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Why do they recommend 750+ watt PSu's for SLI/Xfire?

post #1 of 44
Thread Starter 
I am a noob in the process of still learning, and i myself have a 850wat PSU for my sli setup.

But i keep track of all these gfx card reviews and what not, and i never understood, and no one has really explained why people tell others to go for 800+ wat psu for sli setups, when i just watched a video review on youtube and a whole system running GTX580sli takes 465 watts under full load from the wall.
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post #2 of 44
Total wattage or power, being the advertised metric I suppose is ok, personally I would look for the Sli/Xfire certification on the psu before making a purchase of a psu with the implied purpose of Sli or Xfire.

As far as the reason behind this, previously the psu's did not supply an independent power source/TR/capacitor/VR (so on and so forth) (not siphoned off one of the system rails or rail) for the video card power demands, and as the demands both went up and the voltages required tightened up, the performance that would be felt on the card(s), and the stability, would suffer under different load conditions.

Simply, a set of design changes within the psu allows for greater voltage control and cleaner voltage signal when the psu is tasked with supplying power to video cards, resulting in better clocks, and improvements to stability under load conditions.
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post #3 of 44
Because people are idiots.
post #4 of 44
Thread Starter 
Quote:
Originally Posted by Soggysilicon;12863813 
Total wattage or power, being the advertised metric I suppose is ok, personally I would look for the Sli/Xfire certification on the psu before making a purchase of a psu with the implied purpose of Sli or Xfire.

As far as the reason behind this, previously the psu's did not supply an independent power source/TR/capacitor/VR (so on and so forth) (not siphoned off one of the system rails or rail) for the video card power demands, and as the demands both went up and the voltages required tightened up, the performance that would be felt on the card(s), and the stability, would suffer under different load conditions.

Simply, a set of design changes within the psu allows for greater voltage control and cleaner voltage signal when the psu is tasked with supplying power to video cards, resulting in better clocks, and improvements to stability under load conditions.

So i saw this 620 Watt PSU thats sli ready and 80 plus certified, thats completely fine for sli580's when the under full load they are 465watts measured at the wall?
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post #5 of 44
Quote:
Originally Posted by Phaedrus2129;12864652 
Because people are idiots.

Exactly what I was going to say.
Quote:
Originally Posted by Soggysilicon;12863813 
Total wattage or power, being the advertised metric I suppose is ok, personally I would look for the Sli/Xfire certification on the psu before making a purchase of a psu with the implied purpose of Sli or Xfire.

SLI/Crossfire certification doesn't mean jack.
Edited by GameBoy - 3/25/11 at 8:37am
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post #6 of 44
ive seen a whole i7 system with GTX 580 sli takes 777 watts from the wall...
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post #7 of 44
Thread Starter 
Quote:
Originally Posted by ShortySmalls;12865490 
ive seen a whole i7 system with GTX 580 sli takes 777 watts from the wall...


skip to 4:56

[ame="http://www.youtube.com/watch?v=DI3W2ljcuEo"]http://www.youtube.com/watch?v=DI3W2ljcuEo[/ame]
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post #8 of 44
His power meter is being fooled by APFC circuitry.
post #9 of 44
Quote:
Originally Posted by Phaedrus2129;12867287 
His power meter is being fooled by APFC circuitry.

Considering just one 580 in a system may use http://www.guru3d.com/article/geforce-gtx-580-review/7 447 watts (from the wall, of course) I'd say you're right.

I've seen 460 SLI reviews hit ~450 watts. I'm sure 2 580s use quite a bit more.

Let's not forget Nvidia 5xx cards throttle in Furmark.
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post #10 of 44
I looked @sapphires site before i chose a PSU and they recomend crazy stuff there.
Iirc 500w+! It`s really funny that the rest of the comp doesn`t need that much power just the graphic card is hungry biggrin.gif
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