i really cant understand PSU combined power

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gabi014

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Jul 10, 2012
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hey guys,
i have something that disturbing me, i just cant understand how much wattage delivering the 12v output if all outputs are working. for example this power supply:
S12II-Bronze-03.jpg


how much wattage can S12II-520W it deliver on the 12v output when all outputs are working?
 
Solution
ko888
If you draw less than 40 Watts from the combined +3.3V and +5V rails then you will be able to draw up to 40 Amps from the +12V rail.

If you're drawing the maximum 130 Watts from the combined +3.3V and +5V rails then you will only be able to draw a maximum of 390 Watts or 32.5 Amps from the +12V rail.

The PSU's total power output of 520 Watts is the limiting factor.

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gabi014

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dude thats 40A when all outputs arent working exept the 12v output.. thats mean when a full pc will connected to that power supply so the 480w will be lower. so whats i want to know is, how much wattage can it deliver when all outputs are working? surely thats isnt 480w
because if you will calculate 480w+130+9.6+12.5 thats 630w and not 520 (thats wrong). so i need to know how do i know the combined power.
 
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Unolocogringo

Unolocogringo

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The 520 has a max output of 480watts max on the 12v rail when the 5v and 3.3v are outputting 40watts combined.
If you draw more(unlikely) from the 5v &3.3v lines the 12v max will drop accordingly.
Very few components draw from the 3.3v and 5v lines on modern computers. Hard drives and optical drives as well as USB devices.

So unless you have an uncommon amount of HD,OD or USB devices you will get a max of 480watts of 12v.


 
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geofelt

geofelt

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The multiple rails are an artificial UL safety spec. In this case, it limits the output to 20a each. The max output is rarely additive. That really does not matter since virtually all psu's really only have one rail power source.
The operative limit is the 40 combined amps. =12v is what the cpu and particularly the graphics card uses today.
 
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gabi014

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are you sure that will draw 480w? that doesnt seem right. so basically if i will connect all components that the pc will need that still will deliver 480w on the 12v rail? i dont think so, the power will be lower, doesnt it right?
 
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ko888

ko888

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Feb 18, 2009
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If you draw less than 40 Watts from the combined +3.3V and +5V rails then you will be able to draw up to 40 Amps from the +12V rail.

If you're drawing the maximum 130 Watts from the combined +3.3V and +5V rails then you will only be able to draw a maximum of 390 Watts or 32.5 Amps from the +12V rail.

The PSU's total power output of 520 Watts is the limiting factor.

gr2.gif
 
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gabi014

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Great!! thanks.
but how do i know when im drawing 40w or 130w from the 3.3V & 5V rails?
 
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gabi014

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ok last question... all the modern rigs today that people have, like the Haswell, Ivy bridge, and Sandy, how much they're drawing average from the 3.3V and the 5V?
 
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ko888

ko888

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For a modern mainstream gaming system the combined +3.3V & +5V power draw is around 31 Watts.

For a high-end gaming system the combined +3.3V & +5V power draw is around 41 Watts.
 
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