Question about PSU rails

[qwerty99]

For example Bitfenix Formula 550W has 3x12v rails (mb,cpu,gpu) but 650W version has 4x12v(mb,cpu,gpu1,gpu2). If I get 650W version and use only 1 gpu, does that mean the second gpu rail won't be used at all? Thanks.

[Bananasplit_00]

If you only use power from one cable from the PSU then yah 

[qwerty99]

5 minutes ago, Bananasplit_00 said:

If you only use power from one cable from the PSU then yah 

does it also mean that I wont get to use all 650W by using 1 gpu (since some power is reserved for gpu2 rail)?

[SupaKomputa]

Yes the last rail won't be used at all.

There's a max current for each rails.

[Stefan Payne]

32 minutes ago, boboo said:

does it also mean that I wont get to use all 650W by using 1 gpu (since some power is reserved for gpu2 rail)?

The way you phrase it makes no sense. That's not how it works.

If you want to know how it works: Look at your breaker Box.

 

You have something coming in, wich is equal to 12V Combined power.
And yo have a ton of breaker. Each breaker is equal to one Rail of the PSU.

 

So you have 650W.

That 650W is split into 25A for CPU and 25A for Drives/ATX and 30A each for PCIe.

650W however equals ~54A.

These 54A can be used with any combination of each rail, however you can not use more than set amps per rail. (or not).

 

So if you would, theoretically, load the GPU Rail and CPU Rail to its max, you'll already be over the max wattage of the PSU.

I hope this helps more...

 

PS: some GPU won't work with just one rail and need both for some reason.

 

And if you load one rail to the max and the others not at all its also not a problem as, as said earlier, its only roughly equal to a breaker box. So nothing gets damaged....

[qwerty99]

7 minutes ago, Stefan Payne said:

The way you phrase it makes no sense. That's not how it works.

If you want to know how it works: Look at your breaker Box.

 

You have something coming in, wich is equal to 12V Combined power.
And yo have a ton of breaker. Each breaker is equal to one Rail of the PSU.

 

So you have 650W.

That 650W is split into 25A for CPU and 25A for Drives/ATX and 30A each for PCIe.

650W however equals ~54A.

These 54A can be used with any combination of each rail, however you can not use more than set amps per rail.

 

So if you would, theoretically, load the GPU Rail and CPU Rail to its max, you'll already be over the max wattage of the PSU.

I hope this helps more...

 

PS: some GPU won't work with just one rail and need both for some reason.

Okay, makes sense. Thanks for explaining.