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Can I do Crossfire with this PSU?

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  • Graphics Cards
  • Crossfire
  • Graphics
  • Product
Last response: in Graphics & Displays
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July 24, 2011 6:51:56 AM

My rig is using the following components:

GIGABYTE GA-880GA-UD3H AM3 AMD 880G SATA 6Gb/s USB 3.0 HDMI ATX AMD Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

AMD Phenom II X4 975 Black Edition Deneb 3.6GHz Socket AM3 125W Quad-Core Desktop Processor HDZ975FBGMBOX
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

COOLER MASTER Silent Pro M600 RS-600-AMBA-D3 600W ATX12V V2.3 SLI Certified CrossFire Ready 80 PLUS Bronze Certified Modular Active PFC Power Supply
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL7D-8GBRH
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

XFX HD-687A-ZDFC Radeon HD 6870 1GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card with Eyefinity
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I would like to add a second XFX HD-687A to use with Crossfire. There is an issue with my PSU though. It only has space for two 6-pin PCIe power cables, and each XFX card requires two 6-pin PCIe power cables (4 required, and my psu only has two).

Could I use the following splitter?
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I would buy two of them, placing one on each of the 6-pin PCIe cables, so that each graphics card could have 2 6-pin PCIe connections

Would my PSU be powerful enough for this?

Thanks

More about : crossfire psu

a c 177 U Graphics card
July 24, 2011 7:05:06 AM

LOL, your "600W" has as much 12V power as my 500w. I'll let you guess where this is going.

34A * 12V = 408W. You have a 125W CPU, and I think the 6870 is around 150W. If you want to run two of those, you'll need 300W for the cards, 125W for the CPU, and lets say 50W(ish) for the board, ram,etc. 475W(ish) for a CF 6870. You have 408W, so I'll say no. The 6850 is around 130W, so even thats out. You could get away with CF'd 5770s. (110W each)
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a b U Graphics card
July 24, 2011 3:03:54 PM

You should be ok if your not overclocking. That psu has 40a and puts out an actual 600w. Not sure how 4745454b comes up with 34a or 408w (LOL?) Now I see the humor.

I don't know what kind of connector that is your showing but your video cards come with a molex-pci-e adaptor in the box, you don't need to buy one. If you DO go that route, I would use one pci-e and one molex for each card, not 2 pci-e on one card and 2 molex on the other.
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a b U Graphics card
July 24, 2011 3:17:02 PM

No that Antec does not have more power. Not sure what you guys are smoking today.

The psu he has is just fine for Xfire 6870's. 40a's, 5yr warranty, Johnny Guru rated 9 of 10.

Get your facts straight people.

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a c 107 U Graphics card
July 24, 2011 3:19:42 PM

You could, but you probably shouldn't. Sure 6870s are pretty efficient and shouldn't draw more than 151W each under load (except with Furmark :p ) but I think your PSU is cutting it close

http://www.legitreviews.com/article/1445/17/

So if you consider about an 86% efficiency at that load with a Corsair 850TX you're looking at about 386W used in the system, perhaps a little more. That doesn't seem too bad, till you look at it as most of that will be on your 12v (40A) rail which only provides up to 480W.

It looks like the PSU itself is decent. Other than the inconvenience of messing with molex adapters for the second card it should be able to handle it. The question is for how long as this will be a significant load for that PSU. Let's face it, you want to play Crysis in DX11, and that ain't easy on the system. You are going to stress out that PSU and it will probably die a horrible death in the middle of gaming a year or two down the road :D . O.k well it might last longer than that, but then again it might not. I'd advise against it, but you should be able to run it for a while anyway.
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a c 107 U Graphics card
July 24, 2011 3:22:11 PM

Oh and don't use a splitter for the PCI-E. Just don't do it.
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a b U Graphics card
July 24, 2011 3:24:50 PM

The psu is fine for his system, besides it has a 5yr warranty, so if it dies, he gets an advanced replacement from CM.

Using the Molex adaptors is just fine as a second power source to the card. If it wasn't safe, they wouldn't include them in the box with the cards.

The manufacturer of his card recommends a 600w psu for xfire, and they recommend higher than needed because some people have cheap psu's. His is not a cheap psu.
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a b U Graphics card
July 24, 2011 3:27:59 PM

4745454b said:
LOL, your "600W" has as much 12V power as my 500w. I'll let you guess where this is going.

34A * 12V = 408W. You have a 125W CPU, and I think the 6870 is around 150W. If you want to run two of those, you'll need 300W for the cards, 125W for the CPU, and lets say 50W(ish) for the board, ram,etc. 475W(ish) for a CF 6870. You have 408W, so I'll say no. The 6850 is around 130W, so even thats out. You could get away with CF'd 5770s. (110W each)


Don't do math while smokey smokey :lol: 
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July 24, 2011 4:37:35 PM

Thank you for your replies

You have given me renewed hope

For some reason they did not include a molex-pci-e cable in the box, but I should be able to order a couple for cheap

Thanks again
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a c 177 U Graphics card
July 24, 2011 4:48:16 PM

I listed 34A because of the youtube vid on that page. Looking at the newegg pics, I see where its listed at 40A. Thanks for the correction.

40A * 12V = 480W. Using the link from legitreviews that megaman posted, they show 450W needed for a 6870 CF setup. (wow, and my "smokey smokey" math said 475. Pardon me, I was 25W off. STFU if you don't know whats going on.) 450W needed and you have 480W available? Now instead of a no I change my answer to bad idea. You shouldn't run a PSU that close to its abilities. If he had a 42A or 45A PSU like most 650W then he'd be fine.

Edit: That Antec has the same usable power, 40A. Who cares if the CM has more power on rails that computers these days don't use?
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a b U Graphics card
July 25, 2011 2:58:28 PM

You only calculating the 12v rail, which is 480w, your forgetting about the rest of the output. The total tested wattage was 593w @ 82.3% eff @ 43c max.
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a c 177 U Graphics card
July 25, 2011 3:56:24 PM

Why would I worry about the 5V or 3.3V rail when we are looking at the CPU and GPUs, which draw from the 12V rail? The way your looking at it you'd think you can do this if the "600W" PSU had 60A 3.3 and 5V rails. 500W would be tied up in rails that the CPU and GPUs can't use. These days you only need a bit of power on the 3.3 and 5V rails. Both the OPs and that Antec have the same "usable" power, 40A.
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a c 130 U Graphics card
July 25, 2011 4:26:54 PM

geekapproved said:
No that Antec does not have more power. Not sure what you guys are smoking today.

The psu he has is just fine for Xfire 6870's. 40a's, 5yr warranty, Johnny Guru rated 9 of 10.

Get your facts straight people.

GeekApproved is right. Even this review shows power consumption for the system to be under 450W with the 2 6870s:

http://www.guru3d.com/article/radeon-hd-6850-6870-cross...

This reminds me how some people give advice regarding how much power it takes to run 2 580s. These experts claim you need at least a 1000W supply to run 2 580s. I've measured the load from the wall using an appliance load tester just to be scientific about it. My whole system with these things peaked (99-100% load in GPU-Z) requires under 700W total. People have been adamant about telling me how wrong I am. It's almost comical. People go overboard with power suggestions because they just don't know.

I'm not trying to put anyone down, but it's amazing what you find when you test things out for yourself. I was misguided myself before I had. Once I did, I found my findings are very close to those in the site above:

http://www.guru3d.com/article/geforce-gtx-580-sli-revie...

In my case, some of the difference has to do with the fact that I don't have my processor clocked at its max turbo rating and don't have the voltage set static and may have a slightly different efficiency rating on my power supply.

To sum it up, GeekApproved is right.
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a c 177 U Graphics card
July 25, 2011 5:51:12 PM

I'm missing something. Where did I say the OP needed anywhere near that much power? Here is a review where CF 6870s need 436W. This gives us a range of 412W from ubers link, to 450W from Megaman's. 435W avg?

Yes, I had the original output of the OPs PSU wrong. I have no clue why the newegg page shows a video where they show 34A. (I didn't watch the video, I simply saw that on the page and assumed it was the output of the PSU. I'M SORRY. Happy?) Even at 40A however its still pretty close. 40A * 12V = 480W. Yes, that 435W figure does include some 5V and 3.3V power, but VERY little. Nearly all of that 435W is needed on the 12V rail.

For the sake of easy math, lets pretend 15W isn't needed. 420W? (no, I'm not smoking anything.) 60W leeway? 5A? You really want to run your PSU that close to the edge? I know CM doesn't want you to or else they would have included enough plugs. But I'm sure you guys are smarter then they are right? I already said I was wrong in my first reply, it can be done. But like Megaman, I think it's a bad idea.
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a c 130 U Graphics card
July 25, 2011 6:26:02 PM

True. Definitely not ideal. Ideally everyone could run with an 80-plus Gold-rated 1200-1500W supply.

Although, given limited resources, this is not always possible.

Would I do it personally? No, I'd be more comfortable with a Corsair 650, but it can be done with OP's current power. That is the question we're answering here.

If OP were starting new, my recommendation would be the Corsair 650 tx/hx has up to 636W to offer up on the 12V rail:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

It gives me more of a warm cozy feeling primarily due to my own paranoia caused by the contact buzz from the "smokey smokey".

If OP were to OC in the least, I'd recommend a new PSU for sure. No question about it.
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a c 177 U Graphics card
July 25, 2011 10:30:13 PM

And that's my issue with this thread? Some have said its fine to do it? One even said do it, and when the PSU fails it should do it in the warranty period and you just get a new one? To me, that's like OCing a new CPU and upping the Vcore to much. You then send it back to XXX claiming it mysteriously failed. Thank you for causing higher chip/card prices because YOU made a bad choice.

I think I've said all that I should on this subject. Hopefully the OP has enough data to make his choice.
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a c 130 U Graphics card
July 26, 2011 9:33:58 AM

4745454b said:
And that's my issue with this thread? Some have said its fine to do it? One even said do it, and when the PSU fails it should do it in the warranty period and you just get a new one? To me, that's like OCing a new CPU and upping the Vcore to much. You then send it back to XXX claiming it mysteriously failed. Thank you for causing higher chip/card prices because YOU made a bad choice.

I think I've said all that I should on this subject. Hopefully the OP has enough data to make his choice.

Your or my personal preference doesn't mean the power supply will fail because OP is using it within its capacity to provide power; no matter how close to its max rated W on the 12V. Dell and Gateway have made a business of shipping PCs with "just enough" power for almost two decades.
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a c 177 U Graphics card
July 26, 2011 10:18:17 AM

I'll comment on this because I feel its slightly different. While my "personal preference" doesn't make a PSU fail, running one so close to its 100% rated output will. The closer to the abilities, the more heat will be made, the more stress the unit will be under, and the faster the unit will die. This is fact, no personal preference will change that.

Dell and other OEMs is also a different matter. I disagree that they ship units that are "just enough". (big surprise, I know.) They normal ship weak units, but the parts inside the computer are even weaker. 250W PSU? 300W PSU? When all your running is a 95W CPU and a mobo with onboard, 1 or 2 sticks of ram with 2 disks drives, your looking at using around 150-180W. A 300W PSU is more then enough. This is another reason why OEMs have a locked bios. If you try to OC the CPU, now its drawing 125+W, and your looking at 200+ for a system. Stock the PSU is fine, but OC'd and its not.
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a c 130 U Graphics card
July 26, 2011 11:37:07 AM

The amount of heat a power supply generates has to do with its efficiency; not whether or not it's operating close to its maximum output.

Less efficient power supplies will lose more energy to heat. The 80-plus rated power supplies are rated based on efficiency. With this Cooler Master Silent Pro 600W 80-plus bronze power supply, if it were operating at 100% capacity, <=18% of the watts are lost as heat with this power supply.

Anyone interested should look look up '80-plus' or 'power efficiency' sometime. It's interesting info.
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a c 177 U Graphics card
July 26, 2011 1:05:11 PM

Quote:
The amount of heat a power supply generates has to do with its efficiency; not whether or not it's operating close to its maximum output.


You really believe that? No wonder you guys think the way you to. (the correct answer is they BOTH relate to heat output.) If you are only going to be difficult, I guess I'm totally done with this thread no matter what. Obviously you are only here to disagree. (another thing that matters to heat is design. The newer designs that parts of the 12V rail thermally attached to the PSU casing run a LOT cooler then other designs. But of course in your world it ONLY has to do with efficiency.)
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August 1, 2011 12:23:18 AM

Best answer selected by samJL.
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a c 107 U Graphics card
August 7, 2011 1:31:10 AM

+9000 to 4745454b
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a c 274 U Graphics card
August 7, 2011 1:32:35 AM

This topic has been closed by Mousemonkey
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