tcassisi Posted January 17, 2008 Share Posted January 17, 2008 This may be a silly question, but I don't understand which of the two statements below is correct regarding the rating of a PSU (e.g. HX620W) 1) EVGA support says: In your example: 620 W at 80% efficiency means a realistic 496 Watts. 2) A different forum on EVGA says: The way a PSU works is that it will actually draw MORE from the wall in order to deliver it's output needs. Like I said, it will need to draw more than 620w from the wall if it is only 80% efficient. Since the PSU is converting AC to DC it will never be 100% efficient. The efficiency rating of a unit is a measurement of this. It does not mean that it will only deliver 80% of it's rated capacity. It means that it will convert 80% of the AC current to DC current. See here for the original thread if it is unclear: http://www.evga.com/forums/tm.asp?m=151488&mpage=3&key= Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted January 17, 2008 Corsair Employees Share Posted January 17, 2008 #2 is correct. For example if you have a 1000w PSU that operates at an average of 80% then when operating at 1000w the PSU is actually drawing 1250w from the wall. 80% of 1250w is 1000w. Higher efficiency PSUs actually save you money on your power bill! edit: Fixed my math! Link to comment Share on other sites More sharing options...
Wired Posted January 18, 2008 Share Posted January 18, 2008 #2 is correct. For example if you have a 1000w PSU that operates at an average of 80% then when operating at 1000w the PSU is actually drawing 1200w from the wall. Higher efficiency PSUs actually save you money on your power bill! AC * Efficiency percentage = DC , so to calc the AC: DC / Efficiency percentage = AC 1000W / .80 = 1250W Link to comment Share on other sites More sharing options...
tcassisi Posted January 18, 2008 Author Share Posted January 18, 2008 Higher efficiency PSUs actually save you money on your power bill! Yes - however that applies regardless of the "convention" of PSU power rating... So to be clear: the convention is to quote the DC W available post conversion from the AC? If that is so, then in reviews of systems how are they reliably determing the "total W draw" from a system? Are they in fact just measuring the AC side and I still have to take 80% of this to get the DC side? I am trying to reliably determine whether during particuliarly intensive game scenes I am peaking just over what the HX620W can deliver. However I do not have the necessary DMM or knowledge of where to place it to take my own measurements... Link to comment Share on other sites More sharing options...
JoeBob Posted January 18, 2008 Share Posted January 18, 2008 Well, most places I've seen that review hardware, quote the AC draw from the wall socket, not the estimated output from the DC side. Link to comment Share on other sites More sharing options...
tcassisi Posted January 18, 2008 Author Share Posted January 18, 2008 Okay - so if a review says the AC draw is 775W, then that means the DC available/used (assuming 80% efficiency) is 620W? But the PSU itself would be called a 620W (or above in this case, as it might not be maxing out the power usage) PSU? So I suppose one way to easily check my system under load would be to buy a simple at-the-socket device, multiply by 80% and see how close the result is to the rating of my (HX620) PSU? Link to comment Share on other sites More sharing options...
EliteKiller Posted January 18, 2008 Share Posted January 18, 2008 Okay - so if a review says the AC draw is 775W, then that means the DC available/used (assuming 80% efficiency) is 620W? Yes. You'd need a monster system to consume 775W from the wall. But the PSU itself would be called a 620W (or above in this case, as it might not be maxing out the power usage) PSU? It could be a quality 600W or larger psu. So I suppose one way to easily check my system under load would be to buy a simple at-the-socket device, multiply by 80% and see how close the result is to the rating of my (HX620) PSU? Pick up an inexpensive Kill-A-Watt to measure A/C power consumption. It doesn't handle transient loads very well, but it is a useful tool. http://www.newegg.com/Product/Product.aspx?Item=N82E16882715001 To stress test I would recommend you run Prime95 25.5 (automatically stresses all 4 cores), loop 3DMark06, rip a DVD, and copy gigs of data from one HDD to another. Link to comment Share on other sites More sharing options...
Corsair Employees RAM GUY Posted January 18, 2008 Corsair Employees Share Posted January 18, 2008 AC * Efficiency percentage = DC , so to calc the AC: DC / Efficiency percentage = AC 1000W / .80 = 1250W Thanks for correcting that! I must have posted a little too hastily! Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.