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Supplies and SLI

M

mckeonm

n00b
Joined
Sep 26, 2006
Messages
22
I'm looking to get a new supply and if I ever run an SLI setup I want to be ready. But I'm confused as to how some of these supplies qualify. The specs for some of the new cards require quite a bit of amperage, like the GTX 260 requires 36 amps. So two cards would be 74 amps right? If a supply says it delivers 60 amps, is this combined 12 volt rails, or can each rail deliver 60 amps?

http://www.newegg.com/Product/Product.aspx?Item=N82E16814150329

In the specs above, the card requires a 630 watt supply or 680 watt for SLI. How is this possible? Why only 50 more watts, why is it not much much greater? The specs don't always say what each wattage setup requires, it just gives you amperage, so how do you tell what you need for SLI?
 
The pci express slot can give up to 75 watts of power
each additional 6 pin power connector (also known as pci express 6 pin) can provide another 75 watts of power.

A gtx 260 only has two additonal 6 pins and the slot itself, thus only able to drain from the power supply a maximum of 225 watts.

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Now a gtx 260 doesn't drain 225 watts in reality it drains less than that. 2 gtx 260s would drain less than 450 watts. But once you add the other components and the graphic card manufacture wants to add some safety tolerance for the people with extreme amount of hard drives, overclocked quads, motherboards that aren't efficent, and cheap power supplies they want to be on the safe side.

Thus in theory you only need a little over 500 watts to run 260 in sli, but I would feel much more comfortable in the 600 to 700 range.
 
That 36A rating is for the system + the video card, not just the video card itself. Generally when a PSUs says i t provides 60A on the +12V rail, that's usually the combined total on the +12V rail.
 
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