# Single Rail vs. Multi Rail *Explained*



## Phaedrus2129

First off, I'd like to give credit to Jonny Gerow (former star of JonnyGURU.com, now PSU project manager at BFG) for writing what I consider the definitive article on power supply "rails", one which educated me. If you want an accurate historical and mildly technical explanation of power supply rails, read his article here:
http://www.jonnyguru.com/forums/showthread.php?t=3990

Also, I'm going to not bother mentioning the +5V and +3.3V rails, because it just confuses the matter. In this article I will talk only about the +12V rail, and single/multiple versions of it.

So let's get down to it.

"Single rail power supplies are best!"
"No, multi rail units, stupid. You've got like five times as many rails to power your parts."
"No, single rail is best, are you an idiot? Look at how much more I can overclock!"
"You're just a moron, you don't know what a rail is!"
"You're just jealous because I've got a single, massive, powerful rail, if you know what I mean."

Children, children, calm down and shut your traps. You're both wrong! It doesn't matter, at least not in the way 99% of enthusiasts think.

What is a rail?










No, now stop being a smartass.

Seriously, most people have very strong opinions on what rail distribution is best, without understanding what a rail is. The common misconception is that a rail is a part in the power supply that provides power. This is utterly and completely false. You can have two power supplies that are 99% identical and one be single rail and one be multi.

No, rather a rail is a group of traces on the PSU's mainboard that are monitored by an OCP circuit.

"What?"

I said, it's a group of traces on the--

"Shut up until you can speak English."

Fine. A trace is a pathway of copper on a circuit board that carries electricity. You can see them as the faint copper-y lines running all over your motherboard. In this instance, I'm referring to the traces on the power supply that the wires in the cables are soldered to, specifically the ones carrying +12V power. With me so far?

"Yes. Speaking of tracing, I'm going to go get some stencils."

Whatever. Now, OCP is Over Current Protection. What OCP does is it monitors an output on a power supply. If the amount of current--

"What is--"

Read this: http://en.wikipedia.org/wiki/Electric_current
If the current going through a given output exceeds a certain amount, it will shut the power supply down.

What does this have to do with single or multiple rails?

"I was about to ask, yes."

Glad to know. The difference between single or multiple rails is this:

Multiple rail: each trace is monitored separately, so if, say, one trace goes over 25A the power supply will shut down.

Single rail: all traces are monitored all together, so if the total current going through the +12V outputs goes over, say, 60A, the power supply will shut down. Alternatively, no OCP may be present at all on the +12V rail.

Make sense? Nothing about single rail having extra power or being more stable, on either side. You could have two identical power supplies with the only difference being how the OCP chip is configured, and one could be single rail and the other multiple. Understand?

"No, I--"

Yes you do, if you don't go back and read through again.

So which is better? Well, neither has any affect on voltage stability or ripple suppression or efficiency or anything, really, at least not to a measurable degree. So all those arguments are bogus. A single rail PSU will not let you overclock any higher than a multi rail, or vice versa. However, there is a difference.

Let's imagine you have a short circuit on the +12V and the SCP (Short Circuit Protection) doesn't catch it. If you have a single rail power supply the draw on that one +12V wire and that one +12V trace will climb until either the combined OCP point is reached, or until something burns; the cable, your power supply, your motherboard. With large units, usually something will burn before the OCP point is reached.

In a multi-rail unit, the current would climb until it hit that rail's OCP point, at which point the PSU would shut down to protect itself and your computer. Ideally you'd have a rail for every wire, but that would be impractical, so you generally see 2-8, depending on the power rating of the PSU and the design philosophy.

So multi-rail is inherently safer, correct? Yes, but early on there were some problems. You see, when multi-rail units were first introduced, the specification at the time was poorly written, and power supply engineers made a mistake; they put all the cables that power heavy-draw components like your CPU, mobo, and graphics card(s) on one rail, and all the light-draw stuff like HDDs and fans on the other. This meant that you had one rail that might be pulling, say, 24A, and another pulling 5A.

"I see! They were unbalanced, so the man inside the PSU fell off his unicycle and--"

No. If your PSU's OCP trip point for that main rail was set to 24A, then your system could easily hit that trip point when under load, causing the PSU to shut down to protect itself. That could cause you to lose data, or leave your friends without backup while playing TF2.

"Wow that sucks."

Yes indeed. The power supply was just as powerful as the single rail units of the time, but would shut down under heavy loads because of the poor cable distribution among the OCP rails.

However, that is no longer an issue. The problem units only existed around 2006; since 2008 virtually all power supplies have had intelligent cable arrangements, with only a few gaffes here and there. On a modern multi-rail power supply there is virtually no chance of tripping a rail's OCP in normal use unless you're running way too much for the power supply to handle anyway.

So final verdict? Single rail or multi rail? Well, with low-wattage units it doesn't matter. OCP on a single rail is useful up to about 40A or thereabouts, which is where most 550W power supplies fall. So with 550W and under power supplies, it's a moot point. However, with high wattage units, >45A on the +12V (650W and higher) picking a multi-rail unit will provide you with an extra layer of protection. It isn't essential, and it has no impact on the power supply's performance. However, it does provide an extra layer of safety in case you get a short circuit. And I would consider it a must for >1000W power supplies; [H] recently tested the single rail Corsair AX1200, but they had an accidental short circuit, and since the PSU's OCP is set for over 100A, the short overloaded and destroyed most of their testing equipment. So there is a danger with single rail units over 1000W.

So multi-rail is mildly better, especially with high wattage units, but it won't have any impact on your performance or overclockability.

There, does that settle it?

".... HAHA TOLD YOU MULTI RAIL WAS BETTER."
"You can kiss my rail for all I care!"

*sigh*

This has been your friendly neighborhood Phaedrus, signing out.

*Further Reading*


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## PhaedraCorruption

You have my vote for sticky.


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## DuckieHo

What about the Enermax Galaxy 1000w or Corsair 1000HX? I heard they have "true" multiple rails.









Did you want to mention the one of the originators of the misconception and the reason for the "myth"?


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## Phaedrus2129

Quote:


Originally Posted by *DuckieHo* 
What about the Enermax Galaxy 1000w or Corsair 1000HX? I heard they have "true" multiple rails.









I swear if you make me go into that I'll dock you 100 internet points...









It's still irrelevant though.


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## Lord Xeb

LOL Very intersting way of explaining things! Good job!


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## computeruler

Very helpful. I've always wondered this.


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## CarFreak302

Thanks for that, it cleared a lot up for me. Great write up!


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## Lord Xeb

Quote:


Originally Posted by *computeruler* 
Very helpful. I've always wondered this.

Same


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## Stensby

Very useful, was having this argument the other day with my buddy!


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## shinji2k

Quote:


Originally Posted by *DuckieHo* 
What about the Enermax Galaxy 1000w or Corsair 1000HX? I heard they have "true" multiple rails.









Did you want to mention the one of the originators of the misconception and the reason for the "myth"?

One of? They where _the_ origin







. But I'd like to keep my blood pressure down so let's not talk about that. They are dead to me anyway.

I find myself to be apathetic to the whole thing anymore. I can't be bothered to debate it even with people who know what they are talking about. It doesn't even factor into my own PSU buying decisions. In all of my years of computers I have never had a short or seen another computer in real life that shorted and melted/burnt something due to lack of OCP. I know it happens, but the frequency is so low I am much more concerned about the dangers of driving home from work than a freak accident with my computer.


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## Phaedrus2129

Quote:


Originally Posted by *shinji2k* 
One of? They where _the_ origin







. But I'd like to keep my blood pressure down so let's not talk about that. They are dead to me anyway.

I find myself to be apathetic to the whole thing anymore. I can't be bothered to debate it even with people who know what they are talking about. It doesn't even factor into my own PSU buying decisions. In all of my years of computers I have never had a short or seen another computer in real life that shorted and melted/burnt something due to lack of OCP. I know it happens, but the frequency is so low I am much more concerned about the dangers of driving home from work than a freak accident with my computer.

Yeah, it's no factor to me either, but I'm getting sick of debating it just like you are. So I decided the best way to settle it is an article. Multi-rail has a slight advantage because of OCP, but it doesn't really matter most of the time.


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## Hephasteus

I like single rail. It's better for burning down your tower when you accidently screw diver it with the power on.


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## Bal3Wolf

Nice read and easyer to understand then some others that try to explain it. 1 thing i would like psu makers to do is mark what rail goes to what so you can balance the load out.


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## Phaedrus2129

Some already do.

In case you're wondering, your M12D is labeled as being multi rail when it's actually single. SeaSonic is weird like that.


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## gymenii

Yes! Great read. This should certainly clear up any debate. Oh, and I vote to sticky and recommend everyone must read this before making a purchasing decision.


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## Kaninja

Great write-up.







One of the major reasons we see so many PSU's with single rails these days is because ATX2.2 lifted the 240va limit requirement and made it merely a recommendation. This is, I believe, a major contributor to why we are seeing rails that exceed 20A. PC P&C isn't such a bunch of rebels anymore.......not much of anything anymore actually.


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## Bal3Wolf

Quote:


Originally Posted by *Phaedrus2129* 
Some already do.

In case you're wondering, your M12D is labeled as being multi rail when it's actually single. SeaSonic is weird like that.

Yea i know but its still a nice psu i bought it cause i got it for 130 and jonnyguru gave it a good review. And i did notice its labled on inside but not outside i just need to remmber first 2 plugs go to rail 1 and 2nd to last one.

Quote:

This would be a good time to mention that the two 12V rails share a single source. They are split using overcurrent protection, just like 99% of the other multirail units out there.


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## lurkingdevil

At first thought it appears as if the different rails have different source, so load on one rail won't affect the other. However they share the same source, so all this multi rail thing is very misleading.


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## Oklahoma Wolf

Quote:


Originally Posted by *Kaninja* 
PC P&C isn't such a bunch of rebels anymore

They weren't really in the first place - several industrial OEMs, most notably Zippy, never really adopted the 240VA requirement in the first place. They had some models that conformed to it, and some that didn't... both before and after the 240VA limit was imposed. It was just business as usual for them.

PC P&C actually tried on the 240VA limit for everything above the old 510W before realizing the SSA spec wasn't right for home computers and going to single 12V rather than make the rail distribution make sense.

Quote:


Originally Posted by *lurkingdevil*
At first thought it appears as if the different rails have different source, so load on one rail won't affect the other. However they share the same source, so all this multi rail thing is very misleading.

Only up until you realize it's the same sort of idea used by your household breaker box.


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## Bal3Wolf

yea way i understand it is each rail has a failsafe and is only allowed say 40amps befor it triggers the failsafe compared to a single has to go way higher befor it trips it.


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## Kaninja

Quote:


Originally Posted by *Oklahoma Wolf* 
They weren't really in the first place - several industrial OEMs, most notably Zippy, never really adopted the 240VA requirement in the first place. They had some models that conformed to it, and some that didn't... both before and after the 240VA limit was imposed. It was just business as usual for them.

PC P&C actually tried on the 240VA limit for everything above the old 510W before realizing the SSA spec wasn't right for home computers and going to single 12V rather than make the rail distribution make sense.

Only up until you realize it's the same sort of idea used by your household breaker box.

It was meant as a poke at PC P&C. Their old PSU Myths page tried making them sound like a bunch of single-rail rebels in a world of multi-rail madness.


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## onoz

Thanks for all the good work!


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## WTHbot

Bump for great justice.


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## Volvo

Sticky vote.


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## Nemesis429

Holy cow, i think im going to cancel my order for the AX1200 and go for the enermax 1050


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## TheLaw

Quote:


Originally Posted by *Nemesis429* 
Holy cow, i think im going to cancel my order for the AX1200 and go for the enermax 1050

Indeed


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## Nemesis429

Or does anyone know any other PSU i can go for besides the Enermax revolutions 1050?


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## TheLaw

Quote:


Originally Posted by *Nemesis429* 
Or does anyone know any other PSU i can go for besides the Enermax revolutions 1050?

This is what you should be getting: http://www.newegg.com/Product/Produc...82E16817814010


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## TheLaw

Oh sorry I did not see you live in the UK. Regardless, the Enermax is an awesome supply and will not let you down.


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## Nemesis429

Oh, okay sweet, that new maker for Corsair was a bad decision lols, revolutions it is then







.


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## Power_user_EX

This is called an eye-opener!!!


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## voixdelion

Have you ever considered writing a "For Dummies" book?

Clearly you have a gift for writing as well as technical savvy: a rare and beautiful combination. Thanks for making stuff both intelligible and also fun to read whilst demystifying common confusions.


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## Zap

Would be a short book.
Quote:


> Originally Posted by *PSU Rails For Dummies*
> Buy a decent PSU.
> Don't worry about rails.
> EOF


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## scrotes

Loved the dialouge of this thread helped keep my interest on a boring subject that I told myself I must learn. +1 to u sir. Not that u need it, but hey its the thought that counts


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## poiu

perhaps interesting for you









difference between good and not so good single Rail PSU *lol* and Multi Rail

http://www.hardwareclips.com/video/2080

http://videos.pcgameshardware.de/video/2080/PCGH-in-Gefahr--Rauchexplosion-bei-Netzteilkurzschluss

the PSU´s

LC Power Legion X2 1000W (aka Andyson K Series)
Corsair AX750
Corsair AX1200


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## Spooony

Question

Ain't gpus limited to 480w per gpu thru the connectors that's not including the 75w of the slot?


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## Phaedrus2129

Quote:


> Originally Posted by *Spooony;13613404*
> Question
> 
> Ain't gpus limited to 480w per gpu thru the connectors that's not including the 75w of the slot?


No, 375W total according to PCIe spec. 150W per 8-pin, two 8-pins max, 75W for the slot. Anything more violates the PCIe spec.

Realistically they can draw more.


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## Spooony

Quote:


> Originally Posted by *Phaedrus2129;13613807*
> No, 375W total according to PCIe spec. 150W per 8-pin, two 8-pins max, 75W for the slot. Anything more violates the PCIe spec.
> 
> Realistically they can draw more.


thx. Its a unclear issue. Coz are the psu->gpu connection still part of the Pci-e spec? Some would argue thats its a straight connection to the card. lets say the 6990 it takes 4x 8 pins that's a possibility of 600w to the card. That's why I am asking just want to make sure


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## Phaedrus2129

PCIe power connectors are still part of the PCIe spec.


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## Spooony

Quote:


> Originally Posted by *Phaedrus2129;13621897*
> PCIe power connectors are still part of the PCIe spec.


so if Pci-e 3 comes out are they going to up that spec?


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## adriangb

Somehow I ended up soldering a train shaped trace on my MB with a stencil.

Great read.


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## Nemesis429

Why is it then that everyone manufacturers Single Rail PSUs?


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## Phaedrus2129

Quote:


> Originally Posted by *Nemesis429;14560306*
> Why is it then that everyone manufacturers Single Rail PSUs?


Because PC Power & Cooling said it was better
Because Corsair copied PC Power & Cooling
Because everyone else copied Corsair
Because everyone fell for the marketing FUD
Because "single powerful rail" sounds good to the uninformed
And it's slightly cheaper to manufacture


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## Nemesis429

Does anyone manufacture Multi Rail power supplies?


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## Phaedrus2129

Quote:


> Originally Posted by *Nemesis429;14570559*
> Does anyone manufacture Multi Rail power supplies?


If no one made them I wouldn't have made an article on it.


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## Nemesis429

-.-' I meant to say Which manufacturers make Multi rail power supplies.


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## PCCstudent

Are you up to giving the "rail talk" you avoided some months ago concerning the Corsair 1000HX? I ask for you to just make the technical points and you will not hear from me.I ask this as there is a group of us that use this power supply and we want to know details other that what is put out in the reviews.If not link me to a review of the rail system.The rail setup is a bit confusing on this power supply,so confusing that there is a sticky on the Corsair forum ,but it only talks about what is grouped on what rail,I politely ask for more.No conflict,I just ask what you know about the rail system in this power supply.I am going to keep using it so I might as well become better educated.


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## Phaedrus2129

Well there's not much to say.

It turns out when I said a while back that a Channel Well PUC (used in the Corsair HX1000 and others) _isn't_ two 500W PSUs stuck together, I was misinformed. I was under the impression that the PSU had a single primary and two secondaries. Turns out it's two primaries and two secondaries, only things not duplicated are the EMI filter and +5VSB circuit.

So it's two 500W PSUs "mashed together" on one circuit board. One provides +12V and +5V, the other provides +12V and +3.3V. And each provides power to different output wires. It's possible to overload one of the PSUs, causing it to exceed ripple or voltage specs or even shut down.

Why did Channel Well design it this way? Because it was cheap. Not cheap to make--no no, PUC has one of the highest BOMs and manufacturing costs per watt of any consumer PSU. Cheap to design. Channel Well was late to the game with 80PLUS capable 1kW+ units, and didn't want to spend a great deal of time or money catching up. So they spent a weekend fitting two 500W units onto one PCB, then got to work on DSG which is an actual single PSU design capable of high efficiency at 1kW loads--although not much higher than 1100W. Channel Well is still riding on PUC for almost all of its >1kW units, because it's so scalable.


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## RobotDevil666

Great read thank you !!


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## Phaedrus2129

Quote:


> Originally Posted by *Nemesis429;14571334*
> -.-' I meant to say Which manufacturers make Multi rail power supplies.


Lots of them do, more than I can list.


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## akrEAGLE

Thanks for the great guide, just wanted to mention that I bought an HX1000 a few months ago, and somehow something must have shorted with the PSU. I found out when my 8 SSD's caught on fire... Probably could have easily been prevented if it had more rails. Kind of similar to what happened when [H] tested the AX1200.


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## penguinlove

I really liked the article. Your a genius. I'm in need of clarification, though.

"Good" multi rail systems are spreading the total 12V load over all the rails, no matter where the demand is, and bad ones keep the 12V rails isolated?


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## Phaedrus2129

Quote:


> Originally Posted by *penguinlove;14681292*
> I really liked the article. Your a genius. I'm in need of clarification, though.
> 
> "Good" multi rail systems are spreading the total 12V load over all the rails, no matter where the demand is, and bad ones keep the 12V rails isolated?


There's no such thing as "spreading" load or "isolating" load. The only difference is what cables, what wires leaving the PSU, are protected by which circuit. Think of OCP circuits as like the circuit breakers in your house. The concept is exactly the same. Put too much on one breaker and it trips and everything on that circuit turns off.

So you have a circuit breaker box in your home, and you have one that maybe does a bedroom and the microwave, another that does the family room and the fridge, another with the office and the stove (see the pattern? they like to bundle high-draw appliances with comparatively low-draw rooms that will just have lights and the like). What's going on on one circuit has no effect on any of the others. If you've got 15A breakers then you can load that circuit up to 14.9A with no ill effects, but if you hang at 15A for more than a few milliseconds, blip, the breaker trips and everything shuts off.

OCP is just like that, only instead of circuits in your house it's wires leaving your PSU. On a good 750W unit with, say, four 24A rails, you'll have the ATX and EPS12V connectors on one OCP circuit; then one with two PCIe cables; then a PCIe cable and a couple molex/SATA chains; then the last PCIe and some molex/SATA chains on the last circuit. That way any given rail will be loaded between 0A and ~20A, and shouldn't go over 24A unless something has gone wrong the user has hooked up way more stuff than the PSU is designed for in the first place.

What a lot of early multi-rail units did, because the spec was written by an idiot, was they'd use two OCP circuits. They'd rate one for 16A and put the ATX12V/EPS12V CPU cable on it and that's it. Then they'd rate the other rail for 14A and put the PCIe cables, ATX connector, molex and SATA cables on that one. So you'd have one OCP circuit operating at nowhere near its trip point, and another one operating at or above it (when using a high-end system).

On modern units, that shouldn't be an issue.


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## penguinlove

So, its possible you might be feeding your CPU with a rail, your mobu power with a rail, and the accessories with another?
If there is a particularly hungry component to your system, are you stuck looking for a multi-rail system with individual rail amperages sufficient to power that one component?
That makes things much harder selecting psu's...


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## Phaedrus2129

Quote:


> Originally Posted by *penguinlove;14681970*
> So, its possible you might be feeding your CPU with a rail, your mobu power with a rail, and the accessories with another?
> If there is a particularly hungry component to your system, are you stuck looking for a multi-rail system with individual rail amperages sufficient to power that one component?
> That makes things much harder selecting psu's...


Not really.

[email protected]+12V is 288W. That's a LOT. And when a rail is rated for 24A, the OCP trip point is usually at around 28-32A, so call it 336-384W. Not many components will draw more than that.


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## shadman

Wow, this was very well written. I understood most of it. Very well-written!


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## mnkeyprince

please sticky the thread...

its scary how some people not only help, they give info that could be fatal, like this guy

"I do not have any of the PSUs mentioned here but if I were to buy a 1200 watter I would not even consider anything but Corsair. I have only owned corsair power supplies(save one by seasonic) and they have all worked perfectly, while I have seen many stories about the antecs failing and even blowing in some cases. *But the primary reason I like the AX1200 is the single 12 volt rail. I really can't see why anybody would want to get a PSU with multiple rails.* With the Corsair you only have to worry about overloading the PSU's total power output, whereas with the Antec you need to worry about the power conumption of each individual rail. I would leave antec alone"


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## Matari

For me, this thread was a very interesting read. I am building a new 2600k + dual 580 GTX and looking for 1000 W + PSU. I am looking for a fully modular PSU, what are your recommend?


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## weaselciuy

Best article i read in the last months . Good job and thumbs up.

Now i know what to pick.


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## Benz

Yeah same here.









I'm soooo glad that I have a Quad Rail PSU with 32A on each one.


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## t3haxle

Thanks man, now I know single rail PSU's overclock farther and cook me pancakes.


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## mlp

I still don't fully understand the single rail vs multi rail argument.

Most of the article sounds like multi rail is way better because it offers better protection, but in the end it says it doesn't really matter.

What are the real chances of a single rail exploding vs a multi rail? Not something I should be concerned about? From these postings it seems like you are getting into the danger zone with 750+ watt PSU's on single rails but yeah, like I said I don't understand it.

I'm stuck choosing between an XFX 750w with a single rail or the Antec High Current Pro which has multiple rails but is $30 more.


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## Phaedrus2129

A single rail PSU won't blow up on its own or anything. But if the power circuitry on your motherboard or graphics card fails in one of a number of certain ways (not uncommon) the single rail PSU will keep supplying current until either it fails, or the card/motherboard catches on fire.

So in other words, if you plan to use anything from MSI or a reference GTX570, it's best to use a multi-rail PSU.







Otherwise it's not critical. The complaint against single rail PSUs is more that they're claiming the *lack* of an important protection as a feature.


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## mlp

Thanks Phaedrus for the quick response.

I just ordered an MSI graphics card to SLI so erp.. guess single rail is out.

I think the XFX was a better PSU but the Antec should be fine. JohnnyGuru likes it, HardOCP doesn't, and there's only 1 newegg review on the HCP-850.


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## Slappy Mcgee

Bravo to you sir







Thank you for explaining that. Really loved how you did the explination.

PS I know this is an old thread but I just came across it


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## Phaedrus2129

Quote:


> Originally Posted by *mlp;15075259*
> Thanks Phaedrus for the quick response.
> 
> I just ordered an MSI graphics card to SLI so erp.. guess single rail is out.
> 
> I think the XFX was a better PSU but the Antec should be fine. JohnnyGuru likes it, HardOCP doesn't, and there's only 1 newegg review on the HCP-850.


The MSI thing was more tongue-in-cheek, since their budget (and even some high-end) motherboards tend to have very weak voltage regulators that can blow up if you overclock the system too much. It's not a 100% thing though, just a bit more common than with other companies' products. And their graphics cards aren't any worse than usual when it comes to VRM failure.

Just poking fun at them was all.









As for the XFX BE 750W vs. the Antec HCP-750, it's kind of a toss-up, really.


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## mlp

Quote:


> Originally Posted by *Phaedrus2129;15075602*
> The MSI thing was more tongue-in-cheek, since their budget (and even some high-end) motherboards tend to have very weak voltage regulators that can blow up if you overclock the system too much. It's not a 100% thing though, just a bit more common than with other companies' products. And their graphics cards aren't any worse than usual when it comes to VRM failure.
> 
> Just poking fun at them was all.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> As for the XFX BE 750W vs. the Antec HCP-750, it's kind of a toss-up, really.


Ah, I gotcha now.

As for the actual cards I am in between the XFX Pro 750w XXX edition... can't find the BE anywhere.

http://us.ncix.com/products/?sku=62224&vpn=P1750BNLG9&manufacture=XFX

And the Antec HCP-850 because it is only $5 more than the 750 model. Then again, the XFX 850 is only $10 more than the 750 heh... I can see how this can start to be excessive.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371053&Tpk=hcp%20850

Pretty sure I read somewhere that single rails start getting into trouble when they have 70amps on a single rail, that xfx i linked has 62a not sure on the 850w model. That is what has me scared!


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## jwalker150

This has been very useful since I am looking at power supplies as i am upgrading my system. Will now go back and re-look at all my considerations and see how they all stand.
Thanks again.


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## adridu59

Nice guide, can you make the "questions" on OP bold? it will be easier to read.


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## Killz2.0

Hi, Excellent guides, helps a lot.

I have read quite a few of your threads, but either I missed it or it hasn't been brought up.

When I look at many multi-rail power supplies, the added amperage of both rails far exceeds it's actual possible output. Does one rail balance out the other rail ?

For example , This 750w Enermax Naxn (who went solytech all of a sudden!) has 2 x 35amp rails, but only a total output of 648w. So instead of 70a/840w like some people might think, it really only has a total 54a/648w.

Hardware Secret overloaded both rails to 30amps each before the fail safes shut down the power supply ...
http://www.hardwaresecrets.com/article/Enermax-NAXN-82+-750-W-Power-Supply-Review/1275/8

Same thing goes with the 650 Antec Earthwatts with 2 x 38amp rails, but only 650w max.

Do these rails do a balancing act like a teeter totter ? If 1 rail is pulling 34a/408w that means the 2nd rail will only have 648-408w = 20a/240w to work with ?

Or do both rails have the proper connectors to each rail on the Enermax and Antec that it would be almost impossible to trip them ?

Thank you.


----------



## Phaedrus2129

The rails don't exist. That's the main thing I have to get across first it seems. The rails... Are not actual "things". It's a concept, and a very simple one.

You know that circuit breaker box outside your house or in your garage? That's what rails are, they're like circuit breakers. All they do is kill the circuit if you draw too much power on one set of outlets (PSU connectors) to stop a fire from starting. They have no impact on the power being drawn whatsoever.


----------



## Arinoth

I figured I'd post in here my question rather then creating a new thread as its related to the multi-rail power supplies.

I'm assuming that if I have a true multiple rail power supply I should be reading two different voltage levels, though how can I tell I have a multi-rail power supply without actually knowing the model of the psu itself. As in what rails differ that I should/would need to probe to ensure I know if its a single or multi-rail?


----------



## Phaedrus2129

Quote:


> Originally Posted by *Arinoth;15290679*
> I figured I'd post in here my question rather then creating a new thread as its related to the multi-rail power supplies.
> 
> I'm assuming that if I have a true multiple rail power supply I should be reading two different voltage levels, though how can I tell I have a multi-rail power supply without actually knowing the model of the psu itself. As in what rails differ that I should/would need to probe to ensure I know if its a single or multi-rail?


You would have to open it up and look at the design. The voltage level would likely be similar between independent rails and would fall within the margin of error caused by varying wire resistance, etc. The only time they'd be markedly different would be when one is under a heavy load and the other a light one.

Yours incidentally, is single rail.


----------



## Arinoth

Quote:


> Originally Posted by *Phaedrus2129;15291570*
> You would have to open it up and look at the design. The voltage level would likely be similar between independent rails and would fall within the margin of error caused by varying wire resistance, etc. The only time they'd be markedly different would be when one is under a heavy load and the other a light one.
> 
> Yours incidentally, is single rail.


I wasn't asking about my power supply specifically. See I'm designing a device that will calculate the power draw of each individual computer component (graphics card, hard drive, fan, mobo, etc) by measuring the current and voltage rails while in use. I'm trying to figure out a way for me on the measurement side to distinguish if I'm dealing with a single or multi-rail so I can use the correct formulas.

(Yes I'm the same guy who responded to your PSU Calc thread on HwC)


----------



## Phaedrus2129

Quote:


> Originally Posted by *Arinoth;15291673*
> I wasn't asking about my power supply specifically. See I'm designing a device that will calculate the power draw of each individual computer component (graphics card, hard drive, fan, mobo, etc) by measuring the current and voltage rails while in use. I'm trying to figure out a way for me on the measurement side to distinguish if I'm dealing with a single or multi-rail so I can use the correct formulas.
> 
> (Yes I'm the same guy who responded to your PSU Calc thread on HwC)


Derp, just realized that as I saw your user name.









I'd have to have a clearer idea of what you're doing and what you have so far. Are you using a set of ammeters, or a clamp meter, or? Let's continue this in PM.


----------



## oke

I have a small question.
I have an msi r5670 graphics card. It requires 26A on 12V. I could get myself a psu with 4x18A. The card has no PCI-e extra power connector. Will it get enough juice off the rails without triggering OCP? Maximum for the psu is total about 50A.


----------



## Original Sin

Quote:


> Originally Posted by *oke;15631656*
> I have a small question.
> I have an msi r5670 graphics card. It requires 26A on 12V. I could get myself a psu with 4x18A. The card has no PCI-e extra power connector. Will it get enough juice off the rails without triggering OCP? Maximum for the psu is total about 50A.


Yes, the 26A recommendation is for the entire system.. that card can hardly pull 10A


----------



## oke

Thanks a lot , i always wondered how the hell it could pull so much, lol.


----------



## chrisguitar

So would the Silverstone ST75F-G and the ST85F-G be good?


----------



## Jayjr1105

Very good reading in the OP. However I still have a question. How do you compare a dual vs single in amperage. Do you add up the amperage on the 2 rails of the dual and compare it to the amps on the one 12v+ rail of the single?

For example, would the 12v+ amperage on this power supply be 69A?...
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371016


----------



## DarthBaiter

Sry, TLTR

single rail










multi rail










J/K

Phaedrus2129, I learn something new every time I read your posts.


----------



## DuckieHo

Quote:


> Originally Posted by *Jayjr1105*
> 
> Very good reading in the OP. However I still have a question. How do you compare a dual vs single in amperage. Do you add up the amperage on the 2 rails of the dual and compare it to the amps on the one 12v+ rail of the single?
> For example, would the 12v+ amperage on this power supply be 69A?...
> http://www.newegg.com/Product/Product.aspx?Item=N82E16817371016


No.... it has to tell you the combine max current. In your example, it says 12V1+12V2+12V3 = 444w (37A).

Some cheap PSUs don't tell you this information and just label the unit as higher rating. Never buy these.

i.e. You have a big pipe capable of 37gal/min. You connect three 18gal/min pipes to it. How do you know the max capacity of the system with only the knowledge of the three smaller pipes? You can't.


----------



## Jayjr1105

Quote:


> Originally Posted by *DuckieHo*
> 
> No.... it has to tell you the combine max current. In your example, it says 12V1+12V2+12V3 = 444w (37A).
> Some cheap PSUs don't tell you this information and just label the unit as higher rating. Never buy these.
> i.e. You have a big pipe capable of 37gal/min. You connect three 18gal/min pipes to it. How do you know the max capacity of the system with only the knowledge of the three smaller pipes? You can't.


Got it. Makes sense now. Check the sticker for the combined 12v+ wattage and divide by 12.

Edit: Ok... one last thing I'm curious about... When two high quality 500watt power supply's have different amperage on the 12v+ the extra watts/amps seem to get distributed between the +3.3v and +5v on the unit with the lower +12v amperage rating. What is the advantage ~disadvantage to this?


----------



## Selquist979

Glad I saw this at the top of the PSU thread. my mates and I were debating this the other day. now I can come into the fray better informed!


----------



## itzzjason

Quote:


> Originally Posted by *Phaedrus2129*
> 
> So final verdict? Single rail or multi rail? Well, with low-wattage units it doesn't matter. OCP on a single rail is useful up to about 40A or thereabouts, which is where most 550W power supplies fall. So with 550W and under power supplies, it's a moot point. However, with high wattage units, >45A on the +12V (650W and higher) picking a multi-rail unit will provide you with an extra layer of protection. It isn't essential, and it has no impact on the power supply's performance. However, it does provide an extra layer of safety in case you get a short circuit. And I would consider it a must for >1000W power supplies; [H] recently tested the single rail Corsair AX1200, but they had an accidental short circuit, and since the PSU's OCP is set for over 100A, the short overloaded and destroyed most of their testing equipment. So there is a danger with single rail units over 1000W.
> 
> So multi-rail is mildly better, especially with high wattage units, but it won't have any impact on your performance or overclockability.


How come I don't see more multi-rail PSUs in OCNer's sig rigs?
I'm also looking for a multi-rail PSU with 1000+ watts for multi gpu setup


----------



## bR0ken_pr0Jector

Quote:


> Originally Posted by *itzzjason*
> 
> How come I don't see more multi-rail PSUs in OCNer's sig rigs?
> I'm also looking for a multi-rail PSU with 1000+ watts for multi gpu setup


Because a lot of people are still paranoid/uninformed about them even though there is no reason to be. And single rail PSU's still dominate the market.


----------



## itzzjason

Quote:


> Originally Posted by *bR0ken_pr0Jector*
> 
> Because a lot of people are still paranoid/uninformed about them even though there is no reason to be. And single rail PSU's still dominate the market.


I'm trying to buy a 1000+ watt PSU, and the OP says it's a MUST for 1000+ watt PSUs
So should I still be looking for a multi-rail or just buy a Corsair AX1200 or Seasonic Platinum 1000?


----------



## bR0ken_pr0Jector

Quote:


> Originally Posted by *itzzjason*
> 
> I'm trying to buy a 1000+ watt PSU, and the OP says it's a MUST for 1000+ watt PSUs
> So should I still be looking for a multi-rail or just buy a Corsair AX1200 or Seasonic Platinum 1000?


I'd buy one for the safety net in the event a short occurs as was described in the OP. You don't _have_ to buy a multi-rail PSU, but it's just a better idea to do get one anyway at such high wattage.


----------



## itzzjason

Quote:


> Originally Posted by *bR0ken_pr0Jector*
> 
> I'd buy one for the safety net in the event a short occurs as was described in the OP. You don't _have_ to buy a multi-rail PSU, but it's just a better idea to do get one anyway at such high wattage.


Where can I find multi rail PSUs? All the good ones are single rail (Corsair AX1200, Seasonic Platinum 1000, Seasonic X series, etc)


----------



## qwan456

Quote:


> Originally Posted by *itzzjason*
> 
> Where can I find multi rail PSUs? All the good ones are single rail (Corsair AX1200, Seasonic Platinum 1000, Seasonic X series, etc)


The Lepa G1600-MA, Enermax Platimax 1200w, Antec High Current Pro 1200w, XFX Pro Series 1250W (labeled as a single rail but in actuality a multirail - the same goes for the Seasonic X-1250 that the XFX is base on), and a few others.

Now the question is what are your graphic card setup? The Gaming V1 specification can be powered on a quality 850w even if you were to Tri-SLI a GTX680.


----------



## itzzjason

Quote:


> Originally Posted by *qwan456*
> 
> The Lepa G1600-MA, Enermax Platimax 1200w, Antec High Current Pro 1200w, XFX Pro Series 1250W (labeled as a single rail but in actuality a multirail - the same goes for the Seasonic X-1250 that the XFX is base on), and a few others.
> Now the question is what are your graphic card setup? The Gaming V1 specification can be powered on a quality 850w even if you were to Tri-SLI a GTX680.


The x-1250? Really? But even the seasonic website says it's single rail though


----------



## Vuashke

what are you going to trust, reviews done by knowledgeable people with electronics backgrounds or corporate marketing?


----------



## itzzjason

Quote:


> Originally Posted by *Vuashke*
> 
> what are you going to trust, reviews done by knowledgeable people with electronics backgrounds or corporate marketing?


But even the reviews say it's single rail though and that's who I trusted in the first place


----------



## Original Sin

Quote:


> Originally Posted by *itzzjason*
> 
> But even the reviews say it's single rail though and that's who I trusted in the first place


It's a quad rail design.


----------



## itzzjason

Quote:


> Originally Posted by *Unoriginal Sin*
> 
> It's a quad rail design.


Really?! Proof please
















I'll definitely buy it if I see the proof


----------



## Original Sin

Quote:


> Originally Posted by *itzzjason*
> 
> Really?! Proof please
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> I'll definitely buy it if I see the proof


Doing research, while scary, won't make you sick... no chlamydia, no leprosy, no nothing...

ps. read *this* thread.


----------



## mrwesth

A few questions:
Is there a min watt where multiple 12v rails would be unnecessary?
You compare the rails to a circuit breaker--what happens when that circuit overloads in a psu? Does cycling power of and on "flip the breaker" or what exactly?
Do multiple rails limit power draw to certain connectors? Such as the pcie connectors--could they not draw more then X watts on a 2X total watt PSU?

Would single rail PSUs benefit from larger gauge wire or would that just move any potential fire from fault to system component as opposed to wiring?

PS I'm an economics guy--all this stuff is a hobby so bare with me


----------



## Original Sin

Quote:


> Originally Posted by *mrwesth*
> 
> A few questions:
> Is there a min watt where multiple 12v rails would be unnecessary?


This question has no correct answers.... presuming you buy a proper PSU for your hardware(not oversized and not undersized), up until ~800W the rail configuration doesn't really matter... beyond that, a multi-rail PSU it's safer, because beyond that you'll probably be running some very demanding hardware, which can in some circumstances overload various connectors which then melt and things go from bad to worst really fast.
Quote:


> Originally Posted by *mrwesth*
> 
> You compare the rails to a circuit breaker--what happens when that circuit overloads in a psu? Does cycling power of and on "flip the breaker" or what exactly?


When a rail gets overloaded the OCP triggers, and it safely shuts down the system.
Quote:


> Originally Posted by *mrwesth*
> 
> Do multiple rails limit power draw to certain connectors? Such as the pcie connectors--could they not draw more then X watts on a 2X total watt PSU?


Yes.
Quote:


> Originally Posted by *mrwesth*
> 
> Would single rail PSUs benefit from larger gauge wire or would that just move any potential fire from fault to system component as opposed to wiring?


That is a correct assumption, a larger gouge will benefit single rail units just as much as it will multi-rails.


----------



## Vuashke

Quote:


> Originally Posted by *itzzjason*
> 
> But even the reviews say it's single rail though and that's who I trusted in the first place


http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=273

"So what's the deal? Well, it turns out that EasyRail isn't EasyRail after all. This power supply actually has four +12V rails. "
"EasyRail is a marketing term for a single +12V rail, but this power supply has four +12V rails."


----------



## eXXon

One of the coolest reads period. I never LOL when trying to learn something, but this read made me crap my pants









I have a 4 year old PSU which I wanted to replace (due to its 'old-tech' multi rail design) with the new & 'better' single rail design but then I read this thread and it just made my day (& saved me cash).

However, it seems my PSU is 2 units joined by a single PCB, which according to the OP is not a good (cheap) design.

Should I be worried?

EDIT: no need for 'proof' or reviews......


----------



## Phaedrus2129

It's not cheap. In fact it's very expensive to manufacture. It was just easier to design that way back in 2007, when CWT realized that everyone else was making 1kW+ power supplies and they hadn't done the research on transformer technology needed to match those designs. So they "cheated" and put two PSUs on one PCB, giving them a serviceable 1kW+ design in a minimum amount of time, and it actually happened to outperform much of the competition at the time too. It's a little long in the tooth now, but it's still a quality power supply and _*ridiculously*_ overkill for your needs. It should do fine.


----------



## eXXon

Thx for clearing it up & cheers for the quick response.

Still one of the best Threads out there....


----------



## eXXon

Quote:


> Originally Posted by *Phaedrus2129*
> 
> .......and _*ridiculously*_ overkill for your needs.......


Back then, I thought PSU's loose some of thier output power over the years(10% every year but no more than 50% overall) & I needed mine to last for 5+ years for all my upgrades. I also thought they worked best @ 50% load (I think my 2x275GTXrig consumed 750watts so I went looking for +1.5kwatt PSU's) .
That's why I got the biggest I could find .....back then.

Is that true btw, time does damage the PSU's power output? what about ripples, do they increase as the PSU ages?

Cheers


----------



## Phaedrus2129

A quality PSU generally does not degrade significantly over its intended lifetime (warranty length basically). Ripple might drift up 10-20mV over the years and it might develop a quirk or two, but a quality PSU should last a long time.

Now, if the manufacturer uses cheaper capacitors than are necessary to last out the warranty period, you might get issues. Like if a company uses Taiwanese capacitors in a PSU with a 5+ year warranty, or if Chinese capacitors are used in a PSU with a 3+ year warranty, or if Fuhjyyu or ChengX capacitors are used period. Then ripple might increase by 20-50mV and if the primary capacitors degrade the total output capability could decrease as well.

However, your PSU and most PSUs recommended on Overclock.net are not subject to that type of degradation and should maintain acceptable performance throughout their lifetime.


----------



## bengal

Ok, lets say a graphics cards requires 30A on the +12v rail. Would it be better to have a single 30A rail or two 15A rails?


----------



## Phaedrus2129

Quote:


> Originally Posted by *bengal*
> 
> Ok, lets say a graphics cards requires 30A on the +12v rail. Would it be better to have a single 30A rail or two 15A rails?


Irrelevant. The quality of the power supply matters much, much more than what rail configuration it has.


----------



## bengal

Quote:


> Originally Posted by *Phaedrus2129*
> 
> Irrelevant. The quality of the power supply matters much, much more than what rail configuration it has.


So what you are saying is it doesn't matter? Either of the PSUs can run the 30A card perfectly fine?


----------



## mikeaj

Quote:


> Originally Posted by *bengal*
> 
> Quote:
> 
> 
> 
> Originally Posted by *Phaedrus2129*
> 
> Irrelevant. The quality of the power supply matters much, much more than what rail configuration it has.
> 
> 
> 
> So what you are saying is it doesn't matter? Either of the PSUs can run the 30A card perfectly fine?
Click to expand...

It's just a matter of safety trip points, where the cables are hooked up. If they're set stupidly, then you can have limits reached while running a legitimate, intended load, resulting in unintended shutdowns (false alarms, pretty much). Every multi-rail PSU in modern times has sensible trip points and rail configurations, and you'll never trip the protections unless there's actually a problem like a short circuit. If you have fewer of them (single rail), then they might not catch an actual problem that another design could have, like an unintended short circuit. There's no difference in other electronics and power output quality or reliability.

Depending on the specifics of your hypothetical example, like what the limits are set to and which wires are distributed to which rails, the one with two 15A rails may trip the safety protection feature (during normal operation, so not desired behavior) and thus not work. That's because your hypothetical example is not realistic.


----------



## eXXon

Quote:


> Originally Posted by *bengal*
> 
> So what you are saying is it doesn't matter? Either of the PSUs can run the 30A card perfectly fine?


Dude, Rail is not power. Its like a fuse that cuts off power when its maximum is reached....and it shouldn't/can't determine the quality of the PSU.


----------



## eXXon

Mr. Phaedrus2129

Is this PSU recommended ? for 169$
http://www.amazon.com/gp/product/B00607JL5C/ref=s9_simh_gw_p147_d0_i2?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=138ZRAA4KXR8FPVXWD2B&pf_rd_t=101&pf_rd_p=1389517282&pf_rd_i=507846

Can I also ask about your thoughts on EVGA's 1500 PSU with thier funky software?
EDIT: they implemented 'Single & Multi' rail design in it which is controlled by the software.


----------



## Phaedrus2129

The X1050 is an excellent power supply.

I actually worked for EVGA and worked on the NEX1500. My opinion on it is complicated and involves information that would get me sued for posting it on a public forum. In general though, it's a good powersupply, it has a couple shortcomings, but it also has a lot of cutting edge features and the highest power output on the market. I would not hesitate to use one myself.


----------



## eXXon

Quote:


> Originally Posted by *Phaedrus2129*
> 
> The X1050 is an excellent power supply.
> I actually worked for EVGA and worked on the NEX1500. My opinion on it is complicated and involves information that would get me sued for posting it on a public forum. In general though, it's a good powersupply, it has a couple shortcomings, but it also has a lot of cutting edge features and the highest power output on the market. I would not hesitate to use one myself.


Thanks mate


----------



## eXXon

deleted


----------



## viprk24

I honestly don't care about RAILS but the power behind the trololol story got me hooked


----------



## bfromcolo

So if I am understanding this correctly I don't need to worry about choosing the "right" cables of a power supply with a split 12v rail to avoid overloading one rail?

Case in point cheap crap old power supply from parts bin apevia win-500xspx http://www.apevia.com/ProductsInfo.asp?KEY=WIN-500XSPX which has a split 12v rail.

I am building a system from the parts bin to play with the Linux Steam Beta. The GPU is a GTX-260 which requires 2 6-pin connectors, power supply has one and for the other I was going to use a 4-pin to 6-pin adapter. The rest of the parts are fairly low power, Gigabyte mATX mobo, e5400 CPU, Artic 7 low profile cooler, 2x2G DDR2-800, ATA WD 80G HDD and generic CD/DVD, and a couple case fans.

Should be plenty of power for everything, so long as everything isn't trying to use one rail for all the +12v.

Thanks as usual.


----------



## Phaedrus2129

Actually it's a single rail, they just say it has two rails because flargleboopadougablargh. Piece of crap though, no GTX260 deserves that thing.


----------



## bfromcolo

Quote:


> Originally Posted by *Phaedrus2129*
> 
> Actually it's a single rail, they just say it has two rails because flargleboopadougablargh. Piece of crap though, no GTX260 deserves that thing.


Ha! Well the GTX260 came out of my kids system and served him well for years, I doubt its worth much at this point considering the power it consumes and heat it generates, and its got about the horse power of a $100 card these days. Seems to work fine, I got it up and running under Ubuntu with the Steam Linux Beta this evening. Haven't had a chance to push it yet.

I tried googling "flargleboopadougablargh" no luck.

Thanks


----------



## Phaedrus2129

It's not just about the performance man, it's the legacy too. The GTX260 was one of the great cards of the last few years. I say any card that was fairly high-end upon release and was widely used deserves a measure of respect, out of nostalgia at least.

Seems like a card that's brand new is treated like a god, one year old and it's an old warhorse, two years old and it's a clunker, three years old and it's junk... Then five or six and suddenly it's a great nostalgic piece.


----------



## nyxagamemnon

So what happens when Multi Rail can't support your hardware?

4x titans watercooled oc 3930K there are times I pull more than 25A off the rail and sys shuts down I have to use single rail mode on a EVGA Nex 1500


----------



## PsyM4n

There's no such thing as "multi-rail" not supporting your hardware. It's all about the implementation. It depends on the limits set by the manufacturer. The stuff Delta makes for Antec for example have quite high amperage limit per "rail".

Also, the rail explanation on this thread while not plain wrong, is quite inaccurate.

Physically speaking, an electrical rail, by definition, starts from the output source (the transformer or the voltage regulator). So in that sense (literally) most atx power supplies are physically single rail when it comes to the 12v output. Exclusions exist in the form of some exotic high power power supplies that actually are two power supplies in a single housing (thermaltake had some of those if i recall).

Now, you could make a power supply with as many "rails" as its output wires as long as you had enough resistors and ICs for current limiting... and plenty of room. That would be the absolute best approach in terms of both performance and safety, without putting any nonsensical limitations to the end user, but of course it'd be prohibitively expensive.

Again, resistor and IC pairs that limit the current do not magically create rails. Not in a physical sense. But they actually do it in a virtual sense. However, keep in mind that you can just short circuit the outputs with each other using a piece of metal/copper/etc and get rid of the multiple "rails" on most multi-rail implementations (some of them even actually do that, see some Enhance units). You could do it without sorting too if you had the resistors and ICs responsible taken out (which is harder to do without breaking the psu).

Anyway, the opener passes the message quite clearly and that's what really matters here.


----------



## davcc22

good read man verry intesring im thing of getting into testiong and revewing powersupplys but it cots a load to set i heard


----------



## cjc75

Tried reading through this, but I still have questions...

SO!

I am looking at getting a better quality PSU to support a better quality GPU.

For example, I am looking at the Seasonic 620w models, and they all list that they have multiple 12v rails at 24A each. But the video card I am looking at, states that it requires 42A on a single 12v rail...

So how can they be safely run on one of those Seasonic 620's if they're only putting out 24A on each rail, and then would it not be safer to get a PSU with a single rail putting out say 52A on that rail?


----------



## Diablosbud

Thanks for making this thread, one day I hope to understand as much as you do about power supplies.


----------



## Dt_Freak1

cjc75, the seasonic 620 watt power supply will easily handle the graphics card you mention just on power specifications. the multirail design has over current protection and would shut down if it were overdrawn. the unit your asking about is known to put out more then 620 watts at maximum draw anyway. realistically speaking that seasonic 620 watt should easily produce about 700 watt at max draw. and again with the over current protection if the unit senses it will over current it will shut down.


----------



## DrClaw

if i dont have any graphics cards installed atm, should i still enable OCP? i have an ax1200i and i removed my gpu earlier, going to get a few 290s soon, in the meantime i dont expect a short circuit but still wondering if enabling it would do any good without gpus installed?


----------



## sergeym

Why would you disable it in the first place? It does not affect performance in any way.


----------



## DrClaw

i never disabled it, its automatically off, im using corsair link software to monitor my power draw,

What confuses me is that it lists OCP under PCIe1-8
see look


so there are 8 slots to customize the ocp amperage, up to 40(20 @ default), but i have no graphics cards installed, so would it be useful to enable ocp, or does it only protect whats installed in these slots
heck i dont even have that many pci slots but i heard operating systems or bios? can only detect max 8 gpus, so maybe thats why
there are 8 slots


----------



## IMKR

good read. however, there is 1 thing that i dont understand still.
Quote:


> Multiple rail: each trace is monitored separately, so if, say, one trace goes over 25A the power supply will shut down.
> 
> Single rail: all traces are monitored all together, so if the total current going through the +12V outputs goes over, say, 60A, the power supply will shut down. Alternatively, no OCP may be present at all on the +12V rail.


first, with this quote.
this is what im getting.

"lets say a PSU has a two rails with 18A on the 12v rail. this means that if 1 of the rails passes 18A, the PSU will shut down to protect itself"
"for the single rail psu, if it has 40A on the rail, of all amps combined is 40A or higher, it will shut down"

correct?

however, in this two cases, which has a better 12v rail current tolerance? i was told when buying a PSU, to pay attention to the 12v rail. thus, one of the factors for me in buying a PSU is to have a high current on a 12v rail. (like the rose will capstone 450W has like 40A, single rail)

however, in a dual rail with 18A, how can I understasnd if its good or not? is it equivalent to a single 36A 12v rail? (18A x 2rails = 36A)


----------



## DrClaw

if you turn on the rail protection the powersupply will shut off to protect one particular rail

thats why its good to have ocp on, overcurrent protection for as many rails as you have running, your graphics card or pci express x16 is one slot. Therefore turning on ocp is good to protect even just one rail

my ocp is rated maximum at 40 amps, if i leave it off, then the default ocp for the entire powersupply is much greater and i can risk frying the whole system. OCP for each rail turned on is good so you cut your losses in the event of over-current

now the problem is i dont know what to set ocp to for each rail on my system, i only have one r9 290, im guessing the amps it pulls on 12v rail, thats the number i set the ocp to?
obviously not for every rail, just the rail for pci-express 2 slot, the mobo does name each slot if you look at it carefully.


----------



## INCREDIBLEHULK

Trying to understand a bit more, instead I am confusing myself.

Let's say I have 2 system with 2 cards, one with 290x and one with 780ti kpe.

One runs a Lepa G1600 with 6 12v rails of 20/30A

One runs a Supernova 1300G with 1 12v rail of 108A

I understand on the single rail I would need to surpass 108A really strong to short circuit and by then risk all the components melting into liquid metal. In this sense the multi rail offers that added protection as mentioned

What I don't understand is, how will a Lepa 1600 with rails limited to 20A and 30A power a 30A++ card off one rail, one connector has 2x 8pin pci-e. One rail provides less Amps than the card requires. Does this mean I need to use 4 seperate wires and power up the 2 cards with only 1 set of the 8pins from each?

Now for the system with the 780ti KPE overclocked which is going to pull insane amount of power. Do I literally connect 3 seperate cables (3 seperate rails) to deliver the power to one card?

I do not know at what point I am getting this mixed up and will appreciate any help


----------



## PsyM4n

Quote:


> Originally Posted by *INCREDIBLEHULK*
> 
> I do not know at what point I am getting this mixed up and will appreciate any help


You get this mixed up from the start.

The medium used to bear the electricity (wires have this role here) has its limitations. When the said limit is reached, various side-effects take place.
The limitations of standard wires used for power delivery depend on many factors, such as the wire width and length, the way its connected and the environmental variables. The typical limit of the standard 18AWG wires used on ATX power supplies is around 10 amperes, with the recommended being 2-3 amperes less.
Amongst the most visible side-effects of a wire reaching its limit is the high increase in its temperature, resulting in potential fire hazard.

The role of "rails" on most ATX power supplies is to try and detect when the wires get overloaded and have the power supply turn itself off, in order to avoid caching fire.
A power supply using a single "rail" essentially has the amperage limit (the one used to turn itself off) set too high. It does not protect the wires from being overloaded.
Multy-rail power supplies do that (in theory, if made properly), but if the limit is set too low, or if your hardware does not confront to the standard specifications, then they turn themselves off without reason.

Now, the Lepa G1600 has a 30A limit on the PCIe power cables (that's 360w) and the 290x draws less than 360w, so as long as you use one card per rail it won't turn-off. The question however, is if the 30A limit really represents the properties of the wires, or if even that limit is set too high.


----------



## INCREDIBLEHULK

Quote:


> Originally Posted by *PsyM4n*
> 
> You get this mixed up from the start.
> 
> The medium used to bear the electricity (wires have this role here) has its limitations. When the said limit is reached, various side-effects take place.
> The limitations of standard wires used for power delivery depend on many factors, such as the wire width and length, the way its connected and the environmental variables. The typical limit of the standard 18AWG wires used on ATX power supplies is around 10 amperes, with the recommended being 2-3 amperes less.
> Amongst the most visible side-effects of a wire reaching its limit is the high increase in its temperature, resulting in potential fire hazard.
> 
> The role of "rails" on most ATX power supplies is to try and detect when the wires get overloaded and have the power supply turn itself off, in order to avoid caching fire.
> A power supply using a single "rail" essentially has the amperage limit (the one used to turn itself off) set too high. It does not protect the wires from being overloaded.
> Multy-rail power supplies do that (in theory, if made properly), but if the limit is set too low, or if your hardware does not confront to the standard specifications, then they turn themselves off without reason.
> 
> Now, the Lepa G1600 has a 30A limit on the PCIe power cables (that's 360w) and the 290x draws less than 360w, so as long as you use one card per rail it won't turn-off. The question however, is if the 30A limit really represents the properties of the wires, or if even that limit is set too high.


Understood







thank you PsyM4n
With that being said, If I choose to put a card that eats up more than 40-50A when overclocked during load, I would realistically have to have it connected to multiple rails in order for that power supply to feed it power or it would be continually shutting off?


----------



## PsyM4n

Quote:


> Originally Posted by *INCREDIBLEHULK*
> 
> Understood
> 
> 
> 
> 
> 
> 
> 
> thank you PsyM4n
> With that being said, If I choose to put a card that eats up more than 40-50A when overclocked during load, I would realistically have to have it connected to multiple rails in order for that power supply to feed it power or it would be continually shutting off?


In theory, that's pretty much it. In practice, it depends on the actual limit, for the listed limit is sometimes less than the actual limit. A power supply might list a 30A limit, but in practice the limit might be set a few amperes higher.


----------



## DrClaw

anybody know the max amperage for r9 290 on 12v rail?


----------



## eXXon

Quote:


> Originally Posted by *INCREDIBLEHULK*
> 
> Understood
> 
> 
> 
> 
> 
> 
> 
> thank you PsyM4n
> With that being said, If I choose to put a card that eats up more than 40-50A when overclocked during load, I would realistically have to have it connected to multiple rails in order for that power supply to feed it power or it would be continually shutting off?


I think you misunderstood the OP.

The power delivery of a multi-rail & a single-rail PSU is exactly the same. Their shut off points (a.k.a. Rails) are set up differently (single-rail will have a higher shut off point than its multi-rail twin), that's about it.

So all you need is a decent PSU that can handle your +12v line requirements.

In your case, for a single GPU to consume 500w-600w under load is extremely unlikely unless under LN2 with very high volts (think 290X or 780Ti with +1.4v).

However, any 900w - 1Kw PSU would have no problem powering the system. Although, for such extreme OCs, you might be better off with a single or dual rail PSU.

Quote:


> Originally Posted by *DrClaw*
> 
> anybody know the max amperage for r9 290 on 12v rail?


Peak power consumption for a stock R9-290 is around 265w. 265w/12v= 22.08A. (Source).


----------



## DrClaw

Quote:


> Originally Posted by *eXXon*
> 
> In your case, for a single GPU to consume 500w-600w under load is extremely unlikely unless under LN2 with very high volts (think 290X or 780Ti with +1.4v).
> 
> However, any 900w - 1Kw PSU would have no problem powering the system. Although, for such extreme OCs, you might be better off with a single or dual rail PSU.
> Peak power consumption for a stock R9-290 is around 265w. 265w/12v= 22.08A. (Source).


thanks man, i want to enable ocp protection in the rail for my gpu









also how do you put that database link in your sig? dont mind me if i do the same?


----------



## twerk

Quote:


> Originally Posted by *DrClaw*
> 
> thanks man, i want to enable ocp protection in the rail for my gpu
> 
> 
> 
> 
> 
> 
> 
> 
> 
> also how do you put that database link in your sig? dont mind me if i do the same?


Just click Edit Signature on your profile.



Here it is for you to copy and paste, to save you a bit of time.








Code:



Code:


Look up this [URL=http://www.overclock.net/t/183810/faq-recommended-power-supplies]Database[/URL] before buying a PSU.


----------



## eXXon

Quote:


> Originally Posted by *DrClaw*
> 
> thanks man, i want to enable ocp protection in the rail for my gpu
> 
> 
> 
> 
> 
> 
> 
> 
> 
> also how do you put that database link in your sig? dont mind me if i do the same?


Just edit your sig like below and paste the link in it:


Edit: Ninja'd


----------



## hieb

Came across this on google, very good info.
So if I'm understanding correctly, since a "rail" is not a physical component so to speak, even if you have a multi-rail system you can support high-end GPUs just fine?

The way it sounded to me the power delivery on a "single rail" system is identical to a multi-rail PSU and it still uses multiple traces to deliver power, it's just monitored altogether when it comes to OCP... just want to clarify that it would be ok to use a GPU that requires more amperage than a single rail in a multi-rail PSU can provide?

e.g. if I have a PSU with 3 rails at 20A each, it would be okay to use a GPU that would require around 30A since the total power delivery can do so?

From what I gather it sounds like power delivery is split evenly (to some degree) across the "rails" and the OCP just prevents one rail from receiving a ****ton more amps than it is supposed to


----------



## shilka

Quote:


> Originally Posted by *hieb*
> 
> Came across this on google, very good info.
> So if I'm understanding correctly, since a "rail" is not a physical component so to speak, even if you have a multi-rail system you can support high-end GPUs just fine?
> 
> The way it sounded to me the power delivery on a "single rail" system is identical to a multi-rail PSU and it still uses multiple traces to deliver power, it's just monitored altogether when it comes to OCP... just want to clarify that it would be ok to use a GPU that requires more amperage than a single rail in a multi-rail PSU can provide?
> 
> e.g. if I have a PSU with 3 rails at 20A each, it would be okay to use a GPU that would require around 30A since the total power delivery can do so?
> 
> From what I gather it sounds like power delivery is split evenly (to some degree) across the "rails" and the OCP just prevents one rail from receiving a ****ton more amps than it is supposed to


You cant use a GPU that will draw more amps then the rail has, the result of that is the PSU will shut off, if its a decent one a crappy one might just die.


----------



## hieb

Quote:


> Originally Posted by *shilka*
> 
> You cant use a GPU that will draw more amps then the rail has, the result of that is the PSU will shut off, if its a decent one a crappy one might just die.


But in the original post it states that power delivery is the same, the only difference is how their power is monitored.

It sounded like the way it works is in a "single rail" system the power delivery is still using multiple traces, and it delivers power the exact same way as a multi rail system... the only difference being that if a single one of the "rails" gets too much power it shuts off, whereas in a single rail system if one of the rails (it still uses multiple rails to deliver power) gets too much power, it is more likely to be damaged since the PSU will not shut off until the overall power exceeds its rated 600W or whatever.

Can you explain further on your post please because it seems to go against what the OP states


----------



## shilka

Quote:


> Originally Posted by *hieb*
> 
> But in the original post it states that power delivery is the same, the only difference is how their power is monitored.
> 
> It sounded like the way it works is in a "single rail" system the power delivery is still using multiple traces, and it delivers power the exact same way as a multi rail system... the only difference being that if a single one of the "rails" gets too much power it shuts off, whereas in a single rail system if one of the rails (it still uses multiple rails to deliver power) gets too much power, it is more likely to be damaged since the PSU will not shut off until the overall power exceeds its rated 600W or whatever.
> 
> Can you explain further on your post please because it seems to go against what the OP states


Video cards draw power from the 12v rail(s), if you have a video card that draw 45 amps and your PSU only has 30 amps it does not matter if íts a single 30 amp 12v rail or 2x 15 amps rails rails its still too little power.


----------



## twerk

Quote:


> Originally Posted by *hieb*
> 
> But in the original post it states that power delivery is the same, the only difference is how their power is monitored.
> 
> It sounded like the way it works is in a "single rail" system the power delivery is still using multiple traces, and it delivers power the exact same way as a multi rail system... the only difference being that if a single one of the "rails" gets too much power it shuts off, whereas in a single rail system if one of the rails (it still uses multiple rails to deliver power) gets too much power, it is more likely to be damaged since the PSU will not shut off until the overall power exceeds its rated 600W or whatever.
> 
> Can you explain further on your post please because it seems to go against what the OP states


That is 100% correct. The reason multiple rails are used is mainly for safety. Think the circuit breaker in your house, the overall goal is to limit the power going through each wire.

You can draw the same amount of power from the PSU but you have to make sure you draw it evenly, if you plug a GPU that requires 30A into a single 20A rail, when you turn the computer on the OCP will kick in and the PSU will shut off immediately. So you just have to make sure to connect it up to two of the rails allowing you to draw a total of 40A.

Just as an example, triple rail PSU's normally have one rail to the CPU, one to the PCIe connectors and one to everything else. Although triple rail PSU's are rare nowadays.


----------



## hieb

Yes but what if it is monitored as 2 rails with 20A each but my GPU draws 25A. The total amperage is 40 which is more than enough, I just want to confirm basically that the power delivery is divided among the rails... because I know someone using EVGA SuperNova 650W, it has 4 12V rails with 20A each, and they run an overclocked GTX 780 Ti... its tdp is 250w at stock so i imagine overclocked it'd be using around 300W, which would be over 20A. So either he's getting lucky and it's just not quite drawing enough power to shut the PSU off or the power is divided over the different rails so it's taking maybe 13A on 2 dif rails


----------



## shilka

Quote:


> Originally Posted by *hieb*
> 
> Yes but what if it is monitored as 2 rails with 20A each but my GPU draws 25A. The total amperage is 40 which is more than enough, I just want to confirm basically that the power delivery is divided among the rails... because I know someone using EVGA SuperNova 650W, it has 4 12V rails with 20A each, and they run an overclocked GTX 780 Ti... its tdp is 250w at stock so i imagine overclocked it'd be using around 300W, which would be over 20A. So either he's getting lucky and it's just not quite drawing enough power to shut the PSU off or the power is divided over the different rails so it's taking maybe 13A on 2 dif rails


If he has money for a new PSU he should replace its not great.


----------



## hieb

Quote:


> Originally Posted by *twerk*
> 
> That is 100% correct. The reason multiple rails are used is mainly for safety. Think the circuit breaker in your house, the overall goal is to limit the power going through each wire.
> 
> You can draw the same amount of power from the PSU but you have to make sure you draw it evenly, if you plug a GPU that requires 30A into a single 20A rail, when you turn the computer on the OCP will kick in and the PSU will shut off immediately. So you just have to make sure to connect it up to two of the rails allowing you to draw a total of 40A.
> 
> Just as an example, triple rail PSU's normally have one rail to the CPU, one to the PCIe connectors and one to everything else. Although triple rail PSU's are rare nowadays.


Oh, okay. Thanks!


----------



## tuklap

Soo does a Cooler Master V1000 has OCP and considered Single rail?

Based on their site it does not have OCP and is Single Rail..
http://www.coolermaster.com/powersupply/v-series-psu/v1000/


----------



## shilka

Quote:


> Originally Posted by *tuklap*
> 
> Soo does a Cooler Master V1000 has OCP and considered Single rail?
> 
> Based on their site it does not have OCP and is Single Rail..
> http://www.coolermaster.com/powersupply/v-series-psu/v1000/


Its a single rail unit but its not a bad unit at all.


----------



## BrettJSr72

Makes more sense to me now AND helps me decide on what to look for for my next PSU. Great humor in explaining this.


----------



## Synthaxx

Really a good read and a very humouristic way of explaining it to dummies like me








But I still have some questions about multi vs single rail, and an application to my case, in which I would like your opinion.

I recently acquired 2 295x2s and I'm still in need of a PSU that can handle these beasts. The whole PC will need more than 1500watts, even more when I decide to overclock the GPUs. According to AMD, they recommend 28A per 8Pin, and each card has 2 8pins. More information about the requirements in this link:

I'm intrested in a PSU above 1600watts, and currently, I think I have 2 options.

Option 1
The EVGA supernova 1600 g2, single rail, 133Amps total.

Option 2
Lepa MaxPlatinum 1700w, can peak 1800watts, multirail, 141Amps(?) total
Officially, the lepa has 30A rails, but the 295x2 already uses 28A/8pin without an OC, isn't this too close?
So would I then need to use 4 different 12v rails for each 8pin?
I read somewhere that OCP triggers at 40-55A.

What would be best in my case? My case does not support dual PSUs, so that would require to much modifications...


----------



## eXXon

Quote:


> Originally Posted by *Synthaxx*
> 
> Really a good read and a very humouristic way of explaining it to dummies like me
> 
> 
> 
> 
> 
> 
> 
> 
> But I still have some questions about multi vs single rail, and an application to my case, in which I would like your opinion.
> 
> I recently acquired 2 295x2s and I'm still in need of a PSU that can handle these beasts. The whole PC will need more than 1500watts, even more when I decide to overclock the GPUs. According to AMD, they recommend 28A per 8Pin, and each card has 2 8pins. More information about the requirements in this link:
> 
> I'm intrested in a PSU above 1600watts, and currently, I think I have 2 options.
> 
> Option 1
> The EVGA supernova 1600 g2, single rail, 133Amps total.
> 
> Option 2
> Lepa MaxPlatinum 1700w, can peak 1800watts, multirail, 141Amps(?) total
> Officially, the lepa has 30A rails, but the 295x2 already uses 28A/8pin without an OC, isn't this too close?
> So would I then need to use 4 different 12v rails for each 8pin?
> I read somewhere that OCP triggers at 40-55A.
> 
> What would be best in my case? My case does not support dual PSUs, so that would require to much modifications...


Congratz on your new monster cards.

Just to clarify, an 8-pin PCIE connector is not a Rail. A Rail is the OCP trigger point on the 12V line and other minor Lines.

A single 295x2 requires around 500w from the wall under full load at stock speeds (source).

Add another stock 295x2 and they should pull around 1Kw from the wall under full load.

Depending on your setup, it would be rare to see 4 GPUs under 100% load for long durations in the real world (games/drivers are not coded well enough) unless you mainly bench/mine/fold...etc.

The G2 should be more than enough for your needs and it is an excellent PSU with one of the best OEMs/Outstanding warranty.


----------



## Synthaxx

Quote:


> Originally Posted by *eXXon*
> 
> Congratz on your new monster cards.
> 
> Just to clarify, an 8-pin PCIE connector is not a Rail. A Rail is the OCP trigger point on the 12V line and other minor Lines.
> 
> A single 295x2 requires around 500w from the wall under full load at stock speeds (source).
> 
> Add another stock 295x2 and they should pull around 1Kw from the wall under full load.
> 
> Depending on your setup, it would be rare to see 4 GPUs under 100% load for long durations in the real world (games/drivers are not coded well enough) unless you mainly bench/mine/fold...etc.
> 
> The G2 should be more than enough for your needs and it is an excellent PSU with one of the best OEMs/Outstanding warranty.


Thanks for your comment.
It's great to hear that the EVGA 1600 would suffice. I know that an ax1500i failed when both cards had a mild OC (1100/1400), while playing games, but maybe there were other factors involved (bad unit, many hdd/sdd,...).


----------



## zvonkorp

When i overvolt and oc my 290x's to 1.35 or more - the draw for each card is 480+ watts? Is that right?

I'm crypto mining right now at 1000/1500and i overvolted to 1.35 for this experiment, the power draw at the wall accordign to my killawatt is 1210 watts with bth gpus on and no load on the cpu

I disable one of the gpus and the load avg drops to about 730

Taking 730 from 1210 gives a final figure of 480 watts that isnt being drawn anymore by the card i just turned off

How is this possible?

The psu is a thermaltake 1350, which is a CWT puc unit with the dual psus on one pcb deal you mentioned in the OP

Is this even safe?!

Both cards are powercolor axr9290x-4gd5 oc reference models under water with EK full cover blocks (@60*c load if this makes any difference), with stock clocks that came at 1030/1250 flashed with the pt1 modified asus bios and overvolted/overclocked by sapphire trixx


----------



## twerk

Quote:


> Originally Posted by *zvonkorp*
> 
> When i overvolt and oc my 290x's to 1.35 or more - the draw for each card is 480+ watts? Is that right?
> 
> I'm crypto mining right now at 1000/1500and i overvolted to 1.35 for this experiment, the power draw at the wall accordign to my killawatt is 1210 watts with bth gpus on and no load on the cpu
> 
> I disable one of the gpus and the load avg drops to about 730
> 
> Taking 730 from 1210 gives a final figure of 480 watts that isnt being drawn anymore by the card i just turned off
> 
> How is this possible?
> 
> The psu is a thermaltake 1350, which is a CWT puc unit with the dual psus on one pcb deal you mentioned in the OP
> 
> Is this even safe?!
> 
> Both cards are powercolor axr9290x-4gd5 oc reference models under water with EK full cover blocks (@60*c load if this makes any difference), with stock clocks that came at 1030/1250 flashed with the pt1 modified asus bios and overvolted/overclocked by sapphire trixx


The 290X definitely won't be drawing 480W on it's own, especially at stock clocks.

A 1000MHz/1.35V 290X will draw around 351W +/-5%. Even if you overclocked it to 1200MHz and upped the voltage to 1.4V it would still draw less than that, at around 453W.

Are you taking efficiency into account? At that sort of power draw your PSU will be roughly 86-87% efficient.


----------



## zvonkorp

Quote:


> Originally Posted by *twerk*
> 
> The 290X definitely won't be drawing 480W on it's own, especially at stock clocks.
> 
> A 1000MHz/1.35V 290X will draw around 351W +/-5%. Even if you overclocked it to 1200MHz and upped the voltage to 1.4V it would still draw less than that, at around 453W.
> 
> Are you taking efficiency into account? At that sort of power draw your PSU will be roughly 86-87% efficient.


Thats what i forgot. Efficiency LOL thank you so much for remind ingme!


----------



## jdstock76

Good reading. Thank you OP!


----------



## kallamamran

F**k! I really thought I'd find the answer in this text, but I didn't.

I have a multi-rail PSU 22+22+25+25A which previously ran a GTX970 with 8+6PIN ATX-power which would mean 22+22=44A maximum at least right?
Now I have installed a GTX 1070 with a single 8PIN AT-power and rumors say 1070 need 30A.

This might be a problem (If it's not my motherboard that is broken) right?

Having the card installed I lose 4/6 SATA-connectors and everything connected to those










Running benchmarks Time Spy lags incredibly and reports a result of 1.200p when it should be around 5.500p
FurMark works without pproblems though. So do Unigine benchmarks and gaming Dying Light for example

I don't get it!

I've even tried to pull the power to the GPU with two molex connectors and a Y-splitter to pull the power from two different rails. That didn't help other than I got my SATA-ports working again. The benchmarks still reports the same









I wonder if a Single rail PSU with +12V 50-60A would be a better choice!?


----------



## AverdanOriginal

Like @eXXon stated above, another 8+6pin pci or molex connector/cable isn't another rail.

I have a similar problem as you. I have the beQuiet Straight Power 10 600W CM and it has 4 rails 18/18/20/20.
After using many psu calculators and calculating the Wattage needed for my system, I came to the conclusion 600 Watt would be enough even if I do a good but not too aggressive overclock. (CPU i5-6600k @4.5GHz with 1.3V and MSI R9 390 @1150Mhz with mv+25). tests worked fine, but were a bit unstable.

now my R9 390 pulls about 19 Ampere when I don't overclock it and run heaven unigine (see gpu-z)

Once I put in +50mv to get a higher overclock the Ampere drawn, according to GPU-Z, is 23.2 (I even reached 25 in some cases). 

So 23 Ampere is of course way higher than 18 or 20 Ampere allowed per rail.
So i came to the conclusion that my PSU shuts down or puls back (or whatever) due to the relation Ampere needed to Ampere provided per rail. So I also used 2 different PCi connectors/cables from the PSU instead one 8+6, I used one 8, and another cable with 6 pins. that made it slightly more stable but still experienced dropouts.

Anyway, I am guessing (correct me if I am wrong) rails means it splitts the overall allowed Ampere to be more safe. Problem is, if you have one component that draws more Ampere than one of the rails, the comp might shut down due to safety reasons. And it does not mean, connecting more cables to that one component allows you to deliver more Ampere than per rail.

So in our case, we would need a psu with multi-rail Ampere of min 30 per rail (and then you find yourself in 850W PSU like the Dark Power) or single rail PSUs.
But I need a minimum of 650 Watt and 30 Ampere which leaves me with fairly expensive multi-rail PSUs or I go single rail with 50+ Ampere but that gets to unsafe for me, as I like to cut PSU cables to fit perfectly in my fairly small case Anidess A7.

The choices we have to make


----------



## P0V0

okie dokie could you tell me about whats good when it comes to designs that produce the rail in the first place say , buck converters or clamp circuit designs basically the dc to dc thingy
. see i have been through around 5 psu's in the last 5 years all differant sizes and sorts sometimes because i had pluged in video cards all on one cord which i have assumed is called a rail i am learning trying to at the moment i,l get it right this time .
what makes it hard is that the technology doesnt change it,s nappie quite as fast as intel and amd through my mobo and and cpu in the bin, and i still find myself looking up the same amazing psu that has awsome features that i did back when i was spooning over core proccesors and hdmi .
wiki pedia didnt help me much anymore then the guy at the computer store did infact they both think they know everything its just the guy at the computer store assures me that the x psu is capable of providing and wikipedia assures me that they are lying and using false advertising ect quote " many manufacturers have chosen to ignore the requirement and increase the current limits above 20 A per rail, or provide "single-rail" power supplies that omit the current limit circuitry. (In some cases, in violation of their own advertising claims to include it.[8]) The requirement was deleted from version 2.3 (March 2007) of the ATX12V power supply specifications.[9]
Because of the above standards, almost all high-power supplies claim to implement separate rails, however this claim is often false; many omit the necessary current-limit circuitry,[10] both for cost reasons and because it is an irritation to customers.[11] (The lack is sometimes advertised as a feature under names like "rail fusion" or "current sharing".)
i like nuc devices but i am trying to build a pc so any help about the electronics would be helpful ,
i think my biggest problem is i am trying to use a 95 watt high powered cpu on a device that only has around 120 watt being the 5 vlt and 3 vlt combined but only have 20 amps due to restriction associated with the 20 amp rule. (I wanna know about the device cause I don't always see the relevance mathematically between the amps and watts.) so it needs to be jerry rigged , so what ! also The board only uses 550 watts but i need around a 1000 watt to get it started and even then the whole machine runs at 0.5 amps which is just defeating the whole kinda idea in the first place. ( maybe jerry rig the 3 and 5 rails to be stronger or better and get rid of the excess watts outa the 12 volt main rail cause I was never really using them, then I just have to find a way to let it idle with out burning on the wires for no reason.) any way this time i hope i get a decent psu cause the guy down at the electronic repair man got to keep the last 4 or 5 cause he knows how to fix it probably but its kinda a hassle and cause the stickers have been removed its too hard to buy those parts ect ect.


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## AidanofVT

Thanks a lot. That explains it.


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