The splitting of the +12V rail

[bobsmith1492]

Ok.. This FAQ is a good place to settle this....

When a graphics card company tells you you need "22-28 amps" for a particular graphics card, they're telling you that you're going to need this much power FOR THE ENTIRE PC. NO graphics card NEEDS 22A. That's 264W!

"Mechanically" you can't even deliver over 150W to the card (75W through the slot and 75W through the 6-pin). Never mind 264W! In reality, you're probably only going to need 6 or 7A of power to the card. Everything else is gravy.

So don't sweat it... your PSU is way more than enough for your proposed graphics card upgrade.

I'm not sure this is accurate anymore; aren't the new 5970 and whatnot cards pushing up close to the 300W PCIe power specifications?

 

[PM650]

I'm not sure this is accurate anymore; aren't the new 5970 and whatnot cards pushing up close to the 300W PCIe power specifications?

Could be either way really. Ati & nVidia provide both the max board power & the recommended system supply, although Ati's specs are on different pages (feature summary gives max board power, system requirements gives system psu size).

 

[bobsmith1492]

Well according to Anandtech's review, the card itself draws up to 294W while the cooler can dissipate 400W, allowing some room to overclock the thing:

http://www.anandtech.com/video/showdoc.aspx?i=3679&p=1

 

[PM650]

Well according to Anandtech's review, the card itself draws up to 294W while the cooler can dissipate 400W, allowing some room to overclock the thing:

http://www.anandtech.com/video/showdoc.aspx?i=3679&p=1

Overclock being a relative term. HD5970/GTX295 are down-clocked from their single-gpu cousins (5870/285) precisely to remain below the 300W limit - it wouldn't be PCIe 2.0 compliant if it exceeded that afaik.

 

[WinGeek]

Wao impressing. The article like Post of yours was quite informative. I am new to forums but i have started loving it because of posts like that.
You may increase your knowledge staying at home :awe:

 

[faxon]

For those who question the validity of the "it's for safety" argument, please have a look at these photos:

http://www.jongerow.com/BFGPOWER/images/DSC02898.jpg

http://www.jongerow.com/BFGPOWER/images/DSC02899.jpg

http://www.jongerow.com/BFGPOWER/images/DSC02900.jpg

I actually see this quite often. Usually with the floppy connector when attached backwards to a Creative sound card or a floppy drive, but this time it was a four pin Molex and it was NOT attached backwards. What it was plugged into shorted and caused this.

The PSU works fine. In fact, if I isolate the exposed wires so they don't short, I can actually hook it up to the load tester and run it.

The short caused the +12V wire to heat up and melt it's insulation off. The wire never shorted so short circuit protection never shut the PSU off. If the PSU had not shut off once the resistance of the short created a > 20A load, the heat would've melted the other wires' insulation, the sleeve, etc.

was rereading this, just thought i would mention that this post's images are clearly not working anymore, and i was kinda hoping to see these pics again since i direct newbs here all the time to read up on why its important to have a good PSU

 

[jonnyGURU]

Oops. Unfortunately, I don't have those pictures any more.

I forgot that I even had them up there. When I got axed from BFG, I wiped that whole BFGPOWER folder.

 

[mv2devnull]

Here is a "good" one:

I just received a prebuilt system. A bit after reading this sticky (like we all always start by reading the stickies, right?)

A modular Nexus RX-8500 in it. "Four rails", it says. "20A each", it says. Fine.

Three sections for the modular cables: +12V1DC (two slots for PCIe), +12V2DC (two slots for PCIe), and +12V4DC (six slots for peripheral/floppy/SATA). All 10 slots seem identical, resembling 6-pin PCIe. Fine.

Three cables are in the slots. They lead to two 500GB drives, a DVD-RW, a floppy, and two 6-pin PCIe to Geforce GTX460. (Fans perhaps too.)

All three are "neatly" in the +12V4DC section.


Well, that if I'm not mistaken, the 20A is more than enough for that load, but I cannot keep thinking whether the builders did that on purpose or by habit.


Edit: I am mistaken. The two 8-pin PCIe cables are not modular after all, and are on separate rails.

 

[trexpesto]

Links are gone to default in post #15 of this thread, too bad too.

 

[LiuKangBakinPie]

Did Johnny write that? Cant believe it I didnt laugh lol

 

[Epsilon-Zero]

Very good read from well over 3 years ago.
Not much has changed since then.

PSU designers and OEMs still play the same tricks with their marketing.

I guess the only thing different now is that seeing 6 rails with 6 x 6+2 pin connectors is becoming more comon with the Big Daddy as jonnyGuru put it now being 8 rails with 8 x 6+2 connectors.

The more things change the more they stay the same I guess.

 

[lehtv]

Oh wow, I never noticed this thread before. Excellent read, now I know more :thumbsup:

 

[Smoblikat]

Very informative.

 

[RU482]

Antec PSU Mythbusters

 

[lehtv]

Antec PSU Mythbusters

I especially like this part

Myth 3: A Single Rail Power Supply Is As Safe As Multi Rail Power Supply!

NO!

But...

Ok... What's the bottom line?

The bottom line is, for 99% of the folks out there single vs. multiple +12V rails is a NON ISSUE. It's something that has been hyped up by marketing folks on BOTH SIDES of the fence.

(My emphasis.)

 

[PreferLinux]

But still note the "for 99% of the folks out there" – it is an issue for some. In both ways, depending on the PSU and the situation. A high wattage single-rail PSU would almost make a reasonable arc welder (especially if it was used as the power source for a constant current supply). A PSU with poorly-balanced rails would be bad too.

 

[PandaBear]

What about reliability. Will single rail be more reliable than multiple rail?

 

[PreferLinux]

Probably in theory, but probably only around 0.001% more reliable (just a random guess) in practice!

 

[Arxinall]

Idk. 12v RAILS are pretty complex.

 

[CZroe]

I have two PC Power and Cooling Turbo-Cool 1KW PSUs. One seems to have three rails at a total of 66A (22A per rail?) at 70A peak, the other is one large 12V rail at 78A peak.

Reading the OP I see that three-rail PSUs are not good for PCs requiring four PCIe connectors. Sure enough, it only has two despite being "SLi-ready." That seems to be a huge waste of a 22A rail. Because none are 8-pin, I want to send it in and get the wiring customized with a couple extra. Can they simply add more to the same rail? Is this wise?

Edit: Looks like it's more inadequate than the OP describes for this particular PSU. One rail is for the motherboard (24-pin ATX), one rail is for the CPU (dual 8-pin EPS connectors), and the PCIe connectors are on the same rail as everything else (thanks for the info, Meghan54). I obviously don't need two EPS connectors and splitters are available if I ever do so I should be able to convert one to a couple PCIe connectors and share that under-utilized rail. A whole rail dedicated to 24-pin ATX also seems horribly under-utilized so I guess I should grab some 12v lines from there too though I'm not sure how to do that cleanly without splitting at the connector and having a connector with more total length than it should have.

 

[Imran520]

thanks for sharing

 

[CZroe]

thanks for sharing

Worse than the people my sig references. Free iPod?

 

[helliCruck67]

I think I ought to be fine with what I have the extent that power supply goes. Will anybody provide for me a warm fluffy that I'm not going to obliterate my new cpu with inadequate force?

 

[flatty]

So, in conclusion, an Antec High Current Pro 1200W that have 8 rails, will handle a GTX 580 SLI overclocked? Im rite?

 

[MongGrel]

Split rails on a well built PSU was pretty much irrelevant these days I'd thought.

depends on the PSU I guess maybe.

*edit* NM should have just read the whole oridgnal post to begin with.