Why were split 12V rails ever introduced?

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EnderW

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Why were split 12V rails ever introduced?
I've never understood the purpose of them.
Just makes things more complicated - you have to watch what devices you have on which rail so one doesn't get overloaded.

First it was 2 rails.
Then 3, then 4 and the amount of watts per rail kept going down.
So companies started coming out with stuff like Mushkin's "RailFusion" to allow the 12V rails to work together.

And now, some companies are transitioning back to single rail right where we started.
Don't the new Seasonic M12 only have 1 actual 12V rail?
And I know the new 1KW-SR has a single 12V rail.
 
The ATX spec, while it doesn't mandate 240VA limitations, mentions UL and EN 60950, which says that (if I understand correctly - I can't find a copy of it anywhere) low-voltage things in general should have a current limit so that they won't output more than 240 VA (volt-amps). Thus, the multiple seperate limiters are necessary.

However, as you've remarked, the number of rails was getting ridiculous. It can lead to problems with having the wrong amperages in the wrong places. Ideally, I think, one should have a large rail with an adjustable output limiter. This would allow you to allocate more amperage to rails that need more power, so if you have a lot of drives or a high-demand graphics card you can deal with it, but still maintain the 240VA limit.

 
EnderW said:
Why were split 12V rails ever introduced?
I've never understood the purpose of them.
Just makes things more complicated - you have to watch what devices you have on which rail so one doesn't get overloaded.

First it was 2 rails.
Then 3, then 4 and the amount of watts per rail kept going down.
So companies started coming out with stuff like Mushkin's "RailFusion" to allow the 12V rails to work together.

And now, some companies are transitioning back to single rail right where we started.
Don't the new Seasonic M12 only have 1 actual 12V rail?
And I know the new 1KW-SR has a single 12V rail.
Click to expand...
You can thank the all knowing Intel, BTX anyone? :cool:
 
How can you even determine what's getting plugged into what on those kinds of power supplies? Maybe it's because I've never used one of the ones with the split 12v rails before, but how do you know what device is getting plugged into a specific rail? In the reviews for them I don't see anything that defines one set of connectors to go on say like, the first one, and then another one will run on the second. The only thing I have been lead to understand is that on the new split type, PCI-E video cards requiring a direct power input from the power supply get their own rail, or something to that effect.

Any "For Noobs/PSU cave-dwellers" explanation here please?
 
On dual rail PSU's one of the rails (12V2DC) is connected to the motherboard and the other (12V1DC) is for the drive connectors etc.
See ATX12V PSU Design Guide V2.2 (as referenced in the ATX spec V2.2)
http://www.formfactors.org/developer\specs\ATX12V_PSDG_2_2_public_br2.pdf

3 or more rails should have labels showing which rail the connectors belong to.

edit:
To clarify further, 12V2DC is for powering the CPU only and connects via a 4 pin plug to the motherboard.
12V1DC is fed to the motherboard in the main power connector to drive the motherboard and associated electronics. It also feeds the drive power connectors etc.
 
edit:
To clarify further, 12V2DC is for powering the CPU only and connects via a 4 pin plug to the motherboard.
12V1DC is fed to the motherboard in the main power connector to drive the motherboard and associated hardware. It also feeds to the drive power connectors etc.
Click to expand...
Nice save. ;)
 
Chernobyl1 said:
please explain
Click to expand...
No, I hate long, long, long post & you love them!

As you edited your post with the correct information, it is obvious you know what I am refering too.
 
Not really.
Nothing posted was incorrect, I decided to clarify it further to help the OP understand better.
 
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