oconn11 Posted November 8, 2007 Share Posted November 8, 2007 Hi Cannot get a straight answer...What are rails referring to? Are they individual connectors/plugs? Why would you even need more than one rail? For example I am looking at the new Asus MB with the X38 chipset and DDR2 memory, how many rails does that require? Or am I just not seeing/realizing something? I am looking at the new CMPSU-650TX which is a single rail. Do I use a splitter? Thanks to all Link to comment Share on other sites More sharing options...
Wired Posted November 8, 2007 Share Posted November 8, 2007 Google is your friend :) http://en.wikipedia.org/wiki/Power_supply_rail Link to comment Share on other sites More sharing options...
oconn11 Posted November 8, 2007 Author Share Posted November 8, 2007 Thanks I have seen that. But it does not say why I would need 2 or 3 or 4 rails as opposed to a single rail. Is a rail a single 12v connector. Are the connectors considered rails? 3v 5v 12v ? Power supplies have changed a bit since I did a complete build- had to be 10 years or so. I am trying to get a supply that is powerful enough w/out being excessive, but I may want to play a little - O/C, or two video cards. And what about the graphics cards, the new 8800GT or the new HD3800s. Do they get a rail? They will have a 6 pin or an 8 pin connector for additional power. I know I am missing something. For eg if I look at the sticky above these posts showing me two rails - what MB uses two 12v connectors? Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted November 8, 2007 Corsair Employees Share Posted November 8, 2007 The way multiple rails relate to a PC PSU primarily relates to points at which the PSU has overcurrent protection. IIRC, one of the specifications introduced over the past few years (from Intel IIRC) limited 12v rail current to 18 amps. So, let's say we have a PSU with 36a on the 12v rail, the specification would dictate that you have 2 rails minimum so that no single rail can pull over 18a. Neither single nor multi rail is inherently better than the other assuming they are built correctly. The current trend seems to be towards larger single rail PSUs as systems become more demanding. Link to comment Share on other sites More sharing options...
oconn11 Posted November 8, 2007 Author Share Posted November 8, 2007 The Corsair TX650W/TX750W power supplies are engineered using advanced technology and components typically found with high performance power supplies. SLI-Ready, 5-Year Warranty With design features such as a dedicated, single +12V rail offer the maximum compatibility with the latest system components. (this is off the web site) Following your reasoning/logic how can this be a single rail when the 650w has 52A and the 750w has 60A "A larger number of +12V output rails is not always better. The max power limit of the combined outputs must be considered. Most PSUs with multiple +12V line have a max combined output limit which is smaller than the sum of the individual 12V lines. It is the sum of the +12V lines that is the most important. Furthermore, Intel drafted the ATX12V v2.0 design guide to keep each +12V line to be lower than 20A in order to comply with UL & EN-60950 safety specification. Any PSU that allows a +12V line to exceed 20A does not comply with the ATX12V v2.x spec." (not trying to be a pain) Now the power supply itself 'pulls' 10A from the wall is that continuous or only under max load? Link to comment Share on other sites More sharing options...
Corsair Employees Power Guy Posted November 8, 2007 Corsair Employees Share Posted November 8, 2007 (not trying to be a pain) Don't worry about it. It's a common concern. The ATX 2.0 spec put a 240vA limitation on any single rail, which means the 12V rail was limited to 20A each. However, as of the ATX 2.2 spec, that limitation was removed and reduced to a "recommendation" instead of a requirement. This makes it easier on the consumer since they don't have to worry about which cable gets plugged into which devices anymore. Our HX520 and HX620 are also "single rail" designs even though they are spec'd as triple rail designs. It just makes it easier for compatibility, and there's no real safety concern. Now the power supply itself 'pulls' 10A from the wall is that continuous or only under max load? The Power Supply will only "pull" from the wall what it needs to produce power. The formula looks like this: Input * efficiency = Output So let's say your system requires 350 watts of power. This means that the PSU needs to output 350W. Input * efficiency = 350 Our PSUs are all 80%+ efficient, but let's use 80% because it's a nice round number. Convert to decimal, we get .8. Input * .8 = 350 That means our input is right about 437W 437 * .8 = 350 (approximate) So at this point, your PSU would be drawing about 437W from the wall in order to produce 350W. At 115V (US) that's less than 4A, and at 230V (UK/EU) that's less than 2A. Of course, if you have a less efficient PSU, say an older 500W that is only 70% efficient, you'd have different numbers. 500 * .7 = 350. So with a 70% efficient supply, in order to produce 350W, you need to draw 500W from the wall. That's 63W more. Added up, that can be significant. Link to comment Share on other sites More sharing options...
oconn11 Posted November 9, 2007 Author Share Posted November 9, 2007 Phenomenal answer, perfect, excellent, wow! Thank you CMPSU-750TX soon! with a COSMOS case. Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted November 9, 2007 Corsair Employees Share Posted November 9, 2007 Phenomenal answer, perfect, excellent, wow! Thank you CMPSU-750TX soon! with a COSMOS case. Thats why he is the Power Guy! Link to comment Share on other sites More sharing options...
DerekT Posted November 9, 2007 Share Posted November 9, 2007 A very clean, concise explanation given in excellent layman's terms. A great Avatar too :D: Link to comment Share on other sites More sharing options...
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