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PSU question

post #1 of 10
Thread Starter 
what is the difference, performance wise, to have a single rail with a high amperage or multiple rails with a lower amperage on each?

for example,
a psu with four 25a +12v rails
or one with one 50a +12v rail.

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post #2 of 10
Here's your answer from jonnyGURU: http://www.overclock.net/power-suppl...ml#post3614982
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post #3 of 10
Thread Starter 
awesome

that's some great info

thank you
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post #4 of 10
Rails are really kind of an overated factor when it comes to PSU's. A lot of it will boil down to how the PSU is set up internally.

A true dual rail set-up has multiple circuitry systems so that each rail is an independent source. Unfortunately - many dual rail PSU's have ONE circuit but it is split into 2 rails. Basicly - It's a single rail that is split.

A real dual rail system will be better then the single rail because each rail has less of an amperage draw on it, however - A dual rail that is not a true dual rail may not be as good a single rail with a higher amperage.

If it makes sense better this way....

A True Dual Rail w/ 20a +12v is better then a single 40a +12v

but

A fake dual rail w/ 2 20a + 12v is NOT as good as a single 40a + 12v


That's where quality comes in. Stick with the good brands and you will have indpendant 12v rails.
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post #5 of 10
Thread Starter 
here is a ocia.net reivew of my PSU, it states that it has 4 +12v rails. can you tell if it is a fake 4 rails or real 4 rails?
because if i ever grab another GPU or add alot of peripherals i would like to know
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post #6 of 10
Quote:
Originally Posted by clbkdaz View Post
A real dual rail system will be better then the single rail because each rail has less of an amperage draw on it, however - A dual rail that is not a true dual rail may not be as good a single rail with a higher amperage.

If it makes sense better this way....

A True Dual Rail w/ 20a +12v is better then a single 40a +12v

but

A fake dual rail w/ 2 20a + 12v is NOT as good as a single 40a + 12v
In theory a true dual rail is better because like you said, they each have to provide half the power so compared to a similar unit with one transformer they don't have to work as hard and usually perform better.

One thing to note is that there are very very few true dual rails PSU and most of them are 1000W+. So at this range, the rail only has to provide ~500W and usually perform better than a PSU with one 12V source since it is much easier to make a 500W PSU that performs well compared to a 1000W.

But your scenario doesn't exist. At 40A, it's pretty easy to provide good performance with one 12V source so two is completely unnecessary.
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post #7 of 10
Thread Starter 
Quote:
Originally Posted by shinji2k View Post
In theory a true dual rail is better because like you said, they each have to provide half the power so compared to a similar unit with one transformer they don't have to work as hard and usually perform better.

One thing to note is that there are very very few true dual rails PSU and most of them are 1000W+. So at this range, the rail only has to provide ~500W and usually perform better than a PSU with one 12V source since it is much easier to make a 500W PSU that performs well compared to a 1000W.

But your scenario doesn't exist. At 40A, it's pretty easy to provide good performance with one 12V source so two is completely unnecessary.
possibly an example with easier numbers to explain something to a noob?
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post #8 of 10
Quote:
Originally Posted by shinji2k View Post
In theory a true dual rail is better because like you said, they each have to provide half the power so compared to a similar unit with one transformer they don't have to work as hard and usually perform better.

One thing to note is that there are very very few true dual rails PSU and most of them are 1000W+. So at this range, the rail only has to provide ~500W and usually perform better than a PSU with one 12V source since it is much easier to make a 500W PSU that performs well compared to a 1000W.

But your scenario doesn't exist. At 40A, it's pretty easy to provide good performance with one 12V source so two is completely unnecessary.
Oh - Completely agreed...

I just like to point out that just because it is advertised at 4 rails or 3 rails or whatever...it's not always better then a single rail. There are plenty of single rail PSU's that are better then many dual rails. Especially those Logisys ones they sell on the Egg for like $25.

Heck - do they still limit each rail to 20a?
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post #9 of 10
Quote:
Originally Posted by smoke12291 View Post
possibly an example with easier numbers to explain something to a noob?
Let's see if I can explain it better.

Take PSU 1:
1000W PSU
Single 12V rail design

PSU 2:
1000W PSU
True Dual 12V rail design (imagine 2 500W PSUs in the same case together providing 1000W)

A quality 500W PSU is pretty easy to make. The parts needed don't need to be all that special. It's kind of like building a car that can go 100mph or building one that can do 200mph. The 100mph car is typicaly much more simple, easier to make and cheaper. You don't have to have a lot of horsepower or tires and suspension that can handle 200mph. The 100mph car is much cheaper and easier to make even if the cars have similar acceleration up to their top speed.

So by that, PSU 1 needs to have very high quality parts to be able to provide 1000W adding costs and complications. Since it is much to easier to make a 500W, putting 2 together in one package to reach 1000W (PSU 2) is cheaper and much easier to get similar or better performance as PSU 1.

edit:
Quote:
Originally Posted by clbkdaz View Post
Heck - do they still limit each rail to 20a?
EPS 12V standard (which is what multi-rail PSUs are designed to adhere to) says the limit must be 18A for each connector. Most companies typically just go with 18A per rail and stick one or two connectors on it (PCI-E, CPU 12V, etc...).
Edited by shinji2k - 6/27/08 at 7:59pm
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post #10 of 10
I have a Corsair 650TX and that has a 52A single rail. Energy is not wasted splitting among rails like in multi rail PSUs. However I have yet to come across a true multiple rail design.
    
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