Thinking of buying a diual-rail PSU? Think again...

TheOtherOption · 2 Mar 2006 at 19:43

anyone know if the Enermax Liberty series switch automatically as i'm pretty sure there isn't a switch - i have the 500w variant btw

lay-z-boy · 2 Mar 2006 at 19:50

Richdog said:
Website specs state combined 12v is only 30A.

The manual and the psu state 35a here.

Also, im not sure on the libertys, but as it doesnt seem to have the switch one would assume that it doesnt have the option.

MikeTimbers · 2 Mar 2006 at 21:32

Richdog said:
Website specs state combined 12v is only 30A.

PDF manual says 35A

Explicit · 2 Mar 2006 at 21:41

Interesting article, but thank goodness for Tagan

Richdog · 3 Mar 2006 at 07:45

lay-z-boy said:
The manual and the psu state 35a here.
.

I think that's the max possible figure, not the average.

Dutch Guy · 3 Mar 2006 at 08:40

lay-z-boy said:
Also, im not sure on the libertys, but as it doesnt seem to have the switch one would assume that it doesnt have the option.

I don't think Enermax have that option, the Liberty PSU's are 2x22A though which is a lot.

TechnoCorruption · 3 Mar 2006 at 09:58

Yes, even the 400w liberty which I have has 20amps on each rail, to be honest I think the point about dual rails has just got so over exagerated, its a joke. The way I see it is that g-cards tech progression is going forward at such a rate, that the X19 series and the GTX 512 series are just leeches sucking power like theres no tomorrow.

Stick 2 in a machine with all the extra bits that a high end user has and there still using power supplys that havent really progressed at all in the last 3years, the average supply is still in the 400-500w range with only a slight amp increase, for these cards to shine we need to see big (700-1000w units with around 50amps) power supplys hitting the market.

Just my opinion at the end of the day but it seems g-cards are moving forward and psu's are not.

Richdog · 3 Mar 2006 at 11:21

Agr3sive said:
Stick 2 in a machine with all the extra bits that a high end user has and there still using power supplys that havent really progressed at all in the last 3years, the average supply is still in the 400-500w range with only a slight amp increase, for these cards to shine we need to see big (700-1000w units with around 50amps) power supplys hitting the market.

Nah, with high-end crossfire + dual-core systems with an average amount of components/devices all you need is 34A on a single rail and it will cope fine.

Quad SLI then yes you are then probably looking at ~40A needed but to me that's a non-issue as I would never be silly enough to buy it.

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Regarding the Tagan combined rails, the official Tagan specs .pdf says 32A combined http://www.tagan.com/pages/products/2forceS/TG-580-U22_Tagan_UK_mini.pdf

Think i'll wait till they (hopefully) bring out a 630w (or whatever) model...

TechnoCorruption · 3 Mar 2006 at 11:42

They need more than that mate. Even ATI say that 38A is the minimum they reccomend for a crossfire rig, thats before you oc the cards to the max and introduce a heavy oc'ed dual core into the equation which needs more power still.

http://www.ati.com/products/RadeonX1900/specs.html

Dutch Guy · 3 Mar 2006 at 11:55

The problem isn't pure watts though, in theory a PSU giving 400W is enough to handle a top spec SLI rig but the power distribution has to lean towards the 12V rail(s) even more as the 3.3V and 5V rails are hardly used anymore.

The big problem is that in the past CPU's used the 5V rail (or 3.3V) for power and todays CPU's use the 12V rail, that's why older PSU's have strong 3.3V and 5V rails and a weak 12V rail, that is why GPU manufacturers say you need a 600W PSU for SLI to give them a safe margin.

What they need to do is advise the PSU manufacturers of their plans so they can change the design.

What I don't understand is this bit from this review:

One oddity is the 22A rating of the +12V rails: Intel's main justification (in ATX12V v.2xx PS Design Guide) for two 12V rails is to keep the current on any individual rail below 240VA. It seems odd that the 12V lines should be rated above 20A (20A x 12V = 240VA). In real usage, neither rail is ever likely to approach its rated maximum, so the point is mostly moot, but it does make the "separate" rails kind of pointless.

Richdog · 3 Mar 2006 at 12:33

Agr3sive said:
They need more than that mate. Even ATI say that 38A is the minimum they reccomend for a crossfire rig, thats before you oc the cards to the max and introduce a heavy oc'ed dual core into the equation which needs more power still.

http://www.ati.com/products/RadeonX1900/specs.html

I have a mate that has dual X1900XT's and a 3.0ghz FX-60 running on a PCP&C 510 (he's a crazy bencher) with no problems whatsoever. The quality of the PSU counts a hell of a lot.

Dutch Guy said:
What I don't understand is this bit from this review:

With that quote, i'm not sure they were taking uber-rigs with lots of devices into account.

Intel stated a dual-rail specification requirement and have since backed away from it slowly.

TechnoCorruption · 3 Mar 2006 at 14:55

Richdog said:
I have a mate that has dual X1900XT's and a 3.0ghz FX-60 running on a PCP&C 510 (he's a crazy bencher) with no problems whatsoever. The quality of the PSU counts a hell of a lot.

I dont disagree with you, the quality and power of the psu is probly the most important thing in a pc, my point is in article you linked too people like Sampsa from XS kane computers to within inchs of there life.

If ATI say you need 38amps to run crossfire on a average rig, then to run it on a rig of someone like Sampsa whose machine is voltage modded in every known form, running g-cards at 1000/2000 and pushing cpu's to there limit you probly need a psu that can supply around 50a.

I would imagine that if you hooked up one of those rigs to a pcp+c 1000w which slams out 66a with a peak of 70a, then there would be no problems using a multi rail psu.

Richdog · 3 Mar 2006 at 15:16

Agr3sive said:
If ATI say you need 38amps to run crossfire on a average rig, then to run it on a rig of someone like Sampsa whose machine is voltage modded in every known form, running g-cards at 1000/2000 and pushing cpu's to there limit you probly need a psu that can supply around 50a.

The guy I told you about, Dynasty, has a system like that, volt-modded to **** and phased. He is in the top 10 on the orb. There's no way you need close to 50A for a rig like that, and as I said, he runs it on a PCP&C just fine.

Here's a quote from a good thread about PSU requirements http://www.hardforum.com/showthread.php?t=1017620&page=2

Now we get into dual PCI express video cards. Let's say you're using SLI or ATI's Crossfire. One would think that two video card means twice the power requirement, but that's actually not true for the same reason as your performance not doubling when you have two video cards. The additional power requirement for the second video card is still fairly significant, though.

* Add 4A if you have a pair of video cards and neither of them have their own power connector.

* Add 6A if you have a pair of video cards with a power connector for each.

As you see, not as much as you;d think. Volt-mods also add fairly little to the overall loads in the grand scheme of things.

I would imagine that if you hooked up one of those rigs to a pcp+c 1000w which slams out 66a with a peak of 70a, then there would be no problems using a multi rail psu.

One problem with massive PSU's like the 1kw is that to prevent cross-loading issues you really need to be utilising a whole lot of its power in order for there not to be problems. You would need an uber-rig of uber-rigs to justify one, and even then it would likely be excessive.

TechnoCorruption · 3 Mar 2006 at 15:38

Hmmm, im not convinced its the fault of dual rail psu's though, some maybe but not all, I find it wierd how the inquirer reports that multiple rail psu's are providing problems with top cf/sli rigs and then links to a thread at XS where the original poster cures his power problems with his cf rig by buying a psu that has multiple rails. :confused: