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[Question] Is power draw from "over-kill" PSU higher compared to lower wattage PSU in same rig?

post #1 of 14
Thread Starter 
To keep semi-short, I have a near brand new EVGA SuperNOVA G2 1600w & 550w PSUs. The 550w is currently in my rig but want to use that for a build for my girlfriend. I was thinking about putting the 1600w into my rig in exchange, but my question is will this 1600w draw more power (e.g cost me more money in electricty) than the 550w was?

Does the 1600w have a base/floor wattage value where it will always idle at or will it just draw whatever the computer needs and supply that?
post #2 of 14
Quote:
Originally Posted by drazah View Post

will it just draw whatever the computer needs and supply that?

This.
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post #3 of 14
Power supplies have an operating point where they run at maximum efficiency. That is, the power losses converting from AC to DC are minimized. A good rule of thumb is to assume this maximum efficiency point is around half the total wattage rating for the power supply. So the ideal situation would be if your computer were using 800 Watts and had the 1600 watt PSU.

That being said, efficiency losses from your PSU are going to be a very small portion of your overall energy usage. If they weren't, the PSU would be very hot since power loss is converted to heat. If you're concerned about your energy bill, turn off, hibernate, or standby when the system isn't in use- that will make a much bigger difference.
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post #4 of 14
Power supplies don't "push" power into components. The components "draw" whatever power they need from a power supply. That's the way god made electricity work!

If you put a 100 watt ( 1 amp) light bulb into a socket on a 20 amp circuit the bulb doesn't draw 20 amps. It draws the 1 amp it needs and that's all. If it didn't work that way you'd need a separate circuit (with the appropriate amperage) for every single electric/electronic device in you house.

But power supplies have different inefficiencies. How much power they themselves "draw" versus how much of that power draw they can pass along to components

A 1000 watt PSU that is supplying 400 watts and is 90% efficient draws 444 watts from the wall outlet - 400 divided by .9 = 444 watts from the wall and it passes 400 of those watts to the components.
But a 500 watt PSU that is supplying 400 watts and is 80% efficient draws 500 watts from the wall outlet - 400 divided by .8 = 500 watts from the wall and passes the same 400 watts to the components
 
 
Edited by billbartuska - 8/25/16 at 6:38am
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post #5 of 14
Quote:
Originally Posted by billbartuska View Post

Power supplies don't "push" power into components. The components "draw" whatever power they need from a power supply. That's the way god made electricity work!

If you put a 100 watt ( 1 amp) light bulb into a socket on a 20 amp circuit the bulb doesn't draw 20 amps. It draws the 1 amp it needs and that's all.

With power supplies there may be different inefficiencies though.

A 1000 watt PSU that is supplying 400 watts and is 90% efficient draws 444 watts from the wall outlet - 400 divided by .9 = 444 watts from the wall.
But a 500 watt PSU that is supplying 400 watts and is 80% efficient draws 500 watts from the wall outlet - 400 divided by .8 = 500 watts from the wall.

I'm rather coninced that a PSU with 90% efficiency does not have 90% efficiency in the whole range.
post #6 of 14
Thread Starter 
Quote:
Originally Posted by billbartuska View Post

Power supplies don't "push" power into components. The components "draw" whatever power they need from a power supply. That's the way god made electricity work!

If you put a 100 watt ( 1 amp) light bulb into a socket on a 20 amp circuit the bulb doesn't draw 20 amps. It draws the 1 amp it needs and that's all. If it didn't work that way you'd need a separate circuit (with the appropriate amperage) for every single electric/electronic device in you house.

But power supplies have different inefficiencies. How much power they themselves "draw" versus how much of that power draw they can pass along to components

A 1000 watt PSU that is supplying 400 watts and is 90% efficient draws 444 watts from the wall outlet - 400 divided by .9 = 444 watts from the wall and it passes 400 of those watts to the components.
But a 500 watt PSU that is supplying 400 watts and is 80% efficient draws 500 watts from the wall outlet - 400 divided by .8 = 500 watts from the wall and passes the same 400 watts to the components
 
 

This is exactly what I was thinking but was not sure. So technically I should be okay, if not "better"? Still contemplating on selling the 1600w for whatever I can get for it (not many people buy em) and just buying a less-expensive PSU and pocket the rest, even though in the end it would be a $$$ loss
post #7 of 14
Quote:
Originally Posted by Klocek001 View Post

Quote:
Originally Posted by billbartuska View Post

Power supplies don't "push" power into components. The components "draw" whatever power they need from a power supply. That's the way god made electricity work!

If you put a 100 watt ( 1 amp) light bulb into a socket on a 20 amp circuit the bulb doesn't draw 20 amps. It draws the 1 amp it needs and that's all.

With power supplies there may be different inefficiencies though.

A 1000 watt PSU that is supplying 400 watts and is 90% efficient draws 444 watts from the wall outlet - 400 divided by .9 = 444 watts from the wall.
But a 500 watt PSU that is supplying 400 watts and is 80% efficient draws 500 watts from the wall outlet - 400 divided by .8 = 500 watts from the wall.

I'm rather coninced that a PSU with 90% efficiency does not have 90% efficiency in the whole range.
To find out that information you have to read detailed Power Supply test results.
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post #8 of 14
Most power supplies are at their quoted efficiency numbers between 40-60% max load, so your 1600w unit you would need to be drawing 800w or so to be ideal. But that said the difference is probably a couple bucks a year.
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post #9 of 14
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post #10 of 14
Let's say that your comp draws 100W idling and 400W @ full steam.
efficiency.jpg

r_600x450.JPG

At 100W draw the 1600 efficiency is ~83%, the 550 is ~89%.

At 400W draw the 1600 is ~92%, the 550 is ~91%.


Leaving aside that small drop in efficiency at low loads (idling), and the higher initial purchasing cost, overkill PSUs are advantageous all over (lower ripple and fan noise, longer hold-up time, better reliability and longevity, etc.)
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