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500w psu with 2 18a 12v rails enough for GTX 260?

Discussion in 'NVIDIA' started by jimbob, Feb 4, 2009.

  1. jimbob New Member

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    I have an OCZ StealthXStream power supply at 500w.
    It has 2 12v rails at 18A each. According to EVGA's site their gtx 260 ssc requires 35A of power on a 500w PSU. Now I realize my psu does not exactly meet that standard, so I started looking at other cheap psu's that could handle it. the cheapest looking one is this:
    http://www.newegg.com/Product/Product.aspx?Item=N82E16817148010
    at 34 a. if this is enough it would be a minimal cost in upgrading. If it isnt, I would likely move up to this:
    http://www.newegg.com/Product/Product.aspx?Item=N82E16817341011
    A much bigger cost, but would allow for sli of a second 260 later.

    The first PSU I listed has one 12v rail with 34A, Just short of the 35 required. Would this suffice, not just the amperage, but say it were a 35A, it only has one rail, would it still have enough power with every other component also running on it?

    Now for my real question. I started to realize that the fact that my psu has 2 18A rails may be to my advage when I saw this post:
    http://www.hardforum.com/showthread.php?t=1389830
    When asked what psu he used for 5 gpu's (2 gtx 295's) and an 8800 gtx, none of which are low power cards, in one computer I went to read the Amperage specs on the one he listed.
    they are as follows:
    +3.3V@40A,+5V@40A,+12V1@18A,+12V2@18A,+12V3@18A,
    +12V4@18A,+12V5@18A,+12V6@18A,-12V@0.8A,+5VSB@3. 5A
    It has 6 12v rails and is 1000w, but each rail is only 18A.

    This leads me to beleive that my 2 18a rails just might suffice for a single gtx 260, if the 2 rails were added together.
    My PSU has one pcie 6 pin connector, maybe I would need to isolate the 2 (4 pin peripheral) adapter that would account for the second pcie plug needed to the second rail.

    anyone have any advice on this? It would be great to not have to buy a new psu, as the card is expensive enough as it is.
    Thanks
  2. Damian^

    Damian^ New Member

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    EVGA recommends 35A for the entire system.
    Your OCZ should suffice.
  3. phanbuey

    phanbuey

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    dont risk ur hardware for a crap PSU... nothing is more frustrating than hearing a *POP* and then wishing you spent the extra $$ because now youre gonna spend it anyways and ur hardware might be dead.

    Youre right on track with a PSU with a single, massive rail. That PP&C is nice - so is the TX750W from corsair (whichever you can find cheaper)... I can tell you that this PSU will last you 5+ years, which would make it one of the cheapest components in ur system over time. Anything that can power a 2900XT crossfire setup is pretty damn good :D. Plus you should totally go for SLI with your 260 (its friggin great).

    EDIT:

    this guy sums it up the best (from newegg review):

    "...CPU or RAM [or GPU aren't] going to consume 60 amperes; but the pulses they generate as they switch will make HUGE picosecond demand on the abillity of the power supply to source or sink current. It's this ability to handle spiky demand on the rail that really makes for stability. If the supply can't cope, these rapid changes in demand will turn into NOISE on the rail, and the CPU and RAM will have a hard time telling the difference between noise on the rail and actual signals on their buses. This is why big, clean power supplies help the stability of a PC. Of course, all your drives, fans, video cards and so on also need capacity so this is also part of the equation.
    Last edited: Feb 4, 2009
  4. jimbob New Member

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    so the 2 18A rails can be added together? Do I need to isolate the second rail for the pcie adapter that comes with the card, for the second 6 pin plug i'll need?
  5. phanbuey

    phanbuey

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    you can and that PSU will (probably) meet the demands of your system... but I would go for overkill... why? because PSU issues are a B$*H to detect, and when youre gtx260 starts artifacting or all of a sudden memry sticks start dying it sucks.

    EDIT: you will need to isolate the second rail, btw.
  6. ShadowFold

    ShadowFold New Member

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    I ran a GTX 280 on my Antec 500w. It's got two 22a rails and ran it fine.
  7. nafets New Member

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    What else are you running in your system off the PSU?

    CPU (OC'ed?)
    HDDs
    Optical

    Your OCZ StealthStream 500W can hardly be deemed a "crap" PSU. It's fairly decent and could be a whole lot worse.

    Unless you're some hardcore OC'er with a quad core, I'd say you should have no problems with a GTX 260. If the GTX 260 you're looking at is a 55nm model, then you'd be even better off, as it requires even less power than the 65nm models.
  8. jimbob New Member

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    I am looking at a 55nm model clocked at 675 mhz stock. My cpu is a phenom 9950, probably the most power intensive cpu on the market, but only by a few watts, so I doubt it makes that much of a difference.
    HDD'd are both seagate. one 750gb sata, one 500 gb ide. one crappy dvd drive I never use. not even sure if its plugged in right now. My cpu is overclocked from 2.6 to 3.0 ghz, so not a huge amount. I'm still using the stock cooler, but I have a freezer 64 pro I plan on installing soon as I get a new video card and tear the thing apart.
    i'd really like to keep this psu for the time being, if possible. I realize its not the greatest, but your right, it can hardly be caled a crap psu. I did spend a small penny on it, and figured it would suffice for anything I would need at the time. I was not aware at the time however that gfx cards required 35A of current. Thats a LOT of current for anyone who knows a bit about electricity.
    Thanks for the replys. I'm new on this board, and I am really liking it so far.
  9. jimbob New Member

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    Have you (or anyone else) had these things happen? does it really ruin your hardware? My psu Does have active PFC. I'm not sure if that would help protect the hardware from what you are talking about, but it is certainly designed to protect the hardware.
    My guess would be that when the PSU goes POP from too much current being drawn, it would just affect the psu, and I could get a new one.
    Like I said, if at all possible I want to wait on upgrading the psu til I upgrade my system to an i7/x58, and add one or 2 more gtx 260's or 285's/gt212's If I do evga's trade up program when the gt212 come out.
  10. nafets New Member

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    If I was in your shoes I'd have no qualms running that system with a new GTX 260 55nm. But I'm no expert.

    Based on the opinions of others I'd recommend going ahead with it with the following stipulation, just to be safe, better than sorry: Try it out first with your Phenom set to stock speed.

    Your CPU (and how hard you OC it) is the biggest factor in your system that decides how stable your configuration will be with the new video card. If all is well after a good number of days of testing and stress, you can slowly work the CPU OC back to it's 3.0GHz speed. Chances are good you won't have any problems, with the CPU OC'ed or not. There is never any certainty with PCs...

    As I said before, this is just a precaution, and should be a better path to take if you're nervous or just unsure. Good luck!
    Last edited: Feb 4, 2009
  11. jimbob New Member

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    I guess my last question, (pending any further info on my last few posts) would be, has anyone tried this on a similar setup? ShadowFold, seems like you came pretty close, as the 280 uses a little extra power than the 260. In fact i'll look that up right now.

    Actual Power Consumption Nvidia Graphic Cards
    2D Desktop in Watts______________ 3D Full Load in Watts___________ Current in Amps (A)
    GeForce GTX 280 (1024 MB)
    43.7_________________________________ 204.4______________________17.0
    GeForce GTX 260 (896 MB)
    38.7 _________________________________191.2 ________________________15.9

    I hope that comes out right. (edited to make it look better)
    So the gtx 280 uses about 15 more watts, and 1.1 more amps. so someone with a psu with a little lower power and this or a card that uses a similar amount of power, which you can look up here:
    http://www.tomshardware.com/reviews/geforce-radeon-power,2122-6.html
    would be helpful.
    Thanks again for all the info
  12. bigtye New Member

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    Yep, believe I have.

    Running a TT 430W (turned out to be rebadged 350W) and upgraded from 1950 pro to 9600GT. Recieved a low power warning on screen from Nvidia drivers telling me card was switching to low power mode due to insufficient power. Rebooted and found that all my usb ports on my mobo were no longer working. Have replaced PSU with corsair 620w but usb ports on mobo dead. Considered myself lucky.

    Tye
  13. JrRacinFan

    JrRacinFan Served 5k and counting ...

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    The GTX260 will be fine but ....

    What games do you play? What resolution? What's the rest of your specs?
  14. jimbob New Member

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    Here are my specs:
    amd phenom 9950 be 2.6 ghz oc'd to 3.0 ghz on stock fan (amazing)
    MSI DKA790gx motherboard (non platinum version)
    4gb corsair dominator ddr2 1066
    dvd drive
    2 seagate hdd's 1 750gb sata 1 500gb ide
    dlink wifi card
    PSU 500w ocz stealthxtreme. but you already know that

    I plan to play farcry2, crysis, stalker, fallout 3, and all the other new fps games out.
    Farcry and crysis engines clearly perform better with nvidia.
    The gtx 260 just dropped significantly in price, so I plan to order within a few days unless someone can talk me out of it because of my psu. all the parts in my system are brand new, and are still under warranty, so in theory they should be ok if for some reason something gets dead.
    edit: oh and I plan to play at 1680x1050, if possible, as thats the native res of my samsung 22" lcd
    the recent price drop though is even more motivation to use my psu if I can, as the investment has become less, I would like to not have it become more again.
    Last edited: Feb 6, 2009
  15. nafets New Member

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    You can ask around left and right for days on end, but nobody can guarantee you it either will or won't work.

    As I said before, if you're nervous, just put the Phenom to stock clocks when you put the GTX 260 in. If everything runs fine (which it most likely will), then work the OC back to it's previous speed...
  16. mav2000

    mav2000 New Member

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  17. jimbob New Member

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    well I guess we will all find out soon enough, when my card comes sometime next week.
    thanks all for the help. I'll be sure to let you all know how it goes.
  18. Joe Public

    Joe Public

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    It's hard to tell what the combined 12V rating on the SXS PSUs are, as they only provide the combined wattage for 3.3V, 5V and 12V. I wish they'd be more specific like that.

    As for rail configuration, with only two rails I would believe that the PCIe connectors are on one rail along with everything else (mainboard, drives etc) except the CPU, which would be on the other rail on its own.
  19. Flyordie

    Flyordie New Member

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    I am not gonna lecture but here are the facts.
    OCZ PSUs RIPPLE HEAVILY under load. (80%+ load is dangerous on most accounts.)
    A very high quality 500-550W would easily handle your system.
    Spend the $80 on a good PSU like I did.
    http://www.newegg.com/Product/Product.aspx?Item=N82E16817151027
    SeaSonic S12 Energy Plus SS-550HT 550W ATX12V V2.3 / EPS12V V2.91 SLI Certified CrossFire Ready 80 PLUS Certified Active PFC Power Supply
    +3.3V@24A, +5V@30A, +12V1@18A, +12V2@18A, +12V3@18A, +12V4@18A, -12V@0.5A, +5VSB@3.0A

    This PSU has VERY stable +12V rails... mine has under .5% ripple, its awesome, I love how they designed it with dual magnetic amps. This PSU also does have authentic 4x 12V Rails. Each one has their own source of voltage. The rails are marked on the connectors btw. I will label what they are-
    12V1= CPU
    12V2=Mainboard+Peripherals
    12V3=PCIe1
    12V4=PCIe2
    Using that to power the system in my specs.
    Last edited: Feb 9, 2009
  20. JrRacinFan

    JrRacinFan Served 5k and counting ...

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    The OLDER OCZ power supplies do. Thew newer ones which have PCP&C under the hood don't ripple as much.

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