Need PSU recomendations for 6950 xfire

[NTAC]

This is my current setup:
CPU: i5 750 @ 2.66 (NOT oclocked at the moment)
Cooler: Noctua NH-D14
Memory: 4GB
PSU: OCZGXS700(700W) - http://www.newegg.com/Product/Produc...82E16817341002
GPU: 2x Saphire Dirt 3 edition 6950 (stock spd and bios)
MOBO: ASUS P7P55D Deluxe

I tried this setup with that PSU but I'm not getting the best results. If I try to O'clock the proc back to 3.7ghz where it was at initially, the system reboots on me after about 1 or 2 min of gaming.

You can see this thread for details on my process so far:
http://forums.anandtech.com/showthread.php?t=2202259

Anywho, it sounds like I need a better PSU to make all this work well, including an O'clock to 3.7 - 4.0 on that processor.

If that is the case, what do you guys recommend? I understand that the one place I don't want to skimp out on is a PSU, but at the same time I would really not want to spend over $150 IF possible... but if I have to then I'll figure it out somehow.

Also please take into consideration that I might potentially try to flash those 6950s to 6970s, which I assume would need more juice if I'm successful

Thanks!

Would this do the job? http://www.newegg.com/Product/Produc...82E16817139030

Or this one?

http://www.amazon.com/Cooler-Master...MBAJ3-US/dp/B002RWJGC2/ref=dp_cp_ob_e_title_0

 

[lehtv]

Well, overclocked and unlocked 6950's use 200W each, and i5-750 OC'd properly will also use perhaps up to 150W (?). 750W would do, 850W would have more breathing room.

XFX 850W $75 AR expires today [free shipping]. Even without rebate ($105) it's still the best 850W deal I can find. For comparison, what I can find from newegg:

TX850 V2 $135
TX750 V2 $105 (these are equivalent to the XFX versions, both made by Seasonic)
XFX 750W $121 w/ shipping
Antec EA750 $80 ($60AR) limited Shell Shocker deal, no cable sleeving, no power cord, Delta-manufactured

 

[NTAC]

So do I want to go 850 or is 750 enough? My current one is 700 and it is struggling, but is it having a hard time because its not enough Wattage or because it has some limitations on how it was built?

I really don't understand enough about PSUs

In this review they like the 650 and the 750 from that line but say that the 850 is the "ugly duckling" of the group: http://www.hardocp.com/article/2011/01/31/xfx_pro_series_core_edition_power_supply_review/10

Any thoughts on that? That's mainly why I asked about the 750 vs the 850, although maybe what they are concerned with might not apply to me?

 

[lehtv]

Go with 850W, the price on that XFX is so good. The 750W one on ncix is like $5 cheaper

is it having a hard time because its not enough Wattage or because it has some limitations on how it was built?

I'm a little bit surprised that it is having problems on your setup, given it's supposed to be 700W. Are you sure you're doing the overclocking right? Maybe the PC reboots not because of inadequate power, but because of inadequate CPU voltage. Did you stress test the CPU with a proper stress test program like LinX or Prime95?

The GameXStream 700W is split into four +12V rails at 18A each. I suppose it's possible that one of the rails is being overloaded. 18A translates to 216W, which isn't too far from what half a 6950 and an i5-750 need combined. Still, 18A per rail is more than should be needed and it's not like gaming stresses the CPU to 100%. (I'm assuming here that each of the PCIe power connectors is on a different rail.)

I really don't understand enough about PSUs

Here's a good intro about +12V rails http://forums.anandtech.com/showthread.php?t=157583
If you want to know about efficiency www.hardwaresecrets.com/article/742

Generally, Seasonic is the no.1 manufacturer and brands including Corsair, Antec and XFX sell their units (they use other manufacturers too). Plenty of other manufacturers are good as well, but when you can get an 850W Seasonic for $70 AR... you won't need to upgrade the PSU for 5+ years no matter what dual-GPU setup you throw at it.

 

[NTAC]

Go with 850W, the price on that XFX is so good. The 750W one on ncix is like $5 cheaper

I'm a little bit surprised that it is having problems on your setup, given it's supposed to be 700W. Are you sure you're doing the overclocking right? Maybe the PC reboots not because of inadequate power, but because of inadequate CPU voltage. Did you stress test the CPU with a proper stress test program like LinX or Prime95?

The GameXStream 700W is split into four +12V rails at 18A each. I suppose it's possible that one of the rails is being overloaded. 18A translates to 216W, which isn't too far from what half a 6950 and an i5-750 need combined. Still, 18A per rail is more than should be needed and it's not like gaming stresses the CPU to 100%. (I'm assuming here that each of the PCIe power connectors is on a different rail.)

Here's a good intro about +12V rails http://forums.anandtech.com/showthread.php?t=157583
If you want to know about efficiency www.hardwaresecrets.com/article/742

Generally, Seasonic is the no.1 manufacturer and brands including Corsair, Antec and XFX sell their units (they use other manufacturers too). Plenty of other manufacturers are good as well, but when you can get an 850W Seasonic for $70 AR... you won't need to upgrade the PSU for 5+ years no matter what dual-GPU setup you throw at it.

Any concerns regarding that review and the 850w being named the "ugly duckling" of the group?

I've also experienced one reboot without any overclocking at all, but that was only one time, however I do get a blue flicker here and there during BF3, but not sure if that's the cards not drawing enough power or something completely different.

I don't know how to tell what cable is on what rail, I think that is my main problem when connecting these things up.

I have a cable labeled PCE-1 that is by itself coming out of the PSU, I assume that means it is its own rail and that it is sharing with nothing? That cable is plugged into Video card #1.

I have another cable just like that one labeled PCE-2, which is plugged into Video Card #2.

Now I'm left with two more 6 pin connectors to plug into the 2 video cards, and here is where I don't know what to do... I don't have any more single cables coming from the PSU, at this point they are all split and going into different directions... how do I know which 6 pin connectors i need to hook up to the two video cards at this stage?

Thanks for all your help thus far!!

 

[lehtv]

Any concerns regarding that review and the 850w being named the "ugly duckling" of the group?

What review?

I've also experienced one reboot without any overclocking at all, but that was only one time, however I do get a blue flicker here and there during BF3, but not sure if that's the cards not drawing enough power or something completely different.

The rebooting definitely makes it seem it's not a graphics card issue. Never heard of faulty graphics cards causing a reboot... PSU sounds like the most likely culprit but CPU, mobo or RAM instability could in also do that. Did you get a Bluescreen, or did it just reset the PC as if you'd pressed the reset button?

Can't really help you with how the cables and rails are set up... sorry. Could email OCZ customer support and ask about it, and also ask if the PSU might be responsible for the instability. BTW do you have warranty left on the PSU?

 

[NTAC]

What review?

In this review they like the 650 and the 750 from that line but say that the 850 is the "ugly duckling" of the group: http://www.hardocp.com/article/2011/01/31/xfx_pro_series_core_edition_power_supply_review/10

"The 850W unit in this lineup is kind of the ugly duckling of the group for a number of reasons. The first being the results you see presented here today are the best results we were able to get from the two units we had tested. Second, with the DC output quality being what it is, this unit would be a hard recommendation even if we had not had to qualify our results for this unit with the phrase "the better of two units." Sure the unit is in specification, but on the 5v rail it is only barely in specification and if the unit had a heavier 5v load perhaps it would not be (then again perhaps it would be)."

The rebooting definitely makes it seem it's not a graphics card issue. Never heard of faulty graphics cards causing a reboot... PSU sounds like the most likely culprit but CPU, mobo or RAM instability could in also do that. Did you get a Bluescreen, or did it just reset the PC as if you'd pressed the reset button?

No no blue screen, just straight up reboot and only when in crossfire mode. I've tested the cards individually and they had no issues, the only thing I haven't tested is a single card in the 2nd slot, I suppose I could.

My constant reboots were because I was definitely not connecting the correct 6 pin to my 2nd card initially, once I fixed that I only had one reboot in a non oclocked scenario in about 5 hours of play time, where as when I had the wrong connectors hooked up I couldn't even get further than 1 or 2 minutes.

Can't really help you with how the cables and rails are set up... sorry. Could email OCZ customer support and ask about it, and also ask if the PSU might be responsible for the instability. BTW do you have warranty left on the PSU?

So how does someone know which 6 pin connectors to use for the 2nd connection on the video card?

Not sure about warranty, its about 3 years old, I can always check.

 

[lehtv]

In this review they like the 650 and the 750 from that line but say that the 850 is the "ugly duckling" of the group: http://www.hardocp.com/article/2011/...pply_review/10

Not a big deal at all. I trust reviews by Jonnyguru and Hardwaresecrets more than HardOCP.

http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=217 9.5/10 in performance
http://www.hardwaresecrets.com/article/XFX-PRO-850-W-Power-Supply-Review/1205/10 Gold Award, excellent power characteristics. Able to deliver 987.8 W in 49C ambient.

No no blue screen, just straight up reboot and only when in crossfire mode.

Huh. OK I'm gonna say it's a PSU issue, but it'd be nice to have some input from others as I'm not entirely sure if this narrows it down to PSU.

Have you tried different combinations of PCIe connectors on your cards? I.e. GPU1 = connectors 1 and 2, GPU2 = connectors 3 and 4. Then GPU = connectors 1 and 3, GPU2 = connectors 2 and 4. And finally 1 & 4 + 2 $ 3.

Not sure about warranty, its about 3 years old, I can always check.

That unit has a 3 yr warranty (all OCZ units do AFAIK).

 

[NTAC]

Not a big deal at all. I trust reviews by Jonnyguru and Hardwaresecrets more than HardOCP.

http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=217 9.5/10 in performance
http://www.hardwaresecrets.com/article/XFX-PRO-850-W-Power-Supply-Review/1205/10 Gold Award, excellent power characteristics. Able to deliver 987.8 W in 49C ambient.

Huh. OK I'm gonna say it's a PSU issue, but it'd be nice to have some input from others as I'm not entirely sure if this narrows it down to PSU.

Have you tried different combinations of PCIe connectors on your cards? I.e. GPU1 = connectors 1 and 2, GPU2 = connectors 3 and 4. Then GPU = connectors 1 and 3, GPU2 = connectors 2 and 4. And finally 1 & 4 + 2 $ 3.

That unit has a 3 yr warranty (all OCZ units do AFAIK).

I was reading that link that you gave me about rails and I THINK that this could potentially be the exact issue I'm dealing with:

"Example 1:

An FSP Epsilon 700W has ample power for any SLI rig out there, right? But the unit only comes with two PCIe connectors. The two PCIe connectors on the unit are each on their own +12V rail. Each of these rails provides up to 18A which is almost three times more than what a 6-pin PCIe power connector is designed to deliver! What if I want to run a pair of GTX cards? It would have been ideal if they could put two PCIe connectors on each of those rails instead of just one, but instead those with GTX SLI are forced to use Molex to PCIe adapters. Here comes the problem: When you use the Molex to PCIe adapters, you have now added the load from graphics cards onto the rail that's also supplying power to all of your hard drives, optical drives, fans, CCFL's, water pump.. you name it. Suddenly, during a game, the PC shuts down completely. "

I think you've been of great help already, I'm probably going to pull the trigger on that link you suggested before it expires, but the more I understand about this stuff the better.

Have you tried different combinations of PCIe connectors on your cards? I.e. GPU1 = connectors 1 and 2, GPU2 = connectors 3 and 4. Then GPU = connectors 1 and 3, GPU2 = connectors 2 and 4. And finally 1 & 4 + 2 $ 3.

So the PSU that I have has only 2 individual PCIe connectors coming from the PSU. So my understanding is that a better equiped PSU would have 2 individual PCIe connectors coming form the PSU, but those connectors would split into two?

I haven't tried all the possible combos, I'll play around with it tonight and if I don't figure something out that works I will order the one you suggested, after the MIR that is just a damn good price.

 

[lehtv]

Ohhhhh I think I need you to clarify something...

You mean your PSU only has two PCI-E connectors? You're running crossfire with one 6-pin connector per card when BOTH require TWO 6-pin connectors? If your PSU doesn't have four actual PCI-e connectors it is definitely an issue!

Or do you mean your PSU has 4 PCI-e connectors - one in a single cable, another in a single cable, and another two in the same cable? If so, I would expect it to work best if you connected the single cables to each GPU and the split cable to both GPUs.

 

[NTAC]

Ohhhhh I think I need you to clarify something...

You mean your PSU only has two PCI-E connectors? You're running crossfire with one 6-pin connector per card when BOTH require TWO 6-pin connectors? If your PSU doesn't have four actual PCI-e connectors it is definitely an issue!

Or do you mean your PSU has 4 PCI-e connectors - one in a single cable, another in a single cable, and another two in the same cable? If so, I would expect it to work best if you connected the single cables to each GPU and the split cable to both GPUs.

Uhmm here is what I have to work with:

http://www.extremeoverclocking.com/reviews/cases/OCZ_GameXStream_700W_3.html

There are two wires that have PCIe connectors, one I plug into Video card 1 and the other into video card 2.

The other two PCIe connectors come from adapters which I can't say at the moment what rails they are plugging into since I"m not home yet...

But those pictures should show you everything I have to work with, so not sure if I'm doing something wrong as far as how I'm hooking it up. I'm about 99.999999% sure that I'm doing the right thing when I'm connecting the individual PCIe connectors to the 2 video cards, that was my initial problem... That's about all I know though.

 

[lehtv]

Yeah, adapters are the problem. It means that you're powering one GPU's worth from one rail, along with tons of other stuff that is powered from that rail. Order the XFX you won't be disappointed!

 

[NTAC]

Yeah, adapters are the problem. It means that you're powering one GPU's worth from one rail, along with tons of other stuff that is powered from that rail. Order the XFX you won't be disappointed!

Sounds like a plan I wish it was a modular PSU, but for that price I can't really argue

Thanks a ton for all your help!!

 

[Skott]

My only advice is don't skimp on the psu. Spend the money and get a good solid quality brand name product. Saving money is great but if that psu fails on you then you will be cursing the gods for not getting a good quality psu in the first place

Good Luck on the build. .

 

[NTAC]

My only advice is don't skimp on the psu. Spend the money and get a good solid quality brand name product. Saving money is great but if that psu fails on you then you will be cursing the gods for not getting a good quality psu in the first place

Good Luck on the build. .

Oh I know, I never do, but this PSU go such good reviews and for that price, it is hard to beat.

We'll see how it goes when it gets here