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What is single rail psu?

Discussion in 'General Hardware' started by evilwillie0614, Nov 29, 2009.

  1. evilwillie0614

    evilwillie0614 New Member

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    :banghead:guys can you teach me about psu? I realy dont have any idea how this psu works,i mean how do you guys determin how much voltage or watts you need for your rig?
     
  2. erocker

    erocker Super Moderator Staff Member

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    evilwillie0614 says thanks.
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  3. Soylent Joe

    Soylent Joe

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  4. erocker

    erocker Super Moderator Staff Member

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  5. Soylent Joe

    Soylent Joe

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    Hmm...It said 492W for my system which seems about right, but I've never actually measured my power consumption from the wall. That calculator you're using is nice, really specific.
     
  6. evilwillie0614

    evilwillie0614 New Member

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  7. evilwillie0614

    evilwillie0614 New Member

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    ill check out your calculator and i guess what i need is to study heheh.. Before end up blowing my rig.
     
  8. angelkiller

    angelkiller

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    Edit: Alot of people have responded while I was typing. That PSU calculator that erocker linked to is probably the simplest way to find out what kind of PSU you will need.

    Ok, first understand you're asking about a huge topic. So there is no simple answer. I could write pages giving you a complete education on power supplies. Instead, I'll try to be brief and give simple answers. Just know that it's a big topic.

    Here's some background. A while ago, before PSUs were 1000+W, Intel added a part to the ATX specification which tells how ATX power supplies are supposed to be made. (all computer PSUs follow the ATX spec) Intel said that in order to be safe, no circuit in the PSU could handle over 20A of current. In simpler terms, Intel put a limit on how much electricity could be in any part of the PSU at one time. Fast forward to today. 20A at 12V is only 240W. But PSU manufacturers make PSUs much greater than this. How? They use multiple rails. Each rail is its own seperate circuit that has less than 20A. So If a manufacturer wanted to have 300W on the 12V rails, it could use a 12A and a 13A rail. That way, you can have more watts without going over the 20A limit. A single-rail PSU is just that. It's a PSU that only has 1 12v rail. (The 12v rail is the most important because the CPU and graphics cards get thier power from the 12v rail, not the others) So a single rail PSU technically breaks Intel's ATX specification and offers 1 very large 12v rail, often around 60 or 70A. The controversey arises as to whether this is a good idea or not. I won't go into the details, as they are quite technical, but some people believe that a large single rail PSU is better (ie more stable) than having multiple rails. And that's the difference.

    Determining wattage is actually pretty simple. Nearly all components have been measured for how much power they use. (Power is measured in watts) For example some CPUs have a 65W TDP, which means that under a worse case scenerio, it will draw 65W of power. To determine how much power your system needs, you simply find out how much power each component uses in a worst case scenerio, and add it together. Now, most people say that running a PSU at 100% isn't a good ida. So if you have a 500W PSU, it isn't a good idea to draw 500W from it. You probably want to use 80% of your PSU at maximum. So let's say you add up the power draw of your components and you get 240W. You just get a PSU that is at least 125% larger than 240, which turns out to be 300W. (240 * 1.25 = 300) In my opinion, that is the minimum that you should get. But getting a larger PSU won't hurt. Getting a larger PSU than needed is only bad when you get a PSU that is wayyyyyyyyy to much. There's no need to get a 1000W PSU if your system only draws 300W. A 500W PSU is plenty. And that's how to tell how many watts your system needs and how to chose an good sized PSU.

    But it's not all that simple. Every component does not have a published TDP. For example the motherboard. Also, you can go over the TDP of a CPU when you overclock it. So many times, you have to make a guess as to how much power your system needs, because measuring it is difficult (for technical reasons) and if you don't have it yet, you can't measure it anyway. So when you make these 'guesses' it's always a good idea to overestimate. That way you end up getting a large enough PSU. It's always better to have too much then too little. With too much, your system will still run. With too little, your rig won't run, or it'll crash when you try to play games and such. So if you're not sure about how much power your system will use, it's always better to ask, as other people may have more experience/knowledge as to how much power it'll use.

    Hopefully this is helpful.
     
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  9. evilwillie0614

    evilwillie0614 New Member

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    i'd like to thank all of you guys.. You realy know how to make newbie like me feel better heheh.. I've read alot of reviews and tutorial but yours angelkiller is way to go.. Thx..
     

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