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Need advice for SLI and PSU please.....

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Anonymous
October 3, 2011 6:29:54 PM

Hi peeps hows you be!!! Anyways I just built my first gamer PC and I need to know if my PSU can handle it all...My Specs are as follows: I7 2600K ,ASUS Deluxe Z68 ,12 gigs vengence ram ddr 3 (3x4 )2000 mhz running in xmp profile,blu ray and dvd burner (one of each) ,after maket cpu fan ultra cooler x7,3
TB hdd ,EVGA GTX 580 SLI (getting them oct 4th) and my Cooler Master HAF 932 Full Tower Black Case running 4 fans plus the cpu fan. being powered by my rocket fish 900 w 80 plus silver PSU. and my monitor is a 52 inch sharp aqious. I sure im good but not sure about the SLI. Thanks. :)  My PC is all built except for my GPU's im waiting on, right now my GPU is a GT 230 lol.

More about : advice sli psu

a b ) Power supply
October 3, 2011 10:02:31 PM

So why are you running this beast in single channel memory mode?
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a c 286 ) Power supply
October 3, 2011 11:42:56 PM

Because you bought a 3x4GB kit, it comes with 3 sticks each with 4GB capacity.

What GPUs are you planning to get? Rocketfish isn't exactly known for making good power supplies so im not sure how well it would hold up to two really high powered GPUs but a pair of smaller ones like 560s it should be able to do well enough.
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Anonymous
October 4, 2011 12:19:48 AM

hunter315 said:
Because you bought a 3x4GB kit, it comes with 3 sticks each with 4GB capacity.

What GPUs are you planning to get? Rocketfish isn't exactly known for making good power supplies so im not sure how well it would hold up to two really high powered GPUs but a pair of smaller ones like 560s it should be able to do well enough.
Two GTX 580 1.5 gb's each SLI
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a b ) Power supply
October 4, 2011 12:53:25 AM

Some points:
1) Use 2x4GB (see motherboard manual for proper spots). Keep that extra 4GB module in a static bag as a spare. 8GB is plenty anyway.

2) SLI. I'm not a fan. There's a great article here at Tomshardware discussing the micro-stutter issue. HEAT and NOISE will be huge. It's also overkill for most games.

I'm running an HD5870 (slightly less than a lowly GTX560Ti) and I can max out most games at 60FPS, 1920x1080, 4xAA etc.

3) I strongly suggest you get a single GTX570 for now and upgrade in the future. The new GTX600 series comes out next year. For you, I'd wait another year or two though until it would make a big difference.

4) Power Supply:
You need to consider overall Wattage as well as the Amp rating for Graphics card. PSU's will list the Amps on its +12V rail (or rails). If multiple rails you must find the COMBINED value, not add them up.

Example:
GTX570, requires 38Amps. (I might recommend a 620W Antec High Power with 48Amps)

If you still got SLI, you add up the Amps (2xGTX570 needs 76 Amps minimum. I'd want at least 90Amps from the PSU's +12V rail)

I usually add up like this:
1) start with 400Watts
2) add the maximum Wattage peak of each graphics card (say 250W per)
3) so for 2xSLI that might be 400W + 250W + 250W = 900Watts
4) then look at the Amps, say 45Amps + 45Amps

So in this example, I'm looking for a 900W PSU (roughly) with at least 100Amps on the +12V single, or combined +12V rails.

The Amps thing is separate. Each card still uses Wattage but you can't simply pick any PSU because it might not have the Wattage where the graphics card can use it, the +12V rail.

I hope that's not too confusing.
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Anonymous
October 4, 2011 1:18:27 AM

Best answer selected by jhborden.
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Anonymous
October 4, 2011 1:22:00 AM

I had to read it through a couple times very good helpful advice I can refrence with.Thank you I already own one GTX 580 that I had with my 900 w rfish PSU in my former Hp-Elite 150-f and had no problems. Some website must have the same ram I have at a 1 or stick kit I would hope :) 
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a c 286 ) Power supply
October 4, 2011 1:26:20 AM

Photonboy, i think you might be rounding up a bit there and may not actually understand how GPU power requirements are written.

The 45A or 38A it says or whatever, is for the system as a whole, when you add a second card that number does NOT double, a 570 needs about 240W or 20 A @ 12 V, not 38 A, so when you add the second card your power requirements dont double, they only go up a bit, in this case to about 60 A or a good 750 W unit.


Also, going down a bit farther, you will never find a 900 W unit with 100 Amps combined power on its 12 V rails(at least not one thats telling the truth), 100 A at 12 V is 1200W, way more than a 900 W unit.


A modern system draws most of its power from the 12 V rail of the power supply, and most modern units get the power for the 5 V and 3.3 V rails from the 12 V rail so almost all of the power of the PSU is available off the 12 V rail so for the most part you can convert how many watts your system needs into about how many amps you will need on your 12 V rail. Watts = Amps * Volts, or in this case Amps = Watts/12 V
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