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How much of a power usage reducation can I expect from 4ghz to 2.66?

post #1 of 15
Thread Starter 
I tuned my bro;s i5 750 down from 4ghz and 1.26?v i think down to 1.16v and 2.66ghz, what sort of power usage could i expect to save fom doing this, anyone any ideas or experiences with underclocking?

Also how much would i stand to save in terms or power/electric bill if i went from 4ghz to stock on my i7 920?
post #2 of 15
First of all, what does a kWhr of electricity cost where you live? Secondly what kind of normal hourly usage at what kind of load do each of these machines due in a month? Given your folding rank, I presume 24/7 full load but it matters.

Also, odds are that your GPU array in your sig rig for example pulls much more power on load than your CPU.
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post #3 of 15
I would venture on somewhere between minuscule to imperceptible. Assuming that the CPU draws its max TDP (in reality it might be a little bit higher) of ~95w, that equals 95w-hrs, which is 0.095kw-hrs. Power is billed in kw-hr units (typically--at least, it is where I live), with the highest price I've seen being about sixteen cents per kw-hr (i.e., if you had something that draws a kilowatt and ran it for an hour straight, it would cost you sixteen cents).

Let's say that downclocking the CPU cuts the power consumption in half (which it won't--probably not even close, but it's a nice illustration), to 50w. If you ran it all day for 24 hours, it would cost less per day by:

16 cents x 0.05kw-hr (the difference in CPU power usage, roughly approximated) x 24hr = 19.2 cents per day, or about $5 per month difference. If it were run 24/7, and assuming the highest cost of power I've seen, and the biggest possible power savings you'd get from underclocking

That's if it's run 24/7 at max clocks vs. 24/7 at lower-power clocks. I'm making a lot of generalizations, but hopefully it illustrates the point that cutting the CPU down in speed really doesn't yield power cost savings to any extent that you'd honestly ever notice it with real-world usage. If the system is used less than 24 hours a day, then hibernating it when not in use, and using speedstep is probably better than any sort of underclocking will do.

I estimated a difference in CPU power usage of 50w for simplicity. In reality, if you underclock it, you MIGHT save maybe 15w--nowhere near 50w, so the savings would be even less.
    
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post #4 of 15
Quote:
Originally Posted by guyladouche View Post
I would venture on somewhere between minuscule to imperceptible. Assuming that the CPU draws its max TDP
http://www.silentpcreview.com/article169-page3.html

Don't assume. TDP is not a measurement of electrical draw. It is a measurement of the maximum amount of heat a given chip is allowed to dissipate at full load.

PS-Not necessarily arguing the point that energy savings may be small in the grand scheme of things, mind you.
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post #5 of 15
Quote:
Originally Posted by Skripka View Post
http://www.silentpcreview.com/article169-page3.html

Don't assume. TDP is not a measurement of electrical draw. It is a measurement of the maximum amount of heat a given chip is allowed to dissipate at full load.

PS-Not necessarily arguing the point that energy savings may be small in the grand scheme of things, mind you.
I know, that's why I made this disclaimer with what I said:

Quote:
Originally Posted by guyladouche View Post
(in reality it might be a little bit higher)
Even if it were 10% more, the effect of underclocking would still be negligible. Just decided to go with the TDP because it's near a nice round 100w to make math simple.
    
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post #6 of 15
Thread Starter 
right so its not really much difference...hmm what about with a gtx 275 in his and 2 gtx 460s in my pc? If they were underclocked much difference?

Just check my electric bill guyadouche, for first 129 kWh it costs 38cents per unit, and next 2400 kWh its 17cents, so how do I work out how much my pc is using roughly if i leave it on full whack per hour?

sorry for difficult question.
Edited by $ilent - 5/18/11 at 1:12pm
post #7 of 15
get a killawatt bro

.1v drop in voltage is probably a 50-60w difference
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post #8 of 15
Quote:
Originally Posted by $ilent View Post
right so its not really much difference...hmm what about with a gtx 275 in his and 2 gtx 460s in my pc? If they were underclocked much difference?
What are you doing with said GPUs? Folding 24/7 on them or what?

Per Nvidia's documentation, at stock, each:

-GTX275 has a max power draw of 219W
-GTX460 has a max power draw of 160W


If we *assume* that each card is at stock at that power draw and going 24/7 all month. These are worst case assumptions based on known data...That ends up being ~550kWhrs of electricity per month (0.760kW*24*30). The key being what a kWhr costs

What does a kWhr of energy cost where you live? In California, rates can be nearly $0.50USD per kWhr...in NoWhere they are as low as $0.06USD per kWhr.

At $0.50USD/kWhr. That ends up being $270USD of electricity per month.. At $0.06USD/kWhr only $33USD per month. For all 4 GPUs going full bore 24/7.
Edited by Skripka - 5/18/11 at 1:12pm
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post #9 of 15
Thread Starter 
skripa my prices are for first 129 kWh it costs 38cents per unit, and next 2400 kWh its 17cents...

Where do you get 0.760kW*Hour*Day, wheres the 760 bit coming from?
post #10 of 15
Graphics cards rarely consume a huge amount of power when idle--they already down-clock if there's no graphical load (i.e. 2D clocks), So clocking them even lower probably wouldn't result in any noticeable difference. Here's a bit of data for the GTX 460 (total system power draw) for idle and load: http://www.bit-tech.net/hardware/gra...card-review/11

Not sure why one would want to down-clock 3D clocks for a graphics card--kinda defeats the purpose of buying a beefy expensive performance card.

Honestly, for the single-computer user for "average" leisurely use, computers rarely attribute a lot to a household's overall power usage.

Can you tell us how your bro uses his computer? How much each day, what he does, etc.?
    
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