Would my XFX XXX 650W PSU be sufficient to run two 7950's? The rest of my system is in my sig. Thanks

I'm going to take a wild stab in the dark and say possibly but you'd be cutting it very very fine, personally if everything is overclocked, I'd say you should be looking around 750w as a minimum. I wouldn't want to take the gamble on 650w.

My SLI 680's with a 3770K draw around 460-500W from the wall on maximum overclocks.

If you could get the CPU running at 100% at the same time as the GPU's running at 100% it'd be close. I think you'll be fine.

In reality in games only one runs at 100% so you always draw less than full whack.

Nuclear Fusion said:

Would my XFX XXX 650W PSU be sufficient to run two 7950's? The rest of my system is in my sig. Thanks

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i'd say no, especially if in catalyst and you select the 20% extra power draw

that is, if i presume you'll be OCing, which i bet you will

i think it would, but it wouldn't leave the power supply a lot of breathing space. 750w is what i'd be comfortable with too

It will be close.

3770K @ 4.7 (1.35V) = 220w
7950 Direct CUII @ 900 = 156w (strenuous gaming)
HDD 10w
Case fans 2w each

As you can see you should be fine (your PSU has a good rating) but any more volts are going to push it further.

Does it come with 4 PCIE connectors or are you planning to use molex-PCIE cables for the second card?

Close call depending on how far you oc them.
Good psu though (Seasonic?)

Uncle Petey said:

Does it come with 4 PCIE connectors or are you planning to use molex-PCIE cables for the second card?

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It has one 6 pin and 3 x 8 pin PCI-e connectors, so no need for adapters.

gregster said:

It will be close.

3770K @ 4.7 (1.35V) = 220w
7950 Direct CUII @ 900 = 156w (strenuous gaming)
HDD 10w
Case fans 2w each

As you can see you should be fine (your PSU has a good rating) but any more volts are going to push it further.

Click to expand...

A 3770k at 4.7/1.35v uses 220W? That's a big increase from the stock 77W TDP. Mine is a 3570k at 4.2 of course (1.16v load) so it shouldn't use too much more than the stock TDP (I think 1.16v is around stock voltage for a 3570k)

Menty said:

Close call depending on how far you oc them.
Good psu though (Seasonic?)

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yea he's right on the nail, especially if he adds the 20% power draw increase to both cards, which he'll deffo need especially if he wants to play borderlands 2 with Physics X

Very fine imo. My 7970 is pushing the limit on my 600w really. I would get an 850W if I was going for xfire just to be safe. 220w for a 3570K, really? How is that possible?

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

According to this I need 541W PSU. If I had 2x7950 apparently I would need 609W.

I still think 850W is a good investment.

So the general consensus is it is too close for comfort (I suspected it would be the case). Well I'll just buy a new card when mine is no longer sufficient, not really worth buying a new PSU. It is generally only worth going for CFX/SLI if you need the power now, normally it makes more sense in the future to go with a new single card as opposed to dual older cards. Hopefully my 7950 will be good enough until something worth upgrading to comes out (though who knows when the upgrade itch will strike again )

Google-'Plug-in Electricity Cost and Usage Calculator'-~£10 delivered, test your system during gaming and see what you hit now, base your decision on that?

Tried 7970 MSI OC+7950 IceQ(GHz) CrossFire(truly mental fps@1080p) ran fine on a [email protected]/16Gb/2 Ssd's/2HD's/DVD/SC and countless USB's on a 750W Seasonic fine last week, but that's not much help.

650w would be fine. Even if it took 600w from the wall, what you actually require is less than that.
It's the ripple that kills components and your PSU at full load has very minimal ripple.
The only way i'd personally ditch that and buy a larger PSU is if you could essentially swap, that being sell yours at the same price as a 750 or 850 unit would cost.

EDIT: My rig, for comparison sake.

3770k @4.8 1.33v
2x7970 @1200/1600 1278mv
2xHDDs 1xSSD 8xFans D5 pump.

Only takes 698w from the wall on max load.
I'm using a AX1200i, the only reason for the overkill is because i wanted it...not needed it.

I see some of the PSU scare mongers are out again. Get a reading from the wall before scare-mongering .

BrianB said:

Very fine imo. My 7970 is pushing the limit on my 600w really. I would get an 850W if I was going for xfire just to be safe. 220w for a 3570K, really? How is that possible?

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You aren't pushing the limit I'd say.

My whole system while running prime on a 4.6 Ghz overclock is pulling 210W from the wall...

Nuclear Fusion said:

A 3770k at 4.7/1.35v uses 220W? That's a big increase from the stock 77W TDP. Mine is a 3570k at 4.2 of course (1.16v load) so it shouldn't use too much more than the stock TDP (I think 1.16v is around stock voltage for a 3570k)

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yea that is high mine is 90W at 4.4

My math was from several sites. This was where I got the data for that CPU from http://www.legitreviews.com/article/1924/9/ If that is a bad site, can a mod please remove it.

If I was the OP, I would get what Tommy suggested and plug it in with all that setup @ stock and see how it goes. No point spending £150 + on some of the guys "Guess work" here with no real research or knowledge.

Edit: I used the 3770K as that was the only true bench I could find.

I think that site was taking measurements of the whole system power consumption from the sounds of it (though it isn't exactly clear) since it shows a 3770k pulling 81w at idle at stock settings, which is higher than the 77W TDP.