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Question about power supplies concerning multiple 12v rails.

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December 4, 2013 9:01:06 AM

I have a Raidmax 850w psu that supposedly has 4 12v rails rated for 34 amps each. From what I've read on the stickied thread on PSUs that means I have 61 amps total however I don't understand what the rails actually are and how people say you shouldn't put too much power on one rail. My PSU is modular so do certain slots on my PSU correspond to different rails inside or what? I just don't get how I'm supposed to avoid overloading one particular rail.

My current setup is:
i-5 3550
4 gigs of ddr3 ram
gigabyte z77-d3h mobo
1tb 7200rpm hdd
amd 6950 gfx

I just got the evga gtx 770 SC and before I plug it in I want to make sure that I have enough power. On the box it says it needs a minimum of 42 amps on THE 12v rail so I don't understand how that relates to my PSU since mine has more than one as well. I think my last psu shorted out from overload and killed two of my hdd's so I don't want to make the same mistake again.

Thanks in advance.
a b ) Power supply
December 4, 2013 9:25:25 AM

don´t worry your psu has plenty of power...
even if it´s really multi rail design (sometimes just false advertising) manufacturer would certainly not put all the stress just on 1 of those rails ,
but rather split the power delivery for the system equally between them...
usually 1 rail is for cpu power , the others for the video card/cards
and the rest of the components like hard drives etc. needs only few watts of power ...
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a b ) Power supply
December 4, 2013 9:26:10 AM

The ATX standard says that you can only have so much current on a 12v rail, (20 amps, i believe), so when graphics cards started demanding more than that, PSU makers started using multiple rails, in order to limit the current on any one rail to the standard. Most multi-rail PSUs are really single rail models when you get into the internals of the PSU. Most modular PSU's do not allow you to select which rail is supplying the power.

That being said, We need more exact specifications for your Raidmax PSU (Model number, etc) in order to advise you. Raidmax buys PSUs from several different OEMs so the quality of it is suspect at best.
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December 4, 2013 10:00:51 AM

dark_globe said:
don´t worry your psu has plenty of power...
even if it´s really multi rail design (sometimes just false advertising) manufacturer would certainly not put all the stress just on 1 of those rails ,
but rather split the power delivery for the system equally between them...
usually 1 rail is for cpu power , the others for the video card/cards
and the rest of the components like hard drives etc. needs only few watts of power ...


So the PSU automatically assigns power to certain rails so I don't have to worry about overloading one? That was my main question.

clarkjd said:
The ATX standard says that you can only have so much current on a 12v rail, (20 amps, i believe), so when graphics cards started demanding more than that, PSU makers started using multiple rails, in order to limit the current on any one rail to the standard. Most multi-rail PSUs are really single rail models when you get into the internals of the PSU. Most modular PSU's do not allow you to select which rail is supplying the power.

That being said, We need more exact specifications for your Raidmax PSU (Model number, etc) in order to advise you. Raidmax buys PSUs from several different OEMs so the quality of it is suspect at best.


I provided the link to the newegg page at the beginning of my OP where it says "a Raidmax 850w psu". If you extend the gallery it has the chart showing the amps and whatnot as well. I'd also heard that Raidmax wasn't very good before but when my old one broke I kinda panicked and just bought one. Are they so bad that I should look into replacing it ASAP or is it ok? It has good reviews on Newegg so I figure its decent.
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a b ) Power supply
December 4, 2013 10:06:02 AM

I have never seen a raidmax PSU that was anything more than a pile of garbage. Did a bit o research and found its made by Andyson, uses the same internals as the Andyson AD-K850AE-D7 and the Ultra X4 750w. I couldn't find any reviews on the Raidmax or andyson, but I did find one on the Ultra, and not surprisingly it failed the review.
http://www.hardocp.com/article/2009/11/24/ultra_x4_850w...
So while it is a step in the right direction for Raidmax, its still not a PSU i would use.
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a b ) Power supply
December 4, 2013 10:33:52 AM

yes units made by andyson are mediocre at best ...
i too didn´t find any review on this particular model
but it´s pretty save to assume it has taiwanese/chinese capacitors on the secondary ...
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December 4, 2013 10:57:42 AM

So can someone just answer my question about what power goes to what rails? Does the PSU assign it evenly across all rails or do I have to do it?
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a b ) Power supply
December 4, 2013 11:02:08 AM

Power distribution should be handled automatically. Just think of the PSU as having a single 61a 12v rail.
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