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Thread: help me understand PCIE 8pin/6pin power connector power usage

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    Default help me understand PCIE 8pin/6pin power connector power usage

    Hey guys, I'm curious if any of you actually tested or know the answer to this.

    On paper 8pin 150W, 6pin 75W and the rest of the gpu use comes from the pcie socket up to 75W.
    Lets say the gpu is using 250W DC, does that mean, 150W on the 8pin, 75W on 6pin and 25W on pcie socket ? Or it can be 100W on 8pin, 75W on 6pin and 75W on pcie socket?

    So does the pcie connector fires up to 100% before taking power from pcie socket or how does this thing work? I'm really curious.

    Thanks!

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    Depends solely on the VRM and PCB design, so it varies from manufacturer to manufacturer.

    The accepted norm, however, is to maximize PCI-E auxiliary plug usage and minimize slot power draw, though sometimes it's not exactly respected.
    Careful what you wish for... You just might get it.

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    Quote Originally Posted by McSteel View Post
    Depends solely on the VRM and PCB design
    And driver too, right (IIRC the recent RX 480 issue)?
    Best, Luca

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    So beside the rx480 driver issue, most cards will use fully the pcie connectors before the pcie slot? Has anyone ever tested this btw ?

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    Yes many, Xbitlabs did is for years, Tomshardware and PCPer still does it. The RX480 was btw not a driver issue, they only fixed it with a driver update.

    Normally with a high-end graphics cards with two PEG connectors the power of the memory chips and GPU goes through the PEG connectors and through the PCI Express slot goes the power of the other controllers like display and BIOS. But it's always a choice of the manufacturer, so it differs from card to card.

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    Quote Originally Posted by quest for silence View Post
    And driver too, right (IIRC the recent RX 480 issue)?
    Not really, the problem was still the VRM design.
    As The Mask said, they just used the driver to solve this issue.
    Via the driver patch they flashed the firmware of the VRM controller so this controller is powering the phases which gets their input from the PCIe Slot less now.

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    Quote Originally Posted by -The_Mask- View Post
    4The RX480 was btw not a driver issue, they only fixed it with a driver update.
    I guess you may have misunderstood, as well as OZSA and broda, maybe due to language barriers: I wrote "RX 480 issue", and NOT "RX 480 driver issue", and there's a difference.

    I commented that, given a specific VRM or PCB design (so something you can't change), a GPU power distribution is not strictly *fixed*, but it can also be somewhat managed by software (so definitely by the card driver, as actually done by AMD to solve the RX 480 issue).


    Quote Originally Posted by »broda« View Post
    Via the driver patch they flashed the firmware of the VRM controller
    What? Is writing a firmware possible within a driver (without using a specific flasher/writer)?
    Last edited by quest for silence; 08-23-2016 at 05:17 AM. Reason: sparing new posts
    Best, Luca

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    I just found this after reading The mask's comment.
    http://www.xbitlabs.com/articles/gra...on-2010_3.html
    Scroll down and there's gpu stress test table. On a few cards the 6pin and 8pin take the same power, 186W on 6pin for the gtx 295, thats huge.

    Do any of you know what is the 3.3v line actually feeding ? I'm using similar pcie riser cables https://www.hashratestore.com/wp-con...e-molex-11.jpg but I have the 12V lines cut before it reaches the pins and powered to molex but I didn't do anything with the 3.3v lines, they appear to be standby when looking at the pcie pinout. Have 4 of these risers in a motherboard, and in the case of 4x5970 cards that would be 17W, thats nothing for a motherboard 24/7 right ? (not sure how much my cards r9 280x&r9 390 use on that 3.3v line).

    Btw, I know if the gpu gets hotter it uses more power but does it need more power if the gpu itself is not hot (under 70C) but the pcie cables are hot ? I tested the gpu hot part but I have no way of testing what happens if the cables get hot, how does that change power needs.

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    Quote Originally Posted by quest for silence View Post
    I guess you may have misunderstood, as well as OZSA and broda, maybe due to language barriers: I wrote "RX 480 issue", and NOT "RX 480 driver issue", and there's a difference.
    If this is a misunderstanding I think I still don't get your point.
    Aren't you talking about the high amount of power the RX 480 got from the PCIe Slot?

    Quote Originally Posted by quest for silence View Post
    I commented that, given a specific VRM or PCB design (so something you can't change), a GPU power distribution is not strictly *fixed*, but it can also be somewhat managed by software (so definitely by the card driver, as actually done by AMD to solve the RX 480 issue).
    I think this depends on the point of view.
    For me the bahaviour of the VRM controller (defined by the firmware) is part of the VRM design.
    Normally the driver just adjusts the power draw of the graphics processor, where the power comes from is still the choice of the VRM controller.

    Quote Originally Posted by quest for silence View Post
    What? Is writing a firmware possible within a driver?
    On the RX 480 it seems to be.
    According to my information they used the I2C protocol to configure the controller in a different way.
    There must be another controller at this bus that is able to configure the firmware in an other way / flash it.

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    Quote Originally Posted by quest for silence View Post
    I guess you may have misunderstood, as well as OZSA and broda, maybe due to language barriers: I wrote "RX 480 issue", and NOT "RX 480 driver issue", and there's a difference.
    I didn't misunderstood anything, OZSA said it was a driver problem and I only corrected him. My whole post was a reply to him, that's why I didn't quote you.

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