# Are Multiple 12-volt Rails Better Than A Single 12-volt Rail?



## freaksavior (Feb 14, 2007)

I've been asking myself that question ever since i decided it was time to get a new psu. so


"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"

Read all the psu facts @ http://www.pcpower.com/technology/myths/


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## Chewy (Feb 14, 2007)

Good post, man. The 1950xtx asks for 30amps on the 12v rail for a fully loaded system... its hard to find that on a multiple rail 12v psu... but I guess thats the max it would ever use.


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## niko084 (Feb 14, 2007)

Chewy said:


> Good post, man. The 1950xtx asks for 30amps on the 12v rail for a fully loaded system... its hard to find that on a multiple rail 12v psu... but I guess thats the max it would ever use.



They ask for 30amps combined rail. Thats the key there that most people miss. The 1950xtx will NOT draw 30amps. The problem with multiple rail systems is very true though. Although its not an issue if you have dedicated high output pci-e rails.

For instance a 20 amp rail that only powers 2 pci-e plugs. That is more than enough power for 2 even 8800s or x1950s.

The problem with most psu's is that they share the same rail for the pci-e with other things like hard drives or your processor. The other issue comes down to 3 rails at 20 amps, although max output is only 42amps, because what they draw off is bottle necked.

But yes multi rail psu's that are not high end, don't waste your time if you have a hot machine. There is a plus to multi rail setups, and thats voltage stability, but then again only in a good psu.


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## mullered07 (Feb 14, 2007)

so could i x-fire  2 x1950pro' on my ocz powerstream 450w with 30a on my single  12v rail ? 

without saying "this amount of amps/volts" is " reccomended" but in real life terms could i do it ?


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## niko084 (Feb 14, 2007)

mullered07 said:


> so could i x-fire  2 x1950pro' on my ocz powerstream 450w with 30a on my single  12v rail ?
> 
> without saying "this amount of amps/volts" is " reccomended" but in real life terms could i do it ?



30 amps on your 12volt leaves you with 360watts for 12 volt... 

That being said its really close... You could probably I hear that OCZ makes good psu's..
But I would be looking for something with a little more punch.


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## mullered07 (Feb 14, 2007)

well my 2nd pci-e slot is only agei (pci-e x4 and b4 anyone says, it DOES support x-fire on the x1950pro) would that make a diff on the draw from the psu being as its only 4x as opposed to 16x, i do plan on doing x-fire ( and yes i know guys there will be perf loss on 4x but there will still be perf gain vs 1 single x1950pro and it will do me fine until my next build/ mobo/dx10 grfx upgrade as i plan on keeping my ram and getting another gig and also my e4300 as i can get 3ghz with my next board upgrade)


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## niko084 (Feb 14, 2007)

Ya it would keep that card a little slow, but I don't know if that would effect the power requirement... Honestly I don't think I would try it... It's not worth the chance at blowing stuff up.


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## freaksavior (Feb 14, 2007)

thanks, there are so many psu question i thought it could be usefull!


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## mullered07 (Feb 14, 2007)

goddam it niko, dont tell me i need another x1950pro AND a new psu lol  i figured so much anyway but i do like to see what i can get away with  who doesnt?

touchwood ive never blown one component before out of 6-7 builds (not including builds for other people)  (although have scratched some mem modules on my old ti4200 with a screwdriver and fooked it, you know the thing im talking bout, multicoloured lines all over the screen  )


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## niko084 (Feb 14, 2007)

Lol... Ya I haven't personally blown anything up on "accident" either. But I'm pretty careful about it.


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## newtekie1 (Feb 15, 2007)

Everyone always points to that article, but they never seem to realize that it is posted on the website of a company that builds power supplies.

The fact of the matter is that single rails are easier and cheaper for a power supply maker to produce, which explains why they want to say it is the better design.

However, the fact of the matter is that the groups passing the standards for power supplies say that multiple rails are better and they usually say something like the limit on a rail should be around 25-30A.  However, they don't ever make that a requirement, just a recommendation.

I disagree with the majority of what that site says, IMO it creates more bad myths than it actually addresses.


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## Chewy (Feb 15, 2007)

My psu makes me wonder... it originally had 4 12v rails, but they decided to combine the 4 rails into one (fuse the 4 rails together) and combined they make 36 amps.. I wouldent want to have the 36 amps going through just one pci-e conector, from what I`ve read the wire could burn-out.. but is my psu an exception to the 25-30amp rule? since it has 4 rails fused together to make 1?


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## niko084 (Feb 15, 2007)

Chewy said:


> My psu makes me wonder... it originally had 4 12v rails, but they decided to combine the 4 rails into one (fuse the 4 rails together) and combined they make 36 amps.. I wouldent want to have the 36 amps going through just one pci-e conector, from what I`ve read the wire could burn-out.. but is my psu an exception to the 25-30amp rule? since it has 4 rails fused together to make 1?



I don't think they are realy combined. If they are giving you a combined total number in the specs its because you can have 3 rails at 20amps per and have a combined total of 50amps. Which obviously isn't 60... The key being if you are pulling 10 on one you can pull up to 20 on the other two. Because they all pull from the same source. Thats where most cheaper brands fall off they say something like 600 watts, then they fail to tell you only 340 of them are 12 volt, and at 70c you get 200 watts.

This is where the real spec sheets come into handy and being able to fully understand them. I couldn't before today, then after about ohh 50 pages of misc reading *and multiple headaches* I got it pretty well figured out.


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## niko084 (Feb 15, 2007)

newtekie1 said:


> Everyone always points to that article, but they never seem to realize that it is posted on the website of a company that builds power supplies.
> 
> The fact of the matter is that single rails are easier and cheaper for a power supply maker to produce, which explains why they want to say it is the better design.
> 
> ...



A good point here.... Multiple rails are used in about every high end power supply. They offer much better stability and they are more efficient. *When built properly*

Don't trust every piece of mumbo jumbo you read.

I came by another write up about how bad modular cabling is... Uh huh, they compared a mid-level Corsair to about 6 other mid-level psu's and found that the Corsair did indeed have .1 lower volts on no load, but on full load had a higher voltage still. They compared 6 of them and they were all decent brands in the same price line. Third party people.


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## niko084 (Feb 15, 2007)

Chewy said:


> My psu makes me wonder... it originally had 4 12v rails, but they decided to combine the 4 rails into one (fuse the 4 rails together) and combined they make 36 amps.. I wouldent want to have the 36 amps going through just one pci-e conector, from what I`ve read the wire could burn-out.. but is my psu an exception to the 25-30amp rule? since it has 4 rails fused together to make 1?



Your power supply has 4- 18amp rails. But a combined max of 38 amps. That gives you a raw 456 watts of 12volt, which isn't too bad for most x-fire/sli setups. The deal is you can only use a total of 38 amps across all rails, each one independently capable of 18amps.


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## Chewy (Feb 15, 2007)

I`m not sure  but originally the m12 series was seposed to have 4 rails (mine was 18 amps per rail), but in some review it said after getting a go ahead from a QC or safety place seasonic decided it was best to combine the rails to one and soddered the 4 rails together in the psu to make one. I seen a picture where it showed the 4 combined inside.. this is prob not the 1st psu that has had this done... I figure since the 4 rails were combined they can handle 36 amps.. but one pci-e conector would burn if it tried to soley deliver 36 amps.



niko084 said:


> Your power supply has 4- 18amp rails. But a combined max of 38 amps. That gives you a raw 456 watts of 12volt, which isn't too bad for most x-fire/sli setups. The deal is you can only use a total of 38 amps across all rails, each one independently capable of 18amps.



Its advertised as a quad rail psu but it really just has one  since they soddered them together.
 Meh no biggy I`ve been tired lately so I have theses stupid questions lol


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## niko084 (Feb 15, 2007)

Chewy said:


> I`m not sure  but originally the m12 series was seposed to have 4 rails (mine was 18 amps per rail), but in some review it said after getting a go ahead from a QC or safety place seasonic decided it was best to combine the rails to one and soddered the 4 rails together in the psu to make one. I seen a picture where it showed the 4 combined inside.. this is prob not the 1st psu that has had this done... I figure since the 4 rails were combined they can handle 36 amps.. but one pci-e conector would burn if it tried to soley deliver 36 amps.



Ya but they wont take the *38* amps. I looked up your psu to get the info.
I guess its slightly possible they decided to join them, but then they are guilty of false advertisement.. I would be taking it apart to find out personally. Either way it goes you are pretty good and solid for most setups.


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## freaksavior (Feb 15, 2007)

ok....ok....you peeps are confusing me!  is it better to have mutli rails or not? this one has 1 12v rail @ 38 A 38Ampr psu on 1 rail comapring psu, (comparing first 2)


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## Namslas90 (Feb 15, 2007)

It's better to have a multi Rail PSU;  Providing the PCI-E Rails support the minimum per rail that each card needs (actualy needs, not "recomended").  

@ NIKO084; Hey looks like you've been doing some research,  good deal.  You've about got this PSU thing figured out!!!  
So, Niko, what PSU are you going to get?


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## niko084 (Feb 15, 2007)

Namslas90 said:


> It's better to have a multi Rail PSU;  Providing the PCI-E Rails support the minimum per rail that each card needs (actualy needs, not "recomended").
> 
> @ NIKO084; Hey looks like you've been doing some research,  good deal.  You've about got this PSU thing figured out!!!
> So, Niko, what PSU are you going to get?



Silverstone ST60F 48amps on 12 Volt 

It's works right into what I planned on spending-
LIAN LI PC-61 USB
ASUS P5B
ATI x1950pro 256mb
Silverstone ST60F
Intel e6300
Corsair XMS2 DDR675 2 gigs 1024x2

I think after this system for a bit, if I decide I want something more again, I'll end up getting another case I was looking at also a Lian Li and might just go dual power supplies if I feel the need.

But this psu should more than power this system. Infact by all means it should power 2 x1950s, x1950xtx's would be pushin it pretty good but, most I think I'll need anytime soon is 2 1950pros, if I even use those... I really play a lot of older games, and quite a bit of cs:source.. Pretty rare I find a new game I like, and non of them really push graphics too much, besides GR:AW. Which I hear runs pretty decent on a single 1950 anyways.

I can't say for most but the 7900 series cards at max draw 5 amps from the pci-e power plug and 5 amps from the board. I was lucky enough to find that info. So 10 amps total actual draw from a video card. Which means a few good rails and 50amps or so of good output at 12volts should hold a set in sli without too much trouble. That puts you around the $200-$250 range for a decent psu.

But like I found its all about the power supply having good total power, and the pci-e rails being dedicated to the pci-e plugs. And most cheaper ones mix them with other power like IDE... Which is why 2 rail psu's are a horrible idea 1 or 3+.


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## niko084 (Feb 15, 2007)

Heh forgot to mention there, the Neo HE 500 is actually a good psu for a single 1900 series including the x1950xt, as long as it was the revsion after A3.. You very well could have had a revision before that which I think shared the pci-e rail with the processor or something else... Which with a hot amd chip and over clocked, would have been pretty bad.. Very well could have been your issue.


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## Namslas90 (Feb 15, 2007)

niko084 said:


> Heh forgot to mention there, the Neo HE 500 is actually a good psu for a single 1900 series including the x1950xt, as long as it was the revsion after A3.. You very well could have had a revision before that which I think shared the pci-e rail with the processor or something else... Which with a hot amd chip and over clocked, would have been pretty bad.. Very well could have been your issue.



No mine was SLI certified with 2 PCI-E rails each w 18 amps per rail,(3 total 12v rails), still wouldn't power my card.  I got the same symptoms most others describe when there isn't enough power.


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## tkpenalty (Feb 15, 2007)

lol SLI Certified does not mean Crossfire nor ATI Certified.


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## niko084 (Feb 15, 2007)

tkpenalty said:


> lol SLI Certified does not mean Crossfire nor ATI Certified.



No what I stated was power supplies that are SLI and Crossfire Certified have dedicated rails to the pci-e auxiliary power plugs. 

I should have said to better clarify though SLI and/or Crossifre.

Basically if you buy a psu that is SLI and/or Crossfire certified it will have one of its 12 volt rails dedicated to the pci-e auxiliary power plugs. Thats the most important part to using a multiple rail psu with hot video cards.

I personally very strongly suggest 1 rail or 3+, as dual rails do not provide more than 40 amps, and must share the rails to a great extent, so they can't dedicate 1 rail to pci-e power.

Anyways I'm going to go to bed far too much reading has been done today and its almost 4am here. I have read close to 900 pages on power supplies and the current draws of video cards, processors, hard drives, ram, fans, optical drives, name it.. My mind is roasted.


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## Wile E (Feb 15, 2007)

tkpenalty said:


> lol SLI Certified does not mean Crossfire nor ATI Certified.


And SLI, Crossfire, or ATI certified doesn't mean squat anyway.


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## largon (Feb 15, 2007)

There are no ground braking advatages multiple rails can offer: 





			
				jonnyguru.com said:
			
		

> the advantages of split 12V rails, separation of "noise" between rails and the protection provided by the separation so a potential short on one rail doesn't harm a device on another


Seasonic M12 series PSUs are advertised as quad rail but in reality they pack one 12V rail.


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## niko084 (Feb 15, 2007)

Wile E said:


> And SLI, Crossfire, or ATI certified doesn't mean squat anyway.



Means quite a bit if you actually check and read exactly what each individual one is certified for... It was a really dumb rule and idea they came up with. And in fact almost completely useless to 90% of the public. Heck I know a lot and it took me about 6-7 hours today to figure it all out. And now finally made my decision on a psu that will more than handle my system with a x1950pro, and I could add another one, but I doubt I will.


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## niko084 (Feb 15, 2007)

largon said:


> There are no ground braking advatages multiple rails can offer: Seasonic M12 series PSUs are advertised as quad rail but in reality they pack one 12V rail.



Beh... I would almost call that quality control...

But I guess with it being a pretty good psu to start with they do run pretty stable voltages. And seasonic is pretty well known for doing a good job. Although it does have 4 independent rails.

The question now is, was that a quality control miss, or is that something they have effectively done on all of them?

I just ordered a psu that was also said to have merged rails, because of the modular cable support, I'll pull it apart when it comes and check to see.


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## Wile E (Feb 15, 2007)

niko084 said:


> Means quite a bit if you actually check and read exactly what each individual one is certified for... It was a really dumb rule and idea they came up with. And in fact almost completely useless to 90% of the public. Heck I know a lot and it took me about 6-7 hours today to figure it all out. And now finally made my decision on a psu that will more than handle my system with a x1950pro, and I could add another one, but I doubt I will.


All I meant was that the only thing that matters is the performance and quality of the psu. Just because it's certified, doesn't mean that it's better in any way.


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## largon (Feb 15, 2007)

*niko084*,
By removing the over current protection Seasonic evaded a flaw in Intel ATX12V spec: 


> Seasonic (...) stated that the "deception" is really quite innocent. Apparently the initial design was for quad rails, and if rails did need to be split up into three or four rails, it would be easy to implement without completely redesigning the platform. Multiple rails can be split up with a separate OCP circuit board, typically screwed to the top of a heatsink.
> 
> What Seasonic tells me is that there was an issue with high end video cards overloading a single 12V rail. So with Intel's blessing, Seasonic removed the OCP. Technically, Intel has removed the 240VA rail limit from the ATX12V specfication
> 
> _- http://jonnyguru.com/review_details.php?id=13&page_num=3_


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## freaksavior (Feb 15, 2007)

Ok, i think i'm getting it. So more than 1 12v rail is better if your going dual gpu cards....right?


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## largon (Feb 15, 2007)

It's all about the definition of "better". 

Multi rail offers no advantages for multi GPUs compared to a single rail. 
Single rail is better if you'r looking for pure amperage. Multi rail allows less distortions in the current and is, in theory, safer in case of a PSU failure.


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## niko084 (Feb 15, 2007)

Wile E said:


> All I meant was that the only thing that matters is the performance and quality of the psu. Just because it's certified, doesn't mean that it's better in any way.



Ya I know I just wanted to clarify on it a bit.


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## niko084 (Feb 15, 2007)

largon said:


> It's all about the definition of "better".
> 
> Multi rail offers no advantages for multi GPUs compared to a single rail.
> Single rail is better if you'r looking for pure amperage. Multi rail allows less distortions in the current and is, in theory, safer in case of a PSU failure.



Largon has the idea here.

The key is to really study your power supply before you buy it, you need to know what the rails are dedicated to *if its multi rail*, and you need to know what the "combined" output of the rails are. Because you can have 3 rails at 20 amps per but only have a combined of 40amps.. Well then 3 rails at 20amps isn't actually what you are going to get. So it would be quite the mess for the non technical savey who wouldn't understand the labels on power supplies very well, or how to convert watts to amps, ext... 

It's a royally big mess, and I personally really hope that companies will start to standardize this a bit. But at the same time I hope they wont because then people who don't know will have to pay me or Alienware to build them a sli/crossfire machine.


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## niko084 (Feb 15, 2007)

freaksavior said:


> Ok, i think i'm getting it. So more than 1 12v rail is better if your going dual gpu cards....right?



Say-
Power supply A-
50 amps on 12volt single rail

Power supply B-
50 amps on 4x 12volt rails Rated at 19 amps per rail

There above are pretty common numbers to see in higher/midrange level psu's $120-$200

Now both power supplies put out a 50amps. On power supply A- the amps are all shared by every component in the system. This isn't really bad because if something wants more power it will take it. On power supply B- you can pull up to 19amps on any individual rail but cannot exceed a total pull of 50 amps. So if your mainboard/ram/pci-e or agp *slot power/expansion cards pulls 15amps, and say your harddrives, optical drives, fans, all that other stuff draws another 10amps, that takes 25amps of power so far, now you have 25 to still work with, but the rail will only use up to 19amps.

So now you kinda have an idea of how that works, the only problem to multi rails is you need to know how they are setup. Dual rails are a bad idea because they don't really split enough up for the full power. You generally have 1 rail for all your drives/mobo and everything else, and then 1 rail for your video card. Well sure the one for your video might be fine, but your video card also depends on voltage from the pci-e slot itself.

*Info from Nvidia* The 8800 series cards will draw at maximum 5.5 amps from the pci-e slot and 5.5 amps from the pci-e plug.*
Now thats 11 amps a piece, but its drawn from 2 different places.

For basic all around needs and the average person either psu will be fine as long as it meets their requirements. Weather to buy a multi rail or single rail? That would purely be by each person weather or not they want to dig for one that will support what they need *they are more complicated to get the full specs on*. So that being said one really isn't "better" than the other, the only positive to a mutli rail is better stability *by design*. This doesn't mean a cheap multi rail will be more stable then a good single rail. So really unless you have a personal reason you just want a multi rail psu, it really doesn't matter too much. Just make sure it will support what you want from it now and possibly in the future.

Remember you can't ever have a power supply thats "Too big". If you put a 1000 watt power supply on your computer that would run fine on a 300 watt, all the means if your power supply has to work all that much less, in fact in most cases it will extend the life of your power supply because you never really push it.

So find a happy medium in what you want, can afford, and what you need, make sure to leave some extra power left over so you don't have to worry about over running your power supply, and so it runs more efficiently. In turn it will last longer, run quieter and cooler.


How to check your power supplies combined output-

Take the whole power rating *600 watts 700 watts*...
Minus the amount of watts max for 3volt and 5volt lines.
This leaves you with the 12volt watts. Take the watts divide by 12*the voltage*
and you will get your amps.

This is an easy way to get your combined amps for your 12volt for manufacturers that don't advertise them.


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## curt (Feb 15, 2007)

*ill keep it short*

all 2 or more rail units iv tryed suck sorry to say 

i have an enermax true460wat single line psu running my comp 33amp out on the 12v 

an i have a 550wat antec dule 12v line at 19amp each psu that can evin run my comp bitches about power an u can hear the psu actuly struggling to run my comp
 your better off doing what if doen i say 

i have my enermax 460wat powering my mobo an video card 

then i have a old dell 250 wat powering my fans hd.s an cdrom  
2 psu.s not 2 12v rails lol   [note psu.s ar not cros wired they run independent of echuther] when windows shuts down hd.s stay on lol but the mobo turn off then i turn off the hd.s power suply

an i allso have a old hp 265wat psu that i modded it allso has lower power spikes then the antec 550 an this lil hp 265 can run my comp its hard on it but it can do it


basik test was doen hp 265wat

12.80v   after just tapping my 12v 2.5amp fan  i got 12.2v 

antec 550wat 12.35v ------------------------ i got 11.35v on rail 1 
---------------------------------------------------same on rail 2
 both rail.s wired together 12.40-------------------  11.65v

gimmi a break its a 2.5 amp fan lmao



keep in tuch with the forum to see my mobo running off battryes soon to come i gota make a 12v bat a 45.v an a 3.6v bat but with high amps 
i allready have the 12v bat 780amp nospill coil 4x4 battrey that thing dsent go below 12v evin startin my olf 1987 f150 v8 hehe lost of power for a test mobo power spikes may be a ting of the past kinda useing the battryes as capasiters leaving a small charge going to them so u dont end up chargen your mobo ever 3 hours lmao

plus i wana be able to play with the difernt rails on ther own like the 3.3v ant the 5v see how much oc.ing helps if ther at say 6v an 4v


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## largon (Feb 15, 2007)

Someone please translate the above post to english.


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## MGrant1957 (Feb 16, 2007)

I don't know where Freaksavior got the info, but he is dead wrong. I have a PS that has 4 12v rails 2 are rated to 18A max and the other 2 are rated to 30A max with a 62A Combined rating for all 4 together. 3.3v good for 30A, and 5v good to 30A as well. BTW it is a Thermaltake W0131RU 850W modular supply. but it does have an efficiency up to 87%. so unless I really push things i think it should run everything I can throw at it.


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## Lazzer408 (Feb 16, 2007)

I certify this forum to be compatable with my computer. See how much better it seems now?  12v is 12v. It all falls on the psu specs. Read and understand them. Some psu companies pull that crap where the 12v rail is 250 watts if the total on the 3.3 doesn't exceed 200 watts or the 5v is 220 watts as long as the combined total doesn't exceed 410 watts and the moon is inline with mars and your girlfriend isn't on the rag.


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## Testing (Feb 16, 2007)

I wonder if half the people who spout their unfounded knowledge of mutli-rail power supplies have actually got a meter out and measured their components under loads.

Niko, Mgrant? 

I don't know where YOU got the info, but I think you should try a few hardwire-on-hand tests. There is no such thing as true combined multi-rail amps, it's still coming from the same power source; there are a few companies that have a 'combining' architecture that supposedly meshes the rail amperage together when required, but the efficiency is awfully low, it's unstable, and it doesn't give you twice the amperage(or three times/four times etc), rather it's 20A+20A = 30 or 31A; you lose power efficiency in the process.

If I'm not mistaken your PSU model and it's similar product line are four rails rated at 12v each, not 12/12/18/18. The "62" amps they speak of is maximum overload, not maximum safe excluding overhead. And the funny part is, in your decision to make up the number for the third and fourth rail of your model you must have miscalculated because you left out to 2amps; unless of course you were being conservative for overhead purposes 


The rule of thumb is, (and especially for gaming) mutli-rail PSU is a hoax. 

Intel was forced to put time into safety technology and then later pulled their findings, admitting that multi-rail power supply was essentially pointless.

Unfortunatley by that time, two years had passed and the market had been bloated with this 'new' technology for PSUs. Even more unfortunate, it became so believed by the masses and computer geeks alike, that companies are STILL getting away with pulling the wool over consumers eyes, by marketing super hyper flashy high wattage ATX 2.2 units.

It's no coincidence that it's difficult to find single rail units supplying over 20 amps to a single rail. Fortunatley, some higher end, or oddball companies are retreating from the saturated multi rail market and are offering up the power that we actually need.

Niko I think you reading 900 pages is what's gotten you confused, like countless other unknowing people. If you'd just found one page, the first page, with the right information you're brain wouldn't hurt as much 


Whoever said multiple GPU with a multi rail PSU made me almost choke. I wouldn't even dare try that. Personally I don't see how other people can even sleep at night, risking running $1,000 worth of GPU cards on such horrible power supplies.

You get a big damn case and mount two single rail high amp units.


The thing that ices the cake, is that because of this market, the companies that sell these products don't give you the most vital information : the amps on the 12v rail.


Freak, if you are only using one late modern GPU, then a 550-600 watt 34+ single rail PSU will do you and your other components fine. Fortunatley you can get one for about $100-120 USD, from a Tier 1 quality manufacturer such as Silverstone.  

Or you can pay $250 + for some absurd 800 watt that will never fully power your card.


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## KennyT772 (Feb 16, 2007)

Testing over half of "multi-rail" power supplies use one set of power generation circuits, but runs them threw regulators capping them to a certain amperage per "line". The thermal take mentioned above is one of the few true dual rail psu's. Even that unit splits the current over two "lines" to adhere to the atx12v maximum spec (18a-20a for 12v). The spec was written to prevent overdraw and heatshorts. 

As far as highend video cards they only draw roughly 11a for x1950xtx, 16a for 8800gtx, 20a for 2800xtx. There is no penalty for going close to the limit on a multi-rail psu, if you over draw you will simply activate the short protection and shut off the system.


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## Namslas90 (Feb 16, 2007)

Lazzer408 said:


> I certify this forum to be compatable with my computer. See how much better it seems now?  12v is 12v. It all falls on the psu specs. Read and understand them. Some psu companies pull that crap where the 12v rail is 250 watts if the total on the 3.3 doesn't exceed 200 watts or the 5v is 220 watts as long as the combined total doesn't exceed 410 watts and the moon is inline with mars and your girlfriend isn't on the rag.



I hearby dub thee; Lazzer408, PSU KING!!


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## GLD (Feb 16, 2007)

PC Power & Cooling. Single 12v rail. One psu to rule them all. No need to say more. You have been learned.


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## KennyT772 (Feb 16, 2007)

They just dont bullshit like every other company..but they also charge a hell of a lot.


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## GLD (Feb 16, 2007)

@ KennyT772

IDK if you meant PC Power & Cooling cost a lot, but IMO, $100-$200 is a reasonable amount to spend on a psu. Especially when guys spend more then that on either their cpu's, ram, and video cards. All those high dollar components need a quality psu to run them. The $99 I spent on my psu is the best money I have put into any of the rigs I have built. 

Of course a basic web surfer pc can run with a $40 psu, but any enthusiast's pc need quality/costly power.


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## niko084 (Feb 16, 2007)

Well I have not tested a bunch myself, but I have been building computers for 10 years now. And personally know people that have tested them. I have dealt with a lot of rack mount equipment, and many others.

The idea of separating rails IS useful, even if it is coming from the same source. The idea is the rail produces the power, that way if 1 rail drops voltage a bit the rest don't. And they WILL drop voltage a bit when going from a low load to a high load. Yes this meaning for most gamers it is not a big deal,all standard home users doesn't matter at all. For those of us who build servers, routers, or simply want the peace of mind of multiple rails because we like better design then it is a plus.

My info is far from off, and further from being incorrect. And like what I said before "@Testing" my psu is not 62amps... It does have multiple rails but its combined total is far from 60 amps.. In fact it wont even do that at overload on 12volt. And yes like I said the quality of the psu is still everything.

Multiple 12 volt rails is not a hoax even for a gaming machine they offer superior stability *by design*. A cheap antec vs what ever you have now doesn't necessarily compare.


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## Namslas90 (Feb 16, 2007)

@ Niko084;  What do you think of I STAR PSU's?


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## KennyT772 (Feb 16, 2007)

Niko if you had read what i said, and done some extra research you would have disproved your own post. there are very few power supplies with multiple generation circuits, mutli-rail psus are single rail with power sectioned off so no one part can draw enough to melt the wiring. if the voltage on one rail drops so does the other, aka how dual/tri/quad rail psus have been proven a hoax. 

if they were all true multi rail and you plugged two different rails into say an 8800gtx, the different voltages would end up shorting things out. 

to this day the only way they can fit dual/tri/quad power conversion circuits into one casing is by making it larger and packing it full. no cheap light psu will be dual rail, just seperated circuits. 

finally it is a better design yes, in theory. it was simply made by intel due to their high draw pentium ds and presscots. they wanted to be sure they would not overdraw any one wire and melt the harness (which has happened a time or two). it is simply a limiter of a bunch of wires/a trip point per say. if the current goes over that trip point the psu shuts off to make sure nothing will start melting.

atx12v is just a cop-out for psu manufacturers so they can use cheap smaller gauge wire. this is non-issue with higher end parts but the higher end is a small margin compared to big box workstations and home pcs.
@GLD - which one of these is a $100? http://www.newegg.com/Product/Produ...&Subcategory=58&description=&Ntk=&srchInDesc=


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## GLD (Feb 16, 2007)

@KennyT772

Newegg is the Bomb, but not for buying 1 of these psu. I got mine from the source: http://www.pcpowercooling.com/home/


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## buffbiff21 (Feb 16, 2007)

GLD said:


> Newegg is the Bomb, but not for buying 1 of these psu.



I agree for two reasons: 
1. It is cheaper from source. 
2. My 850W Zeus just came today , from Egg, and it had just about the crappiest packing job i have ever seen. Definitely the crappiest ive seen from Egg. It was a large box, with a light amount of foam peanuts, and i could hear it shake when moved the box. I have not used my PSU yet... I hope it still works. 

Still though... Everything else from newegg is good.


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## curt (Feb 16, 2007)

*hey*

ok at first i thout dule 12v line psu.s had the 2-4 12v lines conected some where to give u an evin 40 amps boy was i rong 

i have a antec sp-500 12v rail 1 runes everything but the p4 lil square plug an 12v rail 2 runs the p4 plug wich i think is kinda dumb what if the board u run dun have that lil 4 pin plug then 12v rail 2 is use less so i hard wired them together in side i know the psu works but havent tryed it on a comp yeat 

so now both 12v rails run together

my main system is still quite happy running my enermax 460 single 12v line at 33amp with 3 hd.s 2 raided an a 12amp 7800gs

i allso know some psu.s ar well smart like my enermax 

if your sittin in windows doing nothing the volts look kinda low

like 
11.83v
4.85
3.1
but once i fire up a game it jumps an steays steady
12.30
5.18
3.35


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## freaksavior (Feb 16, 2007)

4 psu 2 with 1 12v rail, 1 1with quad and 1 with dual ok so there all about the same except for the 12v rails. i was told i should get the SILVERSTONE SST-ST56ZF, but eventually i will go a dx10 graphics card, and don't want to get another psu when that happens. SO, now after posting this topic i dk which one to get.....


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## curt (Feb 16, 2007)

*hey*

ok the antec 500wat that was modded so both 12v rails run together an its running this comp im typeing on no more noise from the psu playing games an dosent seam to be struggeling to run it any more yay 

just dont buy a 25 doller 500wat lol that a givin 

just get a half desint name brand one an u should be ok like i sead my enermax is a true 460wat has run every thing i throw at it so far an the one i had before this was a 435wat lasted 3 years till my water cooler driped some condesation on it  only prob i ever had was when it got dirty shut off an wouldent come back on cleaned the psu an it was fine 

i only recomend the older dell psu.s if u plan to run 2 psu.s in total cus alot of the dells an compaq psu.s have volt ajusters in side  oh what fun for your mobo some of the newer ones do this antec does not neather does my ener max

but when its only the board running off the modded dell one i get some nice oc.speeds 

thers one they sell like that to its like a 600w with ajusters far all the rails sepritly but was high $$

lol this psu i got frm a dell the one this comp was runnen on is a hipro 253m/n 250wat 12v rail reated at 14 wats an runs this comp fine evin with my power suckin ti4200 on the mobo

now the antec is rated at 17a on 12v rail one y was it havin ishews when a 14a psu from 1998 newer tech amazes me is the sadest ways some times

the antec  is doing fine with the  rails conected thow

i guess that thing u sead about trapped power is true


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## niko084 (Feb 16, 2007)

Namslas90 said:


> @ Niko084;  What do you think of I STAR PSU's?



After reading a bunch of reviews on them, and looking further into them and the kind of business they do. I get the opinion they make a very rock solid, stable, great output power supply. They are very bland and boring looking, but according to everything I came by they are just amazing in output and stability.

Note- People say they are pretty loud....

Remember they make a lot of their stuff for servers, so loud isn't a problem to them. I can't say how loud personally I have not had one, but people say they are pretty loud.


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## niko084 (Feb 16, 2007)

KennyT772 said:


> Niko if you had read what i said, and done some extra research you would have disproved your own post. there are very few power supplies with multiple generation circuits, mutli-rail psus are single rail with power sectioned off so no one part can draw enough to melt the wiring. if the voltage on one rail drops so does the other, aka how dual/tri/quad rail psus have been proven a hoax.
> 
> if they were all true multi rail and you plugged two different rails into say an 8800gtx, the different voltages would end up shorting things out.
> 
> ...



Ohh okay here I see what you are saying now.

Now that is true, I was tired and mis understanding half the things I relying to over the last few days.. And that is another thing you do have to look at is if the psu is true fully supported multi rail or not.


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## niko084 (Feb 16, 2007)

freaksavior said:


> 4 psu 2 with 1 12v rail, 1 1with quad and 1 with dual ok so there all about the same except for the 12v rails. i was told i should get the SILVERSTONE SST-ST56ZF, but eventually i will go a dx10 graphics card, and don't want to get another psu when that happens. SO, now after posting this topic i dk which one to get.....



That 56f is not a very hot psu....

Any of the other 3 should be more than sufficient for a single 8800.
As long as you don't run 4 hard drives at 15k, overclock like a crazy man, and use 8 sticks of ram.


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## EastCoasthandle (Feb 16, 2007)

Testing said:


> I wonder if half the people who spout their unfounded knowledge of mutli-rail power supplies have actually got a meter out and measured their components under loads.
> 
> Niko, Mgrant?
> 
> ...



I'm  quoting this again so people can read it.  This person tells the truth of the matter.  To sum it up muti rail psu's are bullcrap!!!  

It's amazing how no one offers a thank you or rebuttal to what this person said.  And, I believe some of the misinformation posted in this thread needs to come to a stop.  It doesn't take much to realize to buy a decent single rail PSU for your needs over a multi-rail psu or a mutli rail modular PSU (I haven't found a single rail modular yet) thats inefficient, over-rated and underpowered with each additional rail installed.

Also note, there is no standard business practice to show you how that PSU performs at around 30C+.  Nor is their any labeling of what to expect from the 12V, 5V and 3.3V.  Anyone who believes that it's OK to have a psu that's rated at 12V to operate at 11.80V , 5V to operate at 4.80V and 3.3V to operate 3.20V or 12.20V, 5.15V and 3.38V is dilated.  Your video card, ram, cpu HD and MB all require specific voltage (optimal voltage) in order to work correctly.  That means (unless instructed otherwise, which is rare) if you are required to have 12V, 5V and 3.3V then you need a psu that will provide exactly that.  For one, that is why you stay away from modular PSUs (for starters).  Secondly, you test this with a multi-meter under load. Third, research reviews for that PSU which provides other important information like voltage performance, fluctuation, ripple, efficiency, etc.

Personally, I've found no manufacture that has come close to PC P&C (based on my needs).  

Here is how you check your 12V, 5V and 3.3V






yellow + black 12V





red + black 5V





orange + black 3.3V

This isn't for the inexperienced, you have to know how to operate a voltmeter and you have to know what you are doing when using a voltmeter with live wires, connections, etc.  I am not recommending this to those who rarely do this or haven't done this before.


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## MGrant1957 (Feb 17, 2007)

*If you read my first post....*

you would see that the 12v rails are rated for:
12v rail#1 is rated for 18Amps MAX
12v rail#2 is rated for 18Amps MAX
12v rail#3 is rated for 30Amps MAX
12v rail#4 is rated for 30Amps MAX
3.3v rail is rated for 30Amps MAX
5v rail is rated for 30Amps MAX
12v#1+12v#2+12v#3+12v#4 Combined is rated to 62Amps.

Since I have been hand-building Power Supplies for some years, Starting with a MULTI-TAP Transformer that CAN give you multiple 12v rails with a common ground, then run the outputs (Plural) through a full-wave bridge rectifier, followed by the filter capacitors, surge current limiter resisters and voltage regulator/current limiter diodes.

The real limiting factor is the TRANSFORMER.


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## Wile E (Feb 17, 2007)

EastCoasthandle said:


> I'm  quoting this again so people can read it.  This person tells the truth of the matter.  To sum it up muti rail psu's are bullcrap!!!
> 
> It's amazing how no one offers a thank you or rebuttal to what this person said.  And, I believe some of the misinformation posted in this thread needs to come to a stop.  It doesn't take much to realize to buy a decent single rail PSU for your needs over a multi-rail psu or a mutli rail modular PSU (I haven't found a single rail modular yet) thats inefficient, over-rated and underpowered with each additional rail installed.
> 
> ...


Although I know modular supplies are a little more inefficient than standard ones, it doesn't mean they are necessarily bad. mine puts out 12.03v, 3.38v, and 5.06v as measured by the bios.


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## niko084 (Feb 17, 2007)

MGrant1957 said:


> you would see that the 12v rails are rated for:
> 12v rail#1 is rated for 18Amps MAX
> 12v rail#2 is rated for 18Amps MAX
> 12v rail#3 is rated for 30Amps MAX
> ...



Exactly.

And voltage drops even in the least is not good... If optimum is 12, you should run as close to 12 as possible. Too much you start to have problems, too little you also start to have problems..

There is a part a lot of people don't realize. Everyone knows too much voltage is bad, what they don't realize is even slightly under voltage is bad also, when you under voltage something and it requires more power, it just draws more amps... Thats really bad... It's like when you have a bad alternator and battery in your car and you have to start it on low volts all the time,what happens? Your starter burns out... Now 11.8 compared to 12.0 sure not a big deal there, but enough to drive me nuts personally.

Odd's are on my next psu, I will take it apart and stack it with capacitors to get it as close to perfect voltage as I possibly can. Overkill - yes... But I'm a nut about it and want it as close to perfect as I can get it. I have also been considering building my own psu at some point. There are really a very simple design if you know what your looking at.

Multi-rail, single-rail they both work, they have both existed for a long time, and before the P4s. I'm not saying one is really better than the other. It's more of a choice thing, which one would you like, and whats available.

To put it down simple, either one in a good quality psu will handle anything you can throw at it.

Oh--- My friend has dual x7950s on a 4 rail i-star 750watt, he runs 3 scsi 320 10k drives, optical, fans, basic stuff. He has a e6600 and 2 gigs of ram. Absolutely no issues at all. 
4-rail psu rated at 750 watts. So it just goes to show that multi rail can hold it as well. Key being buy a *GOOD* one.

FYI- the 7950s he hasn't tested them pulling more than 4.7amps off the pci-e plug each. So whats the sense in a single rail, when his pci-e plugs can give out 18 amps from their rail?

Well if the 7950 will pull 4.7 and Nvidia says their 8800 will pull 5.5... I don't see any issue coming up here. And thats being realistic. The psu costs about $200 everywhere I find it.

@Namslas90-
Looks like that i-star will do grand! I was talking to him last night and I started talking about power supplies, he said he had it and it ran like a dream. He also said its not really as loud as he thought it would be, but its fairly loud.


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## niko084 (Feb 17, 2007)

Wile E said:


> Although I know modular supplies are a little more inefficient than standard ones, it doesn't mean they are necessarily bad. mine puts out 12.03v, 3.38v, and 5.06v as measured by the bios.



Ya modulars aren't as bad as people make them out to be. The key is being you have the extra connection just to make sure it stays tight. Another trick would be to use a little dielectric grease inside the connections to just aide that much more in current transfer. I myself am ordering a modular to replace my current one with my new system build. I'll post some voltages at idle, and full load after I get it all done.


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## ex_reven (Mar 18, 2007)

small question, someone said something about voltage drops when you have multiple rails

wouldnt a single rail suffer similar problems? I remember being told a while back that if there is an increase in voltage, resistance in the cable increases, which is why at high voltages cables can burn out. Would a multi rail psu reduce this resistance?


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## quasar923 (May 20, 2007)

do u think that a 750 watt psu with a single 12v rail with 60 amps is good enough for my system:

q6600
asus p5b deluxe
8800gts
dvd burner
250 gig 7200 rpm sata hdd
antec 900 case
cruical balistix 8000 (1000mhz)
and  SILVERSTONE DA750 ATX12V / EPS12V 750W Power Supply 100 - 240 V
http://www.newegg.com/product/product.asp?item=N82E16817256017


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## Wile E (May 20, 2007)

quasar923 said:


> do u think that a 750 watt psu with a single 12v rail with 60 amps is good enough for my system:
> 
> q6600
> asus p5b deluxe
> ...


That psu is more than enough for what you have. Hell, you could run a 8800GTX SLI setup on a 60a psu.


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## MGrant1957 (May 21, 2007)

Does anybody out there listen to an electronic engineer? 

PC Power and Cooling does make very good single-rail Power supplies. However, that does not mean that modular systems are junk. any good power supply will have full-wave rectification. several large capacitors for filtering the output of the rectifier, surge current resistors, voltage clamping diodes, power-factor correcting capacitors/inductors, and regulator circuits to keep things in line. the real limiting component in ANY power supply is the transformer, be it a single-tap or multi-tap. a single transformer can have dozens of taps , each one giving a different output voltage. if the Primary coils (ie 120v side of the transformer) are of a sufficient gage, and the input power cord as well, then it can supply enough magnetic flux density to power anything you can through at it.


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## tkpenalty (May 21, 2007)

Hell you could run a 8800GTX SLI setup on my iGreen without a problem.


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## KennyT772 (May 21, 2007)

MGrant1957 said:


> Does anybody out there listen to an electronic engineer?
> 
> PC Power and Cooling does make very good single-rail Power supplies. However, that does not mean that modular systems are junk. any good power supply will have full-wave rectification. several large capacitors for filtering the output of the rectifier, surge current resistors, voltage clamping diodes, power-factor correcting capacitors/inductors, and regulator circuits to keep things in line. the real limiting component in ANY power supply is the transformer, be it a single-tap or multi-tap. a single transformer can have dozens of taps , each one giving a different output voltage. if the Primary coils (ie 120v side of the transformer) are of a sufficient gage, and the input power cord as well, then it can supply enough magnetic flux density to power anything you can through at it.



Nothing against you man, but you are trying to explain japanese to a 4 year old. Few of us know the exact nature of power supplies, we just know what setups are used and how they output power. If you can break down the key difference between single tap/multi tap we would understand more and be able to give comment. 

I do know that for the cheaper "uber high wattage" power supplies they often use cheap caps, and a single transformer. The high end 1000w-1200w psus I've seen have had large and multiple transformers, usually one for the 5v/3.3v/etc and one or two for the 12v lines. From there the lines are seperated out by fuses to prevent overload etc.


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## Dippyskoodlez (May 21, 2007)

newtekie1 said:


> Everyone always points to that article, but they never seem to realize that it is posted on the website of a company that builds power supplies.
> 
> I disagree with the majority of what that site says, IMO it creates more bad myths than it actually addresses.



ANd the little fact you leave out, is that its posted on the company that makes the *uncontested best* PSU's available.

I Have one. You may say Bias, but This thing is amazing. (Yes, I have used a powerstream to compare this to. its just no contest in quality)


The only reason I would really see going multi rail is to save money.

I don't see any BENEFITS to doing it.


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