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Multi +12V Rails VS Single Rail

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May 23, 2011 4:28:58 PM

There are a lot of rumors which one is the best? I did research on some articles and they were recommended single rail, some of them saying there is no different.So in order to upgrade my hp pc p6230f with new HD 5670 video card, does it matter buying power supply provide 450 watt with single or multi rail?? I just wanna make sure all my pc components(cpu, mobo, ram, fans, cd rom, hard drive, and video card) will get enough power if I planed to use multi rail. I dont know if distribution of Amperage will effect in this case because it's divided on two for dual rail for example
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Thanks

Am not a fan of electricity at all

PS. I saw this ads from xfx power supply page, just look at the end of the page it will show an explanation of how multi rail looks scary??
http://xfxforce.com/en-us/Products/PSU/Pro-Series/450W-...
a b ) Power supply
May 23, 2011 4:33:20 PM

drsaog said:
Man.. we get this question daily. I really need to keep a response on my desktop I can copy and paste.

What is "multiple +12V rails", really?

In most cases, multiple +12V rails are actually just a single +12V source just split up into multiple +12V outputs each with a limited output capability.

There are a few units that actually have two +12V sources, but these are typically very high output power supplies. And in most cases these multiple +12V outputs are split up again to form a total of four, five or six +12V rails for even better safety. To be clear: These REAL multiple +12V rail units are very rare and are all 1000W+ units (Enermax Galaxy, Topower/Tagan "Dual Engine", Thermaltake Tough Power 1000W & 1200W, for example.)

In some cases, the two +12V rail outputs are actually combined to create one large +12V output (Ultra X3 1000W, PC Power & Cooling Turbo Cool 1000W, for example.)

So why do they do they split up +12V rails??

Short circuit protection only works if there's minimal to no resistance in the short (like two wires touching or a hot lead touching a ground like the chassis wall, etc.) If the short occurs on a PCB, in a motor, etc. the resistance in this circuit will typically NOT trip short circuit protection. What does happen is the short essentially creates a load. Without an OCP the load just increases and increases until the wire heats up and the insulation melts off and there's a molten pile of flaming plastic at the bottom of the chassis. This is why rails are split up and "capped off" in most power supplies; there is a safety concern.

Is it true that some PSU's that claim to be multiple +12V rails don't have the +12V rail split at all?

Yes, this is true. But it's the exception and not the norm. It's typically seen in Seasonic built units (like the Corsair HX and Antec True Power Trio.) It's actually cheaper to make a single +12V rail PSU because you forego all of the components used in splitting up and limiting each rail and this may be one reason some OEM's will not split the rails, but say they are split. Some system builders adhere very closely to ATX12V specification for liability reasons, so a company that wants to get that business but also save money and reduce R&D costs will often "fib" and say the PSU has it's +12V split when it does not.

Why don't those PSU companies get in trouble? Because Intel actually lifted the split +12V rail requirement from spec, but they didn't actually "announce" it. They just changed the verbiage from "required" to "recommended" leaving system builders a bit confused as to what the specification really is.

So does splitting the +12V rails provide "cleaner and more stable voltages" like I've been told in the past?

It is true that marketing folks have told us that multiple +12V rails provides "cleaner and more stable voltages", but this is usually a falsehood. Quite frankly, the use this explaination because "offers stability and cleaner power" sounds much more palletable than "won't necessarily catch fire". Like I said before, typically there is only one +12V source and there is typically no additional filtering stage added when the rails are split off that makes the rails any more stable or cleaner than if they weren't split at all.

Why do some people FUD that single is better?

Because there are a few examples of companies that have produced power supplies with four +12V rails, something that in theory should provide MORE than ample power to a high end gaming rig, and screwed up. These PSU companies followed EPS12V specifications, which is for servers, not "gamers". they put ALL of the PCIe connectors on one of the +12V rails instead of a separate +12V rail. The +12V rail was easily overloaded and caused the PSU to shut down. Instead of correcting the problem, they just did away with the splitting of +12V rails altogether. Multiple +12V rail "enthusiast" PSU's today have a +12V rail just for PCIe connectors or may even split four or six PCIe connectors up across two different +12V rails. The rails themselves are capable of far more power output than any PCIe graphics card would ever need. In fact, Nvidia SLI certification these days REQUIRE that the PCIe connectors be on their own +12V rail to avoid any problems from running high end graphics cards on split +12V rail PSU's.

There's less components and less engineering to make a PSU that DOES NOT have the +12V rail split up, so it's cheaper to manufacturer (about $1.50 less on the BOM, $2 to $3 at retail) and typically this cost savings is NOT handed down to the consumer, so it actually behooves marketing to convince you that you only need single +12V rails.

But some people claim they can overclock better, etc. with a single +12V rail PSU

B.S. It's a placebo effect. The reality is that their previous PSU was defective or just wasn't as good as their current unit. If the old PSU was a cheap-o unit with four +12V rails and the new one is a PCP&C with one +12V rail, the new one isn't overclocking better because it's a single +12V rail unit. It's overclocking better because the old PSU was crap. It's only coincidental if the old PSU had multiple +12V rails and the current one has just one.

The only "problem" the occurs with multiple +12V rails is that when a +12V rail is overloaded (for example: more than 20A is being demanded from a rail set to only deliver up to 20A), the PSU shuts down. Since there are no "limits" on single +12V rail PSU's, you can not overload the rails and cause them to shut down..... unless you're using a "too-small" PSU in the first place. Single +12V rails do not have better voltage regulation, do not have better ripple filtering, etc. unless the PSU is better to begin with.

So there are no disadvantages to using a PSU with multiple +12V rails?

No! I wouldn't say that at all. To illustrate potential problems, I'll use these two examples:

Example 1:

An FSP Epsilon 700W has ample power for any SLI rig out there, right? But the unit only comes with two PCIe connectors. The two PCIe connectors on the unit are each on their own +12V rail. Each of these rails provides up to 18A which is almost three times more than what a 6-pin PCIe power connector is designed to deliver! What if I want to run a pair of GTX cards? It would have been ideal if they could put two PCIe connectors on each of those rails instead of just one, but instead those with GTX SLI are forced to use Molex to PCIe adapters. Here comes the problem: When you use the Molex to PCIe adapters, you have now added the load from graphics cards onto the rail that's also supplying power to all of your hard drives, optical drives, fans, CCFL's, water pump.. you name it. Suddenly, during a game, the PC shuts down completely.

Solution: To my knowledge, there aren't one-to-two PCIe adapters. Ideally, you'd want to open that PSU up and solder down another pair of PCIe connectors to the rails the existing PCIe connectors are on, but alas... that is not practical. So even if your PSU has MORE than ample power for your next graphics cards upgrade, if it doesn't come with all of the appropriate connectors, it's time to buy another power supply.

Example 2:

Thermal Electric Coolers take a lot of power and are typically powered by Molex power connectors. I, for one, prefer to run TEC's on their own power supply. But that's not always an option. If you had a power supply with split +12V rails and powered your TEC's with Molexes, you would be putting your TEC's on the same +12V rail as the hard drives, optical drives, fans, CCFL's, water pump.. you name it, just as you did with the Molex to PCIe adapters. The power supply could, essentially, shut down on you in the middle of using it. A power supply with a single, non-split, +12V rail would not have any kind of limit as to how much power is delivered to any particular group of connectors, so one could essentially run several TEC's off of Molex power connectors and not experience any problems if one had a single +12V rail PSU.

Typical multiple +12V rail configurations:
2 x 12V rails
Original ATX12V specification's division of +12V rails.
One rail to the CPU, one rail to everything else.
VERY old school since it's very likely that "everything else" may include a graphics card that requires a PCIe connector.
Typically only seen on PSU's < 600W.
3 x 12V rails
A "modified" ATX12V specification that takes into consideration PCIe power connectors.
One rail to the CPU, one rail to everything else but the PCIe connectors and a third rail just for PCIe connectors.
Works perfectly for SLI, but not good for PC's requiring four PCIe connectors.
4 x 12V rails (EPS12V style)
Originally implemented in EPS12V specification
Because typical application meant deployment in dual processor machine, two +12V rails went to CPU cores via the 8-pin CPU power connector.
"Everything else" is typically split up between two other +12V rails. Sometimes 24-pin's two +12V would share with SATA and Molex would go on fourth rail.
Not really good for high end SLI because a graphics card always has to share with something.
Currently Nvidia will NOT SLI certify PSU's using this layout because they now require PCIe connectors to get their own rail.
In the non-server, enthusiast/gaming market we don't see this anymore. The "mistake" of implementing this layout was only done initially by two or three PSU companies in PSU's between 600W and 850W and only for about a year's time.
4 x 12V rails (Most common arrangement for "enthusiast" PC)
A "modified" ATX12V, very much like 3 x 12V rails except the two, four or even six PCIe power connectors are split up across the additional two +12V rails.
If the PSU supports 8-pin PCIe or has three PCIe power connectors on each of the +12V rails, it's not uncommon for their +12V rail to support a good deal more than just 20A.
This is most common in 700W to 1000W power supplies, although for 800W and up power supplies it's not unusual to see +12V ratings greater than 20A per rail.
5 x 12V rails
This is very much what one could call an EPS12V/ATX12V hybrid.
Dual processors still each get their own rail, but so do the PCIe power connectors.
This can typically be found in 850W to 1000W power supplies.
6 x 12V rails
This is the mack daddy because it satisfies EPS12V specifications AND four or six PCIe power connectors without having to exceed 20A on any +12V rail
Two +12V rails are dedicated to CPU cores just like an EPS12V power supply.
24-pin's +12V, SATA, Molex, etc. are split up across two more +12V rails.
PCIe power connectors are split up across the last two +12V rails.
This is typically only seen in 1000W and up power supplies.

Ok... What's the bottom line?

The bottom line is, for 99% of the folks out there single vs. multiple +12V rails is a NON ISSUE. It's something that has been hyped up by marketing folks on BOTH SIDES of the fence. Too often we see mis-prioritized requests for PSU advice: Asking "what single +12V rail PSU should I get" when the person isn't even running SLI! Unless you're running a plethora of Peltiers in your machine, it should be a non-issue assuming that the PSU has all of the connectors your machine requires and there are no need for "splitters" (see Example 1 in the previous bullet point).

The criteria for buying a PSU should be:
Does the PSU provide enough power for my machine?
Does the PSU have all of the connectors I require (6-pin for high end PCIe, two 6-pin, four 6-pin or even the newer 8-pin PCIe connector)?
If using SLI or Crossfire, is the unit SLI or Crossfire certified (doesn't matter if a PSU is certified for one or the other as long as it has the correct connectors. If it passed certification for EITHER that means it's been real world tested with dual graphics cards in a worst case scenario).

Figure out if there are any variables that may affect the actual output capability of the PSU:
What temperature is the PSU rated at? Room (25° to 30°C) or actual operating temperature (40°C to 50°C)
If room temperature, what's the derating curve? As a PSU runs hotter, it's capability to put out power is diminished. If no de-rate can be found, assume that a PSU rated at room temperature may only be able to put out around 75% of it's rated capability once installed in a PC.

After that, narrow selection down with finer details that may be more important to others than it may be to you....
Does the unit have power factor correction?
Is the unit efficient?
Is the unit quiet?
Is the unit modular?
Am I paying extra for bling?
Do I want bling?


http://www.overclockers.com/forums/showthread.php?t=548...

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May 24, 2011 2:52:51 PM

malmental

Thanks for your reply
Believe it or not I know this video card will work on 300 W PS, and many people told me that, but what can you do to the AMD's requirement of 400W, just making you scary to spend money.

I dont think so I need to go more than this video card coz I am a light gamer, and love this card coz its slim and will fit in my mid hp case which has not more space inside?

XIGMATEK ps u mentioned is amazing, unfortunately it wont fit in my PC due depth problem which must be 5.5"

The Corsair CX430 has the dimensions I need but it does not look a good product!!

thanks for sharing
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a c 274 ) Power supply
May 24, 2011 3:30:19 PM

The AMD recommendation of 400W is so they dont get as many service calls from people with POS power supplies that cant handle it calling in and wondering why their system crashes when they go to play a game. Their requirements are done using an extremely powerful system to bias the requirements into a safer region for them.

The dual rail/single rail argument is a dead horse that people like beating, both have a single 12V source, both provide power that is just as clean. A good multirail PSU has the OCP points on the rails set so that there is no "trapped" power like XFX believes, if you add the rails together you will almost always come up with more power than the total source can supply, this means that you will never have some power that you cannot get to.

Just get a unit with enough 12V capacity to handle your system, the manufacturer already took care of balancing the connectors on the rails to avoid you running into issues.

The CX430V2 is a decent unit, better than the CX 430 that predated it, oklahoma wolf at jonnyguru just reviewed the new version
http://www.jonnyguru.com/modules.php?name=NDReviews&op=...
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May 24, 2011 3:55:59 PM

hunter315 said:
The AMD recommendation of 400W is so they dont get as many service calls from people with POS power supplies that cant handle it calling in and wondering why their system crashes when they go to play a game. Their requirements are done using an extremely powerful system to bias the requirements into a safer region for them.

The dual rail/single rail argument is a dead horse that people like beating, both have a single 12V source, both provide power that is just as clean. A good multirail PSU has the OCP points on the rails set so that there is no "trapped" power like XFX believes, if you add the rails together you will almost always come up with more power than the total source can supply, this means that you will never have some power that you cannot get to.

Just get a unit with enough 12V capacity to handle your system, the manufacturer already took care of balancing the connectors on the rails to avoid you running into issues.

The CX430V2 is a decent unit, better than the CX 430 that predated it, oklahoma wolf at jonnyguru just reviewed the new version
http://www.jonnyguru.com/modules.php?name=NDReviews&op=...




hunter315
Thanks for sharing, you mentioned reasonable points.
I was thinking to buy this PSU http://www.newegg.com/Product/Product.aspx?Item=N82E168...

What do you think?
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a b ) Power supply
May 24, 2011 4:03:50 PM

Quote:
^
I'm not reading all that.!
WTF.?!


For you to read??
No way.I am sure you studied this stuff before you even learned to walk.
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a c 274 ) Power supply
May 24, 2011 4:15:52 PM

That XFX unit is decent, the one jonnyguru got had its 12V set high so it got docked for that but its performance was good(kitguru got one with the 12V rail closer to 12V), it has good ripple suppression and can do its power at high temps which is good. It seems a bit expensive for that power class though since the shipping isnt free.


@ghnader hsmithot - Im with malmental on that, its too long to assume someone will read it quick while they are on the forums, a quick concise explanation is all most people want, they dont really need to know why it doesnt make much of a difference, they just want to know that it doesnt make a difference, if it takes more than 3 inches of text to explain it needs to be dumbed down more
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May 24, 2011 4:38:33 PM

Quote:
I was unaware of the physical dimensions, thanks for sharing..
if your certain that your not going any higher than the HD 5670 then you have even more options for PSU's.
please let me know if you still need more assistance in picking out the best one for you.
mal~


Thanks malmental

Im planing to buy this unit
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

What do u think?
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May 24, 2011 4:40:52 PM

hunter315 said:
That XFX unit is decent, the one jonnyguru got had its 12V set high so it got docked for that but its performance was good(kitguru got one with the 12V rail closer to 12V), it has good ripple suppression and can do its power at high temps which is good. It seems a bit expensive for that power class though since the shipping isnt free.


@ghnader hsmithot - Im with malmental on that, its too long to assume someone will read it quick while they are on the forums, a quick concise explanation is all most people want, they dont really need to know why it doesnt make much of a difference, they just want to know that it doesnt make a difference, if it takes more than 3 inches of text to explain it needs to be dumbed down more


thanks body
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May 24, 2011 4:43:47 PM

ghnader hsmithot

Thanks for sharing the long article which I already read before posting my question, it is one of the famous article if you Google it
I didn't like the explanation so much that is why I asked this question to check if people have an experienced using dual rail
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May 24, 2011 4:46:00 PM

Quote:
out of stock..


I know, that is why I place an order 30 min ago from tigerdirect, I hope they have it in their warehouse coz they are silly head online store not like newegg
but what do think about it, good choice??
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May 24, 2011 4:56:36 PM

Quote:
alternative:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

your choice, it looks good I just hope you can get it..


Thanks
I just went with the specification and requirement, and this brand consider Tier 2 unit which has good quality.
Once it shipped, will order the video card from newegg
thanks for your time and share
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June 3, 2011 12:32:44 AM

Best answer selected by drsaog.
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a b ) Power supply
June 12, 2011 3:27:26 PM

This topic has been closed by Mousemonkey
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