power supply SLI

Discussion in 'Power Supplies and UPS's' started by infection, Mar 26, 2009.

  1. infection

    infection Geek Trainee

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    Hi, im new here and i don't know that much about computers,
    but still i'm trying to build one by myself. :)
    I was thinking off putting 2 Gforce 8800 GTX graphic cards in SLI.
    But what kind of power supply will i need for that?
    A friend of mine said that it would run on a 650 watt power supply..
    But will it really be enough? :confused:
  2. Big B

    Big B HWF Godfather

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    A good 650W-800W unit, yes, but ultimately, it comes down to the specific power supply and the entire configuration it's powering. A 650W unit that's going to do the job isn't going to be something under $100 USD and is probably going to have at least 60A on the +12V rail or through a combination (when factoring in multiple +12V rails).

    More and more things draw off the +12V rail, so you really want to pay attention to that. Besides PCIe video cards, the CPU and hard drives are some major components that draw off the +12V line. If they aren't fed the juice, then you'll start to run into issues with stability for starters.

    Typically, a PSU with an SLI Certified sticker is a fairly safe bet. In fact, nVidia has a site with a dedicated list of PSU's for various SLI setups. Many of the PSU's nVidia recommends are closer to 1000W, but the 8800 series, as with most high-end video cards, consume a lot of power.
  3. Net Jockey

    Net Jockey Geek Trainee

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    What one needs to know about...the relation of the negative effects of heat on the computer...That can be caused by the power supply.

    Manufacturers test their PSU's at a set temperature...from this their rating is determined... for most this No. is 25 degrees Celsius...which falls short of the temperature that most computers are capable of achieving.

    Given that a PSU will actually lose 2-5 watts per one degree of heat above the 25 Degree Celsius testing temperature...coupled with the fact that computers tend to run at 10 degrees higher than room temperature... In the summer time when the room temperature can easily reach 80 degrees F... your computer will be running at 33 Degrees C. or 90 Degrees F.

    So the...math can make...your 500 watt power supply into a 460 watt unit.

    In addition to this...what needs to be taken into account is that each degree that your computer components are operating at...under powered...adds more heat to the equation.

    Consider also...the possibility...that ratings given by the manufacturer of single components...such as graphics cards...need to be treated with skepticism...Manufacturers may minimize support issues and under rate the power required...in order to make a larger profit.

    The above has not taken into account...the issue of high quality vs poor quality units...Power supplies convert voltages from wall outlets to lower levels used by the PC. During this conversion, some power is lost as heat. The efficiency level of the PSU determines how much extra power must be put into the power supply to run the PC. A high quality PSU can help reduce the noise and heat generated within a computer system. The higher the efficiency rating the less heat the PSU has to deal with.

    Therefore heat is the computers enemy...The hotter the temperature your PSU is forced to run at...the poorer the supply of power the rest of the components will receive...which has been known to lead to such things as crashes, freezing, rebooting, BSOD’s, and video distortion, as well as partial and complete failure of other components.

    The fact is very few PSU’s are capable of producing the wattage that the companies advertise.

    For a very good comprehension of recommended brand names, wattage, and models in listed categories...Plus much more...check out this link. Power Supply Information and Selection - Tech Support Forum

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