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View Full Version : I Have Always Thought One 12 volt rail was Better then 2 or 4


john19055
02-17-07, 06:53 PM
They are starting to make more and more high amp single 12v rail power supplies.I have always liked them better that way ,you don't have to worry about how the rails are hooked up to get maxumium power.In most confriguration it does' manner so much about if it has 4 12v rails since most componets don't draw enough amps to manner.But with these high current video cards that need two extra power connectors to work right,it manners IMO it makes better since to have just a single 12v rail, so that you don't have to worry about if you have the 12v rail connectors hook up right,since some of them have to be hooked up just right so that you have a even load.
My Thermaltake ToughPower 700watt power supply is starting to mess up again like it did before and I had to RMA it.I am starting to think they have some kind of flaw or I am just unlucky,This is the secound one to do this ,It starts off great my reading are 11.94v-4.95v-3.32v and it works perfect and after months of use my readings starts going down 11.74v-4.86v-3.23v and last week I started haveing random reboots ,games locking up and the BSOD.I was looking at my rails today after a BSOD and it was 11.59v-4.78v and 3.22v and I was looking at the reviews at newegg and I am not the only one haveing this problem.So since I had such good luck with my SilverStone Zues 560watt that is a single 12v rail 38amps,I think I will buy the new Olympia OP650 ,which is a single 12v rail and it puts out continuous 54amps at 50c, plus it also has the new PCIe 8 pin incase I ever get the money to uprade again.It does'nt have a bad price either $149 at newegg ,but after I bought it I have found it as low as $129.

Xion X2
02-18-07, 03:51 AM
It's not so much the unreliability of the 12v rail design as it is the unreliability of Thermaltakes. Thermaltake power-supplies are pure crap, IMO.

I don't see multi-rail PSU's ever fading out; I think they're just giving high-end users a choice between one or the other. Some people, even those with high-end systems, just don't know how to hook up a power supply.

john19055
02-18-07, 05:03 AM
My Opinion is shifting that way since this is the secound one to do this same problem,I been reading reviews at newegg and I see other are haveing the same problem as I am.Some of them are confusion when they have odd 12v rateings like 12v1 23amps 12v2 7amps 12v3 14amps 12v4 16amps,hopely they don't make no more like that.Even when they have 12v1 18a 12v2 18a 12v3 18a 12v4 18a,but they are only capable of a maxumium of 48amps total output across the 4 rails,And there are quite a few companies that don't even tell you what the total output is on the amps,So you have people thinking that there powersupply puts out 72amps since it says 18amps max on all 4 12v rails,when in fact it is really just 12amps per rail with the max of 18amps on one of the rails but not all four at once.So I could see someone that is new at computer building being confused about the power supply.

BrianG
02-18-07, 09:22 AM
Keep in mind that the rail sizes and ratings are based more on internal components and wire sizing than an actual rail. Unless you have four seperate AC inputs running four seperate AC-DC rectifiers, you still have a single common rail providing the DC potential at some point in the power supply. That is why you have a 48A max on four 18A rails; they all tie at some point to one transformer to get to 12V source which is then divided.

PC Power and Cooling has a good FAQ.
http://www.pcpower.com/technology/myths/

Xion X2
02-18-07, 12:59 PM
Again, the main factor is what brand you buy and the quality of it, not the rail design. The only multi-rail PSU I would advise against buying would be a dual-rail because of the processor hogging one of the 12v rails all to itself.

For the ST85ZF Silverstone Zeus 850W quad rail that has 18A across 4 12v rails, they were able to load it all the way to 66A on those four rails w/o a problem:

Load regulation was good, with the 12V rail only dropping 0.17V going from a mere 6A load to a whopping 66A load!

http://www.jonnyguru.com/review_details.php?id=15&page_num=2

They achieved the last little bit of oomph by lowering the voltage on the 3.3 and 5v rails w/ the oscilloscope, but few high-end components actually use these nowadays. The PSU reduces them when under full load and balances out for more power on the 12v line if you need it. You'll also see here that the same is required of a single-rail PSU to achieve maximum amps on the 12v:

Even with a 34A load on the 12V rail, even crossloaded with a low 3.3V and/or 5V load, the Silverstone ST56ZF[single-rail] exhibited fascinating stability.

http://www.jonnyguru.com/review_details.php?id=30

So again, the problem is not build design. The problem is that most people go with cheap PSU's they have no business using on high-end systems instead of sticking with brands like PCP&C, Silverstone, Zippy, Enermax, Seasonic, etc. Brands like Thermaltake, Antec, CoolerMaster, etc just will not cut it many times when it comes to maxing out the power rating. In the case I've shown above, and in many more, multi-rail PSU's perform just as well as single-rail.

john19055
02-18-07, 07:13 PM
They may have a single wound for the 12v rail and four line comeing off of it ,but they still cut off once one of those 12v lines reach a certain number of amps,but as long as it is hooked up right and one line is not drawing to much power,it should be fine.It's just finding a power supply that works good,some ones junk powersupply is some one elses dream power supply. I was told Thermaltake ToughPower Power supplies were good and when I looked at reviews ,they all said it was good ,so I took a chance and It was price higher then some of the other brands that were supposed to be good ,But I learned that Thermaltake sucks or at least the one I have does ,but I also have bought Enermax, Seasonic and Antec and they were juck IMO since they went out or would shut down real easy. ,But I had good luck with my SilverStone Zues 560 watts,Since I don't have $200 to buy a power supply,I think I will go back to SilverStone and try the new Olympia 650watts since it has a nice price and has all the performance power I need .

john19055
02-22-07, 01:13 AM
http://www.pcpower.com/technology/myths/index.php
this is what I was reading when I said I thought one 12v rail was better then 4.

Xion X2
02-22-07, 07:12 AM
john, everything they're saying in that link is true. But this isn't really anything that hasn't been known for a while.

Let me explain what I mean.

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.

Absolutely spot-on, and this is why I always tell people to stay away from dual-rail PSU's. In a multi-rail design, one 12v rail just about always is dedicated to the processor to ensure that the system will always be able to run at the most basic level. This is a serious handicap to dual-rails because that leaves you with one rail with half the advertised amperage total.

And the article is right. Whatever leftover wattage is on that rail generally cannot be used. But having the processor on its own 12v rail is not necessarily a bad thing. It ensures that the entire system won't do a hard shutdown if you exceed your amperage limit. It's actually a safeguard for your components and is the reason they're designed that way.

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.

Very true. But what they don't mention here is that companies nowadays usually tell you what 12v rail PCI-E connectors are pulling from, so that as long as you know the power requirements for your card(s), you just mix and match whatever you need.

Take mine for example. 4 12v rails @ 18A each. Two of my PCI-E connectors pull off 12v4, giving me 18A. If I bought a graphics card that exceeded this spec, well, I would simply plug only ONE of my PCI-E connectors that pulled off 12v4 and take a PCI-E connector that pulled off a different 12v rail to supply power to it. That would insure that it could pull over 18A if it needed, so long as the additional connector wasn't pulling off a rail that was already overpowered. It would receive the full 18A off 12v4 plus whatever was left over on the additional rail I am pulling from.

It sounds confusing, but it's really not that complicated. All of this can be figured out easily with a notepad, pen, and a little math.

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.

I think they're a little presumptuous here with this statement. I don't think multi-rail PSU's are necessarily on their way out; I just think they're becoming less popular because they're not foolproof like single-rails are.

To sum it up, it goes like this.

Multi-rail PSU's are not a bad thing, so long as you can do a little math and figure out how much power is required by your components to run. The only disadvantage--and I don't really view it as a disadvantage as I do so much as a safeguard--is that whatever leftover wattage you have on the 12v rail the processor sits on cannot be utilized.

But everything else can be. You just have to know how to mix and match and pull from the proper place.

TonyM16
02-22-07, 09:10 AM
For multiple graphic cards you won't be able to do that though. So if the rumours of the R600 are true, it seems we will all have to buy a single rail psu to use R600 crossfire to it's full potential. For eg.my Tagan 1100 watt has 40amps for the gpu's, so if I only had one gpu then I could get it connected so that all 40 amps are available to that gpu, instead of just one 20 amp rail (we are talking about gpu's with two power connectors here).

As soon as we go dual though , we have to make sure that both gpu's get enough power, so thats 20 amps each. that may not be enough for R600 overclocked in DX10 , where the power load could exceed 20amps (DX10) , or what ever comes after. As you have to remeber no psu is 100% effecient and they do lie and every psu is different, so in reality each of my rails could only be 15amps, which is definetley gonna struggle with R600 crossfire in DX10.

With an OP1000 or PC+P-sr 1kw we don't have to worry as all gpu's have access to as much power as it needs. If everything is stressed equally at the same time, then the single rail design looses it's advantage, as all the components devour the single rail like hungry hyenas, but I feel the 80amps those psu's have along with the effeceincy if single rail, they should be able to handle it, even if you play a physics/ai laden(overclocked Quad core cpu), graphically intense (both gpu's overclocked slightly) and large free roam (memory stress) DX 10 game, but we can't be sure until the time comes , I think Alana wake would be a good game to test psu for this kind of system.

My 2cents. :p

Xion X2
02-22-07, 02:47 PM
For multiple graphic cards you won't be able to do that though.

I'm not following you.

On most multi-rails, there is plenty of power leftover on other rails to use in addition to what they advertise as "available for graphics."

Here is the rail distribution on my Silverstone:

12V1: CPU-1. Typically powered through the 4-pin connector of a power supply. On the ST75ZF, power for CPU-1 is provided by the first two 12V wires on the 8-pin EPS+12V connector.
12V2: CPU-2. Typically, dual CPU motherboards that would require each CPU have it's own 12V rail would get it's power from the second two 12V wires on the 8-pin connector. Silverstone also puts the SATA connectors on this rail as well as PCI-e connector #3.
12V3: This rail powers many things. The EPS AUX 6-pin is on this rail, as is all of the Molex connectors (used for hard drives, floppy and optical drives, fans, lights, etc.) and the main ATX connectors (powers fan headers and slot powered cards that require 12V.) PCI-e connector #4 is also on this rail.
12V4: This rail is dedicated for use with PCI-e connector 1 & 2.


http://www.jonnyguru.com/review_details.php?id=15

Mine has an available pool of 54A to pull from minus whatever is taken up by SATA and molexes, which isn't much. All you need to do is arrange the connectors properly to pull from that total. Like you wouldn't use both 12v4 PCI-E's on one card, for example, because it would be bottlenecking that one card to 18A. You would share those two and split the other two among the cards. That's the way to get the most amperage to each.

Again, there's no question that single-rails are a more foolproof design, but there's no reason at all that a good multi-rail PSU with good amperage placement can't be just as efficient.

TonyM16
02-23-07, 07:46 AM
I'm not following you.

On most multi-rails, there is plenty of power leftover on other rails to use in addition to what they advertise as "available for graphics."

Here is the rail distribution on my Silverstone:



http://www.jonnyguru.com/review_details.php?id=15

Mine has an available pool of 54A to pull from minus whatever is taken up by SATA and molexes, which isn't much. All you need to do is arrange the connectors properly to pull from that total. Like you wouldn't use both 12v4 PCI-E's on one card, for example, because it would be bottlenecking that one card to 18A. You would share those two and split the other two among the cards. That's the way to get the most amperage to each.

Again, there's no question that single-rails are a more foolproof design, but there's no reason at all that a good multi-rail PSU with good amperage placement can't be just as efficient.


Yeah your Silverstone Zeus allows you to do that, but my Tagan can't. You have your pciec cables spilt across three rails, mine has it split across two. You see what I mean now. I think the average sli certified psu has it's pciex cables spread across just two rails. I know the much vaunted Galaxy 1000watt does for sure. Your Zeus seems to be the the exception here .

Also most psu's have to be connected up in a certain way or else excessive ripple will eventually destroy the cards. I think this is another place where your Zeus wins out. So as long as 850watt is enough I feel no reason why you would ever need a new psu just for single rail, but for others who want to buy those new gpus' with their high power requirments in DX10, they will have to take a look at their psu if it's multiple rail.

Xion X2
02-23-07, 12:39 PM
Yeah your Silverstone Zeus allows you to do that, but my Tagan can't. You have your pciec cables spilt across three rails, mine has it split across two.

It doesn't really matter. You could pull from whatever rail you like on that Tagan; you would just need to use two molexes to one of the y-adapters that came with your graphics card. Then it would pull off a different 12v rail from what your current PCI-E connectors are sitting on.

The same for the Galaxy. You're not limited to the 2 12v rails that it gives you for graphics. That's just what they advertise because they are "PCI-E ready" with the PCI-E connectors. But you can make your own with an adapter or two that comes in the box of your graphics card.

For example, if your PCI-E connectors are sitting on 12v3 & 12v4, and your molexes are sitting on 12v2, then you could take a y-adapter from your 12v2 molexes and run to your card and pull power off 12v2 in addition to whatever's available on 12v3 & 12v4.

Also most psu's have to be connected up in a certain way or else excessive ripple will eventually destroy the cards.

Ripple has nothing to do with how things are "connected;" it has to do with how much of a load the PSU is under in total.

TiKiMaN1
02-23-07, 03:10 PM
http://www.pcpower.com/technology/myths/

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.

Xion X2
02-23-07, 03:35 PM
john already posted that link above, Tiki, and I responded back to it.

That link really does nothing but show that single-rails are a more foolproof option for computer users than multi-rails are. It doesn't show that they're technologically superior.

john19055
02-25-07, 01:21 AM
I think you have a great power supply ,IMO SilverStone makes some of the best power supplies around and I think there Zeus products are great and it does'nt manner if they have one or four 12v rails,Quality is the most important thing.I have just had better luck with one 12v rail power supplies but occourse it was my OCZ PowerStream 470 watt. and my SilverStone Zeus 560watt,If I had bought another SilverStone instead of the junk 700watt Thermaltake ToughPower, I more then likely would'nt have had any problems

Xion X2
02-25-07, 02:43 AM
Thanks. Yeah, the Silverstones are great. But that's not why I'm debating the issue. I used to think single-rail PSU's were superior, but after doing some research into the way multi-rails are designed I no longer think that. That's why I went w/ my quad-rail this time around when I, like you, owned the Silverstone Zeus 560W single-rail with my AMD system last gen.

But there's no doubt that single-rail PSU's are the easier way to go. I just don't believe that they're technologically superior in any way.

john19055
03-16-07, 01:11 PM
I fineally seen a review and it looks like SilverStone has another winning power supply,I know it is rock solid on my system and there is no fluxuation like I had with that junk thermaltake toughpower i had.
http://www.neoseeker.com/resourcelink.html?rid=135920

J-Mag
03-16-07, 01:58 PM
That link really does nothing but show that single-rails are a more foolproof option for computer users than multi-rails are. It doesn't show that they're technologically superior.

Are there any ways that a quad rail PSU is technologically superior if total amperage distribution on the various voltages is held constant? I guess you have less chance of death if you discharge one of the rails capacitors, but thats the only thing I can think of.

kevJ420
03-16-07, 02:47 PM
Why doesn't everyone either get a pc power cooling silencer 750 quad copper or pc p&c's 1kw-sr?

They're by far the best psu's money can buy.

If you buy one you won't regret it.

Only thing that kind of sucks about them is not having 12 molex connectors and not having 8 pci-e connectors.

But that's it. Nothing else about them is not perfect.

Q
03-16-07, 02:54 PM
Why doesn't everyone either get a pc power cooling silencer 750 quad copper or pc p&c's 1kw-sr?

They're by far the best psu's money can buy.

If you buy one you won't regret it.

Only thing that kind of sucks about them is not having 12 molex connectors and not having 8 pci-e connectors.

But that's it. Nothing else about them is not perfect.

They are really good, but not the best and definitely not the best PSU's that money can buy nor the best value for your money.

http://www.jonnyguru.com/forums/forumdisplay.php?f=3

Quite a few of the people here really know what they're talking about.

einstein_314
03-16-07, 04:36 PM
Why doesn't everyone either get a pc power cooling silencer 750 quad copper or pc p&c's 1kw-sr?

They're by far the best psu's money can buy.

If you buy one you won't regret it.

Only thing that kind of sucks about them is not having 12 molex connectors and not having 8 pci-e connectors.

But that's it. Nothing else about them is not perfect.
Well for starters....they're ridiculously expensive? I just can't justify spending $570 (Canadian) on a powersupply. I don't care how good it is. I can get the Silverstone 1KW supply for over $200 cheaper. That's a big price difference for not much of a performance/quality difference.

And what on earth would you need 8 PCIe connectors for?!? Quad SLI with 8800GTX's?!?

kevJ420
03-16-07, 04:47 PM
Well for starters....they're ridiculously expensive? I just can't justify spending $570 (Canadian) on a powersupply. I don't care how good it is. I can get the Silverstone 1KW supply for over $200 cheaper. That's a big price difference for not much of a performance/quality difference.

And what on earth would you need 8 PCIe connectors for?!? Quad SLI with 8800GTX's?!?
well, the future is going to be demanding.

I'm hoping for the release of a pci-E PPU everyday. Sucks to not be able to get max enjoyment out of ALL game.

but you're right, i'd expect it to only use 1 pci-e connector, and of course molex connectors can be used as well.

Also, a pci-e ppu may even get sufficient wattage from the pci-e slot.

einstein_314
03-16-07, 07:34 PM
Not 8 connectors... it's the 8-Pin connector which could be important for upcoming cards.

I imported a PC P&C in 2005, it's a great PSU but it's very loud. I'm gonna buy a Silverstone 1kW soon because of that.
:rofl My bad :p

I didn't know there was a 1200W silverstone....I haven't seen any reviews of it yet. Cool! But I think that's more powersupply than I'll ever need....I'm leaning towards the 850W silverstone for my next upgrade...