MSI GTX 980 two 8pin on a 4,1?

Discussion in 'Mac Pro' started by turboturbo, Nov 4, 2015.

  1. turboturbo macrumors newbie

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    Oct 21, 2015
    #1
    So I bought a used MSI GTX 980 gaming 4G without noticing it actually comes with two 8pins connectors - here is the questions:

    Can I use two 6pin>8pin cables to power it up?

    I assume the extra 2pins are for grounding purpose only?
     
  2. turboturbo thread starter macrumors newbie

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  3. h9826790 macrumors 604

    h9826790

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    #3
    AFAIK, the extra 2 pins will supply another 75W (max) to the card, a single 6pin can only supply 75W, but a 8 pin can supply 150W.

    So, your card has dual 8 pin means it can technically draw up to 375W (150x2 + 75 via PCIe slot). Of course, the card won't draw that much. As you said, it draw just more than 200W max.

    So, now, the problem is how the loading distribute. Since it has dual 8pin, if assuming the loading is equally distributed between them, then the max draw will be about 100W on each 8pin.

    The cMP's 6pin only rated up to 75W, so, I won't recommend anyone do anything over that limit. However, my real world experience (dual 7950) told me that each 6pin can supply 100W without any trouble. (N.B. The self shutdown protect occur at about 120W).

    By considering there will be some power draw via the PCIe slot, the actual power draw via the 6pin will be less than 100W (average).

    Therefore, practically, you can just use dual 6pin->8pin adapter to power your card. However, I have to remind you that it's technically unsafe to do so.

    Also, if the power loading is very unevenly distributed (e.g. 30W from PCIe slot + 50W from 1st 8pin + 130W from 2nd 8pin), your machine may still self shutdown and may suffer from permanent damage.

    A better way to do it may be connect a dual 6pin->8pin adaptor to the mobo, and then 8pin-> dual 6+2pin to the card, which means the 8pin actually serve as a bridge to share the loading between the 6pins regardless how the card draw the power.
     
  4. turboturbo thread starter macrumors newbie

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    Oct 21, 2015
    #4
    Cool! thank you for the detailed explanation.

    Can you clarify the following?
    Are you suggesting that I should combine the dual 6pin (connects to the mobo) > 8pin cables (become a single cable) and split them again to become dual 6+2pin (to 980)? by doing so the "single cable" will always draw the power from the mobo 6pin connectors equally?
     
  5. h9826790 macrumors 604

    h9826790

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  6. turboturbo thread starter macrumors newbie

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    #6
    Here is a quick update:
    Since I cannot find the suggested cable, I powered the 980 with two separate cables (6 to 8pin). The comp has been up and running for over 10 hours and there is no sign of stability issue.

    How do I check the power consumption of the GPU?

    This is the data i got from iStat
    Screen Shot 2015-11-08 at 1.55.07 AM.png

    btw, the fans on the 980 rarely turns on which is a pretty good news!
     
  7. h9826790 macrumors 604

    h9826790

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    #7
    Stress the card (e.g. Run Furmark), than observe iStat...

    [PCIe Booster A + PCIe Booster B + PCIe Slot 1 current (Assuming you install the card in slot 1)] x 12

    e.g. 5.45A + 5.55A + 2.75A = 13.75A

    13.75A x 12V = 165W (This is the rough figure, but good enough to decide if the power draw is within limit.)
     
  8. turboturbo thread starter macrumors newbie

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    Oct 21, 2015
    #8
    indeed spot on
    5.07A + 4.72A + 3.6A x12V = 160.68w is the max it could achieve so far
     
  9. turboturbo thread starter macrumors newbie

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    Oct 21, 2015
    #9
    Ok, did a few more tests just now, the max it could go was 6.2a at PCIe Boost A and B.

    thanks for the help, h9826790!
     
  10. h9826790 macrumors 604

    h9826790

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    #10
    They are all below 6A, so well within the official limit.
     
  11. h9826790 macrumors 604

    h9826790

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    #11
    6.2 is about right at 75W. By considering I can draw another ~50% from it (105W) but the machine still working fine. Occasionally operate right at the limit should not be a problem at all.
     
  12. ActionableMango macrumors 604

    ActionableMango

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    Sep 21, 2010
    #12
    So yet another card with 8-pin power plugs for cosmetic/marketing purposes?
     
  13. h9826790 macrumors 604

    h9826790

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    #13
    I am sure when OC this card, the 8pin will make the different.
     
  14. turboturbo thread starter macrumors newbie

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    #14
    Indeed, altho I wont' OC this 980, but it is said it has great OC potential, so I agree the 8PIN will matter
     
  15. ActionableMango macrumors 604

    ActionableMango

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    #15
    I'm really curious to see if that's true. My experience is limited to the GTX 680, where OC'ing did not substantially change the power draw. I tried EVGA standard clocks, FTW clocks, and Signature clocks.

    Of course Maxwell is a completely different architecture and may act very differently. There are some cards that use way more power when OC'd. If you happen to OC and check the power draw again, I'd love to see what the results are, and it would also be helpful for future guidance for future potential buyers.
     
  16. wolf1734 macrumors member

    wolf1734

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    #16
    [Quote = "TurboTurbo, poste: 22211345, membre: 999511"] Voici une mise à jour rapide:
    Puisque je ne peux pas trouver le câble suggéré, je propulsé la 980 avec deux câbles séparés (6 à 8 broches). L'échantillon a été en service pendant plus de 10 heures et il n'y a aucun signe de problème de stabilité.


    Good evening I wanted to know you have connect both cables mini 6pins / 8 pines on the motherboard of a highly-rated and 8 pines on the video card(map).
    Thank you for your answer
     
  17. turboturbo thread starter macrumors newbie

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    Oct 21, 2015
    #17
    Sorry I dont really understand your question, can you clarify it? My GTX980 is currently running on two 6>8pin adaptors, connected to the motherboard.
     
  18. wolf1734 macrumors member

    wolf1734

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    #18
    Good evening
    excuse my English not well. But thank you for the answer, it is what I wanted to know. Cordially
     
  19. Bytehoven macrumors regular

    Bytehoven

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    #19
    Would another way be to use the (2) MB 6pin -> GPU 8PIN and then use an available drive bay SATA -> GPU 6PINor 8PIN?

    I'm trying to keep my cMP lean inside to better support the extra power draw of the 980 Ti and x5690 processors, so I have a couple of SATA power sources I can tap.
     
  20. SoyCapitanSoyCapitan macrumors 68040

    SoyCapitanSoyCapitan

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    #20
    Pixlas Mod is the cleanest and safest solution. Completely reversible.

    http://forums.macrumors.com/threads/pixlas-4-1-mac-pro-mod.1859652/
     
  21. phillyboy82 macrumors regular

    phillyboy82

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    #21
    I would say it is the most elegant of the solutions compared to shoving a second power supply in, but "completely reversible" is not 100% correct. You do still have to splice into the 12V/GND wires on the main connector with those little brown tap splices, so if you took them off to go "back to stock" you'd have bare spots on the cables that would need to be addressed with electrical tape or heat shrink.

    Still, this is one of the cleanest methods I've seen so far to make sure you can tap enough power off for a video card.
     
  22. SoyCapitanSoyCapitan macrumors 68040

    SoyCapitanSoyCapitan

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    Jul 4, 2015
    #22
    Little scars in the wires that can be covered with electrical tape on each wire.
     

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