# What power supply do I need for Radeon 6950 Crossfire?



## jonathan1107 (Apr 22, 2011)

What kind of power supply would I need to power 2 XFX radeon 6950 2gb...

I also intend to power my i7 875k and overclock it... I have many fans too...


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## erocker (Apr 22, 2011)

750 watt or more quality brand PSU will be good.


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## cadaveca (Apr 22, 2011)

erocker said:


> 750 watt or more quality brand PSU will be good.



It's worth noting that my brand-new Silverstone 750W STRIDER GOLD is NOT capable of powering a Sandybridge i7 2600K rig with one reference, and one non reference card, when the system is overclocked, and neither is my new Corsair TX850W.

The TX 850 shows some signs of issues with a mild overclock, and the 750W Silverstone actaully manages to do better, but with the system maxed, it is not. I am not sure if it's the board is a bit tepermental with the 750W, but for sure the TX850 just isn't cutting it.


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## erocker (Apr 22, 2011)

cadaveca said:


> It's worth noting that my brand-new Silverstone 750W STRIDER GOLD is NOT capable of powering a Sandybridge i7 2600K rig with one reference, and one non reference card, when the system is overclocked, and neither is my new Corsair TX850W.
> 
> The TX 850 shows some signs of issues with a mild overclock, and the 750W Silverstone actaully manages to do better, but with the system maxed, it is not. I am not sure if it's the board is a bit tepermental with the 750W, but for sure the TX850 just isn't cutting it.



Sounds like your PSU's are defective or it's an electrical issue with you house. I use a TX850 that is over a year old in my rig that consumes more power than yours and have had zero issues with it..


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## Lionheart (Apr 22, 2011)

Same with what erocker said, a quality 750W PSU should be sufficient


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## fullinfusion (Apr 22, 2011)

Id agree with Erocker as well, Im using an HX850 and 6950's pushed as well as the cpu and all the extra shit sucking power from the psu, hasnt given a problem at all.


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## cadaveca (Apr 22, 2011)

erocker said:


> Sounds like your PSU's are defective or it's an electrical issue with you house. I use a TX850 that is over a year old in my rig that consumes more power than yours and have had zero issues with it..



Could be house power, for sure. 

I think we're *not* about the same for power use, though. I think you've got it backwards, I'm pretty sure I'm pulling more power through cpu/gpus. What I'm missing in waterpump is easily made up in fans, soundcard and USB devices, as well as multiple monitors on the vgas pushing up the GPU a bit.

Both are fine @ stock, 100%. If you figure that AMD recommends a 500w PSU for just one card, and add the possible 225w from the second card, you've got 725w. I think 225w is a safe estimate, as AMD recommends a 550W PSU for single 6970...again, add in a possible 300W, and you are at 850W.

Fully clocked, I'm pushing 5.5ghz on the Sandybridge, and 1050/1450 on the VGAs. PSU is a huge factor when pushing clocks to the max, and I doubt anyone here is currently pushing similar clocks.

Could be because I'm got all the memory slots full, so the cpu is a bit more sensitive. In the end, the Antec 1200w works fine, as does the systems with just one card, and "reasonable" clocks.

Keep in mind, I'm pushing much more than the average user, and am not refering to "daily" clocks...I run stock pretty much day to day.

It's worth noting that XFX has told me that my 750W *should* be OK too.



fullinfusion said:


> Id agree with Erocker as well, Im using an HX850 and 6950's pushed as well as the cpu and all the extra shit sucking power from the psu, hasnt given a problem at all.



The HX is a MUCH better unit than the TX. I think you need to be REALLY picky if going 750W, but 850W is about right for most users.


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## erocker (Apr 22, 2011)

cadaveca said:


> Could be house power, for sure.
> 
> I think we're *not* about the same for power use, though. I think you've got it backwards, I'm pretty sure I'm pulling more power through cpu/gpus. What I'm missing in waterpump is easily made up in fans, soundcard and USB devices, as well as multiple monitors on the vgas pushing up the GPU a bit.
> 
> ...



According to my UPS I'm pulling 655W under full load. My six core AMD chip eats a hell of a lot more juice than your Sandy Bridge, even at 5.5ghz most likely. Then again, I am using a UPS are you? My house is very old and I did have random issues with my computer before using a UPS which have dissappeared after installing it. I would recommend getting one as I'm convinced they make a difference if you have older wiring etc. in your home. I think people need to address the quality of power going in to their PSU's.


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## cadaveca (Apr 22, 2011)

Yep, got a UPS. Single 30A circuit, new, with just the PC, now. Just installed the new circuit recently, actually. I'm doing a fair bit more specific power testing, with the Zalman units...I'm pulling WAY more than you think. I'm pulling about 625w from the wall from the cards alone. They don't draw that much, closer to just under 275w each, but then PSU efficiency takes it's bite as well.

CPU is pulling 195w itself, again, not all is CPU, but VRM's aren't really that efficient just yet.

I've got inline plugs on every power connector except for molex and sata, and 24-pin monitoring power usage.

In the back of my mind I wanna remind you about Peet's e6400 cpu, and what we each thought about how much power was being used.


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## erocker (Apr 22, 2011)

cadaveca said:


> I'm pulling about 625w from the wall from the cards alone.



You must use a different kind of electricity where you live.  I just don't see how that is possible.


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## cadaveca (Apr 22, 2011)

erocker said:


> You must use a different kind of electricity where you live.  I just don't see how that is possible.



What clocks are you running? take off those coolers, see how much the card pull when hot. 

Do you have 1GB cards, or 2GB?


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## erocker (Apr 22, 2011)

cadaveca said:


> What clocks are you running? take off those coolers, see how much the card pull when hot.



Lol. I don't wanna have to deal with XFX support. NO THANK YOU.

I use 1gb cards and I realize they'll use less power. However how do you explain W1zzards numbers? http://www.techpowerup.com/reviews/HIS/Radeon_HD_6950/27.html

190 watts maximum from a single card.


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## cadaveca (Apr 22, 2011)

erocker said:


> Lol. I don't wanna have to deal with XFX support. NO THANK YOU.



 They did keep replacing my cards, although I had issues, I'm rocking it now! 

I was actually pretty shocked by how much they are sucking, but I mean, just go take a look at W1zz's reviews...and the clocks he gets...the lightening 6970 review is a good place to start, that card with reasonable clocks was pulling 250w, and he's not reporting numbers from the wall...he's monitoring from the plugs and the slot. And I'm pushing higher numbers from a worse peice of silicon.


Uh, The 190W you are quoting is @ stock.  An extra 60w is no big deal. Um, erocker...lol, how come you're missing the obvious?



> For our power consumption testing AMD's power control system was set to "0" for all tests. Only for Furmark Maximum, we set the slider to "+20".



If I had really good cards, the power consumption would probably be less, but really mine clock pretty poorly.


EDIT:


A 750W is going to limit clocks. And 850W, gonna limits those looking for extremes. Either can work...although I think many 750W PSU's just won't cut it with overclocking, and will be the weak link.


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## BababooeyHTJ (Apr 22, 2011)

I'm running an i5 760 and two 6950s in crossfire on a Seasonic X650 Gold. This psu has yet to break a sweat. Even with the 760 at 4ghz and the cards at 900/1350 when running three threads of Linx and GPU tool scanning for artifacts my pc doesn't draw much over 500w at the wall including my 28" monitor according to my UPS.


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## cadaveca (Apr 22, 2011)

BababooeyHTJ said:


> I'm running an i5 760 and two 6950s in crossfire on a Seasonic X650 Gold. This psu has yet to break a sweat. Even with the 760 at 4ghz and the cards at 900/1350 when running three threads of Linx and GPU tool scanning for artifacts my pc doesn't draw much over 500w at the wall including my 28" monitor.



That's actually pretty impressive. Just keep in mind that when cpu speed and power increases, so do framerates, meaning a GPU paired with a 4GHz i7 CPU will draw a bit more power than when paired with a 4GHz i5 chip or a 4GHz AMD chip. More frames=more power consumed.


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## BababooeyHTJ (Apr 22, 2011)

Are there any differences between an i7 like the 860 that I had and my current 760 other than hyper threading which actually hurts more often than it helps when it comes to gaming? I'm also not really pushing this cpu too hard as far as voltage goes. My 6950s also sit at the stock 1.1v core voltage. I'm sure that I could get it to draw quite a bit more with some more voltage that I don't really need and something like OCCT's psu test but more than 650w I'm not sure.


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## cadaveca (Apr 22, 2011)

BababooeyHTJ said:


> Are there any differences between an i7 like the 860 that I had and my current 760 other than hyper threading which actually hurts more often than it helps when it comes to gaming?



I haven't found many situations where HT hurts anything. I've the 760(on P7P board I reviewed here) and the 870(on Maximus III Gene, I also reviewed here), as well as the Sandybridge rig. I can get both 1156 CPUS to 4.4ghz though, and came to conclusion that the 870 does better, simply due to being able to push 2400mhz on the ram, while getting much over 2133 on the 760 is near on impossible with the boards I got.

There's been a couple of games that wouldn't play well with HT when released, but that's not really due to the CPU..that's down to poor progamming.


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