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truple
07-17-2011, 07:26 AM
Hi, I'm planning to build a new system with an Asus P8P67 Deluxe motherboard, intel core i7-2600k 3.40ghz with an ATI CrossFireX setup, would anyone know what size of PSU I should be using? any specific suggestions would be appreciated, Thanks.

dosbox
07-17-2011, 07:29 AM
CrossfireX with what cards specifically? A pair of 5770's have very different power needs than a more powerful pairing.

truple
07-17-2011, 07:49 AM
Sorry, I wasn't sure of which graphics card to settle on, I think the 6870 will be the most likely.

dosbox
07-17-2011, 07:57 AM
6870 Crossfire with i7-980X @ 4.51 GHz (http://www.xbitlabs.com/articles/graphics/display/radeon-hd6870-hd6850-crossfirex_12.html#sect0) = 672 Watts while running Furmark + Linpack.

Bear in mind that is power consumption at the wall (i.e. take 10-15% off for the PSU output), and your CPU won't be quite as power hungry.

A really good quality 750W unit would be plenty:

http://www.newegg.com/Product/Product.aspx?Item=N82E16817151087
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139010

A good quality 850W would give you additional headroom:

http://www.newegg.com/Product/Product.aspx?Item=N82E16817151102
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139011
http://www.newegg.com/Product/Product.aspx?Item=N82E16817207017

ELASNO
07-17-2011, 08:05 AM
I would go for a 1000W so you won't have to buy another one in the future.
Anyway, why would you want a 6870 Xfire? Why don't just buy a 6990?

AlecJ32
07-17-2011, 08:34 AM
I would go for a 1000W so you won't have to buy another one in the future.

There is no rule of thumb that power consumption will go up in the future. Newer hardware tends to be, for the most part, equal or better in terms of power consumption. The only exception I've really seen is that top of the spectrum CPUs are going up in consumption, but those are small numbers.

Beyond that, there's an efficiency curve you have to worry about. Power supplies operate at different levels of efficiency at different loads. If you're running a considerably overkill unit, you will get much worse energy efficiency. If, for example, he's not doing anything demanding and his machine is only drawing 100 watts of power, a 1000 watt power supply might only be capable of delivering power at as low as 50% efficiency, which means at the wall it's drawing 200 watts, but the computer only needs 100.

dosbox
07-17-2011, 08:51 AM
I would go for a 1000W so you won't have to buy another one in the future.


Considering a pair of 6870's alone have a idle/peak power draw of 38W/300W, a good quality 750W PSU would still have plenty of headroom, and be more efficient while idle.

In the last five years, we've gone from:

4-pin ATX12V CPU connector to 8-pin EPS12V connector
6-pin PCI-Express connector to 8-pin PCI-Express connector
4-pin Molex to SATA power connector
3-pin fan headers to 4-pin PWM headers
Power efficiency in the 70% range to >85%

In short, power supplies are still subject to the march of progress.

HL2-4-Life
07-18-2011, 05:36 AM
I would go for a 1000W so you won't have to buy another one in the future.
Anyway, why would you want a 6870 Xfire? Why don't just buy a 6990?Man, you think like my nephew, who'd recently mothballed his AMD rig in favor of a spanking new Intel rig -
Asus P8P68 Deluxe
i7 2600k
2x 4GB KHX DDR3 1600mhz
XFX HD6990 4GB
120GB OCZ Vertex 3 + WDC Black 1TB
Corsair AX1200 PSU

His choice of PSU allows for another HD6990 should he want more gfx grunt.....with headroom for more stuff. He now has a rig that overpowers mine quite easily....:(

P.M.
07-18-2011, 05:45 AM
There is no rule of thumb that power consumption will go up in the future. Newer hardware tends to be, for the most part, equal or better in terms of power consumption. The only exception I've really seen is that top of the spectrum CPUs are going up in consumption, but those are small numbers.

Wasn't i7-960 something like 130W and 2600k 80W? I was under the impression that smaller transistors = less power consumption

borg_7_of_9
07-18-2011, 05:56 AM
Wasn't i7-960 something like 130W and 2600k 80W? I was under the impression that smaller transistors = less power consumption

Yes and the I7 2600 is 95W... but only when fully loaded..

dosbox
07-18-2011, 03:39 PM
Man, you think like my nephew, who'd recently mothballed his AMD rig in favor of a spanking new Intel rig -
Asus P8P68 Deluxe
i7 2600k
2x 4GB KHX DDR3 1600mhz
XFX HD6990 4GB
120GB OCZ Vertex 3 + WDC Black 1TB
Corsair AX1200 PSU

His choice of PSU allows for another HD6990 should he want more gfx grunt.....with headroom for more stuff. He now has a rig that overpowers mine quite easily....:(

6990 = 450W peak
i7-2600K = 95W
WDC Black = 11W

Total = 556W

Add 100W for everything else and you get the idea. If he plans on running a pair of 6990's, then fair enough - though I'd question the value proposition of such a system.

HL2-4-Life
07-20-2011, 08:29 AM
6990 = 450W peak
i7-2600K = 95W
WDC Black = 11W

Total = 556W

Add 100W for everything else and you get the idea. If he plans on running a pair of 6990's, then fair enough - though I'd question the value proposition of such a system.I'd actually gotten him a Seasonic X-Series 850W Gold PSU, but it turned out to be a dud......caused numerous BSOD's. He went out and swapped the Seasonic for the Corsair AX1200W PSU (with cash top-up), I wasn't surprised because he will go CF with another HD6990.....but not now. Perhaps in a year's time when a HD6990 would go for much less than now in the used or garage section of local tech forums.