PSU: Rails? Voltage? Amps? Please explain...

I'm building my own PC, and all I know about PSU's is that it has a wattage, and I thought that is all that matters! Now I start hearing about voltage, rails and amps. :heink: What! How does any of this matter? Is it important? And why??

Right now I'm pretty confused about what rails are. And modular cable management. Im trying to read up on that but there are no sites that explain it well. Please try your hardest to explain it to me in layman's terms. (Don't link me to the PSU FAQ please. I read it. Made no sense.)

Basically, if I am planning on using a computer for gaming, with a GTX 280/295, a E8600 (3.33GHz) overclocked and 1 hdd, how much wattage do you think I'll need? I think I'll need at least 600W. What other information do I need to know about a PSU that is important?
18 answers Last reply
More about rails voltage amps explain
  1. A "rail" is an electrical wire. If a PSU has 2 '12V rails' it has 2 seperate wires that end in a plug that supplies 12V.
    The wiring in your house has rails for lights and for appliances. One rail may go to the kitchen, one to the garage and 3 to the living room. On a rail there can be more than one wall outlet.
    Computer components operate on a certain maximum voltage: 3.3V, +5V, +12V, -12V. These components draw a current, which is expressed in amperes. A component that is rated for 12V and needs 3A to operate consumes 36W(atts). Your PSU has to be able to provide enough power at each voltage.
  2. @Vixe,
    There's good info here
  3. Assuming you can buy from Newegg, get the PC Power & Cooling S61EPS 610W.

    Original Price: $199.99
    You Save: $95.00
    $69.99 after $35.00 Mail-In Rebate

    It's a killer deal and has a single 49A Rail. Then you won't have to worry about rails etc.
  4. About watts
    volts X amps =watts
    Power supplies run @ 120v or 240v but watts never change, because 240v uses half the amps as 120v.
  5. Thanks all for your help. Just to let you know, the reason I know so little is because I am an ex-Mac user. I used to own a PC and I would like to go back to it seeing how I'm becoming more of a gamer. I wanna build my own gaming PC. Now that I at least know what rails ARE, I need to ask the idiots questions of: Do I need a rail going to the GPU and motherboard and HDD? Or does it depend? lol I know I probably sound really stupid asking that question but I simply don't know. I haven't seen the inside of a PC in a long time. Is that why I will need 2 rails? So far I know that the 12v rail has to have at least 40±A to power my GPU of choice(GTX 280 or, depending on the price, GTX 295).
  6. Quote:
    You need a "quality" 600 or 650w that has at least 2 12v rails.

    Umm why 2 rails? There is no information that you can show me 2 rails is better than 1.

    Vixe: Best thing to do, when you choose all your parts post them here and someone will let you know which PSU to buy. Other than that you can do alot of reading, i would suggest reading some reviews on as he generally explains basics as he goes.
  7. Like Chookman said, go to JohnnyGuru's and have a read. Then go where they reveiw, stress, and actually tear down PSU's and look inside at the build quality. After that you shuold be well armed to make up your mind.

    Good Luck, and happy computing
  8. chookman said:
    Umm why 2 rails? There is no information that you can show me 2 rails is better than 1.
    Yeah, 2 rails is actually a lot worse than one if it conforms to the ATX standard. Trapped capacity and all that.
  9. I think the only reason manufacturers were making them in the first place is that in the EPS12V standards it gives "recommend" configs... and thats what they are...
  10. I thought it was due to the 240VA (20A) limit per rail in the ATX standard.
  11. What about the CoolerMaster Silent Pro M 700W? With a E8600 (3.33GHz, 8pin) and GTX 280/295 (6 pin + 8 pin). Motherboard MIGHT be an Asus Striker II Formula
  12. I'm not a fan of Cooler Master. Their 1Kw are supposed to be nice, but the small ones are not. I think they are trying to OEM better quality, but I'm not familiar with that one.

    Try a Corsair TX650.
  13. Zorg: According to newegg this is ATX12V certified with a single rail?
  14. Yeah, Nah, you gotta love the single rail.

    It just dawned on me that you were responding to my earlier post, duh.

    I thought that the ATX standard 2.2 changed the 240VA restriction to recommended, I looked, and apparently not. It looks like the EPS 2.0 is the only one that considers the 240VA restriction a recommendation and not mandatory. So I guess I should have said nah instead of yeah.

    I can't stay on top of ATX changes. It appears that no one is really following them and yet saying they are compliant. I believe that PC P&C didn't use to claim to be ATX compliant, because of the single rail, and only claimed EPS compliance. Many other companies are single rail, Corsair to name one, and actually say on their sticker that they are multirail and also market that they are ATX compliant, which is a little disconcerting.

    I looked on the PC P&C site and can't find anywhere that they call the Silencer 750 ATX compliant. The page for the manual download for it shows it as the the "Silencer 750 EPS12V". The problem that they face is that a lot of people see EPS and not ATX and think it's not compatible. I know because I have fielded at least one question like that before.
  15. What are the benefits of 1 rail vs multiple rails? I don't get it
  16. If you get a true multiple rail they are actually better, because the rails are separately regulated and therefore isolated from each other, but they are very very few and far between. 99% that are called multirail are really pseudo multirail, because the "rails" are only separated by a current limiter, much like a breaker in your house. That's the 240VA or 20amp limit.

    The reason for the pseudo multirail is for fire safety. The problem is that the current of each rail can only be a maximum of 20A, so if the rail is under loaded the additional current is unusable. Since the video cards started drawing a lot of current we got the problem of rail balancing to ensure that the video card plus the other components on that rail didn't exceed the current limiter (breaker) on the rail. So many PSU manufacturers raised the current limit on the rails. Or they only put one really high current limiter (breaker) on the whole PSU, which made it a single rail.

    Rather than give you an example I'll just post the one from PC P&C.

    With all the hype about multiple 12-volt rails (ads claim that two rails is better than one, five is better than four, etc.), you'd think it was a better design. Unfortunately, it's not!

    Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply's rating. Those losses occur because power literally gets "trapped" on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.

    Since the maximum current from any one 12-volt rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts = 20 amps), PCs with high-performance components that draw over 20 amps from the same rail are subject to over-current shutdowns. With power requirements for multiple processors and graphics cards continuing to grow, the multiple-rail design, with its 240VA limit per rail, is basically obsolete.

    PC Power and Cooling is once again leading the industry. All of our power supplies now feature a large, single 12-volt rail. The design is favored by major processor and graphics companies, complies with EPS12V specs (the 240VA limit is not a requirement) and is approved by all major safety agencies such as UL and TUV.3
    A single rail provides the total current to all connectors. The amount drawn by the connector is subtracted from the total and the remainder is fully available to all the other connectors.

    The problem with single rail is that if there is a short that doesn't draw more than the PSU current limiter, which is much higher than 20A, then the PSU won't trip off but will continue to deliver power. That current is high enough to melt wires etc. and start a fire, so you have to be more careful when building.
  17. I use to be a mac user so it is pretty hard for me to imagine all of these wires in my head. Maybe I should I should go to a shop and check it out and get a feel for what it looks like, rather than ordering the product over the Internet and sitting like a retard wondering wtf im supposed to do with it! I understand the importance of most of these aspects in hardware, but once I have all the hardware together I won't have an idea what to do with it!
  18. Good luck with it.
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