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Will my system run a 2nd 6870/6850 or am I limited by my psu?

Last response: in Graphics & Displays
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January 20, 2011 12:28:33 AM

I want to a add another 6870 or 6850 to crossfire with my current 6870 in my signature rig below. My question is will the XFX XXX Black Edition 650w power supply be enough to power my system with a 4.0ghz oc on the cpu and both of the gpus will be ran at stock. My motherboard is 8x8, would there be much of a reason to go with a 6850 as a second card? I'm also considering the fact that if I cannot run a 6870 can I at least run a 6850 as a second card since its lower power requirements. When I do psu calculators I find myself using pretty close to what my psu can put out so if someone who has ran 6870/6850 or 6870/6870 corssfire can tell me what there requirements are or what psu they ran it on I would greatly appreciate the input. Also if someone can tell me what the heat will be like since my motherboards pci-express slots are right next to each other,has anyone ever ran these cards lor something similar like this?? I know it is generally not recomended but I have decent cooling so I'm just wondering if its possible and feasible. I will leave a link for the mobo below. thanks

here is my psu:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

here is the MSI mobo so you can take a look and tell me what you think, when I bought it I thought it was quite unique but now I'm having second thoughts on its capabilities if someone could clear that up:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...


the rest of my system specs are in my signature.

thanks a lot for taking time to advise me on my system
January 20, 2011 2:39:51 AM

I wouldn't recommend doing crossfire with those cards... I know XFX make decent PSU's but still, want to play it safe eh?
January 20, 2011 3:02:30 AM

First, thank you for the links. It helps as I don't have to track everything down. According to the pic in your PSU link, your 650W PSU has a single 52A 12V rail. The CPU and GPU (and some of the other things in your system.) pull their power from this rail so thats where we focus our attention. 52A x 12V = 624W.

http://www.anandtech.com/show/3987/amds-radeon-6870-685...

According to Anand's review of the 6870 its max TDP (according to AMD.) is 151W. So you'll need 300W or so to run two. There are several 955 models, some are 125W and others are 95W. Lets assume you have a 125W model and are actually closer to 150W due to the OC. This means you have 300W + 150W + 50W for board and drives which gives you a max draw of 500W. Anand in the same article showed the draw for a 6870 CF setup.

http://www.anandtech.com/show/3987/amds-radeon-6870-685...

415W is what they show. Keep in mind I'm guessing on the CPU and other parts. Also even when gaming the cards probably don't hit their max of 151. Your XFX also has enough plugs on it to run the cards without the use of adapters, so I'd say your good to good.

***Short answer if you skipped all that!***

You have 624W available, and will probably use less then 500W. You're fine.
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January 20, 2011 12:28:28 PM

burble56 said:
I wouldn't recommend doing crossfire with those cards... I know XFX make decent PSU's but still, want to play it safe eh?



XFX makes quality psus, in fact the one that I have is actually a high end seasonic... besides that why woudl you not recomend it? did you calculate how many watts/amps I will be using compared to what I have or are you just throwing you opinion around? 6000 series is supposed to scale great, at least the best amd has seen so far so why would you tell me that you would "not crossfire those cards" explain yourself or don't make vague comments that are of no value, c'mon kid
January 20, 2011 12:30:57 PM



yeah when I have calculated it in the past it seemed to be have enough headroom, what about all my fans and other components beyond the 50w for the board, did you take that into consideration, I only have 1 hdd and 1 optical but Im just saying.. Thanks for your input and overall I think Ill be fine, do you think there is any logic or reasoning to get a 6850 instead for crossfire or should i just go with the second 6870? thanks for the links just get back to me on these minor questions thanks a lot
January 20, 2011 1:07:30 PM

Anand says two 6870s needs less then 500W. You have over 600 so I wouldn't bother with the 6850.
January 20, 2011 1:15:32 PM

ok thanks a lot for your help, at 85% efficientcy in the worst case scenario, my psu will be giving 552 watts (650*.85) or even yet, 624*.85= 530wats, basically I'm just hoping that I don't have to scale back my OC on the cpu... but either way I should be fine I guess

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January 20, 2011 3:38:50 PM
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Doesn't work that way. The efficiency is how well (or efficient) the PSU converts AC electricity to DC. The more efficient, the less AC electricity will be used and the lower your power bill will be. If you needed to output the full 624W and were 85% efficient, then your PSU will be pulling 734.12W from the wall. If we use the more realistic Anand number of 415W then we get 488.24 @85%, or 592.86 @70%.
January 20, 2011 3:54:44 PM

I see, thanks for clearing that up, must have sounded pretty dumb but that is just how I assumed it worked. Either way I got a solid 624 Watts, 52 AMPS which should be more than adequate for crossfire 6870s and my system thanks for your help and input
January 20, 2011 3:54:58 PM

Best answer selected by jjb8675309.
January 20, 2011 3:55:26 PM

moderator can close now thanks :) 
January 20, 2011 6:01:43 PM

This topic has been closed by Mousemonkey
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