Power supply for new system.

[Presnell]

I'm putting together parts for my first desktop. Just about the last bit is the power supply. I've done a fair amount of research, but still haven't come up with a completely solid idea of what I need. Here's a list of what I've got:

Already ordered:
Intel Core i5-2500
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115073

G.SKILL Ripjaws Series 8GB (2 x 4GB) DDR3 1333 RAM
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231311

EVGA Z68 LGA 1155 motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E16813188097

Looking to order soon:
Antec DF-85 Case
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129087

XFX HD-687X-CNFC Radeon HD 6870 2GB video card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150563

Corsair Force Series 3 120gb SSD
http://www.newegg.com/Product/Product.aspx?Item=N82E16820233206

Windows 7 64bit

Still searching:
Wireless adapter (probably internal and either USB or PCIe, depending on which I find is better/cheaper)

BluRay/DVD/CD read/write drive

Of note:
There are 5 120mm LED fans and 2 140mm fans on the proposed case.

I will not be overclocking this rig, I'll just be running it all as is.

I'm also trying to spec the PSU for future upgrades, including an additional 250gb+ disc hard drive, crossfire config with an identical video card, 2 more sticks of the same RAM, and a sound card.

When I added it all up, (2 video cards at just under 500W, i5-2500K at 130W when overclocked (I will not do this, but using as a buffer), 25W for 7 case fans, 60W for 4 sticks of RAM, 150W for motherboard, 30W for a Bluray drive, 10W for a wireless card, 10W for an SSD, 30 for a disc hard drive, and a 50-75W buffer just in case.) I get up to nearly 1000W. Doesn't seem quite right too me, but there it is. I realize I'm being rather generous with some of these figures, but I'm ok with that. If anyone thinks some of these are wildly off, too low or too high, let me know. I got most of these figures from various benchmarks I found through Google. Alternately I used this wattage calculator:

http://extreme.outervision.com/PSUEngine

and came up with a very different result at about 800W. I've also learned that the voltage rails in the PSU are just as important.
A couple problems. I have yet to find a clear way to determine what Amps I need my 12V rail to carry. I think it's the watts divided by 12V, so about 71Amps (850/12=71). But I'm also aware not all of the computer hardware will share the 12V rail(s) as some will be on the 5V and the 3.3V. I haven't been able to find out clearly which parts will receive power from which rail.

Originally, this Corsair AX850 power supply was in my mind:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139022

But now I'm thinking this may not be enough. With 850 watts and a 70Amp 12V rail, I think it may be cutting it a bit close, so I'll upgrade if needed, depending what I find out.

Any thoughts or good resources on the topic of PSUs and determining what a computer needs? Keep in mind, I won't be overclocking and will be using this mainly as a gaming rig, so I'll be pushing the video card a fair bit. Thanks!

 

[azeem40]

For one 6870, a 550W PSU is all you'll need. A good 80+ BRONZE unit from XFX, Corsair, or Seasonic are your best bets. Antec is good but is one tier lower.

 

[aqe040466]

You might want to overclock the CPU in the future because the MB supports overclocking. Here is a link:
http://www.microcenter.com/single_product_results.phtml?product_id=0354589

 

[Presnell]

For one 6870, a 550W PSU is all you'll need. A good 80+ BRONZE unit from XFX, Corsair, or Seasonic are your best bets. Antec is good but is one tier lower.

Gotcha. I'm trying to spec it for 2 6870's, however. Do you think an 850W 80+ Bronze from Corsair would work? Also, from almost every forum, site, etc. I've seen, whenever questions come up about power supplies, usually the only factor in power consumption mentioned is the video card. I realize that these parts are by far the biggest draw, but shouldn't I factor in everything else? Any idea what other parts occupy space on the 12V rail(s)?

 

[Presnell]

You might want to overclock the CPU in the future because the MB supports overclocking. Here is a link:
http://www.microcenter.com/single_product_results.phtml?product_id=0354589

That's a good idea, and I'll consider it an upgrade path, but I've already ordered the i5-2500. I'd regret it as a wasted opportunity, but I got a good deal on it. Thanks!

 

[azeem40]

2 6870s will only need 650-750W.

 

[Presnell]

You might want to overclock the CPU in the future because the MB supports overclocking. Here is a link:
http://www.microcenter.com/single_product_results.phtml?product_id=0354589

Heh. Those Micro Center deals seem to be really good. But they're usually in-store only! I've seen a few others that I was just dying to get, like an i7-2600 for $200, but I live nowhere near one, nor does anyone I know. They have very few locations...

 

[jonathanrhunter]

Yeah make sure you get something with good efficiency, 80+. My recommendation for a PSU would be one made by Corsair in their server-grade category. They are a little more expensive but they come with good wattage and a 7-year warranty. With all PSU's it's only a matter of time before they die.