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Thread: Pin Wars 8pin vs 6pin

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    Default Pin Wars 8pin vs 6pin

    Here you will find an article (in English) that we have wrote about the differences between 6pin and 8pin PCIE connectors.

    http://www.thelab.gr/showthread.php?t=78897

    The main conclusion is that there are no differences. At least with the PSUs that we have used (Silverstone ST1500 and Seasonic X750).


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    I have a 2900XT sitting in my drawer here. From what I understand, it will not let you overclock it unless you feed it an 8 pin.

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    if you short circuit the two extra pins it will. I am doing the same with my 3870X2 for some years now.

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    Quote Originally Posted by crmaris View Post
    if you short circuit the two extra pins it will. I am doing the same with my 3870X2 for some years now.
    that really isn't a smart idea imo...

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    can you please explain to me why? I have an Etasis 850 that does not have 8pin PCIE and I wanted to fool the card and make it think that it has an 8pin PCIE connected (I couldn't find an adaptor these days). I don't see anything wrong in all this and I am working the particular VGA for some years now almost 24/7.

    Also if you read the article you will see that practically there are no differences in Watts rating between 6pin and 8pin.

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    The "extra wire" on the +12V row of the 8-pin PCIe was supposed to be a +12V sense wire. This is as per the PCIe specification.

    None of the GPU or PSU manufacturers wanted to impliment the additional logic for +12V sense, so they just made this wire a ground. If the lead is a +12V sense or ground, the graphics card (if it doesn't utilize +12V sense, which none do) will work either way.

    8-pin PCIe, with the additional ground wire, is technically capable of delivering more juice than a 6-pin, but a 6-pin PCIe is capable of delivering enough juice for a graphics card as well.

    "Requiring" the 8-pin PCIe is simply the industry's way of making sure you have a PSU that's capable of a high powered graphics card. For example: a 450W PSU may have two 6-pin PCIe, but not an 8-pin PCIe. An older PSU with four 6-pin PCIe connectors may have all four PCIe connectors on one +12V rail. One with 8-pin PCIe connectors would not have more than two PCIe connectors on one +12V rail, etc.

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    I did some quick experiments along this line sometime ago and got different results. I knew already that a 6-pin could handle 150W no problem since I'd already loaded many with that and more for extended periods of time but I did the experiment just to see if there were voltage drop differences between the 6 and 8-pin which theory says there should be. Of course I'm using different equipment and I don't even remember which PSU I used for the test but I know it wasn't a Silverstone ST1500 or Seasonic X-750.

    Took me awhile to find the actual voltages I scribbled down in my notepad but anywhere here's what I did....First off I used a single 6+2 connector that was direct wired to the PSU which I can't recall lol Anyway it wasn't a modular PSU and dammit I can't say if it was a group or indy regulated affair but I think it was probably group. I measured voltages on an unloaded molex chain just to tell how much of the voltage drop was due to the PSU's ability to regulate the load and I measured voltages and amps directly at the PCIe connector by probing the connector with a multimeter and using a clamp meter for the amps.

    Voltage were measured with no load on the PCIe and 12.5A load (150W). With no load on the PCIe voltages measured at the molex (first one on the chain and same distance from the PSU as the PCIe connector), 6-pin and 8-pin were all the same. 12.26V

    Then with the 150W load I measured 12.08 at the molex (representing the PSU's internal load regulation). 11.94V at the 6-pin and 11.96V at the 8-pin and I remember removing and replacing the "+2" part of the connector several times and could see that voltage change repeatedly.

    Slightly higher voltage with the 8-pin due to the improved ampacity of the circuit with the additional two grounds was my conclusion. But still not enough to make any practical difference to the GPU.

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    Very interesting thread here . . . so, is it "safe" to simply bridge the extra two "+2" pins on the video card's 8pin power connector? A friend also has an ATI 2900XT not being used because his PSU doesn't have a 6+2 or 8pin connector, it has two 6 pin connectors. I'm not sure of the brand but it's a 550w or 600w about 2.5 years old. His current video card is a lowly 7300GS Nvidia card, and he got the 2900XT for dirt cheap and we tested in my PC and it works great, but he doesn't have the $$$ for a new PSU....

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    as I said above I am doing this for some years now with an Etasis 850 and a 3870X2 and I never had any problems.

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    Quote Originally Posted by dlb View Post
    Very interesting thread here . . . so, is it "safe" to simply bridge the extra two "+2" pins on the video card's 8pin power connector? A friend also has an ATI 2900XT not being used because his PSU doesn't have a 6+2 or 8pin connector, it has two 6 pin connectors. I'm not sure of the brand but it's a 550w or 600w about 2.5 years old. His current video card is a lowly 7300GS Nvidia card, and he got the 2900XT for dirt cheap and we tested in my PC and it works great, but he doesn't have the $$$ for a new PSU....
    IMO it is VERY safe. The extra grounds are only needed to fool the card.
    It's been a hard day's night and I've been working like a dog.

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