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Crossfire Power Requirements

Last response: in Graphics & Displays
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April 24, 2012 10:27:18 AM

Hi All!

I upgraded my PC last year and, now I can afford another graphics card I'd like to get one and run it in crossfire mode. I've currently got a Powercolor HD6850 PCS+ and would like to get a second, identical one.

My current specs are:

Antec HCG-620W PSU
Intel Core 2 Quad 9650 (at 3.0 GHz)
Asus P5Q Pro Turbo motherboard
Powercolor HD6850 PCS+
Asus Xonar DX sound card
Liteon DVD/RW
500GB HDD

I'm also looking at replacing my HDD with a faster one (Velociraptor etc for my OS & games) and a larger one for my documents, music and so on.

Please could you help and tell me how to work out if my PSU is powerful enough to run the above system with a second HD6850 card? Also, I take it that having a second graphics card would give increased frame rates in games?

Thanks in advance, David
a b U Graphics card
April 24, 2012 1:10:23 PM

CPU - 8 amps to 10 amps (overclocked)

2 6850's - 18 amps peaking to 20 amps

The rest of the system - 100 to 120 watts.

I estimate that your PSU will be running at 75% - 80% of rated power when gaming. That is higher than I would like, but it is acceptable.
April 24, 2012 3:29:03 PM

Thanks so far for your replies, can I ask how you convert amps to watts for the CPU and GPU(s) please? Also, why would it be preferable to use less than 80% of my PSU rated supply?

Finally, will my CPU (non-overlocked Q9650 @ 3.0GHz) act as a botleneck for the GPUs? Or will it have enough power to allow them to do their best?

Thanks again, David
Related resources
April 24, 2012 3:34:54 PM

Forgot to mention, my usual resolution is 1440x900 on a 19in monitor. Might be looking to get a HD 23in LED panel in the future which is why I'm considering dualing-up my graphics cards.

Will my CPU be an issue or is it powerful enough to not hinder the graphics cards? Ta, David
a b U Graphics card
April 24, 2012 5:09:59 PM

You might begin to hinder the cards a bit, depending on the game of course.
April 25, 2012 8:47:34 AM

Thanks for all your replies! I mainly play Civ 5, FS 2004 and FSX, Call of Duty MW, Black Ops and WAW. I'm mainly looking for a second graphics card as I'm looking to go to a 23in monitor at a higher resolution than my current 19in @ 1440x900.

Would it also help to get a faster HDD (10k RPM) as well? I've been doing loads of overtime so have enough cash for both!

How much of a hinderance would my CPU be? And would I actually notice it? For example, if I currently get 30-40 FPS in a game, will two GPUs increase this or enable me to maintain it with higher detail levels? Thanks again! David
April 25, 2012 9:12:58 AM

I don't play either of those - I take it I just make sure the games I get in teh future recommend a GPU of less than 1GB to avoid this constraint?
April 25, 2012 10:31:23 AM

Thanks Recon! Just got to order one and fit it - hopefully they'll set up alright! I have been reading that I could put a 68xx with my current 6850, is this advisable? Or is it just easier to put in another, exactly the same, 6850?
April 25, 2012 10:58:09 AM

Thank you again Recon. I will probably then just get another 6850 PCS+ so they're both matched. Getting back to power supplies, the third post (from jsc) has watts and amps - how do I convert one to another? Will I max-out my 620W PSU by going Crossfire?

I'm looking to fit a second HDD in the future too, would this cause issues? Thank you once again!
April 25, 2012 12:31:03 PM

Thank you once again. Out of interest, if I do any further changes in teh future, how do I work out tpower loads etc for myself? Ta!
April 25, 2012 3:02:06 PM

Thanks again, so, in short, my PSU is adequate - I've gone through the thermaltake power calculator online and it says I should need 430W with a stock HD6850 (doesn't list PCS+ version) and with two stock HD6850s in Crossfire I'd need 527W.

That's with putting in 20% capacitor ageing and using the other recommendations (CPU TDP, system load etc).

Am I likely to ruin the PSU by using it within 20% of it's maximum designed output? Are there any other considerations that I should take into account if I do go ahead with the second GPU?

Thank you all for your help!
!