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280x crossfire - Power Distribution/Load Query.

NitthNitth Member UncommonPosts: 3,904
in Hardware

Over the last few weeks i have been building for a gpu upgrade in the form of an additional 280x to enable crossfire for my eyefinity setup.

It quickly became apparent by running some quick calculations that my corsair 650CX wasnt going to cut it for crossfire. So in an effort to save some money i have daisy chained 2 Corsair 650CX's giving my 1300w across 2 psu's..

MY question is: will a dedicated 650w psu be enough to support 2 280x's?

I know its not ideal, but its parts i had spare.

image
TSW - AoC - Aion - WOW - EVE - Fallen Earth - Co - Rift - || XNA C# Java Development

Comments

  • Sk1ppeRSk1ppeR Member Posts: 511

    Check the Max TDP multiply that by ~1.5 (neither of the cards work at their best in crossfire x8/2) add 100W for CPU and about ~20 for every HDD/CDROM/DVDROM/BRROM you have. If you are left with 100W or so at the end, you'd be golden. That's how I built my xfire setup o I had a 2x Radeon HD 6870 and an i5-2500k clocked to 3.6Ghz and an Intel 520 SSD and HDD. Worked with no issues whatsoever. Then I got R9 290X. I kissed that crossfire goodbye. I'm still selling one of the 6870s xD 

    EDIT: All this is running on a 750W Chieftech PSU that was worth 120$ 3 years ago. Makes its 4th now.

  • NitthNitth Member UncommonPosts: 3,904

    Originally posted by Sk1ppeR
    Check the Max TDP multiply that by ~1.5 (neither of the cards work at their best in crossfire x8/2)

    Wiki says (although some benchmarks sites say it draws up to 330w underload?)that the max TDP is 250w, so your saying (250 * 1.5 = 375)?


    add 100W for CPU and about ~20 for every HDD/CDROM/DVDROM/BRROM you have. If you are left with 100W or so at the end, you'd be golden.
    Don't need to, That's hopefully going to be on the other psu.

    PSU1: CPU, MOBO, DRIVES[~300w/650w}
    PSU2: 280x, 280X [375w/650w]

    image
    TSW - AoC - Aion - WOW - EVE - Fallen Earth - Co - Rift - || XNA C# Java Development

  • QuizzicalQuizzical Member LegendaryPosts: 25,355

    The Radeon R9 280X is fairly bad on energy efficiency.  You can ignore that with one card, but with two of them, it's more problematic.

    There's also the problem that CrossFire and SLI are usually a bad idea unless you've got a high end card.  While the Radeon HD 7970 was the best card on the market when it launched, that was more than two years ago, and there are better options now.  If you need an upgrade, you're probably better off replacing your current card with a new high end card.

    I'd also be leery of daisy-chaining power supplies.  It would probably work, but it creates the potential for problems that a simpler single-PSU setup simply wouldn't have.  Furthermore, Corsair's CX line is their low end for a reason; if you can afford to make a sensible CrossFire setup, you can afford a higher quality power supply.  It's not "danger to your system" bad, but a more efficient power supply could easily save you 50 W under gaming loads.

    What case do you have?  You're planning on putting out an awful lot of heat, and you're going to need a lot of space to properly place things.  Some cases can handle it, but many wouldn't fare well.

    Also, you're planning on making a computer that doubles as a 600 W space heater while gaming.  That might be okay if you live somewhere cold and were going to have to heat your room somehow anyway.  But depending on where you live, that might be a big problem in the summer.

    What you're planning on doing is hardly the worst idea that I've seen around here, but I'd still recommend against it.

     

  • QuizzicalQuizzical Member LegendaryPosts: 25,355

    Upon further review, the power supply that you claim to have likely doesn't exist.  You might want to have another look.  Corsair's CX line only hits 430, 500, 600, and 750 W, not 650.

    Corsair has revamped their CX line a few times, and it's possible that there was some short-lived 650 W version of it.  But Corsair's earlier CX power supplies were rather problematic on energy efficiency, and that matters if you're planning on building a rig with two high-powered video cards.

  • RidelynnRidelynn Member EpicPosts: 7,383

    Originally posted by Nitth

    Wiki says (although some benchmarks sites say it draws up to 330w underload?)that the max TDP is 250w, so your saying (250 * 1.5 = 375)?


    Per card, the multiplier is more or less for overclocking - if you don't plan on overclocking then your probably ok with TDP + small margin. SO a pair of 280X's will be 500W at full load stock, and potentially a lot more depending on your overclock.

    Originally posted by Nitth

    Don't need to, That's hopefully going to be on the other psu.

    PSU1: CPU, MOBO, DRIVES[~300w/650w}
    PSU2: 280x, 280X [375w/650w]

    Chaining Power supplies is doable, but not the best idea. Most of the time you see paired power supplies, they are there for redundancy in case one goes out (servers). You would be better off with a single large-enough power supply. BY the time your at 500W for your video cards, you add 200W in for "everything else" - and then add in some margin, a 750W would carry it at stock speeds, and wouldn't need to be daisy chained to anything to do it.

    The obvious drawback to daisy chaining is where do you stick the second power supply, because not many cases will default to allowing 2 to be mounted internally (although anything is possible with a dremel and/or duct tape). The second is reliability, as Quizzical mentions - now you have 2 components that can go bad and possibly fry your entire system, rather than just one.

    The last is that your video cards draw power from 2 sources - you have the PCI bus that it will draw power, from the same power source the motherboard is plugged into, and then you also have the PCIe x6/x8 cables that plug into the top of the card. You can't split out how much load is on which power supply (although you can more or less guess, each of those power sources have published maximum power draws). Both of those need to turn on at the same time or you could damage something on the card - there are ways to do that, it's not impossible, but you need something better than "I'll just turn on both power supplies at the same time by hand".

  • NitthNitth Member UncommonPosts: 3,904

    Originally posted by Quizzical
    The Radeon R9 280X is fairly bad on energy efficiency.  You can ignore that with one card, but with two of them, it's more problematic.

    There's also the problem that CrossFire and SLI are usually a bad idea unless you've got a high end card.  While the Radeon HD 7970 was the best card on the market when it launched, that was more than two years ago, and there are better options now.  If you need an upgrade, you're probably better off replacing your current card with a new high end card.

    I'd also be leery of daisy-chaining power supplies.  It would probably work, but it creates the potential for problems that a simpler single-PSU setup simply wouldn't have.  Furthermore, Corsair's CX line is their low end for a reason; if you can afford to make a sensible CrossFire setup, you can afford a higher quality power supply.  It's not "danger to your system" bad, but a more efficient power supply could easily save you 50 W under gaming loads.

    What case do you have?  You're planning on putting out an awful lot of heat, and you're going to need a lot of space to properly place things.  Some cases can handle it, but many wouldn't fare well.

    Also, you're planning on making a computer that doubles as a 600 W space heater while gaming.  That might be okay if you live somewhere cold and were going to have to heat your room somehow anyway.  But depending on where you live, that might be a big problem in the summer.

    What you're planning on doing is hardly the worst idea that I've seen around here, but I'd still recommend against it.

     

    Originally posted by Quizzical
    Upon further review, the power supply that you claim to have likely doesn't exist.  You might want to have another look.  Corsair's CX line only hits 430, 500, 600, and 750 W, not 650.

    Corsair has revamped their CX line a few times, and it's possible that there was some short-lived 650 W version of it.  But Corsair's earlier CX power supplies were rather problematic on energy efficiency, and that matters if you're planning on building a rig with two high-powered video cards.
    Originally posted by Ridelynn
    Originally posted by Nitth

    Wiki says (although some benchmarks sites say it draws up to 330w underload?)that the max TDP is 250w, so your saying (250 * 1.5 = 375)?

    Per card, the multiplier is more or less for overclocking - if you don't plan on overclocking then your probably ok with TDP + small margin. SO a pair of 280X's will be 500W at full load stock, and potentially a lot more depending on your overclock.

    Originally posted by Nitth

    Don't need to, That's hopefully going to be on the other psu.

    PSU1: CPU, MOBO, DRIVES[~300w/650w}
    PSU2: 280x, 280X [375w/650w]

    Chaining Power supplies is doable, but not the best idea. Most of the time you see paired power supplies, they are there for redundancy in case one goes out (servers). You would be better off with a single large-enough power supply. BY the time your at 500W for your video cards, you add 200W in for "everything else" - and then add in some margin, a 750W would carry it at stock speeds, and wouldn't need to be daisy chained to anything to do it.

    The obvious drawback to daisy chaining is where do you stick the second power supply, because not many cases will default to allowing 2 to be mounted internally (although anything is possible with a dremel and/or duct tape). The second is reliability, as Quizzical mentions - now you have 2 components that can go bad and possibly fry your entire system, rather than just one.

    The last is that your video cards draw power from 2 sources - you have the PCI bus that it will draw power, from the same power source the motherboard is plugged into, and then you also have the PCIe x6/x8 cables that plug into the top of the card. You can't split out how much load is on which power supply (although you can more or less guess, each of those power sources have published maximum power draws). Both of those need to turn on at the same time or you could damage something on the card - there are ways to do that, it's not impossible, but you need something better than "I'll just turn on both power supplies at the same time by hand".

    Case is a HAF 932. - big fans 2 power supply mounts.

    PSU's Are in fact 650w's connected with an adapter that powers them both when the pc pwr switch is hit.

    This is a temporary measure these will eventually be replaced with a 1000w psu when i can afford it,

    so just to clarify: 2 280x's is ok for a 650w pwr supply under load?

    image
    TSW - AoC - Aion - WOW - EVE - Fallen Earth - Co - Rift - || XNA C# Java Development

  • RidelynnRidelynn Member EpicPosts: 7,383

    Split across a pair of 650Ws yeah, it technically should work.

  • QuizzicalQuizzical Member LegendaryPosts: 25,355

    If you're going to have two power supplies in the system, why put nearly all of the load on one of them?  Why not put one of the video cards on each?

    Also, I really think you should check again to make sure that you have the power supply that you think you do.  A Google search turned up nothing on a Corsair 650CX or CX650.  I'd like to see the exact claimed specs on it, so it would help if you could transcribe the whole box of specs here (e.g., 40 A on the +12 V rail, 15 A on the +5 V rail, etc.)

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