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2008-02-07 22:54:34
Rick_O_Shea678
Angry Engy
+95|6767
I've been having little troubles with my system, going to upgrade the 350W PSU that came with it.
Can anyone shed a little light on the rails?  For example, some come with single +12V rail, others with triple or quad +12V rails.
And I ask because it's not just the entry-levels have have single rail:  Corsair's TX750W has a single rail, while the HX520W has triple 12V rails.

(Pls don't direct me to
here: http://forums.bf2s.com/viewtopic.php?id=77096
or
here: http://forums.bf2s.com/viewtopic.php?id=84895
because I read them, thank you to all who posted there.)
2008-02-08 02:59:45
kylef
Gone
+1,352|6507|N. Ireland
Anything that has a motor for the most part usually draws power from the 12V rail. It's best to have as many amps on the +12V rail as possible. Of course, brand matters too.

I have the HX520W and love it, great amps etc but the TX750W is also meant to be superb.
2008-02-09 10:04:05
san4
The Mas
+311|6702|NYC, a place to live
I've never fully understood why it matters to have single or multiple rails. I just know my vid card requires about 25 amps on all the +12V rails combined.
2008-02-09 10:34:14
Stormscythe
Aiming for the head
+88|6563|EUtopia | Austria

kylef wrote:

Anything that has a motor for the most part usually draws power from the 12V rail.
Well, but in comparison to what a CPU/GPU draws, that's so insignificant...

san4 wrote:

I've never fully understood why it matters to have single or multiple rails. I just know my vid card requires about 25 amps on all the +12V rails combined.
Let's put it this way: more ampere on a single rail + you stupid enough to grab it, while the PSU's on = more fatal. There is a restriction of about 22 amps for a single rail, I think.
Most power supplies, however, don't really have split rails. Don't ask me, how that works, however.
2008-02-09 10:52:40
Bertster7
Confused Pothead
+1,101|6596|SE London

The reason for multiple rails is legislation. The 12V rail is by far the most drawn from in high power systems, the HDDs, ODs and GPU will all be drawing power from the 12V rails - so it needs a fair amount of power to be available on it. Because of laws governing how much power can be put on a single rail you cannot have more than 20A on a 12V rail, therefore if a PSU is to supply more than 20A on the 12V rail it must have more than one of them.

I hope that's a concise enough answer to your question.
2008-02-09 10:58:54
san4
The Mas
+311|6702|NYC, a place to live

Bertster7 wrote:

The reason for multiple rails is legislation. The 12V rail is by far the most drawn from in high power systems, the HDDs, ODs and GPU will all be drawing power from the 12V rails - so it needs a fair amount of power to be available on it. Because of laws governing how much power can be put on a single rail you cannot have more than 20A on a 12V rail, therefore if a PSU is to supply more than 20A on the 12V rail it must have more than one of them.

I hope that's a concise enough answer to your question.
That does answer the question. But it raises another: wtf legal restrictions on how many amps on a 12V rail? Who cares???
2008-02-09 11:08:41
Bertster7
Confused Pothead
+1,101|6596|SE London

san4 wrote:

Bertster7 wrote:

The reason for multiple rails is legislation. The 12V rail is by far the most drawn from in high power systems, the HDDs, ODs and GPU will all be drawing power from the 12V rails - so it needs a fair amount of power to be available on it. Because of laws governing how much power can be put on a single rail you cannot have more than 20A on a 12V rail, therefore if a PSU is to supply more than 20A on the 12V rail it must have more than one of them.

I hope that's a concise enough answer to your question.
That does answer the question. But it raises another: wtf legal restrictions on how many amps on a 12V rail? Who cares???
People who want electronic equipment that doesn't explode?

More than 240W (well VA if you want to be pedantic, since it's AC current and it won't be a simple P=VA calculation, and I struggle to remember all my circuit theory about Q points and all that) down a single rail is too much. If you start allowing that sort of thing then the reliability of the device becomes compromised. The best PSUs are the ones that separate the rails properly, ideally with separate transformers. The usage of multiple rails also reduces costs, because the components needed to safely handle more than 240W over a single rail are far more expensive. So all in all the use of multiple rails makes PSUs cheaper, safer and more reliable.

They're not really laws, just standards supported by legislation. You can get PSUs with more than 20A over a single 12V rail and this approach does have its own advantages, but it usually makes more sense to have multiple 12V rails.

It's a good thing.

Last edited by Bertster7 (2008-02-09 11:15:35)

2008-02-09 11:33:58
san4
The Mas
+311|6702|NYC, a place to live
I see. It just seemed strange to think they would cart you off to jail for building a PSU with more than 20A on a 12V rail. But it sounds like my God-given Constitutional freedom to do so isn't really in jeopardy.
2008-02-09 11:42:46
Bertster7
Confused Pothead
+1,101|6596|SE London

san4 wrote:

I see. It just seemed strange to think they would cart you off to jail for building a PSU with more than 20A on a 12V rail. But it sounds like my God-given Constitutional freedom to do so isn't really in jeopardy.
It was EU legislation anyway, it wouldn't apply in the US.
2008-02-09 23:07:02
Rick_O_Shea678
Angry Engy
+95|6767
Thanks to all who attempted to answer and discuss.
After reading kylef's sticky (and other research), I thought multiple rails was advantageous.
It was the Corsair PSU's which threw me...kylef was recommending the HX520W (triple rail)...and then I came across the VX550W:  More juice, but only a single +12V rail. 

Thought I'd ask about it, see what responses came.
I've read allusions at other sites that single rail is perfect for home-theatre PCs, and single graphics cards; multiple rails are offered for SLi/Crossfire, perhaps more HDDs, maybe the dual-core CPUs?  Sales-talk seems to be along the lines of "in case of an accident, if you have multiple rails maybe only some of your stuff will be fried".  But then again Corsair claims the VX550W (single rail)  is Sli-certified.

I would have thought distinguishing single from multiple rails was like Windows95 vs XP...you know, old vs new.  But since they are still producing single-rail, and in ever-increasing capacities, I guess it's not that simple.

Bertster7 wrote:

The reason for multiple rails is legislation...you cannot have more than 20A on a 12V rail...
My friend, this is completely not the answer I was expecting: govn't regulation.  Thanks for posting.
Corsair makes a TX750W, which has 60A on the +12V single rail. 
Have the authorities been informed?
(Alternatively...if its illegal...perhaps not as sexy as getting Cuban cigars for my American friends...but I might be able to get some TX750W for the right Euro offer. )

 

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