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850w PSU good enough for 4890 CF?

Last response: in Graphics & Displays
May 22, 2009 2:07:39 AM

I ordered my system
CPU i7-920 D0 stepping
MB P6t-deluxe v2
RAM OCZ Platinum DDR3-1866 9-9-9 timing
HSF ultra120exteme
HD 7200.12 - 500GB - ST3500418AS
Blu-Ray Pioneer - BDC-202BK - OEM
GPU1 Sapphire 4890-1gb
GPU2 Sapphire 4890-1gb

I got such a good deal on the 4890 $209 with $20MiR so $199, I bought another one for $209 but no MiR. But now I am fairly certian that the PSU will not suffice. I will not be overclocking now, but definitely in the future. I am still waiting on the CPU in the mail.

I don't have power requirements for the fans but this is what I have.
3x250mm @ 700rpm ( I know that they are 230mm but the PSU calculator I used only had a spot for 250mm)
1x140mm @ 1200rpm
1x120mm @ 1200rpm (u120e)

I used to estimate my power draw

and with all my system specs listed above at 100% TDP and 100% load and 25% aging , It calculates 622w. so if a 850w psu is 80% efficient then it will have 680w max, so without overclocking it seems like I am very close to the limits.

Please help! Do I need to return the PSU to Newegg and order another one, or is 850w good for this CF setup, or maybe my calculations are fuzzy?

More about : 850w psu good 4890

May 22, 2009 2:27:34 AM

Your calcs are fuzzy. The rated output of a PSU is based on results after efficiency is considered, not before. An 850 w PSU under full load will pull just under 1100 watts at the AC socket.

850 watt Corsair will be more than adequate.
May 22, 2009 2:28:27 AM

That should do it... 850W for 4890CF... Assuming you entered all your load when you calculate the power.
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May 22, 2009 2:46:41 AM

Thanks jsc. I had the efficiency backwards. Now not feeling so bad about my choice. Can't wait to get the proc and see this thing in action.
May 22, 2009 3:02:50 AM

Would love to see some benchmarks too ^^
May 22, 2009 4:12:15 AM

The 850W Corsair PSU is enough for two 4890's in CF.
May 22, 2009 6:54:20 AM

+1 for the Corsair 850TX...Actually the Corsair 750TX could power 2 HD 4890 in crossfire without a problem...