is it safe to split a 8pin PCIe into 2 8pin PCIe?

Discussion in 'Mining & Cryptocurrency' started by d.v., Feb 13, 2018.

  1. d.v.

    d.v. Limp Gawd

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    i'm asking cause i've seen this on retail psu units. i have not personally done it due to fear and have only used it if the cables already come stock in that fashion.

    for example, some psu comes with cables like this (cable A):

    [​IMG]

    and some are just single like this (cable B):

    [​IMG]

    so my question is if i could take cable B and put a y-splitter on the end and use it for a gpu that requires two 8pin pcie connectors like a evga 1080ti ftw3:

    [​IMG]

    [​IMG]

    my 2nd questions, i assume it would be safe to use cable A for the card above, right?

    so the question remains, should you get a "quality" y splitter and split a single 8pin into two 8pin or just hunt for a power supply that has enough connectors to meet the needs of your gpus? it can get crazy if you are building an 8-gpu rig and each gpu requires two 8pin connectors meaning you need sixteen 8pin connectors, yikes!

    thoughts? or am i way out in left field? i have not personally used splitters yet so i continue to hunt for enough stock 8pin connectors or add another psu.

    as a given: assume only quality psu will be used (as i don't go cheap when it comes to psu but the $ can add up fast).
     
  2. pclausen

    pclausen Limp Gawd

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    I have run many 1080Ti cards using both "A" cables as well as using 6 pin to dual 6+2 pin cables. It is all about the connectors and not really the wire itself.

    According to the wire charts for chassis wiring, these are the allowed capacities on these common wire sizes.

    18 gauge 16A (16A x 12V = 192 watts)
    16 gauge 22A (22A x 12V = 264 watts)

    Since there are 3 yellow leads carrying power on either a 6 or 8 pin cable, that works out to a max capacity of 192 x 3 = 576 watts for 18 gauge and 264 x 3 = 792 watts for 16 gauge.

    I typically don't run my 1080Ti's much past 200 watts, so I have plenty of headroom when using either cable type. Again, the key is the connectors themselves being good and tight, both on the PSU end (if using a modular PSU), the 'Y' cable connection, and to a lesser extent, on the GPU end.

    I think where most people get into trouble is when they start using SATA power cables to power either risers or GPU's directly, especially if they do more than 2 connections per SATA "string".

    Also never load your PSU past 80%.
     
  3. cdabc123

    cdabc123 [H]ard|Gawd

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    you can do it for record i have ran upwards of 500w off one 8 pin. generally i run 350 ish watts off 1 8 pin cpu connector (4x 12v, 4x gnd)
     
  4. Orddie

    Orddie 2[H]4U

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    also check your psu specs to ensure the port can handle the watts
     
  5. pclausen

    pclausen Limp Gawd

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    On an 8 pin power connector, there are 3x 12V and 5x gnd. Why they did it that way, I have no idea.
     
  6. ryan_975

    ryan_975 [H]ardForum Junkie

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    The wires aren't the problem, it's the pins. SATA is rated for 1.5a per pin, so 3 x 12v = 54w (PCIe max slot power is 75w). Per pin amperage for a 4-pin Molex is 8.5a, so you can get 102w from it's +12v pin. I've seen both 11a and 13a for PCIe pins so 3x 12v = 396-468w

    A good quality PCIe splitter will allow up to 198w-234w per graphics card. Since PCIe spec is 150w per 8-pin connector, you'd be well within that limit.
     
    Last edited: Feb 14, 2018
  7. ryan_975

    ryan_975 [H]ardForum Junkie

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    6 pin spec is 2x 12v, 2x gnd, and 1x sense. The sense wires allow the PSU to adjust to voltage to ensure the card receives +12v and not something like +11.4 due to wire and pin resistances.

    8pin spec is 3x 12v, 3x gnd, and 2x sense. The second sense wire tells the card that an 8pin connector is plugged in and is allowed to pull the full 150w. Without it, it's only supposed to pull pull 75w.
     
  8. mkrohn

    mkrohn 2[H]4U

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    Always keep in mind how much power the card is going to use. a 1080ti undervolted can easily get down to 8 pin spec and less. I wouldn't do this on a vega but I would a 1080ti.