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One rail or multi rail power supplies.


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#1 Layback Bear

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Posted 11 October 2009 - 04:16 AM

This is from P/C Power and Cooling.

8. ARE MULTIPLE 12-VOLT RAILS BETTER THAN A SINGLE 12-VOLT RAIL?

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 This is the question. Is this a true statement or just a add for there product. It seems to add up to me. I would like other members opinion.

Edited by Layback Bear, 11 October 2009 - 04:16 AM.


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#2 dpunisher

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Posted 11 October 2009 - 09:05 AM

With rare exceptions, all PSUs are single rail. A multirail model has it's single output divided into "rails", and each of those rails is current limited. There is no advantage to multiple rails. It just causes extra BS when you hook everything up, and my eyes are too old to have to look at what stripe is on what yellow wire. Some multirail PSUs don't even bother to actually split rails anymore. They are simply called "multirail" for marketing reasons.

Watts/amps being equal, I prefer a larger single rail unit.

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#3 garmanma

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Posted 11 October 2009 - 11:59 AM

A large, single 12-volt rail (without a 240VA limit)


The highlighted words being the key words
You still won't see that in the cheaper units
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#4 Layback Bear

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Posted 15 October 2009 - 09:18 PM

I'm not looking for cheep, just good. I'm under the understanding that P/C POWER AND COOLING has been sold and there is a question in some mines that the quality might not be as good as it has been for years. I always start with the best P/S I can find. Is there another single rail P/S that any body would recommend. In the range of 800w to 1000w.

#5 DaffyKantReed

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Posted 16 October 2009 - 06:23 AM

I'm not looking for cheep, just good. I'm under the understanding that P/C POWER AND COOLING has been sold and there is a question in some mines that the quality might not be as good as it has been for years. I always start with the best P/S I can find. Is there another single rail P/S that any body would recommend. In the range of 800w to 1000w.


Corsair HX850W
http://www.hardwaresecrets.com/article/741/1

It is a single rail design and uses some very high quality components.

#6 Layback Bear

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Posted 17 October 2009 - 04:52 AM

Thank you very much DaffyKantReed! http://www.hardwaresecrets.com/article/741/1 is bookmarked. Very nice site. I'm planning on a new build so I do a lot of looking but when it comes to power supplies I haven't been finding. HX850W is looks like one of the good choices. I wonder why there HX1000W isn't a single rail.

#7 dpunisher

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Posted 17 October 2009 - 05:42 AM

I wonder why there HX1000W isn't a single rail.


That PSU is actually 2 500 watt units combined in one case.
http://www.jonnyguru.com/modules.php?name=...ory&reid=89

And another 850 review: http://www.jonnyguru.com/modules.php?name=...ry&reid=153

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#8 Layback Bear

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Posted 18 October 2009 - 07:55 AM

You sure found another good one. That was a very good review. Another bookmark. I sure can do some real research and pick one. Thanks again to all.

#9 the_patriot11

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Posted 18 October 2009 - 05:37 PM

personally, I am a fan of multi-rail solutions, they work well for me. I like them because it divides the power out a little more evenly, and if one rail decides to fry it might not fry your entire computer hehe. and in the older days, if you wanted anything high powered you needed multi rail solutions to handle the voltage. Newer PSU have gone to one or two rails with high voltage limits, so you no longer need to have multiple rails to handle high voltage components. Personally, I dont see anything wrong with either setup as long as the PSU is well built and can handle the setup you are building. My PSU is a 750 watt PSU with 4 19v rails, and it works great for me. :D

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#10 Layback Bear

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Posted 25 October 2009 - 09:28 AM

OK I have picked one Corsair HX1000. Thank you all for your help.




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