When buying a power supply is it better to get one with one massive 12V vrail or is it ok to get one that say has 3 or 4 12v vrails spreading out the load?

Providing several 12v rails is used to comply with UL regulations (recommendations, actually). These recommendations suggest that manufactures should observe amperage limits on individual circuits. UL considers this a safety issue (and it is). They don't mind if you get a tad toasted, just not fried to a crisp! However contrary to this UL recommendation, performance-wise it might be better to have the entire 12v amperage capacity on a single buss. To draw an analogy, all the users would then have a straw in the single punch bowl. If there was enough juice for everyone, no one would go away thirsty. Divvying the available juice up into dixie cups stands the chance that one thirsty user might not get enough. Power supply mfgs have spun this UL recommendation into a "Performance Enhancement" characteristic. It's certainly NoT an enhancement, but at least it might not be doing any harm. For my last build, I was into a "Reduce potentially undefinable problems" mode. PS problems are insidious, tenacious and the hardest to identify. I did Not want a limited 12v buss to even potentially cause one of these phantom problems. I looked long and hard and finally found a Silverstone with a single 12v Buss. It's been fine, but as a practical matter though, it might not matter.

Thanks for the reply, very good description of how it works. While looking around at PS it seems their are more to choose from if you want multiple 12v Vrails and fewer if you want one massive one.

Single rail, all the way. The Silverstone Decathlon, below in my sig, has been rock solid. It's the only PSU I've ever had, that I'd buy again.EwingKATLAlcohol, Tobacco and Firearms should be a store, not a government agency.MSI K8N Neo2 PlatinumAMD Opteron 185 2.6 Ghz Dual Core2GB Kingston HyperX (2X1GB) Dual Channel DDR 2-3-2-6 @ 1TXFX nVIDIA GeForce 7900 GS 256MB DDR3 AGPSound Blaster Audigy LSSilverStone Decathlon 750W +12v@60A [email protected] on WinXPPro (SP1)

>When buying a power supply is it better to get one with one>massive 12V vrail or is it ok to get one that say has 3 or 4>12v vrails spreading out the load?See these guys.. http://www.pcpower.com/index.htmland then you will never have a need to go anywhere else for a PSU

Single rail is better IMO. If you have several 12V lines, it's harder to balance the load..you need to know how many amps each component draws... With a single 12V rail you just hook everything up :)And no need to spend a fortune on gigawatt PSU's unless you're seriously overclocking *and* run multiple videocards.60A @ 12V is 720W.. Typical CPUs draw less than 100W. The 8800GTX (90nm) draws 132W under full load while the newer 65nm 8800GT draws only 78. That's just 19A for a power hungry CPU and GPU. Suppose you have an AMD Phenom (currently one of the most power hungry CPUs at 125W) and run two 8800GTX videocards (old 90nm tech, newer GPUs built on 65nm or 55nm process draw less) in SLI, that's still just 32A or 389W.The Opteron 185 draws 95W, the 7900GS draws only 45W. That's just 12 amps, probably well below 20A even with all other components included ;)Unfortunately, most PSU manufacturers have discovered that a big Wattage rating sells. So they have stopped making lower-wattage models, or only make low-quality models. If you don't want to spend more than you have to, the Corsair VX series are a good choice. The VX550W is a little more powerful with a max output of 492W on the 12V line vs 396W on the VX450W. The VX450W would be cutting it close for the Phenom X4 / 8800GTX SLI rig in my example above, but would actually be enough for nearly all PC configs.

While in agreement with everything JimyG says, oversizing your PSU has the following benefits:1. Potentially less electrical noise as PSU operates further away from 100% rating,2. Potentially higher energy efficiency as PSU operates further away from 100% rating (Max efficiency tends to be around 75% or PSU rating) so you may recoup some of your additional PSU dollars on electricity saved,3. Potentially less actual noise as PSU operates further away from 100% rating (because less heat is generated -so it's actually "cool" to oversize your PSU-, the PSU fan RPMs are lower),4. Spare power in case you decide to upgrade your CPU to a Quad and overclock (can esily have 300W there alone).5. Spare power should you decide to add a second video card (could even be a 2x GPU card) and overclock. Although FSX doesn

There is also a big plus to having multiple 12v rails and I would never put all my faith into one big rail. Each rail is its own regulated power supply. If one rail fails and you still have another rail available you are still in business by simply utilizing your spare rail. If you have one big rail and it dies....well your done.There is a good reason power distribution systems throughout this world are not designed as one big power delivery system that simply is if the one big system fails, everyone looses power. However by dividing the system up into manageable parts failures can be delt with with minimal interruption to customers.Calculating the load you are going to put on each rail isn't a big deal. The biggest load on a 12v rail these days is going to be a video card.In Sam's analogy above (sorry Sam no disrespect but the analogy is a bit flawed) "if there is enough juice for everyone" if that statement is true out of the gate and If there is indeed enough juice for everyone they will get there juice wether it be from the bowl or from a cup.

Myths are fun... they are like the stories we hear around a campfire. When it comes to power supplies there are plenty to go around.http://www.pcpower.com/technology/myths/#8 answers the single rail question

Nick,First of all I'd like to start off by saying that my profession deals with power systems and power delivery albeit on a much larger scale than a computer power supply but the concept does not change one bit.That is PC Power and Cooling marketing hype and nothing else. Effciency has nothing to do with available power that is not used. It has everything to do with power that is asked for vice power that is delivered and power that is lost to the system. We are talking about power factor. True Power, Apparent Power and VARs (Volt Amps Reactive) as they relate to one another. A multi-rail system by design is 95% efficient out of the gate. They are more expensive than single rail systems. PC Power and Cooling saying that "Those losses occur because power literally gets "trapped" on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system." is absolute rubbish and pure marketing. No power is lost and no power is trapped. The power is available and quite simply is not used. Your not making that 10 extra amps and paying for it as a loss. The 10amps is not asked for so it is simply not used. A power supply can only attempt to supply what it is asked to supply.If I have one 12v rail that is capable of supplying 100Amps and I only use 50Amps then I guess you have a big loss because 50Amps is not utilized. No you do not!!! You simply have a power supply much larger than your needs. LOL....what marketing crap.Quite simply PC Power and Cooling has made a decision to manufacture power supplies with a single 12v rail becuase its easier to design and cheaper to build. Less mosfets and regulators per rail means less cost. Statement #8 is an attempt to justify that their design decision is better than an multi-rail system.I have always thought highly of PC Power and Cooling until reading that statement. I am in no way saying that they do not make nice power supplies. Statement #8 however is 100% misleading and is misinformation in its purest sense especially when read by a consumer who is uneducated in electrical theory.

Actually, I like the #1 and #2 reasons. You're right though, #8 is just goofy. The reason I picked a PS with a single rail was pure lazyness. I did not want to become so involved with the technical specifics of my system's power usage that I needed to calculate how much load each 12v buss (12v rail) might encounter, then maybe be wrong. Unless a user is comfortable with faith-based computer building, this would be a critical piece of information to know if one is going to use a multibuss PS. I didn't want to go there. I just wanted one big 12v source for all the users to share. That way, I would not have to worry about any single component being current limited. If I did hit the PS's current limit, it would be the whole system and vastly easier to TS. I know that's a sad administration for a techno-dude, but I try for simplicity whenever possible. Otherwise, I find that I can often out-smart, even myself! But I am also disappointed PC left #8 available for easy misinterpretation. I read right by it 'cuz I knew nothing was being unused because of the multibuss design. However l share your concern that a lay audience could easily achieve this obviously intended and misleading take-way. I hope our guys now "get it." This is disingenuous marketing, to say the lest. However the Q&A brings up some good points. I bought my Silverstone on the basis of reasons #1 and #2 (and #8, but by a more considered understanding). #1) To the defense of PC, that 83% efficiently rating is just terrific. I appreciate this number because I am trying to reduce my "Carbon footprint," and so should we all. If you have kids, this will be their 'job-one.' If you are one of these kids, you already know what this means, Help the old folks understand. So how is this little ol' PC power supply doing its part? Most simply, nothing's free.The PS will use a little electricity for its own power supply purposes. It's gotta transform and rectify and do all those magical things. It will use a little power to accomplish these tasks. We want the PS to use as little electricity as possible for these purposes. An 80% rating means the PS needed to use 20% to accomplish its PS function. My 3 year old Silverstone is at a 78% efficiency rating, meaning it needs 22% for its own purposes. Not bad for then. I see >80% is more of the norm for top grade PSs these days. PC's claimed 83% efficiency means only 17% is being used by the PS. We need to push this number even further. Vote with your credit card. If you are in the market - Please - consider this metric. Civilization will thank you. #2) Again to the defense of PC, they rate loads at real world (or higher) operating temperatures. Those 500watt PSs that come in the store brand computer cases advertise 500 watts. But this load was sustained just long enough for some dude to read an ampmeter. If the tester had left it under that load for another 20 seconds, the dang thing would have burst into flames and exploded! I'm exaggerating, but only by a little bit. Heat is a PS's natural enemy. If there is a single thing to look for that describes a PS's quality, it's the PS's ability to maintain power a high operating temp. The chart they display on their Q&A page is the real deal. PC, Silverstone and others will maintain their advertised output well into the high 40Cs. If you are shopping for a PS, look for this metric.and #8) I still maintain that a single buss is a smarter way to go. It takes less technical knowledge. There is no buss by buss load calculation required. Also if it dies, I do NoT want individual 12v busses to start fading out. I want it Rock-Dead where changing an obvious component fixes an obvious problem. In this case, simple is better.

>is absolute rubbish and pure marketing. No power is lost and no power is trapped. The power is available and quite simply is not used.Sargeski,Both you and PCPower power are correct: Your difference is due to differing semantic use of the words "power" and "used".Your analysis is from an operational point-ov-view, while PCPower's analysis is from a capacity or availability point-of-view.What PCPower are saying is this:Suppose you have a 1200W PSU with four 12V@25A power rails.Suppose also each of those power rails is already delivering 20A to existing devices.Therefore you have a total power surplus of 4 rails x (25A available - 20A actually used) x 12V = 4 x 5A x 12 V = 240W. (Note that "surplus" here means "available but unused".)So you could say "great, I have 240W unused so I can add a fourth video card requiring 180W", i.e. 180W / 12V = 15A.The answer is you can't, because each 12V rail can only give you 5A and you need 15A for the new card, and of course you can't (rather shouldn't) connect the individual 12V rails in parallel lest you get an excellent, albeit short, display of fireworks.This is why PCPower says the "power is trapped" and unusable.If you interpret PSU efficiency from a capacity point-of-view, in this situation with your hardware you would have 1200W installed and only 4 x 20A x 12V = 960W used so "installed capacity efficiency" would be 960W / 1200W = 80%.Operating efficiency would of course be the 800W actually used divided by whatever amps the PSU draws multiplied by 110V (a figure lijkely in the 80% - 90% range.So you see, both you and PCPower are correct if you account for differences in word usage.Of course if you use a PSU with a single 100A 12V rail in the example above, you would have no "unused power trapped" and would be able to istall that additional video card.Finally in the example above you might be able to redistribute power usage for each rail by reconnecting the hardware to the rails in a different manner to end-up with all the excess capacity in one rail so you could power the additional video card, but more likely not.Cheers,jahman.

I know exactly that what we both said is correct and you can be in the same boat with a single rail and not enough power if you do not take your total load into account. Whether you decide to go with a single rail or multi-rail you need to take into account your anticipated total load.....then as a rule of thumb at a minimum add 20% for expansion.As I stated above their statement is a play on symantics and yes it is true in the context in which they used it. However, it is also very misleading.When one really talks about efficiency in power system we are talking the ratio of power in to power out. In a purely DC circuit that ratio is always 1:1 because there is no reactive component only resistance.When talking about a typical power supply such as in a PC we have to take into account another componet the AC power used to power the power supply. In an AC circuit things change drastically in additon to the pure resistance we now have to also take into account inductive reactance and capacitive reactance. In laymans terms those reactances create loses. So for instance lets say my power supply is supplying a total of 900 Watts to my system. I check the load on my incoming 120VAC supply line and see I am using 1000 Watts of power to generate the 900 Watts of power to my system. How can that be?? Because I have lost 100 Watts of power to the reactive component. So in this example we have use 1000 watts of power to produce 900 Watts of power which would equate to a 90% efficiency or a ratio of 1:0.9

>When one really talks about efficiency in power system we are>talking the ratio of power in to power out.That is but one way to talk about efficiency.What I tried to do in my previous post is to show there are other ways, viz. "efficiency of installed capacity", i.e. being able to actually use the the available power.Further, I didn't find PCPower's statements misleading: It was crystal clear to me that they are referring to efficiency in terms of being able to use 100% of PSU capacity.Cheers,jahman.

Hello jahman,I know it is but one way to talk about efficiency and I fully understand what you conveyed in your post. The very first sentence in the myth #8 statement says it all "With all the hype about multiple 12-volt rails (ads claim that two rails is better than one, five is better than four, etc.), you'd think it was a better design. Unfortunately, it's not!Everything to follow sentence one is trying to justify the first sentence which is nothing more than PC Power and Cooling's opinion that a single rail design is better.It's their opinion that their design is better than a multi-rail system because they want to sell power supplies. All I'm saying is that the means to the justification will be misleading to many. All in the hopes of making more sales. Just because the are making a true statement (but not telling the whole truth) doesn't make it right.