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 Post subject: how many watts?
PostPosted: Sun Mar 27, 2011 6:18 am 
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Joined: Fri Mar 18, 2011 5:23 pm
Posts: 4
hi

i am trying to get some sense of the components for my first build. im trying to put together an i7 sandy bridge, and i expect to load the cpu a bit, and i will want 2 hd's and 4g of ram. so i am wondering how much wattage i will need. i came across a mention that the tdp of the sandy bridge is 95w, but

i tried some configs on this and i would guess that 450w would be enough without video card, 600w with:

http://www.journeysystems.com/power_supply/

but it doesnt have the cpu im looking for but you can figure it out anyway.

im especially interested in the fanless psu, but i am wondering what happens, for instance, if the wattage draw is higher than what the psu is rated for? does a fuse blow or something like that, that seems pretty bad??

thanks for any info
-neal


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 Post subject: Re: how many watts?
PostPosted: Sun Mar 27, 2011 6:29 am 
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Joined: Thu Feb 04, 2010 6:06 pm
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Location: US
gongli wrote:
450w would be enough without video card
That seems way to high. From what did you build that number?

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 Post subject: Re: how many watts?
PostPosted: Sun Mar 27, 2011 7:24 am 
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gongli wrote:
i tried some configs on this and i would guess that 450w would be enough without video card, 600w with

Way too high. There's no way a Sandy Bridge setup with a GPU will require a 450w PSU. Not even massively overclocked. Your GPU of choice draws 150w according to that website. Which one is it? 150w would indicate a GeForce GTX 460 or a Radeon 6800 or below.

The 400/480w Seasonic passive PSUs should definitely suffice. If you want to be certain, get a X-560, it's semi-passive and in your setup the fan won't spin up until you fire up a video game.

If you overtax a PSU, esp. a quality one like the Seasonics, the worst you're looking at is the system becoming unstable because the voltages drop out of specification.


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 Post subject: Re: how many watts?
PostPosted: Sun Mar 27, 2011 10:17 am 
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Joined: Mon Jul 16, 2007 2:35 pm
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Location: Greece
450 watts should certainly be enough. A system with the components you mention would draw around 250-300 watts under load (less if only the cpu is stressed) well within the capabilities of a 450 watt psu, with some headroom for overclocking.

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 Post subject: Re: how many watts?
PostPosted: Mon Mar 28, 2011 4:09 am 
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Joined: Wed Jun 13, 2007 10:12 am
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Location: ITALY
gongli wrote:
i tried some configs on this and i would guess that 450w would be enough without video card, 600w with

Something like a Radeon HD 6950? At anyway, AFAIK an oc'ed i7 with a pair of disks and sticks won't pass the 150-180W DC marks ever (with the IGP).

gongli wrote:
what happens, for instance, if the wattage draw is higher than what the psu is rated for?

I mean it depends of the specific PSU: some can get away scot-free when overloaded, some other else just melts. Often, at anyway, there are over-current and over-temp protections which switch off the PSU itself.
To the first type belong the Seasonic X-400FL and X-460FL, I guess.

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 Post subject: Re: how many watts?
PostPosted: Mon Mar 28, 2011 6:08 am 
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Location: Colorado, USA
You could honestly run a Sandy Bridge GPU-less system with a 300W power supply and have plenty of juice left over. Keep in mind that Bridge CPUs can be undervolted and then would not use the full 95 Watts. Hard drives take ~10 Watts max.

Depends what graphics card you have, but the 430W power supply in my system only nees to supply about 200W to my system under full GPU/CPU load.

So, a 450 or 500 Watt should be enough, unless you go with one of the more hungry video cards. If you game, that would be good. If you don't, your just wasting money. A radeon HD 5750 can be made fanless (Arctic Cooling Accelero S-1 rev 2) and underclocked/undervolted to a point where they use very little power.

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