Missing GPU power from a second PCIe slot?

Discussion in 'Mac Pro' started by TzunamiOSX, Apr 2, 2014.

  1. TzunamiOSX, Apr 2, 2014
    Last edited: Apr 2, 2014

    TzunamiOSX macrumors regular

    Joined:
    Oct 4, 2009
    Location:
    Germany
    #1
    Some GPUs need 8+6 Pin to power the GPU.

    150 Watt 8-Pin
    75 Watt 6-pin
    75 Watt PCIe slot

    Is there no way to get the missing 75 Watt from an empty PCIe slot?
     
  2. WildBB macrumors member

    WildBB

    Joined:
    Mar 13, 2014
    Location:
    Pandora
    #2
    To answer your question: I have not heard of a way to pull power from the PCIe ports in the manner you hoping for. There are other ways to power your card.

    Some people use a 6 pin to 8 pin adaptor; others take power from the hard drive SATA power ports. It depends on what your comfort level is as the 8 pin connection can pull more than the 75watts that the 6 pin connection is rated for. Thus far, I have not heard of a user that has run into problems in this 6 to 8 pin configuration, but I don’t necessarily endorse it either ;)

    I ran a test on my GTX680 video card using Furmark in both the above mentioned configurations. My results are displayed in the following post:

    http://forums.macrumors.com/showpost.php?p=18908104&postcount=158
     
  3. TzunamiOSX, Apr 2, 2014
    Last edited: Apr 2, 2014

    TzunamiOSX thread starter macrumors regular

    Joined:
    Oct 4, 2009
    Location:
    Germany
    #3
    6 to 8 pin is no option, because you can burn out the lanes of you motherboard. The lanes are made for 7 Ampere (max.) and not for 14 Ampere.

    I dont think that the lanes of a SATA-Connector are big enough to handle 7 Ampere for a longer time.

    An PCIe Port is exactly made for 7 Ampere (75 Watt) and the +12V rail is designed for this Power. Im not sure, that the SATA rails also designed for this.

    Here are the infos about the 12V rails from a Mac Pro Power Supply
    [​IMG]
     
  4. WildBB macrumors member

    WildBB

    Joined:
    Mar 13, 2014
    Location:
    Pandora
    #4
    I understand the power limitations and I don’t disagree with you. I was just informing you that dozens of people here have run it in the 6 to 8 pin configuration for years and never had a problem. There are many threads in this forum that discuss the same issue you are running in to. Search and read a few to understand the direction others have taken.

    http://forums.macrumors.com/showthread.php?t=1680079
    http://forums.macrumors.com/showthread.php?t=1578255&page=7

    I am currently running a GTX680 6+8pin card. I have both of the 6pin Molex connections from the MB powering the 8pin on the card and two SATA power connection ports from the hard drive bays adapted to the 6 pin on the card. I have monitored the card during multiple stress tests and believe this to be the safest route without feeding in an external power supply.

    My card states it requires up to 300W of power (75 PCIe, 75 6pin, 150 8pin). In my current configuration, 52W were pulled from each 6pin MB connection, 29W from the PCIe connection, and ~50W shared to the SATA ports. Here is my take on the SATA power connections:
    http://forums.macrumors.com/showpost.php?p=18910835&postcount=19

    So, I never asked, what graphics card are you trying to run? What model is your MacPro?
     
  5. TzunamiOSX thread starter macrumors regular

    Joined:
    Oct 4, 2009
    Location:
    Germany
    #5
    A 680 GTX only need the 8-pin for overclocking. A 680 at normal clock speed dont need more than 225 Watt (75 PCIe + 2x6-pin. Not a really good card to test the SATA Power.

    But thanks for the links. I will read it.

    At the moment I have a 680 GTX inside my MacPro 5,1 but in the future I might need something with a 8+6-pin connection (like Titan or 780ti).

    OH, and HD slots are full^^

    I have a Booster X5, but there is a Bug in it. The booster X5 always get an output of 12 V, also when the Mac Pro is tuned off. Here in Germany i dont find a Dealer who sells PSUs for the CD/DVD Slot like a Visiontek oder ePower, thats a problem in the future.
     

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