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-   -   Single vs. Multiple +12V rails: The splitting of the +12V rail (http://www.jonnyguru.com/forums/showthread.php?t=3990)

jonnyGURU 03-28-2008 11:20 AM

Single vs. Multiple +12V rails: The splitting of the +12V rail
 
What is "multiple +12V rails", really?

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

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

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

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

Safety. It's done for the same reason that there's more than one circuit breaker in your house's distribution panel. The goal is to limit the current through each wire to what that wire can carry without getting dangerously hot.

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

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

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

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

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

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

Why do some people FUD that single is better?

Because there are a few examples of companies that have produced power supplies with four +12V rails, something that in theory should provide MORE than ample power to a high end gaming rig, and screwed up. These PSU companies followed EPS12V specifications, which is for servers, not "gamers". they put ALL of the PCIe connectors on one of the +12V rails instead of a separate +12V rail. The +12V rail was easily overloaded and caused the PSU to shut down. Instead of correcting the problem, they just did away with the splitting of +12V rails altogether. Multiple +12V rail "enthusiast" PSU's today have a +12V rail just for PCIe connectors or may even split four or six PCIe connectors up across two different +12V rails. The rails themselves are capable of far more power output than any PCIe graphics card would ever need. In fact, Nvidia SLI certification these days REQUIRE that the PCIe connectors be on their own +12V rail to avoid any problems from running high end graphics cards on split +12V rail PSU's.
There's less components and less engineering to make a PSU that DOES NOT have the +12V rail split up, so it's cheaper to manufacturer (about $1.50 less on the BOM, $2 to $3 at retail) and typically this cost savings is NOT handed down to the consumer, so it actually behooves marketing to convince you that you only need single +12V rails.

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

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

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

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

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

Example 1:

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

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

Example 2:

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

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


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

The criteria for buying a PSU should be:
  • Does the PSU provide enough power for my machine?
  • Does the PSU have all of the connectors I require (6-pin for high end PCIe, two 6-pin, four 6-pin or even the newer 8-pin PCIe connector)?
  • If using SLI or Crossfire, is the unit SLI or Crossfire certified (doesn't matter if a PSU is certified for one or the other as long as it has the correct connectors. If it passed certification for EITHER that means it's been real world tested with dual graphics cards in a worst case scenario).
Figure out if there are any variables that may affect the actual output capability of the PSU:
  • Is the PSU rated at continuous or peak?
  • What temperature is the PSU rated at? Room (25 to 30C) or actual operating temperature (40C to 50C)
  • If room temperature, what's the derating curve? As a PSU runs hotter, it's capability to put out power is diminished. If no de-rate can be found, assume that a PSU rated at room temperature may only be able to put out around 75% of it's rated capability once installed in a PC.
After that, narrow selection down with finer details that may be more important to others than it may be to you....
  • Does the unit have power factor correction?
  • Is the unit efficient?
  • Is the unit quiet?
  • Is the unit modular?
  • Am I paying extra for bling?
  • Do I want bling?

brax 03-28-2008 11:50 AM

Very good!
Can someone tell me how the rails are splited on Toughpower 750w w116ru?
TT has one 8Pci-e and two 6Pci-e connectors,are they split from +12 (Motherboard) and other molex? if not what they are share?
thanks.

jonnyGURU 03-28-2008 12:11 PM

It's actually in the manual and the review:

http://www.jonnyguru.com/modules.php...p=Story&reid=7

The 24-pin and fixed PCIe are on one rail, the 4-pin/8-pin ATX12V/EPS12V are on another rail, the two modular PCIe are on a third rail and all of the Molex and SATA are on a fourth rail.

brax 03-28-2008 12:16 PM

thank you very much!

spursindonesia 03-28-2008 03:19 PM

The GURU is in teaching/tutorial mode, then the pupils should listen & take notes. Great series of explanation jonny, i vote for stickies. :D That should make my job easier in helping my local IT forum members in getting the information they need regarding PSU issues -the wonderful world of web URL linking. ;)

jonnyGURU 03-28-2008 05:02 PM

Quote:

Originally Posted by spursindonesia (Post 37500)
The GURU is in teaching/tutorial mode, then the pupils should listen & take notes. Great series of explanation jonny, i vote for stickies. :D That should make my job easier in helping my local IT forum members in getting the information they need regarding PSU issues -the wonderful world of web URL linking. ;)

I didn't want to clutter the top of the forum with a bunch of stickies so what I've done is linked all of these new FAQ's in the one main FAQ that's already stuck to the top of the forum. ;)

g1raffe 03-29-2008 12:27 AM

Thanks for the read, was a good one.

Just have one question regarding systems with lots of HDD's, lets say 10..

10 HDD's can possibly create a startup power draw of ~300W if I'm not mistaken? With most of it being on the +12V? Assuming the MB doesn't offer any staggered spinup of HDD's or anything, is a single +12V rail PSU better for a situation with 10 or more HDD's?

Or are the molex and SATA power connectors shared around to different rails to avoid problems like this?

jonnyGURU 03-29-2008 12:43 AM

You have a motherboard that supports 10 HDD's????

g1raffe 03-29-2008 12:44 AM

No, just curious. ;)

spursindonesia 03-29-2008 02:26 AM

Quote:

Originally Posted by jonnyGURU (Post 37511)
You have a motherboard that supports 10 HDD's????

If the system uses a PCI controller or two, that scenario might very well be true, right ?:confused:

jonnyGURU 03-29-2008 09:14 AM

Quote:

Originally Posted by spursindonesia (Post 37519)
If the system uses a PCI controller or two, that scenario might very well be true, right ?:confused:

Yes. But the controller's not going to be on the motherboard. That's what I was saying. I would hope that if you had 10 HDD's on a computer you would have staggered start up regardless of what kind of PSU you had.

rip97000 03-29-2008 01:09 PM

jonnyGURU:

i recently saw a couple power supplies that could "switch" (auto and manual) between multiple 12v and a single 12v rail. would this also be a marketing gimic?

Quote:

On Tagan’s website they mention a “Turbo Mode” to which all six rails can auto-magically be converted into a single beady 12v rail.3dgameman.com
Quote:

Manual +12V rails “TURBO” mode can integrate +12V rails into single rail with more DC output for heavy +12V loading. technoyard.com

HOOfan_1 03-29-2008 02:22 PM

I am wondering if that just turns off the Over Current Protection or something.

cypherpunks 03-29-2008 02:27 PM

It's real, once you understand it...
 
Quote:

Originally Posted by rip97000 (Post 37529)
i recently saw a couple power supplies that could "switch" (auto and manual) between multiple 12v and a single 12v rail. would this also be a marketing gimic?

Well, once you understand that "multiple rails" is only about current limits, it should be blindingly obvious what that "feature" does: ignores the current limits. I've seen these "automatic rail fusion" lights, and that's simply connecting the overcurrent detector to an LED rather than shutdown.

So it depends on what you define as a "gimmick". It is something that the PSU does differently, and not just a fancy name for a feature that all PSUs have. But it is just a fancy name for a simple feature, and further misleads the people who think that the power the electric company provides to them is somehow different from the power it supplies to their neighbour.

rip97000 03-29-2008 02:46 PM

cypherpunks:
forgive me i have horrible spelling (gimic vs gimmick above)

i understand current limits and multiple rails, but i was asking more about what jonnyGURU said above (sorry i'm not good at these forums and explaining what i mean yet):
Quote:

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

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

HOOfan_1 03-29-2008 08:47 PM

Quote:

Originally Posted by rip97000 (Post 37535)

so are companies "fibbing" when they claim to switch between single and multiple rails?

looking at Jonny's review of the NZXT (built by Topower) I would say yes....looks like this PSU doesn't use OCP whether the switch is on multi or single

Makalu 03-30-2008 08:57 AM

Good work Jon...something about the "multiple rails trap power" FUD would be nice to see too.

Killy 03-30-2008 11:23 AM

So, in the end, a well done multi-rail psu > single rail?

Stefan555 03-30-2008 11:30 AM

I would say a well done multi-rail = single rail, no differences apart from rail distribution and safety

Smirnoff 03-30-2008 04:29 PM

Very enlightening, and bookmarked for later reference. I was one of those who fell for the "single rail good, multi rail bad" thing.

Spectre 03-30-2008 04:58 PM

Quote:

Originally Posted by rip97000 (Post 37529)
jonnyGURU:

i recently saw a couple power supplies that could "switch" (auto and manual) between multiple 12v and a single 12v rail. would this also be a marketing gimic?

The Topower units I have tested have all been single rail units even when the Turbo switch is supposed to be limiting the rails via the OCP circuit. So...........

cypherpunks 03-31-2008 01:10 AM

Quote:

Originally Posted by rip97000 (Post 37535)
I understand current limits and multiple rails, but i was asking more about what jonnyGURU said above (sorry i'm not good at these forums and explaining what I mean yet):

So are companies "fibbing" when they claim to switch between single and multiple rails?

Um, if you understand current limits and multiple rails, then I don't understand your question.

Oh! Maybe I do. Obviously, any company could advertise a feature they don't implement. I don't know enough to know how common that is.

And any company that claims to "automatically merge rails when needed" is saying that they "automatically disable the per-rail overcurrent shutdown before it triggers", which is a stupid way if saying "our per-rail overcurrent alarms are disabled", which is most easily implemented by simply omitting them altogether.

But ones that have a switch could do something. Whether they do or not is not something I can answer.

Killy 03-31-2008 04:40 PM

Ah, once jonny explains it it makes sense. I WAS wondering about whether rails were 'additive' or not. But in sum, it seems as if virtual rails are (in the Epsilon's case) tapped off a 56.666A rail and then have OCP put on it.

My next question would be: Why do they 'overspec' OCP on each rail? Why not do the math so that each virtual rail, fully loaded, would match the specs of the single rail?

jonnyGURU 03-31-2008 04:53 PM

Quote:

Originally Posted by Killy (Post 37671)
My next question would be: Why do they 'overspec' OCP on each rail? Why not do the math so that each virtual rail, fully loaded, would match the specs of the single rail?

They don't "overspec" it. Again, it's not a designation of capability.

What's considered "safe" is 20A, or 240VA. This is the limit the safety spec uses. Usually an 18A rated rail can do 20A peak. They "overspec" the rails to make sure there's almost twice as much power available to the connectors on the rail as the connectors would actually need. If they really DID take the +12V capability and divide it up evenly across the rails, then you REALLY WOULD have "trapped power". That's what makes the PCP&C FUD so laughable. NOBODY evenly divides the +12V into separate rails. Each rail IS "overspec", as you put it, because you do not want "trapped rails".

Stefan555 03-31-2008 06:50 PM

If we take Be-quiet Straightpower 550W as an example. It has the following spec:

+3.3V +5V +12V1 +12V2 +12V3 +12V4 -12V +5vsb
32A 30A 18A 18A 18A 18A 0,5A 3A

Total comibined output on +12V: 41A (492W) = The PSU's maximum capabiliy on +12V
On each rail on +12V we are allowed to draw 18A according to the spec. A theoretical maximum output of 4*18A = 72A (864W). But 864W is more than the PSU's total output of the psu (550W) and even more than the psu's capability on +12V, 41A (492W).

4*18A = 72A only tells us we are allowed to draw maximum of 18A on each of the four rails on +12V, but not on all of the rails at the same time. The maximum we can draw from +12V at the same time is 41A (492W).

The gap between the theoretical output on +12V of 72A (864W) and the capability of 41A (492W), is the headroom the spec gives us to use "unused amps" on one rail on +12V, on another rail on +12V.

In reality, the gap is bigger, all psu's with a specified maximum output of 18A on the rails, have an OCP which will shut the psu off if the draw from one of the rails on +12V exceeds 20, 22 or even 25A.

The OCP's are always programmed to shut the psu off at a higher current than specified on the label, no matter what is printed on the label.

cypherpunks 03-31-2008 09:19 PM

Quote:

Originally Posted by Stefan555 (Post 37679)
The OCP's are always programmed to shut the psu off at a higher current than specified on the label, no matter what is printed on the label.

Well, actually, the point is that there's some tolerance on the OCP threshold level. The value on the label is a "guaranteed not to shut down" number, while the 20 A limit in the ATX spec is supposed to be the "guaranteed to shut down" number. So they typically design them to 19 A, plus or minus 5%.

All this because measuring more exactly than 5% costs more money.

It'll shut down somewhere between 18 and 20 A, and not even the manufacturer knows where.

Makalu 03-31-2008 11:22 PM

now if I could only wrap my head around what it is this guy is thinking:

Quote:

So one PSU has dual 12V rails, and another has quad 12V rails. The quad rail model is worse off compared to others because a rail is isolated. It can't provide any more amps than it can generate unless it starts to dip the voltage supplied.
http://www.wikihow.com/Buy-a-Power-Supply

:crazy:

Killy 04-01-2008 12:17 AM

I still don't see how it you could potentially trap power though. Even if a rail is OCP'd at, say, 10A or something, if there's no draw from that rail that 10A is still available to other rails, right?

So, in sum, it seems as if OCP is meant to prevent nasty things from happening that end up melting stuff in the PSU. The 20A or something in that ballpark limit is meant to stop a bundle of wires on that virtual rail from carrying more than that and causing some sort of catastrophe. Does this make single rails more vulnerable to melting, as OCP or OPP is only applied to a whole rail, and not into smaller bundles of wires?

If what I'm typing is what I believe I am typing (late at night, eyes unfocused, tired), then isn't multi-rail an inelegant solution to the true way of being safe: putting a mini OCP on each wire for the max current it can draw?

treshix 04-01-2008 06:57 AM

The post that prompted this post by jonnyGURU has been snipped by me. The original post was badly formatted, rambling, and severely lacking in structure. A number of people were either confused or angered by it, so I have chosen the most challenging post to use as a response post to attempt to defend the conclusions I have drawn that I attempted (Very badly, it is true) to communicate in the original post.

It also had a number of statements in it that were blatantly incorrect, and upon reviewing it with my brain's power switch firmly in the ON position, I want to :fire: my foot and then have a six pack of :beer: while going :eek::crazy:

The primary reason I have removed it is simply because it IS extremely confusing, and not at all up to the standards of a post I would like to see submitted to an FAQ thread by anyone - Much less myself.

Not a single word in this post should be in any way construed to be sarcastic, because that's simply /not/ my intent in posting it. When I say "Okay", I mean it - There are many things many of you know that I don't.

At the same time, I am not completely ignorant, I do know how to read specifications, and while it's very true that some things will confuse me in ways that are probably unexpected to all of you, isn't that true of anybody who is a human?

I've also already learned some things from all of this and realizes some of my assumptions were very ill-founded.

This is my attempt at a re-do. Please be critical, please point out anything I've got wrong, and please read the following official statement:

Anything written by the user whose name equals "Treshix" should be assumed to be a statement of perception and/or of opinion. "Treshix" is not ruler of the universe, known or unknown; neither is he infallible, always correct, a font of true knowledge, expert in knowledge of any subject, or a master of anything except his left foot, the right only being mastered with aid of a titanium rod. It should also be noted that he has chosen to be a Jack of All Trades instead of a master of one, in the theory that having a decent bit of knowledge about many subjects can functionally trump somebody who knows nothing but their own niche specialty.

In any case, without further ado, I give you the meat of this post:

Quote:

Originally Posted by jonnyGURU (Post 37639)
Wow. No offense but you really have no understanding of how this works at all. Even your examples are completely whack. Certainly if you read anything that I put in the first post, you did not understand it. And if you didn't understand it, then I need to work on making it easier to understand.

The examples were indeed whack.

However, I resent the bald statement that I understood nothing.

I don't feel you need to work on making the first post easier to understand. Your technical writing is of very high quality.

I believe, instead, I need to work better at explaining what I was trying to say in that post. I'm selecting your response to reply to because it presents the most challenge.

Quote:

Originally Posted by jonnyGURU (Post 37639)
I'm thinking more along the lines of "you didn't bother reading the post" because your example is completely whack. CPU, RAM and cards all on +12V1? I even provide examples of how different PSU's with different rail designations are laid out and you pull that random, non-existant example out of thin air?

Actually, I pulled it out of experiance. Is it possible I was dealing with a defective PSU? Absolutely. Is it possible that I am simply not understanding a single bit of information, which then skews the entire structure of understanding that gets built on top of it?

Yes.

It would not be the first time it has happened, either.

Quote:

Originally Posted by jonnyGURU (Post 37639)
"I don't have to do math?"

I don't have to do the math to try and create the information that /should/ have been present on the label? Actually, when I'm troubleshooting what appears to be a power starvation issue that technically shouldn't occur from the information provided on the labels, yes, actually, I probably will feel that I do need to do the math.

My point is that a single rail with amps limited to the wattage the PSU is rated to provide, there is a lot less math to do. Same with multi-rail PSU's.

It's also worth noting that having all your numbers match logically is not at all required in ATX 2.2 or EPS V2.91 specifications. This is a personal bias.

Quote:

Originally Posted by jonnyGURU (Post 37639)
Why are you doing math backwards? And some of the math you ARE doing is complely wrong.

Yes, V * A = W, but at the same time W / V = A and that's a more effective way to acheive your goal.

(Yes. Some of the math WAS completely wrong. In my Defense, Mr. GURU, some of your spelling is completely wrong!*)

(* - Please note, this is an attempt at humor. )

How I handle mathematics will vary depending on what I'm trying to show, where I'm trying to get, and my methodology of double-checking something.

Quote:

Originally Posted by jonnyGURU (Post 37639)
The thing people have to get into their thick skulls is that the per-rail amperage rating is NOT a rating of capability. It is merely a designation for the limit on any particular +12V rail. You don't add them.... you don't multiply them.... you don't do anything with them. It's just telling you what the current limit is. Nothing more. Any decent PSU is going to tell you the maximum combined +12V rail capability right underneath this and THIS is the number you need to do "your math" with and often times it's no different than any single +12V rail's designation (stated in watts and not amps).

Agreed, but I was talking about indecent PSU's. However, I chose to use a decent one as a counter-example to my examples, in an effort to show that A) This is a personal bias and not always accurate, and B) Good PSU's do not suffer from this shortcoming in the same ways.

As for having a thick skull, absolutely. However, the same difficulty I encounter when learning new information has on more then one occasion prevented me from learning bad information from people who were respected for being the absolute knowledge on a topic.

It has also kept me alive.

Any blessing can be regarded as a curse, and any curse can be regarded as a blessing - It depends on your point of view.

I very much do at times struggle with what other people master easily, now. Nonetheless, it has created a habit of double-checking myself in as many ways as possible.

Quote:

Originally Posted by jonnyGURU (Post 37639)
Even using your HX620 example: Assuming the unit has three 18A rails (which it doesn't) you stated that if you add them up you get 54A, or 648W. Of course, you don't because the actual +12V capability is the number just below this: 600W.

The unit CLAIMS to have three rails. Reference the information at http://www.corsair.com/products/hx.aspx

This is the information I went off of to try and make my case, albeit badly.

The internal wiring was not central to the case I was attempting to make.


Quote:

Originally Posted by jonnyGURU (Post 37639)
THIS IS NO DIFFERENT THAN ANY OTHER POWER SUPPLY ON THE MARKET, SINGLE OR MULTI +12V RAIL.

http://www.newegg.com/Product/ShowIm...W+Power+Supply

Actually, max combined load on 12v: 1080W.

Or 90A.

Amperage if you add up all the rails? 90A.

Snipped here to remove an incorrect statement.

http://www.newegg.com/Product/ShowIm...W+Power+Supply

Now, this is the kind of label I would LIKE to see - we can see easily the difference between the amperage limit on each rail, the amperage limit on the two pairs of rails, and the overall amperage limit on BOTH rails.

Now, you're saying what I'm doing is completely nonsensical, but I fail to understand why.

This unit is capable of delivering 1188W on the 12V rails, which considering that both 5V and 3.3V rails are listed in the same 1200W is perfectly sensible.

Especially considering that the PSU, according to the sticker, has the capability of putting its full 1200 watts on the 3.3V, 5V, and 12V rails.


This SeaSonic http://www.newegg.com/Product/ShowIm...W+Power+Supply Illustrates what I have a problem with:

We have four rails with 18A limits. We have a total combined of 38A.

We can fully utilize 2.11 rails. Why do we have four? We definately did not add an extra rail here because we needed it - No, we have four rails simply for the sake of having four rails. If you try and balance between all four rails, you're actually bleeding them dry at 9.5 amps.


Here's another example, a ThermalTake ToughPower this time: http://www.newegg.com/Product/ShowIm...W+Power+Supply

We have 96A available on all four rails before we hit the limit. We have a total max combined power of 62A. We could toss one of those 30A rails and still have 76A before we hit the limits. We have a 60 second peak limit of 950W on an 850W PSU. Even tossing a 30A rail, we can still hit 912W on the 12V rails alone. The amperage limits are set for a total of 1152 watts according to the sticker.

Quote:

Originally Posted by jonnyGURU (Post 37639)
The extra "48W" isn't going to other rails or anything like that. It was never there to begin with! The 18A per rail are not a measure of capability, but a measure of limit. The capability number is the number just below: 600W. And no, the "four missing amps" are not claimed by the -12V and +5VSB. That doesn't make any sense either.

Okay.

Quote:

Originally Posted by jonnyGURU (Post 37639)
This is the same thing you see on virtually ANY power supply. What makes the Corsair any different? Seriously... Go on Newegg and pull up some PSU labels from their photo gallery and try to find some (decent) units that DO NOT show me the total combined capability. Try to find me some that HAVE their +12V rails equal to that capability.

Units that have their +12V rails equal to that capability:

This SeaSonic: http://www.newegg.com/Product/ShowIm...W+Power+Supply

This CoolMax: http://www.newegg.com/Product/ShowIm...W+Power+Supply

This SeaSonic: http://www.newegg.com/Product/ShowIm...W+Power+Supply

And this SeaSonic: http://www.newegg.com/Product/ShowIm...W+Power+Supply

Another SeaSonic: http://www.newegg.com/Product/ShowIm...W+Power+Supply

SeaSonic Again: http://www.newegg.com/Product/ShowIm...W+Power+Supply

One last SeaSonic: http://www.newegg.com/Product/ShowIm...pply+-Open+Box

An Antec: http://www.newegg.com/Product/ShowIm...W+Power+Supply

Decent units that do NOT show combined capability (For sake of arguement, I'm only using ones that do not show max combined amps OR max combined wattage - ie, you have no way to calculate the maximum amps or wattage:


A SilverStone: http://www.newegg.com/Product/ShowIm...W+Power+Supply

This BFG: http://www.newegg.com/Product/ShowIm...s+Power+Supply

How about a ThermalTake: http://www.newegg.com/Product/ShowIm...W+Power+Supply

Another TT: http://www.newegg.com/Product/ShowIm...W+Power+Supply

One more TT: http://www.newegg.com/Product/ShowIm...W+Power+Supply

Quote:

Originally Posted by jonnyGURU (Post 37639)
You said you did the math on an OCZ. Let's take a look at their 700W and "do the math":

http://c1.neweggimages.com/NeweggIma...341-002-04.jpg

Four +12V rails rated @ 18A.... now I'm going to add them up... no... wait... what does that accomplish? Nothing. Just like adding them up on the Corsair. It doesn't do anything because it doesn't mean anything. They're only saying "we divided this +12V rail up into four rails and put an 18A limit on each rail". Nothing more, nothing less. What's the actual +12V capability? 680W? How do we know this? It says it right on the label. I didn't have to add or multiply to get that. It's right there. What is that in amps? It's 680 / 12 = 56.666A, FYI.

The problem is, is that there's plenty of PSU's which DON'T give full information.

Now, the interesting thing is, the sticker on the OCZ in question does most definitely not match the stickers shown on newegg. I'm going to have the guy snap a photo of it and send it to me; either A) I'm remembering incorrectly - (Very possible), B) I was given bad information and the guy is going to go "Huh, errr" or C) We have a different sticker on this particular OCZ.

Quote:

Originally Posted by jonnyGURU (Post 37639)
What happens if we add the +3.3V, +5V and +12V and the -12V and +5VSB? Who cares. Why would you do that? The +3.3V and +5V are a separate rail capable of up to 155W and the +12V is a separate rail capable of 680W. Why would you add them? The total capability of the PSU is 700W. THAT is on the label already too. No math to do. The info is right there. The -12V and +5VSB? Those guys have their own value too. They're separate from the other rails as well.

Okay.

Quote:

Originally Posted by jonnyGURU (Post 37639)
Now let's go back to the Corsair: http://c1.neweggimages.com/NeweggIma...139-002-04.jpg

+12V is 600W, +3.3V and +5V are 170W, -12V and +5VSB are off to the right there. Do we add up the +12V rails? No, because that's greater the 620W. Do we add up the +3.3V, +5V, +12V, -12V and +5VSB? No, because that's greater than 620W. It's a TABLE because it breaks down individual voltage capabilities:

The total max capability of the PSU is 620W. Of that, it can do 600W on the +12V. OF THAT, no rail shall put out more than 18A. The PSU can also put out up to 170W on the +3.3V and +5V. That's an "OR" not an "AND" of course because 170W + 600W = 770W. The +5BSB is on it's own independent rail because it needs to provide power even when the other rails are "off". This can do 15W. This is INDEPENDENT of the capability of the other rails. The -12V is 0.8A but whatever, that's a rail that's just regulated with a simple diode. Can I add them? No. Does the addition of ANY of these numbers exceed the capability of the PSU? Yes. Why? Because they are OR values, not AND values and many of the numbers are merely statements of limitation, NOT capability.

Then why is total limitation set high enough you could blow the PSU?

Quote:

Originally Posted by jonnyGURU (Post 37639)
As far as per-rail load, there's STILL no math to do. There is no "balance" because in this day and age the power supply should have it's connectors split up across rails that are more than capable of delivering power to the connectors attached to them. If you have a PSU that needs to deliver more power to more connectors, you add more rails. So we go from four to five to six +12V rails. You don't throw caution to the wind and go "screw it, I'm just going to go with a single +12V rail because this is getting 'too hard'."

I've even noted multiple PSU's which have more connectors then they have any USE for - they're adding more rails BEFORE they have any "need" to - How simply can I say this, if a PSU has five rails at 18A, /many/ people are going to assume, probably incorrectly but they will still do so, that it can provide at least a decent percentage of that 18A on all rails! Not "just 64%!" which is what we see in some of the PSU's above that I have listed as having unneeded rails.


Quote:

Originally Posted by jonnyGURU (Post 37639)
"Dance through hoops to make it work"? What? It either works or it doesn't. No dancing and no math. The PCIe connectors are going to be on it's own rail. The CPU's on it's own rail, etc. The way I laid it out in the OP. How would "dancing through hoops" going to change this? Are you planning on opening up the unit and changing where certain connectors are soldered down? Seriously.

Per ATX spec version 2.2, the 24pin connector is going to have two 12v pins, but they are both on the 12V1 rail, and it has to supply the power for the SLOTS on the motherboard - of which the PCI-e mobo SLOT is rated to deliver 75W as well! While it may easily be classified as "Unlikely" for the PCI-e card to draw the bulk of it's power from the motherboard and little from the PCI-e connector, assuming that it will be so is taking a risk.

The good boards use the CPU 4pin 12V connector, which does not have a required rail, however per the ATX version 2.2 spec, this is to be used for the CPU +12v signal voltage regulators.

I find no provision in spec that the PCI-e power on the motherboard slot be provided from an alternate rail. It's entirely possible I'm missing something.

Quote:

Originally Posted by jonnyGURU (Post 37639)
Good for you for suggesting the Corsair PSU. It's one of the better units out there for the money for sure. But your reasons for suggesting it are based on complete ignorance.

Okay, now that's just plain insulting. :wall:

treshix 04-01-2008 07:01 AM

Quote:

Originally Posted by Makalu (Post 37698)
now if I could only wrap my head around what it is this guy is thinking:



http://www.wikihow.com/Buy-a-Power-Supply

:crazy:

Oh, I know what I was thinking.

I couldn't exactly wrap my head around what I SAID, either, so don't feel bad.

I don't think much of anything I said that day actually made a lick of sense.

... Consider this an apology.

treshix 04-01-2008 07:10 AM

Quote:

Originally Posted by jonnyGURU (Post 37667)
I might sound like I'm coming off half cocked, but if treshix posted that as his own "this is what I believe, what do you guys think?" post as opposed to posting as a reply to an FAQ that completely thwarts every aspect of his understanding, I wouldn't get so pissed off.

You know, I think his post was a really stupid post.

As the party capable of being offended, I hereby issue this notice officially:

You didn't go off half-cocked. If it was submitted to a FAQ I wrote, I would have responded much the same way.

sdbardwick 04-01-2008 07:24 AM

Quote:

Now, where are we going to get the information on this one?
Max 3.3V and 5V is limited to 250W - or ~21A. Yet, both rails are individually limited to a maximum of 40A. How interesting - You can see how easily this could be misleading, no?

Now, if max sustained is 250W, do we really expect the PSU to be able to handle a short peak load of 960W on the 3.3V and 5V rails? If it cannot, in fact, deliver 960W, or even 480W on either the 3.3V or the 5V rail, then even having them limited at 40A is almost completely useless, is it not? So why are we doing so? My assumption is that it's labelled as such because many people simply go "ooh, big number good!".

But perhaps I am wrong?
I stopped reading your post here. If you do not understand the relationship between current(A), voltage(V) and power(W), it will be difficult to understand the labels on a PSU(The statement "Max 3.3V and 5V is limited to 250W - or ~21A." is what made me stop reading).
40A @ 5V = 200W
40A @ 3.3V = 132W
21A @ 11.9V = 250W

treshix 04-01-2008 07:29 AM

Quote:

Originally Posted by sdbardwick (Post 37709)
I stopped reading your post here. If you do not understand the relationship between current(A), voltage(V) and power(W), it will be difficult to understand the labels on a PSU(The statement "Max 3.3V and 5V is limited to 250W - or ~21A." is what made me stop reading).
40A @ 5V = 200W
40A @ 3.3V = 132W
21A @ 11.9V = 250W


Okay. Now I'm starting to get angry myself.

I'm sure you all feel that I've proven that I know nothing. However, I continue to believe that what I've proven is that I'm quite human, and I am prone to overstress, mistakes, and making stupid comments - Just like anybody else.

Fallacious information snipped from offending post.

Smirnoff 04-01-2008 07:39 AM

One thing that did confuse with regarding your (both of you) statements about the HX620W, is that you say it's triple rail. I thought the HX series were multi rail on paper and single rail in practice? :confused:

treshix 04-01-2008 07:44 AM

Quote:

Originally Posted by Smirnoff (Post 37711)
One thing that did confuse with regarding your (both of you) statements about the HX620W, is that you say it's triple rail. I thought the HX series were multi rail on paper and single rail in practice? :confused:

They are single rail in practice.

However, that wasn't related to the initial point I was trying to make. There was a rather long, disjointed, rambling, and quite frankly idiotic post I had made yesterday that used that particular model as a reference.

It was so bad I just deleted it and used Jonny's reply as a challenge to try and make the point I had originally attempted to make, badly.

Sorry.

Stefan555 04-01-2008 08:05 AM

In many cases the label on the psu's is a "paper" product, The label show the official UL specification. The reality can be different.

If we look on PSU's where the total output on +12V is not specified, in most cases you can find the combined output on the website, in the manual or in a specification document.

Where the combined power is the same as the sum of A on the rails on +12V, we must remember that the OCP's on the rails are set to shut off the psu at a higher amperage than specified on the label.

sdbardwick 04-01-2008 08:08 AM

On review, my posting came across snottier than intended. Sorry.

treshix 04-01-2008 08:10 AM

Quote:

Originally Posted by Stefan555 (Post 37715)
In many cases the label on the psu's is a "paper" product, The label show the official UL specification. The reality can be different.

If we look on PSU's where the total output on +12V is not specified, in most cases you can find the combined output on the website, in the manual or in a specification document.

Where the combined power is the same as the sum of A on the rails on +12V, we must remember that the OCP's on the rails are set to shut off the psu at a higher amperage than specified on the label.

Ah. So it may very well be UL certified for performance characteristics very different then actual capability? If I'm understanding you right, I didn't know that.

As for the OCP on the rails being set to shut off the PSU at a higher amperage then what is specified on the labels, then that implies that the amperage limits shown for the rails on the labels are not always actually the limits, which explains why my understanding of this is confused.

Thanks for the information - that helps :D

treshix 04-01-2008 08:12 AM

Quote:

Originally Posted by sdbardwick (Post 37718)
On review, my posting came across snottier than intended. Sorry.

Apology accepted. I think that happens to all of us when dealing in a medium that does not allow verbal intonation to pass. I know it's happened to me before. :)

Makalu 04-01-2008 08:25 AM

treshix, there's no need for you to apologize to me...but thanks anyway. And I apologize if anything that I posted implied that you are stupid because you obviously aren't stupid at all. You're just making things more complicated then they need to be...we all do that sometimes.

You're correct in that when you add up the individual 12V rating on some units you will get a number equal to the combined rating (although this is the exception rather than the norm). And they aren't under any real obligation to put the actual OCP limits there...some do seem to do nothing more than split up the combined rating between the number of rails (HEC/Compucase units come to mind). But normally these rating numbers are referring to different aspects of the total system. The combined rating is somewhat like how many gallons per minute a water pump can deliver. The individual rating is like the size of the various pipes connected to that pump and how much each of them can deliver due to their size limitations.

So I think you're still missing something when you say things like "fully utilizing all of the rails" or "bleeding rails dry". The fact that the water pump in our analogy can't pump out enough water to max out the flow capacity of all of the pipes on it all at once isn't a bad thing. This could be considered the same kind of "future proofing" that is often touted as a bonus for a single rail system. It just gives you the ability to connect more devices or higher power consuming devices without the PSU reaching it's limits and shutting off.

Another thing that you're confused about is the association between the 12V rails and the 3.3V and 5V combined rail. The basic SMPS design can't deliver the full rated amount on all three of these rails all at once...even if it's a single rail unit. If the combined wattage for all three of these rails is say 800 watts and the 12V rail or rails have a 64A rating then assuming that we actually have a 64A load on the 12V consuming devices in the system (768W) then the maximum amount we can put on the 3.3V and 5V combined is only 32W even if those two rails are rated for 150W. On the other hand if we have a 150W on those two rails then the most we can put on the 12V is 650W. That's just the nature of the design.

So anyway, hopefully that clears up a couple of things for you. By the way, I find it interesting that you like the Gigabyte label because those confuse me. But I understand that it's because of the dual transformer design that is almost like two complete power supplies in one.

I have to say that you might be better off if you just ignore the individual 12V rail ratings completely except in regard to ensuring that the devices installed on the connectors that are wired into an individual rail don't exceed the OCP limit.


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