Question regarding psu/draw from wall/rating

[Extornia]

I got a Cooler Master V850 atm, with 2 7970's. It is drwaing 660w from the wall. Does this mean it is actually using this much? If not, how do I see how much of the V850 its actually using? I am debating adding an another HD5870, so I need to know if it'd be a viable solution? Can someone PLEASE shed some light on this.

[crazyates]

That's a 80Plus Gold PSU, which on a standard 110V outlet is at least 90% efficient at 50% load, and at least 88% efficient at 100% load.

At 50% load, your PSU would be putting out 425W, but pulling 472W from the wall (calculated by 425/0.90).
At 100% load, your PSU would be putting out 850W, but pulling 977W from the wall (850/0.87).

I'm going to guess that you're probably somewhere around 70% load, which probably means you're somewhere around 89% efficient, judging from the ranges of those two number above.

So if you're pulling 660W from the wall, that means that your system is pulling ~587W (660x0.89) from the PSU.

So your PSU is rated for 850W, and you're only pulling ~587W. That means you've still got just over 260W of headroom, which should be enough for a 5870.

These are all estimates, but they're pretty good guesses. Try it, and see for yourself if it works.

[Extornia]

As Im in europe and I got 230v outlets, is anything different?

[Starscream]

As Im in europe and I got 230v outlets, is anything different?

They have higher efficiency with higher voltage, so in your case (mine too), the efficiency will stand on 90% at 100% load (as opposed to 88% with 110v).

[crazyates]

As Im in europe and I got 230v outlets, is anything different?

Yep, but this is good news and bad news. While you're running more efficient, you actually have less headroom.

http://en.wikipedia.org/wiki/80_Plus#Efficiency_level_certifications

On 230V, your 80Plus GOLD will increase from 90->92% efficient at 50% load, and from 87->88% efficient at 100% load.

This means that you're probably closer to 91% efficient at your 70% load. So now, less of your 660W draw from the wall is due to inefficiencies, and more of it is due to your hardware actually pulling that much.

(660x0.91)=600W. Your hardware is pulling ~600W from your PSU, which is pulling 660W from the wall. Your PSU is rated for 850, but is outputting 600. This gives you 250W of headroom. Not a huge difference, but a little.

Again, you might be able to squeeze by with another GPU on there, but I would be cautious of pushing it >100% the PSU's rating.