Still confused about 12v rail split. Is my PSU underrated?

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wolfestone

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Apr 6, 2011
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I read the sticky but I'm still not quite sure about this.

I have a 500w coolermaster PSU which has 18A on the +12v1 rail and 18A on the +12v2 outputs.

My video card says it requires 25A on the 12v output.

I have a new PSU from corsair which is rated at 600w/40A on the +12v, but it makes an annoying whining sound. Now that I'm getting into RMAs and all that stuff, I figured I should check whether my first PSU was indeed underpowered (18A when the card needs 25) or whether I should have been reading it as having 36A on the +12v rail.

thanks a ton for any help.
 
BoomerD

BoomerD

No Lifer
Feb 26, 2006
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http://www.jonnyguru.com/forums/showthread.php?t=5716

Two things immediately caught our attention. First, the fact there is no reference for “500 W” on the power supply.
The second thing that we noticed on the label was the phrase “The +3.3 V & + 5 V & +12V1 & +12V2 combine power shall not exceed 431.5 W”.
Click to expand...

http://www.hardwaresecrets.com/article/728/1

So...it looks like your PSU has two separate rails...if your video card requires 25 amps on the 12v rail...this PSU ain't gonna do it.
 
theAnimal

theAnimal

Diamond Member
Mar 18, 2003
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The 25A is not a requirement, just a recommendation (which is usually overrated). It is also for the total 12V amps and not one rail only.
 
fffblackmage

fffblackmage

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Dec 28, 2007
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How the hell did this PSU get a 500W rating when it's not supposed to exceed 431.5W combined? :confused:

Anyways, the label says the combined +12V1 and +12V2 rails maximum output is 360W (30A). The PSU seems pretty crappy, but assuming it can really output 360W on the 12V rails combined, it should be enough for your video card.
 
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wolfestone

Member
Apr 6, 2011
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Any suggestions for a brand of PSU that won't make whining/squealing sounds?

This corsair replacement has plenty of juice but the noise is driving me nuts. It sounds like other people are having the same problem so I don't really want to get into RMA'ing it for a replacement, I'd sooner just return it and buy something else.

I was tempted to buy a higher powered version of this coolermaster one as it was very quiet, but it sounds like it's not all that great from what you guys are telling me.

thanks for any more suggestions.
 
Meghan54

Meghan54

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Oct 18, 2009
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wolfestone said:
My video card says it requires 25A on the 12v output.
Click to expand...




You do understand, or maybe you don't, that when video card manufacturers list an amperage requirement, they're listing a SYSTEM WIDE requirement, NOT a requirement just for the video card, right?
 
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wolfestone

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Apr 6, 2011
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Meghan54 said:
You do understand, or maybe you don't, that when video card manufacturers list an amperage requirement, they're listing a SYSTEM WIDE requirement, NOT a requirement just for the video card, right?
Click to expand...

I realize that now from the responses in this thread yeah. I didn't know that when I posted it.

I'll be the first to admin I'm getting in over my head here, but this doesn't really make sense to me. Wouldn't my choice of CPU, number of fans, hard drives, and whether I'm running multiple video cards all affect that number?

to really simplify it, does this mean that when looking at a system-wide requirement you can add the current output of the 12v rails, but when looking at a single component you can't?

Should have posted this in the beginning too. Here is my video card:

http://www.evga.com/products/moreIn...KR&family=GeForce%20500 Series Family&sw=

Requirements
Minimum of a 400 power supply.
(Minimum recommended power supply with +12 Volt current rating of 24 Amps.)
One available 6-pin PCI-E power dongle


This is clearly a lot more complicated than I originally thought, thanks for all the help here.
 
Last edited:
theAnimal

theAnimal

Diamond Member
Mar 18, 2003
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wolfestone said:
Wouldn't my choice of CPU, number of fans, hard drives, and whether I'm running multiple video cards all affect that number?
Click to expand...
Yes, everything will affect that number, which is one of the reasons it tends to be overrated (the other being the large number of crap PSUs that cannot even provide their rated power). For the vast majority, the recommendation will be fine.

to really simplify it, does this mean that when looking at a system-wide requirement you can add the current output of the 12v rails, but when looking at a single component you can't?
Click to expand...
Generally speaking, you can go by the total 12V output (which BTW is not necessarily just adding up the 12V rails, but for any decent quality PSU will be listed on the label). Of course if you know the 12V draw of each component and which rail they will be connected to, you could get an exact configuration.

Edit: It is also good practice to buy a PSU that includes all the native connectors needed.
 
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wolfestone

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Apr 6, 2011
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I'm looking at new PSUs now and have a couple more questions...

Does single or dual rail have any effect on how likely a PSU is to whine?

And is a higher output PSU more likely to whine?

Or do neither of these things make any difference and it all comes down to a specific combination of components that can cause the noise?
 
A

aylafan

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Jun 30, 2010
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Corsairs are rated as one of the top brand PSUs and are typically more reliable than most Cooler Master PSUs. I think you should get a replacement for it or go buy another reliable brand PSU.
 
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wolfestone

Member
Apr 6, 2011
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Thanks guys, I did read the thread on corsair's forum and tried all the steps suggested. I also saw a couple of other people over there had the exact same issue as me.

I've shipped it back for a refund and am now looking for a new one. I may try another model of corsair, but also are these all quality brands?

seasonic
pc power & cooling
enermax

and/or if not, any others I should be looking at? would like to keep this under $100 as my system isn't anything ridiculous (i5, single geforce 550ti, one sata hard drive, one sata optical drive, and a few regular fans)
 
BoomerD

BoomerD

No Lifer
Feb 26, 2006
65,703
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IMO, the following PSU's are the only ones worth putting in a computer:

Corsair
XFX
SeaSonic
Antec
NZXT HALE units.
 
fffblackmage

fffblackmage

Platinum Member
Dec 28, 2007
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Along with BoomerD's list, Enermax is another excellent PSU manufacturer, but they're just usually a bit too expensive to recommend when there are just-as-good-but-cheaper available.
 
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Blastman

Golden Member
Oct 21, 1999
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As already mentioned the 400W psu recommendation for that 550Ti graphics card is for the whole system -- not for just the 550Ti power requirements.

A 550Ti only draws about 91 watts peak with 5.2A (5.2 x 12) = 62.4W on 12v 6/8 pin connector. Since your psu is rated 18A (216W) on the rail connected to the graphics cards the coolermaster will have plenty of power assuming the rest of your system does not require a lot of power.
 
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