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System=draw?

post #1 of 8
Thread Starter 
Quick noob question. Does the wattage the psu is providing for the computer equal the amount coming from the wall. I had heard some odd things regarding this so I'd like to get it straight. Thanks!
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post #2 of 8
The wattage the PSU is outputting is never what is precisely being pulled from the wall. No PSU is 100% efficient, so all pull more from the wall than what is actually being produced.
    
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post #3 of 8
Even a 90+ Gold rated PSU still draws some extra wattage. About 10% max.

As far as my logic tells me.
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post #4 of 8
Thread Starter 
Even when it's not near max draw? Like a 650w psu is only feeding 450w into a system, that psu is drawing more than 450w from the wall?
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post #5 of 8
Quote:
Originally Posted by Sir Shfvingle View Post
Even when it's not near max draw? Like a 650w psu is only feeding 450w into a system, that psu is drawing more than 450w from the wall?
Yes, you have to add the power lost to the power used at that load. So 90% eff at 450w load = 495 drawn.
post #6 of 8
There is a sticker on your PSU that breaks down the rails and gives totals. These are the output numbers. For instance, my 650W PSU actually states that it's total OUTPUT is 750W. If it is truly an 80% efficient model, than I can calculate that the max draw from the receptacle will be ~937W.

So, if your PSU is only providing 450W to your system max and it is an 80% model, then you can figure that the real draw is something close to 560W. You can measure this yourself in a number of ways.

Put in real terms, that means that every hour your machine is a max usage, you will be buying 1.2KW/hr of energy from your utility. In my area, we pay about $.08 per KW/hr.

From a functional point of view, this also means that you are tapping ~1/3 of the amperage available to a normal 15A household circuit.
(560W/120V=4.66A)

Keep in mind that the efficiency rating is based on ideal conditions in lab environments. Actual usage may vary, lol.

Sorry if I ramble, but I'm an Electrician and I can't help but butt in when talking about energy.
Edited by grishkathefool - 5/19/11 at 5:00pm
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post #7 of 8
Thread Starter 
No man, that's great info, thanks!
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post #8 of 8
By the way, I am seeing that you pay about $.09 per KW/hr. Still very much affordable.

The part about how much you are drawing of the circuit is the reason that I recommend at least one dedicated circuit to a Tech area. I ran a dedicated 20A circuit to my desk. This more than provides for my 2 desktops, phone, router, modem, monitors, and printer. As a rule, we don't like to load out a circuit more than 80%, by the way.
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