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Power Supply / Video Card Question

Discussion in 'Hardware' started by bdg146psu, Jun 19, 2007.

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  1. bdg146psu

    bdg146psu Thread Starter

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    I'm in the process of building my first PC. I just received my power supply today (Corsair 620W). It has four listings for 12V (+12V1, +12V2, +12V3, and -12V), the first three of which are rated at 18 Amps and the last at 0.8 Amps. My video card is a Sapphire x1950XT, which, according to some reviews on newegg, requires 20-30 Amps. I looked on Sapphire's website, but I couldn't find an exact requirement.

    So my question is, am I likely to run into trouble with this PSU / Video card combination? I really thought this PSU had a higher amperage than 18... I guess I read something wrong when ordering it. I did find some reviews of people running 1950Pro's with this Corsair PSU.

    Also, I really don't understand the rails and what all of that means, so could someone post a quick explanation or direct me to an article that would explain the basics of a PSU? I've tried looking at some sites that I know (ie - Tom's Hardware), but I've had trouble finding an article to explain the basics to me.

    Any help would be appreciated.
     
  2. Wasper

    Wasper

    Joined:
    Jul 7, 2005
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    Hi,

    PSUs can be very confusing... the Important amps you need to know are on the +12v rail (rails)... now that Corsiar 620w PSU has three rails marked at 18a each.. so you might think.. "oh I have a total of 54amps.. becuase there are three rails at 18amps each.. right?"

    Nope.... that just means that each individual rail is rated for a maximuim of 18amps each.. thats thier limit lets say.

    If you look at the sticker on the side of the power supply, you can see that the 620w is divieded between all the different rails. the +3.3v & +5v have 170w dedicated to them.. the three +12v rails have 430w deidcated to them, and the -12v & +5vsb have the remaining 20w dedicated to them.

    You take the 430 watts going to the +12v rails and divide that number by 12.. this gives you the total sustainable amps on the 12v rails.. which comes out to 35.8 amps.. so we'll say its 35amps even.

    So, if your X1950XT requires 20-30 amps, then that power supply will be fine. The Corsiar 620w is a very nice power supply and you shouldnt worry that you made the wrong chioce, when in fact you made a great choice.. good job!

    Basically they split the rails for saftey reasons.. they decided that there should not be more then 20amps on any given +12v rail... haveing said that, they still sell power supplies with a large single rail, but these usually have more heavy-duty over current protections and such... which makes them more exspensive.

    I hope this helps,
    Wasper
     
  3. bdg146psu

    bdg146psu Thread Starter

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    Thanks Wasper. You definitely set my mind at ease. Like I said, this is my first build, so I was having one of those "uh oh" moments. From everything I've read, the PSU is a lot more important than it seems at face value, so it's nice to know I did a good job picking one out. Thanks again!

    One other quick question. I've seen most PSUs with the fans mounted vertically, blowing straight out of the back of the case. The fan on my Corsair PSU is mounted horizontally, so it would blow up or down depending on how I mount it (to be honest, I haven't fitted the thing in my case yet). This seems a little backwards to me. I have an Antec P180 case, where the PSU is supposed to be mounted in the bottom of the case in a separate compartment (along w/the HDDs). Am I going to run into cooling issues with the way this is set up? My case has three fans, one at the top of the rear, one on top, and one between the HDDs and the PSU in the lower compartment. It has a place to mount one on the bottom front of my case. Do you think it'd be a good idea to pick up an extra 120mm fan? It just seems odd to me that the PSU fan would blow the hot air into my case, rather than out. Unless of course the PSU fan is intake, instead of blowing air out. Perhaps I should have tested the thing out before asking all these questions, but just trying to think as far ahead as I can.
     
  4. bdg146psu

    bdg146psu Thread Starter

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    Forgot to add a link to my case.
     
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