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# Quick PSU question

OK, if W/V=A, I am assuming that when the list rated A per rail or total available A, that is where the efficiency come in? So, my PSU for example is a 520W, so 520/12=43.3333A. How does the 43.3333A get split and dropped to get the actual output of the PSU? I know the 18A rating per rail is max allowable per rail, but how do I know what the average output is? (aside from pulling out my DMM)
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Quote:
 Originally Posted by dralb OK, if W/V=A, I am assuming that when the list rated A per rail or total available A, that is where the efficiency come in? So, my PSU for example is a 520W, so 520/12=43.3333A. How does the 43.3333A get split and dropped to get the actual output of the PSU? I know the 18A rating per rail is max allowable per rail, but how do I know what the average output is? (aside from pulling out my DMM)
No.

Efficiency is the ratio between what's being put out (in DC Watts) and what's being sucked in (AC Watts). It has nothing to do with how rails are distributed.

A power supply only puts out what's demanded of it. So you're not putting out the max capability of each rail. You're only putting out whatever the load on that rail is. And if that load exceeds the capability of that rail, the PSU shuts down. You can have one rail loaded more than another, and that's why the limits of these rails are not additive.
'Morning Jonny

Also note that you cannot divide the total Wattage by 12 to get the max current on the 12V rails. A part of the power will be needed by the 3.3V and 5V rails (and some other small stuff). If you check the label of your PSU, you'll see the three 12V rails, and below it is printed '480W'. Thus, the max current on the 12V rails is actually 40A (which is pretty darn good for a 520W PSU).
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If your system was pulling 520w, then your PSU would be providing 520w. Assuming 75% efficency, the PSU would be pulling 693w from your outlet.

If your system was pulling 300w, then your PSU would be providing 300w. Assuming 80% efficency, the PSU would be pulling 375w from your outlet.

Now-a-days, you need like 5w per HD on the +5v rail and 3w per DIMM on the +3.3v rail. Plus a tiny bit for PCI cards, standby LED, and a few other tiny things. These all generally draw less than 30-50w.
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And of course, in this specific case we have somewhat of an oddity.

http://www.jonnyguru.com/modules.php...=Story&reid=18

The PSU you have (and I just picked up one myself...) doesn't follow the 'traditional' rules for ATX12V PSUs and rail distribution.

In practical terms, you'll probably never will have any problems, unless you hook monster video cards up to this (most excellent) PSU.

And Jonny: the review states that the design is effectively two-rail. Is this later confirmed? I've heard around that the design is actually single rail... could you please chime in on this one? (just my own curiousity)
 Folding for Team Just Be Cause (13 items)
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Quote:
 Originally Posted by jonnyGURU No. Efficiency is the ratio between what's being put out (in DC Watts) and what's being sucked in (AC Watts). It has nothing to do with how rails are distributed. A power supply only puts out what's demanded of it. So you're not putting out the max capability of each rail. You're only putting out whatever the load on that rail is. And if that load exceeds the capability of that rail, the PSU shuts down. You can have one rail loaded more than another, and that's why the limits of these rails are not additive.

So, there are actually 43.333A available on the 12V rail? I have been meanig to take some measurements as, due to my cable modding, I am running almost everything off one molex lead. I don't have a very demanding system, but I would like to know what the draw actually is.

On a motorcycle, we would sometimes use a shunt to connect a DMM inline with the battery lead to what the ammperage draw is, but I am not sure how to do this with a PSU. I'll have to think on it as, being behind a desk for the last 8 years, my knowlege of these things is slowly being pushed out by other things, lol.
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Quote:
 Originally Posted by Chozart And of course, in this specific case we have somewhat of an oddity. Read this review here: http://www.jonnyguru.com/modules.php...=Story&reid=18 The PSU you have (and I just picked up one myself...) doesn't follow the 'traditional' rules for ATX12V PSUs and rail distribution. In practical terms, you'll probably never will have any problems, unless you hook monster video cards up to this (most excellent) PSU. And Jonny: the review states that the design is effectively two-rail. Is this later confirmed? I've heard around that the design is actually single rail... could you please chime in on this one? (just my own curiousity)

Which PSU Chozart? The 520HX is only single rail and doesn't actually have OCP.

The Corsair and Thermaltake 1000w units (built by CWT) are units that actually do have two +12v rails. I believe the Enermax Galaxy 1000w does as well.
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Intel X25-M 160GB + 3xRAID0 500GB 7200.12 Window 7 Pro 64 Acer H243H + Samsung 226BW XARMOR-U9BL
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 Once again... (13 items)
CPUMotherboardGraphicsRAM
i7 920 [4.28GHz, HT] Asus P6T + Broadcom NetXtreme II VisionTek HD5850 [900/1200] + Galaxy GT240 2x4GB G.Skill Ripjaw X [1632 MHz]
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the 520HX

Quote:
 Originally Posted by jonnygury's review This demonstrates that if the two rails are in fact separate, there is no OCP (over current protection) on each rail. Outside of a few traces zig zagging across PCB, I couldn't find how even 12V1 and 12V2 are separate, but I'm going to give Seasonic (the OEM for the Corsair units) the benefit of the doubt and say that we seem to have two 12V rails here, neither with any kind of "limit" on them.
It's this quote why I asked jonny. Maybe I missed an update on this review, but it seemed at that time the jury was still out on the issue. The 'single rail' notion for that PSU seems to be based on a Jonnyguru review, but this one isn't conclusive.
 Folding for Team Just Be Cause (13 items)
CPUMotherboardGraphicsRAM
E8400 @ 3.8 GHz DFI LANPARTY DK X38-T2R eVGA 8400GS 2GB Mushkin DDR2 800 (single stick)
Hard DriveOptical DriveOSMonitor
250GB WD SATA None Windows XP Pro 32-bit HP Pavilion f1703
KeyboardPowerCaseMouse
N/A Corsair HX520 Coolermaster Cavalier N/A
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 Folding for Team Just Be Cause (13 items)
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E8400 @ 3.8 GHz DFI LANPARTY DK X38-T2R eVGA 8400GS 2GB Mushkin DDR2 800 (single stick)
Hard DriveOptical DriveOSMonitor
250GB WD SATA None Windows XP Pro 32-bit HP Pavilion f1703
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OK, great review. I may have to look and see what is plugged in where. I may move my PCIE power to the other slot just to split the load a little. I am sure nothing is wrong, but why not lessen the strain a hair? Thanks for the info.
 Current (3 items)
CPUMotherboardGraphics
i5 6600k MSI Z170-A Pro RX-480
 Current (3 items)
CPUMotherboardGraphics
i5 6600k MSI Z170-A Pro RX-480
Quote:
 Originally Posted by dralb OK, great review. I may have to look and see what is plugged in where. I may move my PCIE power to the other slot just to split the load a little. I am sure nothing is wrong, but why not lessen the strain a hair? Thanks for the info.
Don't worry about it. I am almost positive the PSU is actually single rail. The "triple rail" diagram was just to trick Corsair and get the unit out the door. Besides, the load is identical regardless of which plug is used.
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i7 920 [4.28GHz, HT] Asus P6T + Broadcom NetXtreme II VisionTek HD5850 [900/1200] + Galaxy GT240 2x4GB G.Skill Ripjaw X [1632 MHz]
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Intel X25-M 160GB + 3xRAID0 500GB 7200.12 Window 7 Pro 64 Acer H243H + Samsung 226BW XARMOR-U9BL