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Quad 12v rails question

post #1 of 4
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Can anyone take the time to explain to me how the 12v rails on power supply's work iequad 12v, dual 12v).

For instance, I have a OCZ gamestream 700w psu with 4 x 12v rails rated @ 18amp per rail. My video card requires 26amps on the 12 volt rail. I am not running SLI but in my case does the quad 12v rails add up to 72amps total, or am I only getting 18amps to my video card?
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post #2 of 4
Quote:
Originally Posted by N00builder View Post
Can anyone take the time to explain to me how the 12v rails on power supply's work iequad 12v, dual 12v).

For instance, I have a OCZ gamestream 700w psu with 4 x 12v rails rated @ 18amp per rail. My video card requires 26amps on the 12 volt rail. I am not running SLI but in my case does the quad 12v rails add up to 72amps total, or am I only getting 18amps to my video card?
To really simplify things here, yes, the four 12V rails add up to supply your system's needs. However, you really only have a maximum of 18amps x 3 to play with. The reason is one of the 12V rails directly feeds the CPU (the four- or eight-pin 12V connector on your motherboard). The rest of the 12V rails are therefore left to combine to supply your system's needs.

So, given that you have a theoretical maximum of 54amps to play with, you also have to consider the power demands of the rest of your system. If we therefore subtract the 26amp requirement for the video card, that gives you a total of 28amps to feed the rest of your 12V needs. Keep in mind, though, that the more components you have on your system, the greater the demand on the 12V rails. HDDs, optical drives, and your cooling system(s) all share the 12V amperage output.

PSUs are immensely interesting components, in my opinion, and lately a lot of my studies are focused on this subsystem. Hopefully this information is communicated correctly here.

Hope this helps!
    
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post #3 of 4
Quote:
Originally Posted by txtmstrjoe View Post
To really simplify things here, yes, the four 12V rails add up to supply your systems needs. However, you really only have a maximum of 18amps x 3 to play with. The reason is one of the 12V rails directly feeds the CPU (the four- or eight-pin 12V connector on your motherboard). The rest of the 12V rails are therefore left to combine to supply your system's needs.

So, given that you have a theoretical maximum of 54amps to play with, you also have to consider the power demands of the rest of your system. If we therefore subtract the 26amp requirement for the video card, that gives you a total of 28amps to feed the rest of your 12V needs. Keep in mind, though, that the more components you have on your system, the greater the demand on the 12V rails. HDDs, optical drives, and your cooling system(s) all share the 12V amperage output.

PSUs are immensely interesting components, in my opinion, and lately a lot of my studies are focused on this subsystem. Hopefully this information is communicated correctly here.

Hope this helps!
That is only slightly true... most PSU's are pretty optimised when it comes to rail layout.

And no, you can't compare amps like 4x 18A.
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post #4 of 4
Quote:
Originally Posted by gonX View Post

And no, you can't compare amps like 4x 18A.
How about a more detailed explanation, please? The sources I've consulted all say that, with multi-rail 12V amp ratings, the necessary number is the aggregate of the different rails. (Whether the reported outputs are true, though, is another thing altogether.)

Thanks.
    
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Lian Li PC-V2000B (with thlnk3r mods) 
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Phenom II X3 720 BE Gigabyte GA-MA790FXT-UD5P Sapphire Radeon HD 3870 2 x 2GB Crucial Ballistix Tracers PC3 10600 
Hard DriveCoolingOSPower
Almost 8TB of storage AMD Stock Cooler Windows Home Server CoolerMaster SilentPro M 700W 
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