Multiple Rails

[FuNKieJuNK2]

Couple of noobie questions about power rails...

What is the purpose/use of multiple rails? Would 12V1@18A and 12V2@18A be any better than a single 12V@36A? Why?

When dealing with multiple rails, is there any difference in hardware? or is it all internal to the PSU? So basically, when buying a PSU with multiple rails, do I need to worry about any motherboard compatibility regarding any physical connections? Or does basically any modern motherboard work with any # of rails?

Thanks

 

[unhappy_mage]

http://forums.silentpcreview.com/viewtopic.php?t=23916

I'm not sure I'd put too much stock in that - the OP claims hard drives draw from the 3.3V line - but it's the best resource I could find on Google in five minutes

 

[Toobernoober]

I have found that different PSU will have different things coming off each +12v rail..... connections atleast. On some modular PSU you can even move say a PCI-Express cable from one rail to the next. So if you wanted you could have 2 video cards running off one rail if you hooked them up wrong.

Check johnnyguru's site. Each PSU he reviews he breaks down what rail goes where.

 

[penguin]

One rail at 36 amps could possibly be better than 2 at 18, but that's a very cost prohibitive way of doing things, as it requires much heavier duty internals. Any motherboard should work with multiple rail power supplies.

 

[J-Mag]

Any motherboard should work with multiple rail power supplies.

Not necissarily true, there are some Super Micro boards that don't like dual 12v rail. (probably due to low amperage on one of them...)

 

[Bbq]

Also, some older Athlon XP boards don't have the P4 connector, which means it draws everything from a single rail, even if you use the 5-rail enermax galaxy.

Buyer beware.

 

[davidhammock200]

Any motherboard should work with multiple rail power supplies.

Wrong.

Older mobos powered the CPU from the +5V rail &
most ATX12V PSU's will crossload out of spec if used with these older mobos.

 

[[Spectre]]

Couple of noobie questions about power rails...

What is the purpose/use of multiple rails? Would 12V1@18A and 12V2@18A be any better than a single 12V@36A? Why?

The short answer is to isolate high draw components from one another and/or to dedicate power to a single high draw device. However, a large single rail can be more flexible as all of it's current is available to any device that needs it.