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Picking a power supply


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#1 Presnell

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Posted 11 March 2012 - 12:51 PM

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!

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#2 DJBPace07

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Posted 11 March 2012 - 02:26 PM

Most graphics cards have a suggested wattage, some even have a suggested wattage for using multiple cards. These suggested wattages take into account your entire PC. For your build, I would say you would only really need a 700W but you should get just a little bit more at 750W or greater just to have a healthy margin.

At the high-end of PSU's, I'd suggest the Sparkle Computer Corp GOLD CLASS SCC-850AF 850W. This would be followed by the XFX PRO750W XXX Edition then the CORSAIR Enthusiast Series TX750.

By the way, have you considered the Radeon 7870 or 7850? These should be out in a week or so and reviews look good. These cards are geared for gamers so expect a premium until Nvidia releases Kepler.

Edited by DJBPace07, 11 March 2012 - 02:27 PM.

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#3 Presnell

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Posted 11 March 2012 - 02:49 PM

Thanks very much. I'll probably snag a Corsair Enthusiast 850W, since it's not much more and I don't know the exact amount of upgrading I'll eventually do. I'll check out those new video cards, too. Good idea. So those suggested wattages take into account the whole PC? Excellent. I'll just see how much more one of the new Radeon's pulls...

#4 Presnell

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Posted 11 March 2012 - 03:03 PM

Ah, looks like those new Radeons are PCIe 3.0. Not going to work with my Sandy Bridge or my mobo. Oh well. When I sell this rig to my cuz a ways down the line, I'll look into doing the 3.0 route. That's on Intel's Ivy Bridge CPU's, yeah?
Going with the Sparkle Corp PSU you listed. I like the excess wattage and 5 12V rails. Modular, too. Thanks for all the help!

#5 killerx525

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Posted 11 March 2012 - 06:34 PM

The PCI-Express slot is backward compatible, so the PCIe 3.0 gpu will work in the PCIe 2.0 slot. Yes, Ivy Bridge will have PCIe 3.0.

Edited by killerx525, 11 March 2012 - 06:35 PM.

>Michael 
System1: CPU- Intel Core i7-5820K @ 4.4GHz, CPU Cooler- Noctua NH-D14, RAM- G.Skill Ripjaws 16GB Kit(4Gx4) DDR3 2133MHz, SSD/HDD- Samsung 850 EVO 250GB/Western Digital Caviar Black 1TB/Seagate Barracuada 3TB, GPU- 2x EVGA GTX980 Superclocked @1360/MHz1900MHz, Motherboard- Asus X99 Deluxe, Case- Custom Mac G5, PSU- EVGA P2-1000W, Soundcard- Realtek High Definition Audio, OS- Windows 10 Pro 64-Bit
Games: APB: Reloaded, Hours played: 3100+  System2: Late 2011 Macbook Pro 15inch   OFw63FY.png


#6 DJBPace07

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Posted 12 March 2012 - 03:01 PM

PCI Express is backwards compatible, you can use those GPU's on any motherboard with a PCI-E X16 slot.

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