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Radeon HD 6950 Crossfire Power Requirements

Last response: in Graphics & Displays
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October 26, 2011 4:30:07 PM

OK, so this is my first post so take it easy on me. I am wondering what I would need for a power supply in order to safely run two (2) Radeon HD 6950's in Crossfire. Here is my current PC (already built):

CPU : Amd phenom x4 955 black edition overclocked to 3.8ghz (stable)

RAM : G.Sklll Ripjaw 8GB Ram (ddr 1333)

Motherboard : GIGABYTE GA-970A-D3 AM3+ AMD 970 SATA 6Gb/s USB 3.0 ATX AMD Motherboard

Power Supply : CORSAIR Enthusiast Series TX750 V2 750W ATX12V v2.31/ EPS12V v2.92 80 PLUS BRONZE Certified (62 Amps on 12v rail)

Graphics Card : SAPPHIRE FleX 100312FLEX Radeon HD 6950 2GB 256-bit GDDR5 PCI Express 2.1 x16

SSD: Crucial RealSSD C300 CTFDDAC128MAG-1G1 2.5" 128GB SATA III MLC Internal Solid State Drive (SSD)

Hard drive : Western Digital Caviar Blue WD5000AAKX 500GB 7200 RPM SATA 6.0Gb/s 3.5" Internal Hard Drive

DVD Drive : ASUS DRW-24B1ST/BLK/B/AS Black SATA 24X DVD Burner x 2

TV Tuner : Hauppauge WinTV-HVR-2250 Media Center Kit Dual TV Tuner 1213 PCI-Express x1 Interface

Now, I am wondering if 750 Watts with a 62 amp 12V rail is enough? Or am I going to be treading dangerous waters? I have been doing a lot of reading and researching and the info seems to be all over the place! Some say 750 Watts (even AMD's own site) with 50 amps is enough but some say 1200 Watts with 80 amps is required. I also used the Extreme Power Supply calculator and it says 750 Watts with 62 Amps is plenty, hence my confusion.

What is everyone's thoughts?

Thank you :) 
October 26, 2011 5:13:44 PM

2 6950 will bottleneck your cpu.get only one
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October 26, 2011 5:26:13 PM

I currently run 2 x 6950OC's on a Corsair HX850, and have had no problems.

Edit - I do wonder what the power draw difference is between my OC'd i5-2500k and an AMD 955 OC'd.......if it's a huge power hog OC'd, you may want to get something over 750 watts.
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October 26, 2011 5:29:12 PM

thanks! Currently my CPU use-age is barely even worth mentioning so I have a hard time believing it will bottleneck but I will admit that I know very little about that. I figured 850 Watts would be plenty but wanted some feedback. Thanks for the thoughts :) 
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October 26, 2011 5:34:22 PM

No problem :)  I was editing while you posted. But yeah, I've had no problems with my 850 so far........I would think anything of quality in the 850-950 range would cover it. If you can afford a big dog, I suppose you can never have too much power :p 
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October 26, 2011 5:38:15 PM

Awesome. I may go for a "big dog" power supply just to be absolutely sure. Now, I am going to look into this cpu bottlenecking issue and see if that would be the case with my current processor! oy vey!
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October 26, 2011 6:57:43 PM

Two things:
The voltage increase associated with overclocking will increase the power consumption of the CPU by about 25%. For a CPU with a 90 watt, that is an extra 20 - 25 watts. That is generally insignificant with a medium sized, modern PSU.

Second, CPU bottlenecking should not be a signicant problem with a modern CPU running at 3.8 GHz.
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October 26, 2011 7:08:10 PM

Crossfire HD 6870s:)  Less power but just as yummy for really high FPS/resolutions! Crossfirex2 = Micro-stuttering :(  x3 = best yum yums for your tum tums
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October 26, 2011 7:16:16 PM

jsc said:
Second, CPU bottlenecking should not be a signicant problem with a modern CPU running at 3.8 GHz.

The only problem is that the 955 isn't a modern CPU :(  I have a 965 OC'ed to 4.2 GHz and it bottlenecks GTX 460s in SLI, I'd hate to see what would happen to 6950s in CF.
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October 26, 2011 7:18:44 PM

If you want to objectively, accurately and scientifically determine what PSU power is required for your Vid card and PC in both watts and 12v rail amps., the forum Utility link below will show you how easy it is to calculate this information and objectively determine which PSUs are quality built, reliable PSUs that can meet your needs. Be advised that the available 12v rail amps. is just as important as the total PSU wattage. You need both to be correct.

http://www.tomshardware.com/forum/314712-28-please-read...
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January 19, 2012 11:09:58 PM

hey guys...

sorry to steal the thread but didnt really want to spam

I got:

750W Antec TruPower

i5-200K (OC to 4.5Ghz)
8GB OCZ 1600 RAM
2x SATA HDDs
2x External USB 1TB drives
2x DVDRW Drives
Saphire ATi 6950 1GB

4x case fans ~120mm

Im thinking of getting another 6950 1GB for CrossFire...
Will my system support it?
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