save me a lot of bucks.
Otherwise, I can just buy myself some peace of mind by paying more than double for a pure sinewave UPS.

This is were choices become more difficult to make.

A 750VA APC costs ~$90 less than a 1KVA APC - both pure sinewave.

What you say - should I get the 750 or the 1k?

I am not sure however, whether APC has derated their UPS or is the VA rating a peak rating.

In case the 750VA is a peak rating - maybe I should, then, get the 1KVA?

This is a horrible dilemma!

 

[mpilchfamily]

Try the pro version of the PSU calc and it will give you recommended UPS rating.

http://extreme.outervision.com/psucalculator.jsp

I would just go with the largest one you can afford. There is no loss on your end since the larger it is the longer run time you have while on the battery.

 

[bigboxes]

I would just go with the largest one you can afford. There is no loss on your end since the larger it is the longer run time you have while on the battery.

I was just going to say that. Also, why wouldn't you place your monitor on the UPS? If you're power goes down for a length of time are you going to put your faith in the software to shut the system down? I don't often have lengthy outages, but when I do I am able to find a stopping point, save work in progress and then shut down. If it's for less than 5-10 minutes then I can keep working like nothing ever happened.

 

[bigboxes]

Wow. The 'Twilight Zone" theme should be playing right now. As soon as I hit the reply button my power went off for a second. And then again. Everything is fine now, just kinda funny about the timing of it all!

 

[PM650]

( sqrt ( 2 ) -> power factor, 1.25 -> 80% efficient SMPS )

An active PFC psu has a PF of 1 ^_^

This choice is really about how much runtime you'll need for outages. If only a few minutes, 750VA will be more than enough for an idling machine. If you want quite a bit of runtime while gaming, you may need substantially more than 1kVA (runtime vs. load tends to be logarithmic). A lot of manufacturers will post a table of runtime for different loads.
APC Back-UPS Pro 650:
100VA / 49 minutes
200VA / 22 minutes
300VA / 14 minutes
400VA / 9.3 minutes
500VA / 7.2 minutes
600VA / 5.8 minutes