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PSU for Dual-GPU setup: single +12V rail or dual-rail?

mwasielewski1990mwasielewski1990 Posts: 343
in Technical Help (nuts n bolts)

Sup people!

As stated in the topic title... I'm awaiting for the arrival of my 2080ti, and I already have a 1080ti. I'd like to run them both, but I'm failing to understand what's the difference between a PSU that has 2 separate 12V rails and a one that has a single 12V rail. What is the benefit when using 2 rails? Is it better for a dual-gpu setup?

Comments

  • kenshaw011267kenshaw011267 Posts: 3,805

    Multiple 12V rails in theory is safer but the separate rails provide less current so they could struggle to produce enough power to run a GPU, since all PCIE power will come from the same rail.

     

  • Dim ReaperDim Reaper Posts: 687

    Last year I went to the same config - 1080ti + 2080ti.  I'm using a Corsair HX1200.  I don't remember setting it up, but I have it set to multiple 12V rails and it has been fine.

    https://www.corsair.com/uk/en/Categories/Products/Power-Supply-Units/hxi-series-2017-config/p/CP-9020140-UK#tab-overview

     

     

  • mwasielewski1990mwasielewski1990 Posts: 343
    kenshaw011267 said:

    Multiple 12V rails in theory is safer but the separate rails provide less current so they could struggle to produce enough power to run a GPU, since all PCIE power will come from the same rail.

     

    Safer how? Sorry I'm not really keen on PSU's :P

     

     

    Dim Reaper said:

    Last year I went to the same config - 1080ti + 2080ti.  I'm using a Corsair HX1200.  I don't remember setting it up, but I have it set to multiple 12V rails and it has been fine.

    https://www.corsair.com/uk/en/Categories/Products/Power-Supply-Units/hxi-series-2017-config/p/CP-9020140-UK#tab-overview

     

    Funny, I was thinking about buying this exact PSU. How about similar quality, but a 1000W? Will it be sufficient? (My cpu is i7 8700, non-K version, running 32gb @2666 ram)

  • Dim ReaperDim Reaper Posts: 687
    mwasielewski1990 said:
    kenshaw011267 said:

    Multiple 12V rails in theory is safer but the separate rails provide less current so they could struggle to produce enough power to run a GPU, since all PCIE power will come from the same rail.

     

    Safer how? Sorry I'm not really keen on PSU's :P

     

     

    Dim Reaper said:

    Last year I went to the same config - 1080ti + 2080ti.  I'm using a Corsair HX1200.  I don't remember setting it up, but I have it set to multiple 12V rails and it has been fine.

    https://www.corsair.com/uk/en/Categories/Products/Power-Supply-Units/hxi-series-2017-config/p/CP-9020140-UK#tab-overview

     

    Funny, I was thinking about buying this exact PSU. How about similar quality, but a 1000W? Will it be sufficient? (My cpu is i7 8700, non-K version, running 32gb @2666 ram)

     

    I'm definitely not an expert in this area, so I tend to over-estimate to be on the safe side.

    I just tried putting in a system with 2x2080ti and your processor and RAM, and it looks to be under 1000W,  but you might be cutting it close depending on what else you have in the rig - SSDs, HDDs, fans etc.  It's definitely worth you trying out a few calculators before buying:

    https://www.newegg.com/tools/power-supply-calculator/

    https://seasonic.com/wattage-calculator

     

  • kenshaw011267kenshaw011267 Posts: 3,805
    mwasielewski1990 said:
    kenshaw011267 said:

    Multiple 12V rails in theory is safer but the separate rails provide less current so they could struggle to produce enough power to run a GPU, since all PCIE power will come from the same rail.

     

    Safer how? Sorry I'm not really keen on PSU's :P

    If the PSU has a single 12V rail it must be able to deliver all the current required to reach the power output rated for that rail. For instance the 12V rail could be rated for 38 amps, pretty common in PC PSU's, so all the components in that rail would need to be able to handle more than 456W. So if anything goes wrong all that current could go into some component or your hand. With 2 12V rails, each rated for 20A very ciommon in 2 12V rail systems, each rail only needs to be  rated for 240W. So lower power components which don't get as hot, which means a longer lifetime generally speaking, and aren't as big a danger if something bad happens.

    However the two rails do not deliver power to the same components. Generally one 12V rail is assigned to the 4/8 pin CPU connector and 24 pin motherboard connector and the other is assigned to the PCIE devices. So you could struggle with multiple GPU's, your cards draw a lot of power and 240W, plus 150W coming from the slot, might be enough.

  • Seven193Seven193 Posts: 1,080
    edited July 2020

    Ignore it.  Just buy a PSU that meets your power requirements.


    Post edited by Seven193 on
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