internal powered: two GTX 980 ti in Mac Pro 5,1 for octane rendering

Discussion in 'Mac Pro' started by shuto, Jul 17, 2017.

  1. shuto, Jul 17, 2017
    Last edited: Jul 17, 2017

    shuto macrumors member

    Oct 5, 2016
    I couldn't find another post of someone else who had used this setup so thought it might be helpful for someone...

    After first using an external power supply for a while, I wondered if I could power two GTX 980 ti cards using the internal power in the 5,1 Mac Pro (I have a firmware upgraded 2009 Mac Pro.)

    I found this method for one card as described by Machines here...

    Which I thought it could work to power two cards.

    So the setup I have is two EVGA GTX 980 ti SC+ in slot 1 & 3 (having a card in slot 3 doesn't seem to slow down rendering in Octane). The two 8 pin power connectors are connected to the two mini 6 pins on the motherboard, and the 6 pins are powered by all four bay SATA ports using two of these adaptors...


    (StarTech Dual SATA power to 6 pin standard PCIe power splitter adapter cable).

    As in Machines guide I also used OWC Newer Technology AdaptaDrive 3.5" to 2.5" form factor adapter to connect the SATA adaptors to. These seem to be a tighter connection than directly onto the motherboard. Machines says it is very important that the SATA cables do not disconnect when the machine is on, but instead of supergluing I used electrical tape. (I can post photos if this is of interest to anyone).

    Then I have my SSD + HDD in the optical bay using a OWC multi-mount.

    When rendering in octane, the card uses 93w to power the 8pin, 54w for the 6pin, and 42W from the PCI connection. This is worked out from using iStat menus to work out the watts from Amps readout x 12v. So this amount of watts seems to be fine for this setup.

    I have tested this rendering over the weekend for 48hrs and all seems stable. I leave the side off the Mac Pro when rendering as those graphics cards just blow the heat around the inside rather than moving it outside like a reference design fan. I probably should have bought reference design cards, but its hard to learn these things before getting started with it!

    The only issue is that with this setup the PCI and power supply fans spin on full when rendering, so its pretty noisy. The speed of the fans seems to be based on power draw rather than temperature so I am using the great advice in this thread...
    which describes the use of Macs Fan Control to control the speed of the fans in the Mac Pro. So I'm making sure the temperature of the Power Supply isn't over 40 degrees, so now its not crazy noisy to work next to.
    (I'm thinking of removing the optical drive as its not even plugged in, and that should help for the air flow to the power supply.

    Maybe this setup wouldn't work if the cards were being used for gaming, or other GPU processing, but this setup works well with Octane rendering.

    I'd be happy to do a more proper write up if it would be helpful for people.

    Here is hoping for a 2018 Mac Pro which can fit more than one nvidea high powered graphics card :)
  2. shuto thread starter macrumors member

    Oct 5, 2016
    just to follow up on this I have attached a photo showing the cabling I use two power the two cards...

    This machine has been great to work with Octane. I tried a PC at one point and it kept crashing with overnight renders so have gone back to the Mac woop!

    Over the winter months the fans have not been spinning as much, so I think my initial claim of the fans being based on power draw is wrong, and the Mac Pros normal fan speed seems to be fine. If the fans get crazy loud in the summer months I'll use Mac Fans Control to lower the speed, but at the moment default seems fine.

    Attached Files:

  3. joot macrumors member

    Nov 3, 2006
  4. h9826790, Apr 28, 2018
    Last edited: Apr 30, 2018

    h9826790 macrumors G5


    Apr 3, 2014
    Hong Kong
    Some info for you. Each SATA port is rated up to 55W. So 2x SATA port actually rated up to 110W.

    If your power draw reading is correct. Then use

    2x SATA (110W) to single 8pin (up to 93W actual power draw) will be within limit.

    It may be better than over draw the mini 6pin (rated up to 75W) in your case.
  5. shuto thread starter macrumors member

    Oct 5, 2016

    thanks for your thoughts h9826790, I know you are more of an expert about these things, so that sounds like great advice.
  6. Jimagine macrumors newbie

    Jun 14, 2018
    --- Post Merged, Jun 15, 2018 ---
    Shuto: Your post is SO relevant. I have been successfully running one Nvidia GTX 980ti (flashed) on a 2010 MP 5,1 (for Thea Render) ... but have recently wanted to add a second one. The added power necessary has been a sticking point.

    First: I'm wondering how the 2 GPU/ internal power setup has worked for you, for the last year or so.
    Second: Did you change your cabling, based on the comment to power the 8-pins from a higher power source?
    Third: You mentioned having run an earlier external power setup. I'm thinking this may be the approach I would take (perhaps overly-cautious): What was your arrangement for that? Thank you in advance for any comments.
  7. Pressure macrumors 68040


    May 30, 2006
    Have you looked at the pixlas mod? It's really simple and easy.
  8. Jimagine macrumors newbie

    Jun 14, 2018
    Thank you for the pixlas mod tip, Pressure.
    I found more than one article online ... but think the "2 Titans in a MP 5,1 with xBox power module" was the one you were referring to. I did see some of those modification articles before ... and consider them too advanced for me (I barely got my one GTX 980ti in my Mac Pro — and running — without help ... :) I don't trust myself splicing cables, etc. (different mod article) ...
  9. h9826790 macrumors G5


    Apr 3, 2014
    Hong Kong
    Just for two 980Ti, the original Pixlas mod is good enough. And this is the easiest guide i’ve seen.
  10. shuto thread starter macrumors member

    Oct 5, 2016
    pleased you found the post helpful.
    1st - this setup has worked really well for me over the past year. Rock solid overnight rendering. Its never switched off due to drawing too much power (when using with Octane render). Really happy with this setup.
    2nd - I didn't change my cabling, just because the setup is working fine as is. But if I was to do it again I would use the advise of @h9826790 they know their stuff!
    3rd - Yeah I tried the external power supply first, but to be honest it felt too hacky a solution. You had to turn on the power supply first by putting a wire in the correct motherboard connector pins, then switch on the computer. And then I always worried about switching the mac off and forgetting to switch off PSU, which maybe would have been fine, but having it all in one Mac Pro system is really neat.

    So yeah my advise is, if you are happy with only having two disk drives (say a SSD & HDD) then this setup of internally powering two 980ti GPU works really well.
  11. MarkC426 macrumors 6502a

    May 14, 2008
    Is there any way to run these (or just one) externally on a 5.1mp, for something like octane?
    Otoy have been hinting for years to bring AMD gpu support, but still nothing.
  12. shuto thread starter macrumors member

    Oct 5, 2016
    I've seen this cubix external PCI expander for a MacPro5,1, some details here...

    I think they are very expensive though like £2600. More than my refurbished Mac Pro cost! So I think for a MacPro5,1 keeping the cards internal is best. Unless you are talking about trash can style MacPro6,1?

    Yeah I've given up hope on Octane working on AMD. And also Redshift renderer is really good and thats Nvidia only. I'm really really really hoping new Modular Mac Pro works with nVidea cards otherwise I'm forced over to PC side for good.
  13. MarkC426 macrumors 6502a

    May 14, 2008
    Thanks, I have seen the cubix on, and as you say they are damn expensive.

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12 July 17, 2017