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Skeptical about PSU efficiency

post #1 of 5
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I swapped my TX750v2 out for an AX750 back in January. I didn't feel like I needed the 850 unit because I will not SLI in the future because there is no need in having 2 obsolete cards in 4-5 years. I always assumed my MSI GTX 680 Lightning only required around 550w but I just checked yesterday and saw that MSI recommends a 650w unit. I know my psu is capable of delivering over the rated 750 due to it being a gold unit but I have been wondering with my i5-2500k being overclocked to 4.5ghz and my voltage fluctuating between 1. 350 and 1.376 on voltage under full load, if my system is around the 50% load mark for best efficiency. In the future I plan to take my cpu to 5ghz when needed and I'm assuming that it will need something over 1.4 volts. I want to stay around the 50% mark and not push my psu to the actual rated 750.
Edited by TheAssassin - 3/24/13 at 11:31pm
post #2 of 5
Quote:
Originally Posted by TheAssassin View Post

I swapped my TX750v2 out for an AX750 back in January. I didn't feel like I needed the 850 unit because I will not SLI in the future because there is no need in having 2 obsolete cards in 4-5 years. I always assumed my MSI GTX 680 Lightning only required around 550w but I just checked yesterday and saw that MSI recommends a 650w unit. I know my psu is capable of delivering over the rated 750 due to it being a gold unit but I have been wondering with my i5-2500k being overclocked to 4.5ghz and my voltage fluctuating between 1. 350 and 1.76 on voltage under full load, if my system is around the 50% load mark for best efficiency. In the future I plan to take my cpu to 5ghz when needed and I'm assuming that it will need something over 1.4 volts. I want to stay around the 50% mark and not push my psu to the actual rated 750.

Its absolutely useless to worry about PSU efficiency unless you are going to run your machine 100% 24/7/365, doing some kind of DC projects or whatever. The "efficiency" adds up to a few dollars a year, if that.

As far as your rig, you are probably right smack in the middle of its output anyways. The 680 Lightning will eat up some power if you push past 1400mhz, mine could pull around 300W by itself when I passed 1350-ish, but your whole rig is definitely not more than 400-450W total.
post #3 of 5
Quote:
Originally Posted by TheAssassin View Post

I swapped my TX750v2 out for an AX750 back in January. I didn't feel like I needed the 850 unit because I will not SLI in the future because there is no need in having 2 obsolete cards in 4-5 years. I always assumed my MSI GTX 680 Lightning only required around 550w but I just checked yesterday and saw that MSI recommends a 650w unit. I know my psu is capable of delivering over the rated 750 due to it being a gold unit but I have been wondering with my i5-2500k being overclocked to 4.5ghz and my voltage fluctuating between 1. 350 and 1.76 on voltage under full load, if my system is around the 50% load mark for best efficiency. In the future I plan to take my cpu to 5ghz when needed and I'm assuming that it will need something over 1.4 volts. I want to stay around the 50% mark and not push my psu to the actual rated 750.

When video card companies make a PSU wattage recommendation, they always inflate it because they know a fair amount of people have crappy PSUs that can only deliver 3/4 of its rated wattage.

According to [H]ard|OCP, the GTX 680 Lightning takes at most 300w from the wall, which translates to ~250w of power delivered from the PSU to the card (which is the number that counts). Even if you were to go to 5.0GHz, there's still plenty of headroom on your 750w PSU.

Also, modern power supplies are almost equally efficient anywhere between 20% and 100%, as seen in the below graph:



As you can see, there's only a 2% difference between its most efficient point @ 50% rating and its low points @ 20% and 100%. It's just not anything to worry about.
Edited by svenge - 3/24/13 at 11:07pm
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post #4 of 5
Quote:
Originally Posted by TheAssassin View Post

with my i5-2500k being overclocked to 4.5ghz and my voltage fluctuating between 1. 350 and 1.76 on voltage under full load,

I am going to assume you mean 1.350 and 1.376

From what I have heard that 50% load for best efficiency is something you do not need to worry about for quality power supplies.
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post #5 of 5
Here's a good read about efficiency: http://www.overclock.net/t/711542/on-efficiency/0_20

And another on the 50% load myth: http://www.overclock.net/t/872013/50-load-myth/0_20

And of course you can always use PSU calc to determine both your PSU requirements and what some good options are: http://www.overclock.net/t/1140534/psu-calc-final-release/0_20

But the short version is this: Scorpion49 is right about your whole system requirements, and your PSU is both top quality and more than adequate for your system. There is absolutely nothing for you to worry about, regardless of how far you overclock your system.
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