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Need help choosing PSU for homebuilt system

Last response: in Systems
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August 4, 2009 12:04:51 AM

I'm building a system for the first time and I'm having trouble figuring out what wattage PSU I need. I've tried using PSU wattage calculators but got very different results.

Here's what I have:

COOLER MASTER RC-690-KKN1-GP Black SECC/ ABS ATX Mid Tower Computer Case - Retail (this has 2 regular 120mm fans and 1 LED 120mm fan)

Western Digital Caviar Black WD6401AALS 640GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive - OEM ( planning to get 2 of these )

XFX HD-489A-ZDFC Radeon HD 4890 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail (two of these for crossfire)

G.SKILL PI Black 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL4D-4GBPI-B - Retail

GIGABYTE GA-EP45-UD3P LGA 775 Intel P45 ATX Intel Motherboard - Retail

Intel Core 2 Quad Q9550 Yorkfield 2.83GHz LGA 775 95W Quad-Core Processor Model BX80569Q9550 - Retail

I've put this through the Newegg PSU calcualtor and got 858W, but the Antec Power Supply Calculator only gave me 368W and the Thermaltake Power Supply Calculator gave me 356W.

I feel like maybe Newegg's calculator is being overly conservative (or trying to swindle me into buying something I don't need), but I can't say for sure since I've never done this before..

What wattage PSU should I get?
Also please let me know if any of my other parts are incompatible or unreliable, or if there are better alternatives.

Thanks :]
August 4, 2009 3:23:39 AM

thanks
extreme says 388W
none of the 400W PSUs say 'crossfire ready' in their title though, is that important?
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August 4, 2009 3:30:26 AM

Something is wrong with their math, if you plug in 4870's in crossfire you get a higher number. Really for 2 4890s in crossfire you should have a 750 watt PSU. And the crossfire ready means that they have atleast 2 PCI-E connectors.

Unfortunately i think the PSU calculator is no longer accurate. A bit of basic math for you here, a card can pull 100 watts from the slot, a 6 pin provides 75, and an 8 pin provides 150. Since it has a 6 and an 8 at the very least each card is capable of drawing more than 250 watts, which means 500 watts for the two fo them, plus the TDP of your processor. Dont try to run a 4890 on a 400 watt, if you do please record the fireworks.
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August 4, 2009 3:33:16 AM

2 4890s not overclocked use 245 watts just by themselves. Your total system at load will probably be over 500w. That would be with nothing overclocked, only a single hard drive and 2 or 3 fans. I would not use anything less then a 750w power supply.
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August 4, 2009 5:02:17 AM

The Newegg calculator is probably taking into account some of it's really cheap PSUs. After all if you get a crappy PSU and it can't hang you're gonna complain to them and they gotta deal with it.

Anyway I'd probably go by the outer vision calculator as far as minimum watts which, with everything at 100% and no overclocking, is about 430W. Even though that's the max your system will use you generally want a little reserve. Of course you also need a goo PSU just to have enough connections for two 4890s ^_^. Well I guess you could just use adapters too. Anyway to help you out as far as PSUs make sure you research PSU tiers

http://www.eggxpert.com/forums/thread/323050.aspx

Generally a good Antec, FSP, Corsair, Silverstone, or PC Power & Cooling will do (my short list is Antec, FSP, and Corsair). A 750W unit from any of them should generally have enough connectors and more than enough reserve power for you to upgrade your system latter.
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Best solution

August 4, 2009 5:02:24 AM

The Newegg calculator is probably taking into account some of it's really cheap PSUs. After all if you get a crappy PSU and it can't hang you're gonna complain to them and they gotta deal with it.

Anyway I'd probably go by the outer vision calculator as far as minimum watts which, with everything at 100% and no overclocking, is about 430W. Even though that's the max your system will use you generally want a little reserve. Of course you also need a goo PSU just to have enough connections for two 4890s ^_^. Well I guess you could just use adapters too. Anyway to help you out as far as PSUs make sure you research PSU tiers

http://www.eggxpert.com/forums/thread/323050.aspx

Generally a good Antec, FSP, Corsair, Silverstone, or PC Power & Cooling will do (my short list is Antec, FSP, and Corsair). A 750W unit from any of them should generally have enough connectors and more than enough reserve power for you to upgrade your system latter.
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August 11, 2009 2:12:06 AM

wow, thanks guys
looks like the consensus is 750W
almost bought a 500W PSW based on the other calculators
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August 11, 2009 3:03:56 AM

the calculator gives the figure you will draw , but you need a psu about twice that so its running at 50% or so

which means 388 x2 or........................... 750 watts
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