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knightwarrior
05-02-2012, 01:11 AM
I'm about to Crossfire my second 6870, and I wanted some advice from you guys. I currently have a Corsair 650W PSU. I've been told by many people that my PSU can handle it without any problem. Since it doesn't have any more connectors for a second graphics card, I got this instead: http://www.newegg.com/Product/Product.aspx?Item=N82E16812198022

My question is it safe to do, cause I don't plan on changing anything for the next several months at the least. Thanks!

Odeon
05-02-2012, 07:32 AM
I have an older 480W PSU that doesn't have a single PCIe power connector, so I picked up a similar adapter. It take two 4-pin molex connectors and adapts them to one 6-pin PCIe connector, which is what my GTS 250 requires (only one). I haven't had any issues that I could attribute to the adapter, but this is a simpler situation than yours.

If your PSU has more than one rail, you should try using a 4-pin molex from two different rails just to be sure there's enough power, but I think the only real problem you might have is the second card not getting enough power. If that happens, you may have trouble getting Crossfire set up in the first place since it might not be able to fully recognize the card. Or if you can get everything set up but the second card is under-powered, it might not be able to do much to improve game performance. Either way, I don't think you have to worry about any kind of damage unless your PSU turns out to not be powerful enough and you don't remove the second card. Guru3D.com recommends (http://www.guru3d.com/article/radeon-hd-6850-6870-crossfirex-review/4) a 700W PSU for 6870s in Crossfire and mentions some potential issues.

But give it a shot and if you can't get Crossfire set up or if you don't get any performance increases, try getting a second adapter and only using one of the PCIe connectors on the one you already have since it's only a few bucks more.

Bungle
05-02-2012, 07:31 PM
I believe Corsair power supplies all have a single +12V rail, which means it all comes from the same place. Using an adapter to pull power from a Molex connector or other connector will not pose a problem. Go right ahead.

gimperial
05-02-2012, 07:40 PM
Won't be a problem. Is it not the TX650 you have? 'Coz it should have 2 graphics card plugs

knightwarrior
05-02-2012, 07:54 PM
try getting a second adapter and only using one of the PCIe connectors on the one you already have since it's only a few bucks more.

Sorry, even though I built my own computer, I'm still not familiar with the PSU stuff and such. What do you mean by getting a second adapter and only using one connector? The adapter I listed gets two molex plugs for two PCIe connectors, since the 6870 requires two PCIe connectors.

@Bungle:

Ah okay, thanks was just worried that my PSU might implode or something.

@Gimperial:

I have the TX650W, and yes it has 2 PCIe connectors, but since I'm Crossfiring, I need an additional 2 for the second graphics card, hence the adapter that I bought.

pakoito
05-02-2012, 08:20 PM
650W would be enough for that? I would bet on 900W better.

gimperial
05-02-2012, 09:26 PM
@Gimperial:

I have the TX650W, and yes it has 2 PCIe connectors, but since I'm Crossfiring, I need an additional 2 for the second graphics card, hence the adapter that I bought.

Ah I see, thought the 6870 only needed 1.

And don't worry about wattage, total system power draw when both GPUs are working at full power in a game is about 400W (http://images.anandtech.com/graphs/graph3987/33245.png), so you have plenty of overhead, and the tx650 is a very good PSU.

knightwarrior
06-02-2012, 08:05 AM
Ah thanks for the replies guys. Okay so I should be fine with two 6870's in Crossfire with that adapter? Cause one of my clan mates just told me that won't work out. :(

Odeon
06-02-2012, 06:20 PM
Sorry, even though I built my own computer, I'm still not familiar with the PSU stuff and such. What do you mean by getting a second adapter and only using one connector? The adapter I listed gets two molex plugs for two PCIe connectors, since the 6870 requires two PCIe connectors.
I didn't take the time to look up your particular PSU when I wrote my first reply, but according to NewEgg (http://www.newegg.com/Product/Product.aspx?Item=N82E16817139005)'s Detail page for that PSU, it does indeed have a single +12V which provides 52A of power. That should really be plenty to do what you want it to do. Some PSU split up the amount of power they can provide into two or more rails for reasons that you don't need to be concerned about because yours has only one, but PSUs with more than one rail make such setups more complicated.

My suggestion about a second adapter was that with a different PSU, you might have needed to have one adapter plugged into two 4-pin connectors from one rail and a second adapter plugged into two connectors from another rail, with only one PCIe connector from each adapter plugged into the second 6870. With your PSU though, I think you're safe with what you've got.

Feldspar
06-02-2012, 07:16 PM
Just take it easy when you first try it, with low resolutions and settings (probably best with a benchmark program) and then work up to max. That way, if there is a problem, you will just get some instability in the power, rather than a complete overload.

knightwarrior
06-02-2012, 08:26 PM
Ah okay, you guys relieved some of the tension I had that I was going to screw everything up with this. I'm going to try it later today though.

@Feldspar:

What's a good benchmark for me to use real quick, and what will I be testing for? Temperature, FPS? Thanks!

Feldspar
06-02-2012, 11:08 PM
I'm not up on current benchmarks, but I suppose it doesn't really matter which one, try 3Dmark. You're looking for sudden lock-up, artifacting or drops in FPS that might be explained by power loss, basically just upping the pressure to see that it can take it in a controlled environment.

knightwarrior
07-02-2012, 12:50 AM
Okay I added everything, and I'm about to run the 3DMark11 test right now. Wish me luck guys, hopefully this'll work out okay. Thanks for all your help though by the way, all of you!

EDIT: Okay, so far I tested out my two GPU's with FURMARK's Open GL Benchmark or something. The highest both cards went was 82C. Is that good?

JohnnyK
07-02-2012, 08:26 AM
http://www.tweakpc.de/hardware/tests/grafikkarten/amd_radeon_hd_6870_hd_6850/s11.php
Text in German, but the images show the 6870 goes up to 87 under load, so it should be fine.

Bungle
08-02-2012, 06:50 PM
I've owned three different CrossFire rigs in my life. The top video card always runs hotter than the bottom card for obvious reasons. It's normal. When you go back a single video card, you'll be extremely happy with how quiet your computer will become again ;)