Can I mix 12Volt rials on 2x SLI ?

Ok, have two Nvidia GPUs that max out at 42 amps each, they use an 8 pin and a 6 pin connector each (GT580 in 2x SLI).
Just purchased a Raidmax 1200AE power supply that has 4 12 volt rails rated at 40 amps each. There is one dedicated PCIe connector, and two modular. What I want to do is to use the three connectors between the two cards so that I will have more than 40 amps available to each card. In theory, the voltages are all referenced to the same ground plane, and this will provide more available current to the cards. Can't see any reason to leave an unattended 12v, 40 amp source just sitting idle. We have had two instances of the PC stopping while playing Battle Field 3 in 24 hours. When we had the 875 watt supply the game and pc would freeze every few minutes. Had I purchased the single rail Corsair supply I most likely wouldn't have this issue. Any thoughts? Basically use 12V1 6 pin upper card, 12V3 8 pin upper card and 12V3 6 pin lower card and 12V2 8 pin lower card. This shares 120 amps between two cards and I should not have any power issues again ?? Ha,,, interesting isn't it.
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  1. The 2 x GTX 580s should draw a total of 52.25 amps together maxed out. I doubt if you will ever incur that, but let's say that's the max. If the PSU's current limiter is working properly, I don't understand why splitting the load between 2 (V2 and V3) rails is giving you problems. Or am I missing something in your explanation?
  2. If you are having problems with the cards on that PSU then I suggest replacing the PSU. At the same time real PSU manufacturers are releasing 1000watt+ PSU's with Gold and Platinum ratings on efficiency Raidmax comes with Bronze. They are known to be at the bottom of the quality barrel anyway!
    A good quality 850watt single +12 volt rail PSU would run your rig fine.
  3. Thers no way your 580's use 42a each. That would be 504w each. Plug a single rail into each of them and use the third for peripherals like HHD's.

    I thik its *interesting* how this is a 4 rail PSU and the Ultra X4-1200w is a single 85a rail even though they are both the same andyson psu...

    If its still returneable, I would take it back and buy something better.
  4. I am only referring to the data on the box of the video card, says needs 42 amps.... so I went with it.

    After reading up on the Raidmax, andyson... blah blah blah... I realized that is why it is $100 less than the corsair. I am using the 1200AE, but the reviews barely gave it a "Pass", and it is now labeled Gold ! LOL, right.

    I am not sure how you came up with 52.5 amps together maxed out, don't know where that info is. Well, the nVidia site show max power, I could have done the math... but why the 42 amps on the box then??

    We were running with a stock Dell 875, but realized that it couldn't handle it under heavy use like playing BF3 etc. The PC would just stop, be unresponsive all together, or green squares start to show up.... we wiped the hard drive (wife and kids actually), re-installed everything..yada yada.. But, still died when playing BF3... power supply....duh.

    It is a major pain to swap supplies because of the case, but it will be well worth it.... Tear down tomorrow am, and get it back together by afternoon.

    Thanks for the info, I will post back the results with a higher end PSU.

    the dude..... will abide.. :sol:
  5. It means 42A for the whole system.
  6. Here is one of several site that show the wattage of various cards as tested, in single and multiple card usage:

    I just used Ohm's Law (P=I*E) to determine the current at +12V.
    (I=P/E) 52.25 = 627/12
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