750w for 2x 680s or 7970s?

SKL1

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I'm running crossfire 7950s with everything OCed...no issues at all ;)
 

Tsumi

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It's enough for two 580s on an SB platform, which draws way more power than two 680s or 7970s.
 

grambo

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2x 680's no problem from the benchmarks I've seen, with CPU overclocking, not sure on GPU.
 

bigdogchris

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The new 680SLI review shows 549 Watts is the maximum power draw. The 2600k was OCed to 4.8GHz. At 80% effeciency you would need around 650-700 Watt PSU for SLI 680's.
 

defaultluser

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The new 680SLI review shows 549 Watts is the maximum power draw. The 2600k was OCed to 4.8GHz. At 80% effeciency you would need around 650-700 Watt PSU for SLI 680's.

You reversed the math here. From the review:

We tested the power utilization at the wall

http://www.hardocp.com/article/2012/03/28/nvidia_kepler_geforce_gtx_680_sli_video_card_review/8

The power draw from the review is AT THE WALL AC.

The RATED POWER from a PSU is internal DC.

If you assume %80 efficiency the true DC power draw of the [H] test system is ROUGHLY 550w * (80/100) = 440w.

Of course this is assuming the measurement device they used is accurate (NEVER to be assumed when measuring AC Power), but even if it's off by 50-100w there's still enough juice from a 750w PSU. Even if the AC wall measurements are way off (say 650w-700w real-world AC consumption) this leaves you a little room for video overclocking.
 
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Tiporaro

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He might have been saying that you don't want to be pushing your psu at a constant 80-90%+ max rated capacity, so provisioned the psu to that end. Although that still leaves what you pointed out as to the draw on the psu itself being lower than 550W, so it in some ways compensates.
 

Amdingo

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Mar 30, 2012
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I always like to have a bit of overage just so I'm not pushing the limit that things *could* hit. That said I OC the hell out of everything I put in my PC.

I'd be more concerned with the brand/build quality of a PSU than the watts, as a lot of the crappier ones can't sustain what they say anyway.
 

bigdogchris

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You reversed the math here. From the review:



http://www.hardocp.com/article/2012/03/28/nvidia_kepler_geforce_gtx_680_sli_video_card_review/8

The power draw from the review is AT THE WALL AC.

The RATED POWER from a PSU is internal DC.

If you assume %80 efficiency the true DC power draw of the [H] test system is ROUGHLY 550w * (80/100) = 440w.

Of course this is assuming the measurement device they used is accurate (NEVER to be assumed when measuring AC Power), but even if it's off by 50-100w there's still enough juice from a 750w PSU. Even if the AC wall measurements are way off (say 650w-700w real-world AC consumption) this leaves you a little room for video overclocking.

He might have been saying that you don't want to be pushing your psu at a constant 80-90%+ max rated capacity, so provisioned the psu to that end. Although that still leaves what you pointed out as to the draw on the psu itself being lower than 550W, so it in some ways compensates.
No I meant that most good PSU's are 80% efficient. I did not see that they measured at the wall, which I should of known since [H] has measured at the wall for a long time (just picked up my own Kill-A-Watt :cool:)

So as pointed out by default, a 'real world' power usage by 680SLI would be around 440 Watts, which means that you need at least a 550 Watt PSU, but that would be the absolute perfect scenario for power draw and efficiency. I still wouldn't do it with less than 650-700 watt PSU because efficiency does decline over time. Plus if you wants to add additional drives or fans in the future, you need to consider that.

The sad part is that my 2500k @ 4.4 and my GTX 570 pull 550 watts at the wall (when stress testing which means most things are 100% pegged). Their system is the same power usage but much more powerful :(
 

harmattan

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Feb 11, 2008
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I cant believe people even considering running a boarderline PSU in their system. Even if your 750w will "cut it" you'll likely be red lining it with an OCed system. I'd go for a good quality 850w. I know it's more money, but after 20+ years building systems (Jesus, I just realized this... Getting old), I've learned you do NOT want to run a PSU at close to the limit for an extended period.
 

renji1337

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Mar 31, 2011
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but 750 isn't red lining it according to alot of ppl lol.


i run 2 6950s that r overvolted and ic'd i5 2500k and everythings been great since 6950s came out.
 

MrCaffeineX

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Since the numbers they are talking about in the review are power draw at the wall, I would say that a quality 750W PSU should be capable of powering your target system, even accounting for some age-related decline in performance. According to Anandtech's bench, a 6950 CF system was pulling a little less than the [H]'s 680 SLI system. You're talking about a 40W or so difference in consumption, which I believe they also measure at the wall. Unless you are going to be BitCoin mining or some other activity where your entire system will be pegged at 100% utilization, you should theoretically be able to run up to 600W of equipment (on the DC side, not at the wall) and still be at no more than 80% of the PSU's rated output. PC Power & Cooling has been known to make some good PSUs so I think you should be fine. The only other problem I can think of would be if you have a lot of extraneous devices hooked up in your rig. Perhaps a more detailed system description wouldn't hurt the discussion.
 
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