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Thread: How psu send power to a graphic card?

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    Default How psu send power to a graphic card?

    Hello everyone, i am a new member in the forum.
    i have a big doubt for long time ago.
    i want to buy a gtx 660 and i have an ocz modxstream pro 500w that has two 12v rails and a total of 432w that is 216w per rail.
    My doubt is:
    The gtx 660 full load has about 110w power consumtion. It has 6pin pci connector and i know that this connector provides 75w but i dont know if the rest is provided by pci express slot that i know that has 75w, so the pci express slot provides 35w and the rest by 6 pin, or pci express slot provides 75w and the rest by 6 pin.
    I dont know if i can explain in the correct way my doubt.
    Hope you can help me.

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    Some years ago, xbitlabs always did those measurements. It always depended on the grafics card how much current goes through the connector or PCI express slot.

    Here is a review from a GTX 295. http://www.xbitlabs.com/articles/gra...m_5.html#sect0


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    diezjackdaniels (09-10-2013)

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    Quote Originally Posted by diezjackdaniels View Post
    Hello everyone, i am a new member in the forum.
    i have a big doubt for long time ago.
    i want to buy a gtx 660 and i have an ocz modxstream pro 500w that has two 12v rails and a total of 432w that is 216w per rail.
    No. It isn't. Rails aren't additive. There's a total of 432W available on the +12V, with two rails each limited to deliver no more than 25A (300W).

    My doubt is:
    Quote Originally Posted by diezjackdaniels View Post
    The gtx 660 full load has about 110w power consumtion. It has 6pin pci connector and i know that this connector provides 75w but i dont know if the rest is provided by pci express slot that i know that has 75w, so the pci express slot provides 35w and the rest by 6 pin, or pci express slot provides 75w and the rest by 6 pin.
    I dont know if i can explain in the correct way my doubt.
    Hope you can help me.
    You are correct that power is supplied both by the 6-pin connector and a PCIe power connector, but electricity is going to travel the path of least resistance, so most will go through the PCIe power connector, but it's not going to pull EVERYTHING from the 6-pin and then whatever else it needs from the slot after the fact. It's going to draw power from both at the same time.

    So what's the issue? Even if your card needed 150W, your power supply has more than enough power even if it was drawing ALL of the required power from one rail.

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    diezjackdaniels (09-10-2013)

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    Default

    Many thanks to help me. Now i undertand that graphic card, in my particular example need about 55w each pci slot and 6 pin.
    i have this doubt because i want to buy a new pc.
    i want to to buy an AMD FX 8350, an ASROCK 990fx Extreme 4 and 16g RAM ddr1866 two sticks, plus two sata 7200 rpm and the gtx660
    I can see benchmarks that fx 8350 in full consume nearly 200w, and the psu has one rail for mainboard, and cpu, and another one for the rest, sata, pci express 6 and 8 pin etc.
    So i think it hasnt enough power in my psu because this rail need to send power to cpu (200w), and the rest to pci express slot i think i can overload this 12v1 rail, and i dont want to change the psu.
    Maybe i am wrong

    Master jonnyGURU, after re-read your post i understand that my psu can deliver nearly 300w per rail?, 600w in total? i cant understand this one, because if psu only has 432w in 12v rails, how it is possible?.
    i have a very few knowledge about psu, so maybe i´m asking a stupid question.

    Many Many thanks
    Last edited by diezjackdaniels; 09-10-2013 at 05:26 AM.

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    Quote Originally Posted by -The_Mask- View Post
    Some years ago, xbitlabs always did those measurements. It always depended on the grafics card how much current goes through the connector or PCI express slot.

    Here is a review from a GTX 295. http://www.xbitlabs.com/articles/gra...m_5.html#sect0

    Mr The Mask, in this table which is the pci express slot comsumption, maybe the yellow 12v one?
    I have a little psu knowledge
    Last edited by diezjackdaniels; 09-10-2013 at 05:28 AM.

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    +12V is the PCI express slot, +12V ex. 1 is a connector and +12V ex. 2 is the second connector. 3,3V is also the PCI express slot.

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    PCI express slot uses 3,3v too?
    Its a surprise for me, i think it only uses 12v

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    PCI Express slots use 3.3v, always have.

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    No. It isn't. Rails aren't additive. There's a total of 432W available on the +12V, with two rails each limited to deliver no more than 25A (300W).
    Actually, ModXStream Pro 500W has rail limits of 2x18A which adds up to 432W. I know it is not a general case, but it works in isolated cases like this.

    Rail distribution is: one rail for hardwired connectors, other for modular ones.

    If you don't OC or do so lightly, you should be fine.

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    Quote Originally Posted by diezjackdaniels View Post
    Master jonnyGURU, after re-read your post i understand that my psu can deliver nearly 300w per rail?, 600w in total? i cant understand this one, because if psu only has 432w in 12v rails, how it is possible?.
    i have a very few knowledge about psu, so maybe i´m asking a stupid question.

    Many Many thanks
    No. That's not the case either. Please read this:

    http://www.jonnyguru.com/forums/showthread.php?t=3990

    Rails are virtual. Not a set capability. You have a +12V rail that's capable of a certain capacity and then that is split into two circuits, each with a limit placed on them.

    Quote Originally Posted by rafal_iB_PL View Post
    Actually, ModXStream Pro 500W has rail limits of 2x18A which adds up to 432W. I know it is not a general case, but it works in isolated cases like this.

    If you don't OC or do so lightly, you should be fine.
    Well that's horribly stupid. The 600W, for example, is completely different. It has a 504W (42A) +12V rail and two rails with a 25A (300W) each OCP on them.

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