How do I measure the real power output of my PSU by reading its sticker?

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Rafael Mestdag

Rafael Mestdag

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Mar 25, 2014
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There are amperes and voltages sread into 2 categories on my PSU's sticker: Voltage and Current, there is also Frequency but this one only has measurements in Mhz. How do I add it all up in order to find out my PSU's real wattage output?

The total wattage between these two categories is shown as 500W on the PSU's sticker.

PS: The only site where I could find some extra info on my PSU claims it has 70% efficiency.
 
Solution
Karadjgne
It's impossible to add up wattage on a psu and come out even with the psu claimed wattage. For instance, my Seasonic 520w has 40A on the 12v rail (480w), 24A on 5v and 3.3v rails (130w comnined) 9.6w on - 12v and 12.5w on the 5vVSB. Here's the kicker, you can't physically run all the rails to 100% load at the same time. So you'll only get a variable portion of several rails at any given load. So if you use most of the 12v, you'll only use some of the 5v and 3.3v in conjunction, not separately.

Frequency is immaterial, if you buy a psu, it's designed to work with your power at the house.

Currently, 12v is the major rail, its used by the cpu, fans, motherboard, gpu. 5v and 3.3v are the minor rails, used by USB, hdds, and in part by...
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Amperage X Voltage = Wattage
83.3A X 12V = 999.6W
meaning the power supply can provide 83A at 12V
each Voltage Rail will have a different ratings
Numbers are from EVGA G3 1000W your PSU will vary
some manufacturers will provide tons of wattage on the 5V or the 3.3 V., while they technically provide X wattage it is only in the 5V and 3.3V variety the 12V rail that a GPU needs will fail.
add all rails total wattage together. as you can see from the G3 numbers above really good power supplies will only count the 12V rail.

if your power supply is 70% efficient and your system needs 300W of actual power then the power supply will draw 390W from the wall in order to deliver 300W to the PC the 90W is wasted as heat and other inefficiencies.
 
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So, to come up with my total watts all I need to do is to sum up the total Amperage(or just the 12V ones?) and multiply that total by 12?
 
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12V is mostly everything, 5 V feeds USB, 3.3 V feeds the lower voltage items like the on board sound and the chip-set devices.
The CPU has a 12V dedicated supply line via the 4/8 pin AUX line. the GPU gets the power from 2 places 75W from the motherboard via the slot, and up to 150W through the 12V aux line plugged directly into the GPU (not all GPU's will require the aux line and so not every GPU has them GTX 750 for example)
the 12V line also feeds low amperage lines to the SATA power and Molex power for hard drive and optical drive, but each plug also carries 5V to the devices.

add up just the 12V for matching specs, IE a video cards that needs a 450W PSU, make sure it can provide that much on 12V as that is where the card will get the juice.
 
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I have an old GTX 460 which draws 160W, my PSU claims to have a total of 500W, but the 12V rail Wattage on the sticker says 360W. Should I remove this card immediately or can I simpy underclock it to a minimum and hope for the best?

PS: My PSU has a 6-pin connector which I use to power the card which in turn requires another 6-pin connector which I adapted from one of the PSU connectors. The PSU heats up almost everytime I play a demanding game and I'm worried because this same model of PSU simply died a week ago while I was playing a demanding game.
 
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Well, 160W for the GPU and up to 90 for the CPU if it's Intel, if it's AMD up to 120, if it's not 9590.
160 + 120 = 280 + 50 for motherboard = 320 + 30 for small stuff = 350W.
I would say don't use it. As it is most likely a bad PSU, you don't know what'll happen.
 
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the gtx 460 can draw 26A. your PSU can only deliver 30A total. that is cutting too close for my tastes. there will be other devices that will need power and 4A is not enough play for me. you are literally pushing the limit.
What is the rest of the system? can you afford a new PSU/what is budget?
 
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You're talking about your "Hoopster" PSU, as seen in other threads?

Actual reliable output of that would be somewhere between 0 and 10 watts.
 
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Ok, please help me keep this card. If for example, I disabled(like I have now) 2 of the 6 cores, put Windows power management in "balanced" plus if I down clocked the GPU down to a playable limit where with reduced details and resolution I could still play with a reasonable FPS. Suppose I do all that, could I keep this card without running the risk of the PSU dying again? Or at the very least reducing dramatically this risk?
 
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What are the typical symptoms of a dying PSU? Overheating? I'm currently stress testing my 4 active cores with Prime95, it's been about 5 minutes and the PSU is still cold.
 
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It's impossible to add up wattage on a psu and come out even with the psu claimed wattage. For instance, my Seasonic 520w has 40A on the 12v rail (480w), 24A on 5v and 3.3v rails (130w comnined) 9.6w on - 12v and 12.5w on the 5vVSB. Here's the kicker, you can't physically run all the rails to 100% load at the same time. So you'll only get a variable portion of several rails at any given load. So if you use most of the 12v, you'll only use some of the 5v and 3.3v in conjunction, not separately.

Frequency is immaterial, if you buy a psu, it's designed to work with your power at the house.

Currently, 12v is the major rail, its used by the cpu, fans, motherboard, gpu. 5v and 3.3v are the minor rails, used by USB, hdds, and in part by the cpu and other components. So you could stress test the cpu all day and never overheat the psu. Games are different.

The biggest power hog by far is generally the gpu and this is what'll really determin the size of the psu. You can find size recommendations for psu listed on most gpu boxes, manufacturers websites or barring that either amd or nvidia websites.

A good psu will have a 12v rail that's a major portion of its total wattage, and have pcie power connectors to match. For a 500w unit, this means that it should have at least 38A (456w) on the 12v rail and a 6pin and 6+2pin pcie. Since your psu has only the single 6pin, at best it's designed not for gaming use (no decent gpu) but for office use with more than just 1 hdd. At 30A 12v, it's severely lacking, it's either a very old design or very cheaply made and the manufacturer knows this, so only supplies a single 6pin, knowing that it'll not handle any real power draws. At 70% efficiency, I'd lay bets it's actually both, any modern psu of any kind of quality is at least rated Bronze (The 80 Plus Bronze rating means that the PSU is rated for at least 82% efficiency at 20% load, 85% at 50% load, and 82% at 100% load.)

Best advice if you want to keep your gpu is get a better psu (not necessarily meaning bigger is better, just a better quality). Most recommended are the xfx ts/pro 550w, Antec HCG-M 520w, Seasonic S12-II or M12-II 520w, Corsair CXM 550W. Any of those would be suitable, whichever is cheaper. Definitely mean you can now throw away that stupidity of an adapter, those things lead to just what is happening to you with using them, burned out psus or even pc's literally catching fire when too much amperage is passed through wires not designed for the load and melting.
 
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Solution


lol, but before that, the PSU would have to be really hot.
 
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