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Why do they recommend 750+ watt PSu's for SLI/Xfire? - Page 3

post #21 of 44
I have an X650 running my system. No problems.
post #22 of 44
I wanna know if the x650 could power an overclocked 9XX and sli 580.
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post #23 of 44
For every good PSU there is probably another 10 Cheap China PSU's which is what they factor in.

Most of us having Good PSU's but maybe someone doesnt and Nvidia cater for that in there "Generous" Min PSU Requirements.
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post #24 of 44
Quote:
Originally Posted by Madstrike View Post
So, would a good psu like ax750w be enough for sli gtx 580(mild overclock) with i7 920(mild overvolt)?
Absolutely. Guru3D tested the power draw from the wall outlet from a system that had two GTX 580s in it, and while under extremely full load, the entire system pulled a maximum of 719W from the wall:

http://www.guru3d.com/article/geforc...-sli-review/14


Here is their test system:

http://www.guru3d.com/article/geforc...0-sli-review/3

So let's say that their PSU was 85% efficient during this power draw. If it was, then the system itself was pulling about 611W from the power supply which would be a very easy job for the mighty AX750 (which has a +12V capacity of 62A which is 744W). If their PSU were 80% efficient, then that would be approximately 575W.


Quote:
Originally Posted by rxsocal View Post
I wanna know if the x650 could power an overclocked 9XX and sli 580.
I think I have to say no.

However, I would love to see someone test it! Seriously!


Quote:
Originally Posted by Jesse^_^ View Post
For every good PSU there is probably another 10 Cheap China PSU's which is what they factor in.

Most of us having Good PSU's but maybe someone doesnt and Nvidia cater for that in there "Generous" Min PSU Requirements.
The reason why their power supply requirements are said to be "generous" or "bloated" is because they are talking about PSUs that have a peak rating.

For example: the GTX 580 has a power supply requirement of 600W to power a system with one GTX 580 in it. This means that at minimum, a power supply with a 600W "peak" rating is required. Therefore, even a quality 550W would handle such a system just fine because most good 550W power supplies have a 550W "continuous" rating while their "peak" rating exceeds 600W (their peak approaches 650-675W).

This applies to AMD too.
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post #25 of 44
For SLI, the better the power rating and overall quality of the PSU, the better. I mean, if you can afford multiple GPUs then a good over powered PSU can't be too much of a financial burden.

I have a 850W PSU because I like a bit of headroom for future upgrades. PSU aren't really something to skimp on.
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post #26 of 44
Quote:
Originally Posted by Phaedrus2129 View Post
His power meter is being fooled by APFC circuitry.
then what is a proper device to check with? Because if checked with my Zalman MFC2, a UPS that it's on and a belkin "kill-a-watt" type device and they all show my system pulling over 800W at the wall (with a 90% efficient psu thats about 720W)

edit: and for the record im not trying to argue, i just want to know the truth and how to find what my system really draws
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post #27 of 44
A lot of tech guys want to live in a world of overkill.
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post #28 of 44
Quote:
Originally Posted by Blindsay View Post
then what is a proper device to check with? Because if checked with my Zalman MFC2, a UPS that it's on and a belkin "kill-a-watt" type device and they all show my system pulling over 800W at the wall (with a 90% efficient psu thats about 720W)

edit: and for the record im not trying to argue, i just want to know the truth and how to find what my system really draws
No. At 90%, 800W from the wall is 888.89W total.

EDIT I am wrong (again). I hope I screwed up your day.
Edited by spaceballsrules - 4/3/11 at 10:40am
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post #29 of 44
Quote:
Originally Posted by spaceballsrules View Post
No. At 90%, 800W from the wall is 880W total.
umm no, those numbers are measured at the wall, thus what is actually going to the components on the inside is less
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post #30 of 44
Quote:
Originally Posted by GameBoy View Post
Exactly what I was going to say.



SLI/Crossfire certification doesn't mean jack.
Sure it does, for all the reasons mentioned in this thread.

Of course you are certainly welcome to go and buy some knock-off 850w HEC power supply and toss the dice for yourself.

Am I implying that you want to build your system around some sticker on a box? Hell no. It just happens to be the first thing I look for when shopping psu's for the purpose of an SLi/Xfire build, beyond that there are plenty of things I want to see to determine if the psu is of quality or not, as well as make some predictions as to where the system efficiency is going to fall when its all said and done.
 
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