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what components draw power from each PSU Rail?

D

dantonic

Member
Ok so I'm shopping around for a PSU, and as always, before I purchase something I am trying to learn as much as I can about the component.

I understand generally how a psu works, and how the Wattage is split among the different rails 3.3V 5V and 12V single or mutliple rails.

What I am trying to figure out is if there is a specific standard of what all the components run on?

From reading online, I've been able to determine that the CPU, hard drives, optical drives, fans and such run on the 12V rail,

But what runs on the 3.3V and the 5V rails? is there a list somewhere or a site that explains where each component draws its power from? and how much power does that component draw?

Some PSU calculators simply show the total Wattage required for a specific system with specific components, but I want to better understand how each component draws its power.

Thank you for any comments.
 
Hard drives and optical drives draw approximately equal current from both +12V and +5V (SATA drives may draw from +3.3V in the future)
Fans draw from +12V
Motherboards draw from +12V, +5V, +3.3V and almost nothing (or perhaps nothing) from -12V
CPU draws +12V from the 2x2 auxiliary CPU power plug
 
Well, Thank you very much for those posts, they really helped me understand.

Now however here is another question:

In a PSU with multiple 12V rails for example a PSU with 2 14A rails, does the power get automatically distributed to whichever component needs it most?

Basically what I'm asking is are all the cables coming from the psu able to access both rails if required? Here is an example:

Say my videocard, HDs and OPtical drives are on one rail, and my CPU is on the other rail. If at some point the load becomes too big and the 14A is not enough for the GPU, HDs etc., does the psu automatically divert power to those components from the second rail? Making it effectively a 28A capable rail?(of course a little less than 28A because the rails are not perfectly additive.)
Or am I limited to however much power that single rail can offer.

Thanks, I hope thats not too confusing.
 
each of those rails should be dedicated to a part of your system, for example my psu had 4 x 12v rails
1 = PCI-X 1
2 = PCI-X 2 & MB
3 = CPU
4 = Peripherals

i'm not sure if those are 100% correct but it is something like that
 
Originally posted by: dantonic

In a PSU with multiple 12V rails for example a PSU with 2 14A rails, does the power get automatically distributed to whichever component needs it most?

Say my videocard, HDs and OPtical drives are on one rail, and my CPU is on the other rail. If at some point the load becomes too big and the 14A is not enough for the GPU, HDs etc., does the psu automatically divert power to those components from the second rail? Making it effectively a 28A capable rail?(of course a little less than 28A because the rails are not perfectly additive.)
Or am I limited to however much power that single rail can offer.
Click to expand...

Not confusing at all. But i also don't know about this so i too want to see an answer. Wanted to post about this loooong time ago but seems to forgot about it for while.

Please help guys......
 
Originally posted by: LOUISSSSS
each of those rails should be dedicated to a part of your system, for example my psu had 4 x 12v rails
1 = PCI-X 1
2 = PCI-X 2 & MB
3 = CPU
4 = Peripherals

i'm not sure if those are 100% correct but it is something like that
Click to expand...

Ok so does that mean that the PSU is NOT capable of splitting splitting the power?

So with a multi rail PSU (which I have never owned) is it easy to identify which cables get their power from which rail?
 
Originally posted by: dantonic
Originally posted by: LOUISSSSS
each of those rails should be dedicated to a part of your system, for example my psu had 4 x 12v rails
1 = PCI-X 1
2 = PCI-X 2 & MB
3 = CPU
4 = Peripherals

i'm not sure if those are 100% correct but it is something like that
Click to expand...

Ok so does that mean that the PSU is NOT capable of splitting splitting the power?

So with a multi rail PSU (which I have never owned) is it easy to identify which cables get their power from which rail?
Click to expand...


PSUs that have multiple rails are not capable of splitting the power between rails. The rated output of each rail is an indicator of how much it can output max. Well if it goes over the limit (most likely around 18~20A) it won't draw power from the second rail. This is an issue with multiple rail PSUs where the current distribution is not balanced. This is one of the reason why large single rail PSUs are recommended.

And yes it is easy to identify which cables get their power from which rail. It is indicated on the PSU unit itself.

Hope this helped.

Laters
 
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