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PSU for quad core, CrossfireX

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January 29, 2009 11:53:37 PM

Hi there
I need some help figuring out what PSU i need. Im looking to upgrade to a Phenom II and a 4870 Crossfire build. Currently i have a single 4850 and Athlon X2. My main concern is the fact that a quad core CPU draws WAY more power than a dual-core, especially when overclocked. I used that Xtreme PSU calculator and to overclock the Phenom II 940 to 3.8 @1.48v draws about 235W :o  . Obviously the draw from the two cards is also going to be significant. After inputting all my other devices the final figure came to about 625W, give or take 25W depending on some minor changes i may or may not make. The question i have is, ultimately, which PSU will i need. If the final number is 650, does that mean a 700W psu is adequate? How will it react under heavy load? How high should I go with that build just to be safe, but without going overboard? 750W? More? Im a bit of a PSU n00b so im not sure how to figure this stuff out myself. Thanks.
January 30, 2009 4:54:58 PM

most 650, 700 and 750 are very clost to same thing there is a lot overlap

antec 650 equals a cheapy 750 or 800

ratings have a lots of wiggle room

total watts maximumu to start / .6 = my psu selection for you a 750 is good
January 30, 2009 4:59:19 PM

over board is less then 30-40% on average usage

if you have 1000w psu and you use 300w average it is too big

as you approach 40-50% of load the 1000w is big but not too big

look at effieceny curves for your psu
then look at power conmption of like systems THG has good articles
then add up the power usage

your estimated + similar systems/2 = better estimate

better estimate max x .6 = ideal psu size w/ upgrade built in

too big is bad but too small is woarse - nobody buys 1000w psu and sticks a built in gpu mobo (onboard graphics) in and 45w cpu and one hard drive but many people try to get by with 90% psu or case psu that is stamped 600w but is really a 450w when compared to antec, silverstone, thermtake, corsair other the other high end units

January 31, 2009 2:01:54 AM

Nice formulas. Using those i got about 555W. Im going to take your advice and get something nice. Its between a PC Power and Cooling SB75QB and a Corsair 750-TX, with the latter being the popular choice at the moment. Thanks for all your help.
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