MacPro 5.1 GTX 980Ti

Discussion in 'Mac Pro' started by &dj, Oct 3, 2016.

  1. &dj macrumors newbie

    Joined:
    Oct 29, 2015
    #1
    Hi

    Sorry if this has been covered elsewhere, but I've been reading alot about this configuration and am quite confused.

    In the FAQ about Nvidia Cards

    http://forums.macrumors.com/threads...out-nvidia-pc-non-efi-graphics-cards.1440150/

    It says "The rule of thumb is this: if the card has one or more 8-pin power connectors, it might draw too much power and you should check to see what its TDP is. It is generally safer to stick with cards that have one or two 6-pin power connectors. Note that many GTX 680 cards do have both a 6-pin and 8-pin power connectors, though their TDP is down in the 190W range and should work fine."

    I noticed the Galax Card has 6 & 8 pin power connectors, but it is rated at 165W

    http://www.galax.com/en/graphics-card/900-series/galax-geforce-gtx-980-ti.html

    Does this mean it should be safe? Ive noticed the EVGA 980ti is rated 250W

    Thanks!
     
  2. farkleboy macrumors newbie

    Joined:
    Mar 10, 2015
    #2
    I have the last cheese grater mac made, and installed a 980Ti with an external PS. Didn't want to risk frying my motherboard for the small cost of a power supply. Had a friend with the same system install the same card without the external PS, and he had constant black screen shutdowns. Technically the 980Ti is under the limit if you use the proper splitter and power feeds from inside the mac, but its too close for comfort for me.

    I'e been using this config for about 6 months now, and its been pretty stable. My 980Ti is not flashed.
     
  3. &dj thread starter macrumors newbie

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    Oct 29, 2015
    #3
    Thanks for your reply. I wouldn't go down the external PSU route just to keep things tidy in a shared office environment and am thinking of going for a 980 with 2 6 pins which I've read should be ok, but I just saw the power rating on this board and wondered if it was lower power than the other 980ti cards. I will be using it for GPU rendering so an extra 2GB and more CUDA cores would be ideal.
     
  4. farkleboy macrumors newbie

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    Mar 10, 2015
    #4
    I might be ok, supposedly the 980Ti was supposed to be ok with my setup as well, even with stealing a power tap from the spare DVD slot. You can certainly try it, and if you get lots of black screen shutdowns, then you know what th problem is. I got an obnoxiously large PS, but I was planning on adding a second 980Ti, but you can get PSU's that are quite small and will sit right on the top of your mac and wire in nicely. Keep in mind with GPU rendering, that thing will be lighting up all those CUDA cores and sucking all the juice it can, and if it can't, it will degrade the performance of the card or kill your motherboard. Better to be safe than sorry. Let us know how it turns out, the 980's are great cards at good prices right now.

    PS now that I think about it, you might be OK, the Ti version had the 6+8 power taps, so that needed the extra power.
     
  5. ActionableMango macrumors 604

    ActionableMango

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    Sep 21, 2010
    #5
    That is absurdly low for a GTX980Ti. That has to be a typo or "copy and paste error". That's 85W lower than a typical GTX980Ti.
     
  6. farkleboy macrumors newbie

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    Mar 10, 2015
    #6
    Unless they throttled it waaaaaay back to keep it under the power requirements to not require an external PSU.
     
  7. h9826790 macrumors 604

    h9826790

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    Hong Kong
    #7
    Sure that 165W is a typo.

    1) No other 980Ti has anything close to this TDP

    2) that page state that the PSU should be 600W or above, that's far too high for a max 165W card. And, it's the exact requirement for the 250W 980Ti on the Nvidia official page.

    3) 165W is the exact figure for 980's TDP (on Nvidia official website)

    4) this 980Ti's clock speed is not significantly lower, there is no reason that it can save so much power when compared to other 980Ti.

    Anyway, the 980Ti is really right at the edge of the mini 6 pin can supply (if you only use a simple mini 6 to 8 pin adaptor). There are a few reports that this card can shutdown the Mac. However, if you get some extra power from SATA port, go through the Pixlas mod, or share the loading between the two mini 6pins. It should be a piece of cake to driver the 980Ti with internal power only.

    Technically, the cMP can drive a card at least up to 300W without any issue by the mini 6pin and the slot power only. However, it's all about how the card draw the power.

    If a 130W TDP card draw all 130W from a single 8pin, and the user only use a single mini 6pin to 8pin adaptor to drive this card. The cMP will shutdown when the power draw hits ~120W.

    On the other hard, if a 300W card draw 75W from slot, 112W from 8pin A, and 113W from 8pin B. This 300W card can run without any issue in the cMP by simply connected via 2 independent mini 6 pin to 8 pin cable.

    At the end, it's all about if any of the mini 6 pin hit that 120W real world limit. If you can evenly share the loading between the mini 6pins, the 980Ti should not cause any power issue to the cMP.
     
  8. &dj thread starter macrumors newbie

    Joined:
    Oct 29, 2015
    #8
    Thanks for the advice everyone I thought it sounded too good to be true. So to be safe, I would need to use the 75W from the card slot, an adapter from the 2 x 6 pin plugs to one 8 pin plug, and then find a power source from another part of the system. Is there a diagram anywhere of where I can get another power source? I heard people using the CD drive power. I have 2 HDD's and there are 4 bays, can I use a HDD power supply?
     
  9. h9826790 macrumors 604

    h9826790

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    #9
    2x SATA to 6pin can solve your problem.
     
  10. JesterJJZ macrumors 68020

    JesterJJZ

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  11. Draeconis macrumors 6502a

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    May 6, 2008
    #11
    980 is 165w or there abouts, should have 2x 6-pin. 980Ti is 8+6 and draws 250w; too much for our machines without a dedicated PSU.
     
  12. h9826790 macrumors 604

    h9826790

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    #12
    Not really, there are plenty of ways to power a 980Ti in the cMP without an extra PSU. Even though you don't want to go over 75W from the mini 6pin. e.g.

    2x mini 6 -> 8 pin + 2x SATA -> 6 pin

    can power the 980 Ti without any mod, and make sure all parameter stay within official limit.
     
  13. ActionableMango macrumors 604

    ActionableMango

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    Sep 21, 2010
    #13
    @h9826790 has a lot of detailed experience with GPUs and power draw. I'd follow his advice.
     
  14. Murray M macrumors regular

    Murray M

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    Apr 19, 2010
    #14
    I'm powering a 980ti from both of the mini 6 pin power supplies, one of them has an 8 pin split. It's a flashed card for Mac Video Cards and I'm using the wires that came with it.

    Everything has been working fine for the last month I've had it. And I've been doing crazy renders that rev my 12 cores up just about the entire last 4 weeks. Not a single issue or crash.

    I'm not sure what a "2x mini 6 -> 8 pin + 2x SATA -> 6 pin" is. Is that what I've got?
     
  15. ifraaank macrumors regular

    ifraaank

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    #15
    No, based on your first sentence, you don't have that. I power it the same way as you, and it has never shut off.
     
  16. Synchro3 macrumors 65816

    Synchro3

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    Jan 12, 2014
    #16
    Same experience: I'm powering a MVC GTX Titan X from both of the mini 6 pin power supplies, with one 6 to 8 pin cable and one 6 to 6 pin cable. No issues so far.
     
  17. h9826790, Oct 4, 2016
    Last edited: Oct 5, 2016

    h9826790 macrumors 604

    h9826790

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    #17
    No, what you are doing now is.

    Cable A: mini 6pin -> 6pin
    Cable B: mini 6pin -> 8pin

    So, what actually happening is.... Your card draw
    1) up to 75W from the slot, Nvidia usually make good use of the slot on high end card. So, let's say it draw 70W.
    2) up to 75W from the 6pin. So, again, we assume another 70W from one of the mini 6pin.
    3) all the rest from the 8pin. So, it may be up to 110W from the other mini 6pin.

    Since no manufacture will intentionally make a card that draw more than 75W from the PCIe slot (well, apart from the RX480). So no matter the card is the base model or OC model, they are only designed to draw more (when required) from the 6pin / 8pin, but not from the slot.

    The cMP's mini 6pin official limit still 75W, same as normal 6pin. However, it can actually deliver up to 120W before the cMP shut itself down. So, in your case, even thought the 8pin may constantly draw more then 100W, the cMP still working as usual.

    MVC know this limit very well. May be he did fine tune the card and make sure it's power draw always stay within the real world limit. Or simply your 980Ti always pull less then 120W from the 8 pin even under 100% load.

    However, the power draw vary between cards. If another brand's 980Ti (or any other 250W TDP card) draw power as follow.
    1) 60W from the slot
    2) 65W from the 6pin
    3) 125W from the 8pin

    It still stay within the 250W TDP limit, however, the cMP will shut itself down when the 8pin draw more then 120W.

    This is why some 980Ti users reported that their cMP suddenly shutdown when stressing the GPU.

    Since the 980 Ti is not designed for cMP, no manufacture will try to make the 8pin power draw stay within 120W. In fact, it make more sense to utilise the 8pin but not stressing the 6pin / slot to 100%.

    Anyway, it's a little bit hit and miss. It's depends on if you get a good card, from which manufacture, and how's the firmware programmed to draw the power.

    If you want to make sure everything stay within the official limit, and you don't want any extra PSU, or mod. You can...

    Cable A: 2x SATA -> 6pin
    Cable B: 2x mini 6pin -> 8pin

    In this config, 2x SATA rated up to ~110W, and the 6pin should only draw up to 75W. 2x mini 6pin rated up to 150W, and exactly fit the 8pin power draw limit.

    So, even though any 6+8pin graphic card really draw 75+75+150 = 300W. The cMP will still able to perform, and in fact, everything stay within official limit.

    For anyone already fill up all HDD / optical bay. There is another method which to make sure won't over stress any mini 6pin to reach the 120W limit.

    Cable A: 2x mini 6 pin -> 8pin
    Cable B: 8pin (female) -> 2x (6+2)pin

    So, we will plug Cable A into the cMP's logic board, and connect Cable A and B together, then plug one of the 6+2 into the 6pin, the other 6+2 into the 8pin.

    In this case, the power draw will be something like
    1) 70W from the slot
    2) 110+70=180W from Cable A

    Since Cable A is connected to both mini 6pin, therefore, each mini 6pin only need to deliver around 90W. A little bit above the official limit, but still well below the shut down protection limit.

    Anyway, since your card works fine. So, obviously no need to do anything.

    And OP has 2 HDD bay empty, he can choose to get a 2xSATA -> 6pin cable to power his 980 Ti.
     
  18. Draeconis macrumors 6502a

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    #18
    I use all the SATA ports, so it's not an option for me :)
     
  19. Murray M macrumors regular

    Murray M

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    #19
    h9826790: God bless you. This forum is lucky to have your experience and generosity. Have a great day.
     
  20. AkuskaUK macrumors 6502

    AkuskaUK

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    #20
    Would this work with a Titan X too, or would that pull too much power?
     
  21. h9826790 macrumors 604

    h9826790

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    #21
    Same, standard TitanX has same TDP as the 980Ti, and their power draw is similar.
     
  22. SoyCapitanSoyCapitan macrumors 68040

    SoyCapitanSoyCapitan

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    Jul 4, 2015
    #22
    The reason you can run the Ti is because the drivers and the macOS APIs can't take full advantage of the power of the card. Boot into Windows and then you will see that with good drivers and intense use of the GPU then the cMP can shut down.
     
  23. Shamgar macrumors regular

    Joined:
    Jun 28, 2015
    #23
    Mac drivers are inferior in performance, but that's not relevant here. I have had zero issues in boot camp with a reference 980 Ti running off of straight 6-6 pin and 6-8 pin power. There's a margin above the rated spec on the power lines before safeties kick in, and on the flip side, TDP is just a ballpark figure. Both the 980 Ti and the 780 Ti are rated at 250 watts, but the 780 Ti draws more power in practice and cannot run on the Mac Pros 6 pins. The 980 Ti draws below its TDP by enough to stay within the 6 pin actual limits. Usually. There's no guarantees when exceeding the specs.
     
  24. Synchro3, Oct 5, 2016
    Last edited: Oct 5, 2016

    Synchro3 macrumors 65816

    Synchro3

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    #24
  25. xactoman macrumors member

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    Jul 9, 2015
    #25
    I have a GTX 980ti FTW in my mac pro. It has two 8 pin connectors. Running one off the logic board (joined) and the other off the CD bay leads (joined) I have no problems. I run both windows and mac os. Certainly Windows takes full advantage of the card, and I have not had any problems or shut downs. It runs very hot though, so all the fans ramp up when it is under load.
     

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