850w PSU good enough for 4890 CF?

I ordered my system
CPU i7-920 D0 stepping
MB P6t-deluxe v2
RAM OCZ Platinum DDR3-1866 9-9-9 timing
CASE HAF932
HSF ultra120exteme
PSU CORSAIR CMPSU-850TX
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.
Fans
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 http://extreme.outervision.com/PSUEngine 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?
7 answers Last reply
More about 850w good 4890
  1. 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.
  2. That should do it... 850W for 4890CF... Assuming you entered all your load when you calculate the power.
  3. 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.
  4. Would love to see some benchmarks too ^^
  5. fosho
  6. The 850W Corsair PSU is enough for two 4890's in CF.
  7. +1 for the Corsair 850TX...Actually the Corsair 750TX could power 2 HD 4890 in crossfire without a problem...
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