Single rail and multiple rail.

[Harshil]

hey guys,

 

Just wanted to know what's the difference between a single rail psu or a multiple rail one.

 

[Woodypc]

It is as it says. But a single good rail is better up to about 1000watts, with multi rails you need to balance them to be like cpu on one and gpu on the other. Cheaper PSU often have more than one rail to get more wattage but this is not better, 2 crap rail is not as good as one good one.

[Andi]

It is as it says. But a single good rail is better up to about 1000watts, with multi rails you need to balance them to be like cpu on one and gpu on the other. Cheaper PSU often have more than one rail to get more wattage but this is not better, 2 crap rail is not as good as one good one.

this really makes no sense...a crappy singlerail is worse than a good multirail.

 

Multirail has one big advantage, and that's security. If on rail dies because of whatever, the others won't. Singlerail can kill everything together.

 

Singlerail has one big advantage aswell. IF you have 40A or more on one rail you don't have to worry what rail you have to use for what. Some Multirail PSUs don't have enough Amps for every setup. But most of the time you won't have any problem with a good multirail setup. Even a GTX Titan will work fine with ~18A.

[Harshil]

How's the seasonic 1050xm 80+ gold?

[Andi]

How's the seasonic 1050xm 80+ gold?

excellent...but you need 1050W maybe for a tripple SLI Setup. Don't know what you are planing :D

[Harshil]

well if really want to know my setup is gonna be-
Rampage iv extreme
i7 3930k
gtx 780 or gtx 760 sli ( don't know yet )
corsair h100i
120gb samsung ssd
16 gb corsair vengeance 1600mhz
1tb wd caviar black
NZXT phantom 820

[Andi]

so... what you need is a 600W psu. maybe 700W :D  And if you want to go 780SLI in the future 850W is more than enough.

 

 

If would go with the Sea Sonic X-Series X-750/850 KM3. Revision KM3 has nice black cables

 

http://geizhals.at/p/2507/902507/902507-5.jpg

[IPCharger]

A 750w PSU should be more than enough for SLI 780s.

[Woodypc]

this really makes no sense...a crappy singlerail is worse than a good multirail.

 

Multirail has one big advantage, and that's security. If on rail dies because of whatever, the others won't. Singlerail can kill everything together.

 

Singlerail has one big advantage aswell. IF you have 40A or more on one rail you don't have to worry what rail you have to use for what. Some Multirail PSUs don't have enough Amps for every setup. But most of the time you won't have any problem with a good multirail setup. Even a GTX Titan will work fine with ~18A.

No a good single rail is better than 2 crapy rails. Some cheap PSU will use 2 rail to get the wattage as they dont use rail strong enough to do it on their own. Not all multi rail will pick up where the failed rail left off. I have had a few PSUs die and never damaged any other components. Stick with good brands ans you will be sweet.

[quan289]

A good single rail power supply is better than a crappy multi-rail power supply.
A good multi-rail power supply is better than a crappy single rail power supply.

A multi-rail isn't there to make up one rail inability to supply power.
Most multi-rail power supply has a single +12v source where a group of wires is monitor by an Over Current Protection (OCP) - kind of like a circuit box in the house. When the OCP is set off, the unit stop supplying power and the system shut off. This is an extra safety net to prevent a group wires supplying too much power and the wires/connectors melts or catches on fire. It's also a safety measure in case an external short cause by a failed components (a fan, HDD, VRM, etc) and the PSU keep supplying more and more power until something catches on fire or the OCP trip off.
A single rail unit either has a single OCP or in many cases, none at all, where it relies on the Over Power Protection (OPP), which is slower to respond as the capacity of the unit goes up.

While multi-rail units is technically safer, it can be seen as a negative at the same time. Because it limits a certain group of wires for power, it can be problematic for some people who have power hungry components drawing from that particular rail, where a poorly configured OCP as well as cable configuration may trip the OCP despite that you should have enough power for it. If you frequently bench and overclock your components to extreme levels, you may trip the OCP as well and a single rail PSU may be ideal to have.

For most modern day power supply for let's say under 700w, single-rail vs multi-rail is pretty irrelevant. They should both shut down in case of something like a short should happen (a short that the SCP doesn't detect). Most manufacturer nowadays configured the cables in a way that you should be able to get full power from the +12v source without tripping the OCP, but the problem still exist of accidentally overloading one of the rails, where you need to make sure you hook it up properly.

Whether your should get one or the other, depends on what you will be powering and what you are doing. There are power supplies that has features that allows you can switch between single and multi rail mode depending on your uses, such as the BeQuiet Dark Power Pro 10, Corsair AXi, and EVGA SuperNova NEX1500.

And just a FYI, there are power supplies out there that is labeled as a multi-rail but in actuality a single rail. The same is true for multi rails units being market as a single rail. Here's two example as such:
XFX ProSeries 1250w (a Seasonic X 1250w internally) : http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=273
Seasonic S12II 520w (noted at the bottom of that page) : http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=185
There's also discussions regarding it at Jonnyguru about some of the "single-rail" models from Seasonic. One of which noted here: http://www.jonnyguru.com/forums/showpost.php?p=92999&postcount=5