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Comptible PSU required for SLI?


im thinking of going SLI but have heard that it needs a compatible power supply.  How do I tell if I have one of these already?  Do you end up plugging a power directly into the gfx card?

A brief 2/3 line overview would be great :)


2 Solutions
higher-end graphics cards typically do get their power from direct connections to the power supply (vs the motherboard slot), like a floppy or hard drive. i've even seen one that has it's own external power brick that plugs into a power jack next to the vga connector.

nvidia has a certification or logo program for 'nvidia sli ready' or 'certified' hardware. i don't think it's an absolute "must" to have one that is 'sli certified', but you'll most likely find mainstream 'regular' power supplies just don't have enough 'oomph' to power two higher end graphics cards.  

different sli graphics cards will have different power requirements, so shop for your pair of graphics cards first, then find a power supply that can run them and everything else. this search should get you started: http://tinyurl.com/f2827  ('nvidia sli certified' power supplies @ newegg.com)

as far as telling if yours is or isn't... google the part number & mfg to find the specs, or check the power label on the unit itself. the first thing to look for would be two +12v lines, like this one: http://tinyurl.com/hlgft

nvidia's 'howto' build your sli system: http://www.nvidia.com/object/slizone_howtobuild_1.html 
the slizone does have a (partial) list of 'certified' power supplies here: http://www.slizone.com/object/slizone2_build.html#certified_powersupplies
and nvidia has a user forum for sli discussions here: http://forums.nvidia.com/index.php?showforum=39
The key to providing sufficient power for SLI is the ability to deliver high current on each of the rails, especially the +12v rail, so don't go strictly by the wattage rating.  Good power supplies nowadays split the +12v into two rails, to avoid putting more than 20a on a single line.  There are also brands which are known to be quality manufacturers, so stay with their offerings: PC Power & Cooling, Seasonic, Antec Trupower, Enermax, Zalman, and Thermaltake are examples.

Motherboards with SLI capabilities with high end CPU's do require a higher standard of PSU due to the sheer amount of power consumption for graphics and components.
 Check this PSU calculator out for systems that are extreme including SLI systems http://www.extreme.outervision.com/psucalculator.jsp
MikeeMiracleAuthor Commented:
Thanks you for your helps guys.  The nvidia SLI guide explained it all.  Have given some points for Callandor for pointing out that I need to lookout for the voltage on both 12V lines.

My ultimate question was do th gfx cards have a direct power supply for the PSu and it seems they do.

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