conquistadorst

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This is actually a question just out of curiosity. Given a standard name brand (say Antec or Tt) 480watt PSU, does the unit actually eat ~480w out of the main power consistently, or does it fluctuate based on the needs of the rest of the system? ie go up and down while different components are being used.
 

etp777

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FLuctuates based on needs, and remember that if it's not a PFC pwoer supply, atually only runs at 70% efficiency, so if you're drawing 420 watts from computer side, actually pulling 600 watts from socket.
 

conquistadorst

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You may be right about the fluctuation based on need but about the rest I don't think is quite right. As far as I know OEMs rate their units on the power they draw from the socket and efficiency (65~68% not 70%, depending on brand) is what the computer receives. This is why those with low efficiencies like most off-brand PSUs get a bad rap.

Here is an article from a reputable site you can read to get yourself up to speed:
http://www.anandtech.com/showdoc.html?i=1841&p=1

As for PFC, to my understanding (I may be wrong) most PSUs, if not all, have it. It keeps the DC flow clean and consistent (some decrease in output efficiency here). However most units do this through a passive method, but then there are those who use an Active method (APFC) like in some units distributed by Tt or Forton. The active method basically does an even better job at providing a cleaner DC flow but again decreases output efficiency even more by powering the active mechanism.

I think I'm somewhere near the target but someome please correct me if I am wrong, I like to know how things -really- work :)
 

etp777

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Look at any power supply, and read the label. Add up the numbers(or jsut read section where they add it up) for the various rails, and you will see it adds up to around the rated wattage of the unit. The labels are describing the output, not the power draw.

And on PFC< most in europe are, due to EU regulations, but not here in states. Not worth the extra cost to those of us who don't need it. The minimal savings in electricity aren't worth the additional outlay at the start, at lesat not to me.
 

Obtuse

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Ok, I think this was your question: "If I buy a 480 Watt power supply, is is constantly sucking 480 watts worth of power from the outlet?" Answer: NO. 480 watts is the MAXIMUM that that unit can supply. It will draw enough to power the given components that are running at any given time. So, it does flucuate. When your CD-ROM spins up, it draws more power. When you load up FarCry and turn all your case fans, that draws power. If you just have your comp running idle, it draws less power than when its not. But the part about efficiency is right. Say at a given moment, your system is pulling 210W, and your supply has a .70 efficiency. At that point, your system is actually pulling 300W (because 300 X .70 = 210) from the wall socket. The extra 90W are converted into heat because the supply is not 100% efficient, it loses some of the wattage while it converts outlet power to mobo-acceptable power.

"The only way to overcome temptation is to yield to it" - Oscar Wilde
 

Crashman

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The power supply only draws as much power as it needs. Power supplies are based on small electrical transformers, devices which convert electricity to electromagnetic force and back to electricity at a different voltage. They only discharge as much power as your system can use, therefor they only take in enough power to keep the coils excited.

But they do produce heat, hence an efficiency loss. No huge concern there as most extremely high end systems only pull 200W continuously. So that means even at 70% efficiency it's only pulling 285W. One reason you need such a "big" power supply is that your system might need more 12v power, for example, than a smaller one could provide.

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