Advantage of dual rails?

[orangat]

This may seem like a basic question but what why is it better?
Why is it supposedly more stable?
Is it even recommended for good basic power supplies in the 300-350W range?

 

[imported_rod]

A dual-rail power supply allows PSU manufacturers to build higher-current supplies easier, as you dont need such high current voltage regulators. It also reduces the size of the power cables needed in the case, and reduces the resistance between the PSU and MoBo (because there is a square relationship between current and resistance).

The problem is that the power is split into two areas. For example, if you have two 10A rails, and the components on each rail require 8 A, you'll be fine. But if you have two 10A rails, and one rail requires 12A to power all of the components on that rail, you will run into trouble.

Basically: Dual-rails allow you to have higher-current, more stable power. But you need a higher current to ensure that there is enough to power whatever is required on each rail.

Do you have particular components/power supplies in mind?

RoD

 

[rbV5]

ATX 2.01 specs allow for the CPU to operate on a seperate 12v rail. The dual Rail powersupply allows you to seperate the power draw from your components and your CPU on a supported motherboard.

I just installed a inexpensive 400 watt Fortron with dual 12v rails on my PCIe motherboard to replace my expensive single rail Antec truepower 480, which despite its 22 amp rating on the 12v rail would fold under load and my graphics card would exhibit artifacts. The Fortron works great in the same setup at 1/2 the price and is quieter to boot. So it certainly can be worth it.

 

[orangat]

Originally posted by: rod
A dual-rail power supply allows PSU manufacturers to build higher-current supplies easier, as you dont need such high current voltage regulators. It also reduces the size of the power cables needed in the case, and reduces the resistance between the PSU and MoBo (because there is a square relationship between current and resistance).

The problem is that the power is split into two areas. For example, if you have two 10A rails, and the components on each rail require 8 A, you'll be fine. But if you have two 10A rails, and one rail requires 12A to power all of the components on that rail, you will run into trouble.
.......

Thanks Rod for the explanation. I'm not looking for a power supply, just wanted to know it rationale behind dual rails. I agree that dual rails for lower rated ps is more a gimmick since one rail could be overwhelmed.

But why would power cables be smaller? I don't see the sizes changing for molex cables.

And would it make power regulation more stable?

 

[rbV5]

I agree that dual rails for lower rated ps is more a gimmick since one rail could be overwhelmed.

Its not a gimmick if you have a lower rated powersupply with dual rails matched with a supported motherboard like my example above. The CPU, hardrives and a powerful PCIe graphics card that pulls its power from the PCIe slot was too much for my pretty decent, expensive single rail powersupply. The much cheaper, plain jane, lower rated powersupply with dual 12v rails handles the same loads easily. The solution depends on the application.

 

[orangat]

Originally posted by: rbV5

I agree that dual rails for lower rated ps is more a gimmick since one rail could be overwhelmed.

Its not a gimmick if you have a lower rated powersupply with dual rails matched with a supported motherboard like my example above. The CPU, hardrives and a powerful PCIe graphics card that pulls its power from the PCIe slot was too much for my pretty decent, expensive single rail powersupply. The much cheaper, plain jane, lower rated powersupply with dual 12v rails handles the same loads easily. The solution depends on the application.

What I meant by gimmick was basic power supplies should not have dual rails. Eg. A 300W power supply with dual rails will not produce enough power on at least one rail. Look at the specs for cheap dual rail ps, all ratings are for maximum not sustained output which is a cheap trick.

If its too much for a single rail ps, its not going to work on a dual-rail ps. The only moral of your own story is that Forton>Antec.

 

[rbV5]

Originally posted by: orangat

Originally posted by: rbV5

I agree that dual rails for lower rated ps is more a gimmick since one rail could be overwhelmed.

Its not a gimmick if you have a lower rated powersupply with dual rails matched with a supported motherboard like my example above. The CPU, hardrives and a powerful PCIe graphics card that pulls its power from the PCIe slot was too much for my pretty decent, expensive single rail powersupply. The much cheaper, plain jane, lower rated powersupply with dual 12v rails handles the same loads easily. The solution depends on the application.

What I meant by gimmick was basic power supplies should not have dual rails. Eg. A 300W power supply with dual rails will not produce enough power on at least one rail. Look at the specs for cheap dual rail ps, all ratings are for maximum not sustained output which is a cheap trick.

If its too much for a single rail ps, its not going to work on a dual-rail ps. The only moral of your own story is that Forton>Antec.

How is that the moral of my story? Antec makes damn fine power supplies. Specs on my basic, cheap powersupply have power output and Max output ratings, and it runs my rig fine, where my single rail powersupply would not. Sounds like you're just trying to make some "point".

 

[orangat]

Originally posted by: rbV5

Originally posted by: orangat

Originally posted by: rbV5

I agree that dual rails for lower rated ps is more a gimmick since one rail could be overwhelmed.

Its not a gimmick if you have a lower rated powersupply with dual rails matched with a supported motherboard like my example above. The CPU, hardrives and a powerful PCIe graphics card that pulls its power from the PCIe slot was too much for my pretty decent, expensive single rail powersupply. The much cheaper, plain jane, lower rated powersupply with dual 12v rails handles the same loads easily. The solution depends on the application.

What I meant by gimmick was basic power supplies should not have dual rails. Eg. A 300W power supply with dual rails will not produce enough power on at least one rail. Look at the specs for cheap dual rail ps, all ratings are for maximum not sustained output which is a cheap trick.

If its too much for a single rail ps, its not going to work on a dual-rail ps. The only moral of your own story is that Forton>Antec.

How is that the moral of my story? Antec makes damn fine power supplies. Specs on my basic, cheap powersupply have power output and Max output ratings, and it runs my rig fine, where my single rail powersupply would not. Sounds like you're just trying to make some "point".

My point is that a 300W ps with 12V@15A should not split up the 15A into 2 rails.

If you are saying that a single rail powersupply can't run your rigs properly which look quite basic then you are wrong. Your own hypothesis relies on n=1.
The only conclusion that I can draw is that the Antec was faulty and was going to die anyway.