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Thread: GeForce 8800GT and PSU Question (not enough amps?!)

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    Question GeForce 8800GT and PSU Question (not enough amps?!)

    I just got my 8800GT Superclocked card in the mail today, and noticed soemthing I hadn't before: the box says it requires a 400w PSU with 26 amps on the +12v rail. But the PSU I bought, an Antec NeoPower Blue 650w says this on the box:

    Output Voltage: +3.3V +5V +12V(1) +12V(2) +12V(3) -12V +5Vsb
    Max Load/Charge: 24A 24A 19A 19A 19A 0.8A 3.0A
    Available Power: 170W 624W 9.6W 15W
    650W Continuous output @ 50 degrees C

    I don't know a lot about this, but it seems to me the 12V rails lack the proper amperage. What do I do?

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    AKA daniel.phillips Sprite's Avatar
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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    It should work, most of the time power requirements are over stated, plus it doesn't mean 26amps on all rails.
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    Senior Member 2Cold Scorpio's Avatar
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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    So I plug i nthe graphics card to two rails? I ask because this is my first PC build, and I don't wanna underpower my card.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    The PSU is fine.

    Combined 12V amperage on that PSU is :

    Total Power - 624W / 12V Rail = 52A

    More than enough

    650W Continuous output @ 50 degrees C
    Dunno how Antec arrived at that figure though???

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    I remember hearing before that Antec puts the continuous wattage rather than the peak wattage on these things... *shrugs*

    So I just plug the vid. card into two rails to get the needed amperage?

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    You plug the PCI-E cable from the PSU (it's a 6 pin plug) into the socket on your graphics card. Line the clips up so it fits in properly.

    And I doubt that PSU has 52A on the 12v rails.
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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Your psu could handle two 8800gt's in sli, so dont worry.

    Just plug in a 6 pin pci express connector into the card and it should work fine. Your psu will do the rest

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    It's made by seasonic and more than enough for your card

    When you add up the numbers it's just shy of 800w total, which is probably short period from cold, so 650 sustainable at 50c sounds about right.
    That's a very nice PSU you have there.

    and at £75ish I'm not surprised.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Quote Originally Posted by daniel.phillips View Post
    You plug the PCI-E cable from the PSU (it's a 6 pin plug) into the socket on your graphics card. Line the clips up so it fits in properly.

    And I doubt that PSU has 52A on the 12v rails.

    Its rated as 624W - Do the sums. 624/12
    If Antec are lying i would be suprised. Lets face it, for a good brand PSU rated at 624W, 52A isnt that suprising

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Quote Originally Posted by Blitzen View Post
    The PSU is fine.

    Combined 12V amperage on that PSU is :

    Total Power - 624W / 12V Rail = 52A

    More than enough


    Dunno how Antec arrived at that figure though???
    Quote Originally Posted by Blitzen View Post
    Its rated as 624W - Do the sums. 624/12
    If Antec are lying i would be suprised. Lets face it, for a good brand PSU rated at 624W, 52A isnt that suprising
    You can't simply take all the 3 seperate 12V lines and combine them, not many PSU's work like that.
    You'll commonly see it on dual rail PSUs (the ability to combine rails - Tagans do for example), but triple rail is slightly different (manufacture dependant, of course).

    Pulling 52A down those cables would soon cause them to sizzle - literally

    The important thing that needs to be checked is the maximum amps that can be combined on a single line.
    The oldies here will remember the first dual-rail PSUs and their inability to combine rails which caused systems to not even POST because of the high demands of the graphics card. While its unlikely to see this today, It just illustrates that you can't do rail1+rail2+rail3 = usable ampage on one rail

    The maximum available on one rail should be in the specifications.
    Quote Originally Posted by Saracen View Post
    And by trying to force me to like small pants, they've alienated me.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    it's listed as 19a on each of the 3 rails with a max combined output of 624w
    And as far as graphics card makers are concerned they only ever list the specs as a combined wattage and +12v load

    As far as I remember Seasonic almost always seem to use a single +12v the "rails" split over multiple solder points on the PCB to meet ATX2.2 requirements.
    It's a simplier design than fully seprate 12v rails and alows for more felxability on loads across the rails so no peak demand on a single rail should trip it yet still remain well below "bursting into flames"

    The current highest single load of any graphics card is the HD2900XTX at 20-22a, which would overload any "truely seperate" single +12v rail on an ATX2.2 compliant PSU as they state that power over 18a must be split off onto a seperate rail

    Oh and according to that table a 8800GT requires a whole 5a

    Disclamer: This is all based off my understanding of PSUs so may not be 100% accurate as I'm not a PSU developer
    Last edited by Pob255; 04-12-2007 at 01:14 AM.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Quote Originally Posted by Pob255 View Post
    ....any "truely seperate" single +12v rail on an ATX2.2 compliant PSU as they state that power over 18a must be split off onto a seperate rail
    There would be reasons for doing this, but I can't seem to find it in the offical ATX 2.2 specs.
    Ive had a Google about and there seems to be conflicting info - you got any sources I might have missed?
    Quote Originally Posted by Saracen View Post
    And by trying to force me to like small pants, they've alienated me.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Quote Originally Posted by Agent View Post
    You can't simply take all the 3 seperate 12V lines and combine them, not many PSU's work like that.
    You'll commonly see it on dual rail PSUs (the ability to combine rails - Tagans do for example), but triple rail is slightly different (manufacture dependant, of course).

    Pulling 52A down those cables would soon cause them to sizzle - literally

    The important thing that needs to be checked is the maximum amps that can be combined on a single line.
    The oldies here will remember the first dual-rail PSUs and their inability to combine rails which caused systems to not even POST because of the high demands of the graphics card. While its unlikely to see this today, It just illustrates that you can't do rail1+rail2+rail3 = usable ampage on one rail

    The maximum available on one rail should be in the specifications.

    Agent...i didnt.
    19a x 3 = 57a

    I said the combined is 52a

    Its the stated wattage on the PSU = 624W
    624 divided by 12 (v) = 52a

    So 52A is theoretically the amperage of all the 12V lines together.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Quote Originally Posted by Blitzen View Post
    Its the stated wattage on the PSU = 624W
    624 divided by 12 (v) = 52a

    So 52A is theoretically the amperage of all the 12V lines together.
    Thats still taking the voltage and simply dividing it by the amps, then adding them together to get 52A. You can't do that mate It simply means nothing to the OP.
    The 52A is spread across multiple rails and will distributed differently. There is a very big difference between the maximum amps across all rails, and what the maximum that can be supplied down one rail is (which is whats important for graphics cards)

    Also a lot of tri-rail PSU's have a seperate rail for the motherboard only, meaning you couldn't factor that into any calculations for other components
    Quote Originally Posted by Saracen View Post
    And by trying to force me to like small pants, they've alienated me.

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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    624 on the 12v will be max not sustained most likely, and my maths is fine thank you very much
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    Re: GeForce 8800GT and PSU Question (not enough amps?!)

    Yeah, it'll be peak
    Quote Originally Posted by Saracen View Post
    And by trying to force me to like small pants, they've alienated me.

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