Dual 12v rails

[lcplsickoll]

For the real guru's out there. Well this is actually a really simple question. When you have a PSU with dual 12v rails do you simply add the amperage on the two rails to come up with the equivalent to a single 12v rail. For instance mine is as such:
+3.3V@30A, +5V@30A, +12V1@18A, +12V2@20A, +12V3@10A, +5VSB@2.5A
would this be the equivalent of 38A on a single rail, or 48A?

[Sir. S.A.S]

Re: Dual 12v rails

i THINK you add them together but im not an expert in PSU's

[lcplsickoll]

Re: Dual 12v rails

I would think so also, but it says the PSU is dual rail but there's 12v1,2, and 3? It's 550W total and I know it's more than capable. I've had it for about 3 months now and never a problem. I'm just curious how the dual rail setups compare to a single rail.

[evil.rusk]

Re: Dual 12v rails

for info on dual rails see here

Dual +12V Rails: Most PS’s today supply all of their +12V amperage through one rail, just like almost every PS manufacturer supplies their +3.3V and +5V through one rail each. However some forward thinking manufacture’s are supplying their +12V amperage through more than one rail, the most common today for PC’s is to use two +12V rails or dual rails. The new ATX12 V2.0 spec. also requires dual (or more) +12V rails.

Why more than one +12V rail? Electrical isolation for noise and improved voltage regulation. Some devices, usually electromechanical ones having motors, produce noise spikes & voltage fluxuations, these can include pumps, compressors, fans, drives, lights (when turned on & off) and probably TEC’s & Peltiers. By putting these “noisy” devices, that often turn on & off, or at least often change their power (amperage) demands, on a separate rail we isolate them from the MoBo, CPU, Video Card(s) and the other electronic components that are sensitive to noise & sudden changes in voltage. This is a good thing! ATX12 V2.0 is the future.
Additional Dual Rail Information: http://forums.extremeoverclocking.c...562#post1371562

and additional info on this link: http://forums.extremeoverclocking.co...62#post1371562

you should note that a lot of PSU manufacturers quote the maximum 12V current that can be drawn on each 12v rail, but it may not be possible to get that maximum current on both rails simultaneously on all PSUs depending on their design.

example my Hiper 480W psu is rated as 12V1=18.0A and 12V2=16.0A (together=34A), but what they dont tell you is that if the 12V1 rail is drawing 18.0A then 12V2 will only be able to draw 8.0A and if 12V2 draws 16.0A then 12V1 will only be able to use 9.0A. this means the MAXIMUM 12V load the psu can support is 26.0A not 34A as you would imagine. Note also that drawing lots of current on the 12V rails reduces the amount of current the psu can deliver on the other V rails.

also distribution of the rails is important if you have a lot of drives for instance. the link i gave above explains some about multiple rails (which can be a good thing depending on design). also see this PSU wattage calculator to find out how many watts your psu will need for your system: http://www.extreme.outervision.com/index.jsp

[lcplsickoll]

Re: Dual 12v rails

thanx Evil.Rusk. My PSU actually runs 12,12,6 continuous. I'm not worried about not having enough power, just curious as to how it relates to the single rails. Thanks for the info, I'll continue reading.