How manufacturers determine power supply ratings?

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Stephen_D

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Oct 28, 2013
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Ok, so here it goes, I have a PSU here that is rated 585 watts from Orion. Its an older one and from what I have heard, on older PSU, even its it past my recommended value, It may not always fit since the ratio of wattage per rail/voltage is different. So here are the specs of the PSU.

+3.3v @ 18A (59.4w)
+12v @ 18a (216w)
+5v @ 21a (105w)
+5vsb @ 2a (10w)
-12v @ 0.5a (6w)

From what I calculate this PSU has 396.4 watts. Also under the all the rails, it is clearly indicated 585 watts maximum. So how does the manufacturer calculate wattage here? Also, I know there is some power loss in a PSU caused by the heat it creates. From what I understood, the loss should not be calculated in the maximum rating. Even if it was, a typical PSU would have 75 efficiency still leaving the PSU under 500 watts from its ratings.

So how does a manufacturer determine that this power supply can supply up to 585 watts?!?!

Thanks

Steph
 
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mouse24

mouse24

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Nov 30, 2010
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Mhmm, it stuff like this that make us recommend only certain manufacturers PSUs. AFAIK theres nothing stopping the PSU guys from putting whatever wattage they like on a box. More so if its not even 80+ certified. (not that 80+ is the be all end all, its not)

In short, they just make it up to sell units.
 
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manofchalk

manofchalk

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May 11, 2012
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The wattage written on the box does not necessarily mean so, but it should represent the maximum supported power available over the 12v rail, usually rounded to the nearest 50W.
However there is nothing saying they have too, and budget/no-name brands will often inflate that number by including the wattage of all the rails.

Efficiency doesn't change the output wattage, a PSU could be 10% efficient and still pump out its required 550W. Efficiency is the difference between the power drawn from the wall and how much is output, the difference is lost as heat.
 
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Stephen_D

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Oct 28, 2013
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I understand that the actual ratings might be made up, but I mean I wouldn't think that a company would be dumb enough to make up numbers and not make them add up. I learnt the hard way with the PSU I bought when building my rig, supposed to be 500 watts but can barely put out 300!.And now, having a pretty decent machine, wanting to add a second graphic card, ram and a ssd, I was planning on buying a decent PSU. But still I have remains of what seemed to be an usuable PSU. Being between jobs at the moment, my budget for my PC upgrades are pretty slim. My build is a fx8350 with 8gb (2 sticks) of ram, 1 sata drive (2tb) and a radeon 7770.

In my next upgrade I was aiming for 16 gb (2 more sticks of 4gb) and add something like a radeon 67XX card. I don't use it very much for gaming, mostly multitask alot, so I will be adding the card to have 5-6 screens on my system (I know it seems like much, but
I can assure you I will be using all of them :p).

So basically my question is should I upgrade my psu first? I will definetly be getting a decent PSU before adding my SSD. Also, my system is not overclocked now, but eventually, I plan on doing so.

Thanks

Steph

EDIT: Btw, I don't care if my current psu dies, as its a left over from an older machine, I have a few old psu hanging around so it's not much value for me. But what concerns me if it can be a rsik for damaging my components/set my desk on fire.

Thanks
 
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toyftw

toyftw

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Jul 29, 2012
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Hi - You should be aware that low level PSU suppliers do lie/exaggerate the power ratings. I suspect (& hope for your sake) that
you might have missed a +12v rail power rating (there can be more than one) and that would account for the 'missing watts'.

The 18amps listed for the +12v rail is very low for a unit labeled above 500w, much less 585w. That +12v rating(18a) is typical of a 300w PSU, so there might be another +12v rail on your unit. If not, scrap it & upgrade.

What brand/model i it?

 
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