PSU Single Rail Or Multi Rail ?

Dicehunter · 22 Jul 2015 at 17:37

I got the Corsair RMi 1000w 80+ Gold a few days ago and it's a great PSU but there's 1 thing I was curious about.

It has the ability through the software interface to switch from a multi rail system to a single rail, Would this actually make any difference to the performance of the system ?

new boy · 22 Jul 2015 at 18:57

Multi rail doesn't really have any advantages apart from getting over the problem of making one rail carry a load of power.

Single rail is better because say for example you had a couple of 800w PSUs, one single rail and one dual rail. If you pulled 700w from the PSUs, the single rail PSU would have 100w left on the rail, but the dual rail PSU could have one rail with 150w left, and one rail overloaded by 50w.

Having said all that, it doesn't matter as long as long as enough power is available.

I don't see how you can switch between single rail and multi rail. Sounds gimmicky to me.

Dicehunter · 22 Jul 2015 at 19:05

new boy said:
Multi rail doesn't really have any advantages apart from getting over the problem of making one rail carry a load of power.

Single rail is better because say for example you had a couple of 800w PSUs, one single rail and one dual rail. If you pulled 700w from the PSUs, the single rail PSU would have 100w left on the rail, but the dual rail PSU could have one rail with 150w left, and one rail overloaded by 50w.

Having said all that, it doesn't matter as long as long as enough power is available.

I don't see how you can switch between single rail and multi rail. Sounds gimmicky to me.

Well it has multiple 12v rails so you either have both on or switch to a single rail.

new boy · 22 Jul 2015 at 20:44

Dicehunter said:
Well it has multiple 12v rails so you either have both on or switch to a single rail.

so it has say, two 500w rails and you can either run it as a 500w single rail PSU or a dual rail 1000w PSU?

Dicehunter · 22 Jul 2015 at 20:46

new boy said:
so it has say, two 500w rails and you can either run it as a 500w single rail PSU or a dual rail 1000w PSU?

That's what I got from the review yes although I'm still a little confused on the matter

joeyjojo · 22 Jul 2015 at 22:11

I've always assumed various connectors are wired (internally) to certain rails in a multi-12V-rail supply. Could be wrong.

Single rail is the way to go if possible - no need to worry about overloading an individual rail.

new boy said:
I don't see how you can switch between single rail and multi rail. Sounds gimmicky to me.

It's the (older) specification, single rail PSUs are a more recent development.

https://en.wikipedia.org/wiki/Power_supply_unit_(computer)#Multiple_.2B12.C2.A0V_rails

Greebo · 23 Jul 2015 at 12:20

Brilliant explanation here http://www.jonnyguru.com/forums/showthread.php?t=3990

I really do like Johnnyguru and his psu reviews over anybody elses. Even amkes me laugh sometimes

In general, proper, multi rails are safer. Neither is better or will give you better performance or stability.

AFter reading the review on your psu I would be tempted to run it on multiple rails http://www.techpowerup.com/reviews/Corsair/RM1000i/2.html

Looks like a great PSU and good to see Corsair back to good psu's again. The ones they built after the stunning AX1200 have never been as good.

Greebo · 23 Jul 2015 at 12:30

new boy said:
Multi rail doesn't really have any advantages apart from getting over the problem of making one rail carry a load of power.

Single rail is better because say for example you had a couple of 800w PSUs, one single rail and one dual rail. If you pulled 700w from the PSUs, the single rail PSU would have 100w left on the rail, but the dual rail PSU could have one rail with 150w left, and one rail overloaded by 50w.

Having said all that, it doesn't matter as long as long as enough power is available.

I don't see how you can switch between single rail and multi rail. Sounds gimmicky to me.

Proper multi rails dont work like that.

In your example the 2nd 800W psu would have two rails, each capable of pulling 600W in total probably.

In the ops case his PSU has 8 rails each of which maxes out at 500W. :eek:

Obviously no more than 1000W in total. 500W limit on each rail should be more than enough for any build.

Tealc · 23 Jul 2015 at 21:22

No difference to the performance. Multi rail is safer though. Multi rails, once you go back beyond the over current safety circuits share a common 12v SMPS supply anyway, otherwise we'd have voltage differences and that would be bad.