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im having trouble determining the wattage i need for my power supply. i use the calculators on newegg and other sights and usually come up with high 800-900W requirements. then i read alot of posts saying that 650 or so watts is fine for dual cards. please help, heres my expected build, sorry if im not very specific:

i7 930
crossfire 5850's or sli gtx 470's (or southern islands cards)
3x2GB memory
2x64GB Crucial sataiii ssds
5x 7200 sataii hdds
10ish lowpower fans (a bit excessive i know)
4 cathode lights
high end gaming-centered mobo
koolance pmp 450

it is likely that im going to replace the i7 and mobo w/ sandybridge components, but i am also unsure as to whether that will best support my dual gpus

It is always better to get a heavy 650W PSU than a light 800-900W PSU, because the former will actually last longer and not starve your components. My recommendations are here:

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139005

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139006

Welcome to the Forums! Also, check this out:

http://c1.neweggimages.com/BizIntell/tool/psucalc/index.html?cm_sp=Cat32_PowerSupply_left-_-PowerSupplyFinder030510-_-http%3a%2f%2fpromotions.newegg.com%2fproductfinders%2fpowersupply.jpg

So is the 900W for if everything is going to hell at full-throttle?

The power consumption difference between the GTX 470/480 and the HD 5850/5870 is substantial, even more so in SLI/Crossfire. Check the power consumption numbers here. Going from 2x 5850 to 2x GTX 470 there's a ~250W increase in the worst case scenario, so thats probably why you may end up in the 650 - 900 range suggestions.

i should also mention that im planning on some heavy overclocking to about mid 4 GHz

thanks for the advice on that. ill probably go with the 5850 considering the power draw of the 470, i didnt think it was that much.

Given your components and overclocking desires, I would actually err on the side of caution and go with a reputable higher wattage PSU in the recommended range from the calculators. While your system might not draw as much as 800W under full load, your instantaneous power draw from a cold start is something to consider.

dinsdale333 wrote:

thanks for the advice on that. ill probably go with the 5850 considering the power draw of the 470, i didnt think it was that much.

Look at these: http://www.newegg.com/Product/Product.aspx?Item=N82E16817139011 and http://www.newegg.com/Product/Product.aspx?Item=N82E16817139007

5 HDDs are going to suck up power pretty well at bootup, and I think they're not on the 12V rail either. You'll probably need to look at the specific voltage output ratings on your PSU rather than just the wattage number.

850W is too much for this guy's build. My tower (when it was working at least) could handle five hard disks, two Radeon HD 5870s, and an overclocked Q9650 off of a 750W Corsair. THAT should be your target. You don't want to get too much power supply because then it'll operate at poor efficiency, and too little, well, that's obvious. People tend to grossly overestimate the amount of power needed, I've noticed.

A 750W Corsair unit will do the trick. 750W should be ample for your build, and Corsair is notorious for underrating their power supplies.

I agree that your build will probably not require more than 750 Watts... i think the only way to surpass that is to have quad sli with the dual gpu cards or something.

However, when i was in your position, i found that the most reasonable price was a newegg brand Rosewille 1 Kilowatt PSU. At the time it cost around $120, its probably cheaper now. Yes its overkill, but if you count on the fact that PSU's lose 10% capacity every year, you don't want your psu to run out of juice after only 2-3 years. So check the prices, if its not much more expensive to bump up to a higher wattage, go ahead and get it. Yeah you lose 10 or 20 dollars, but you don't have to worry, which is worth it in my opinion. And let me point out, the Newegg brand stuff is much cheaper but probably just as good quality.

edit-- looks like prices are the same as 2 years ago... hehehe

I have a good Corsair HX650 power supply as well as a system that should draw very similar watts to what yours will be and its 100% fine. In matter of fact from the wall I have a hard time breaking 500watts under full stress test, boot spikes at around 300watts. A 650watt power supply should be fine for anybody with less than crossfire'd 5970's or sli'd GTX480's.

thanks for all the help! i might get this- http://www.newegg.com/Product/Product.a ... 6817207003

What gaming resolution are you looking that requires you to get 2 high end cards? For "regular" gaming needs IMO SLI/CF is not such a hot idea and if you step down to a single card build, then a 500-700W unit would be sufficient.

2/3 1920x1080 monitors

You should still be fine with a 500w - 700w range of PSU.

I would get a very high-quality 750W PSU for that, a Seasonic or a company that rebrands Seasonics.