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Crossfiring 6870s, will this 650W PSU suffice? (Would prefer examples)

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February 22, 2011 11:16:58 AM

Before anyone does: I KNOW ABOUT THE PSU CALCULATOR. I HAVE USED IT. BUT THAT IS A THEORETICAL VALUE.

Okay, that said:

Amazon recently put the Sapphire Radeon 6870 on sale for an astounding $190 ($170 after rebate), and although I told myself I wanted to wait a bit to upgrade to Crossfire, I had to hop on the deal. I already have a 6870, yes. Now, my problem... the PSU I have is a 650W one. Specifically, this one. Gold Certified, good; but also modular (which I heard can reduce its efficiency a bit, maybe someone can dispel that rumor?). Anyways, it's only 650 watts.

Now, my current rig is like this:

CPU - Phenom II X4 955
Mobo - Gigabyte GA-890GPA
RAM - 4X2MB DDR3 RAM (running @ 1333MHZ)
HDDs - 2x1TB 7200 RPM Hard drives
ODD - DVD Super Multi
Fans - 1x120mm, 1x140mm (with LED), 2x200mm (both with LED)

And, of course, the GPU will be dual-6870s.

Now, I know I won't be getting any OCing out of this build, especially with CF'd 6870s, but I have to ask... will I even be able to get the 6870 pair? If anyone has successfully crossfired 6870s on a 650w PSU, that would be absolutely wonderful; I'd prefer actual examples of it working to "THE PSU CALCULATOR SAYS IT'S TRUE SO IT MUST BE TRUE".

Thanks in advance.

EDIT: Wow, can't believe I forgot some components...
a b ) Power supply
February 22, 2011 11:27:45 AM

Well I got good news for you to crossfire the 6870's you only need a 600 watt power supply and even that is a bit overstated. The x650 you have is an outstanding unit and will have no problems with your setup. You should even be able to get some overclocking out of it.

Power breakdown.
2x 6870's 325 watts
Motherboard and RAM 100 watts tops (Overestimation)
HDDs 10-15 watts per HD
Fans 2-5 watts per
Optical drive 15-25 watts depending on model.

So if your system has lets say two hard drives 4 fans and an optical drive you are only looking at a draw of about 500 watts which that SeaSonic can handle without breaking a sweat.

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February 22, 2011 11:31:17 AM

saaiello said:
Well I got good news for you to crossfire the 6870's you only need a 600 watt power supply and even that is a bit overstated. The x650 you have is an outstanding unit and will have no problems with your setup. You should even be able to get some overclocking out of it.

Power breakdown.
2x 6870's 325 watts
Motherboard and RAM 100 watts tops (Overestimation)
HDDs 10-15 watts per HD
Fans 2-5 watts per
Optical drive 15-25 watts depending on model.

So if your system has lets say two hard drives 4 fans and an optical drive you are only looking at a draw of about 500 watts which that SeaSonic can handle without breaking a sweat.


Lovely, this sort of breakdown of all the wattages was exactly what I was looking for.
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a b ) Power supply
February 22, 2011 11:35:48 AM

Your welcome and even those wattage's are a tad overestimated like the motherboard & RAM 50-75 watts is a more realistic number but I like to overestimate to be on the safe side.
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