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Resistance, heat & temperature change

post #1 of 6
Thread Starter 
This came up in a thread on heat a little while back and it did get me wondering about how much difference the temperature of the CPU (and other components for that matter) increase their power consumption.

Simply: When something gets hotter it has more electrical resistance and requires a higher voltage thus uses more power and generates more heat.

Personally, I like to have everything in my case at as close to ambient as I can, since I find having a computer dumping hot air into a corner of the room I notice the temperature change a lot more than if I have a computer putting out air a few degrees above ambient. But in reality, they're using a very similar amount of energy and should be emitting about the same amount of thermal energy (or should they)

Obviously the hotter air will have more drive to change temperatures, especially near the case, but it should diffuse anyway with distance from the case.

My question is, how much does a lower running temperature for the CPU affect the amount of energy used and emitted in heat?

Is it actually a noticeable difference, or is it just my imagination?
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post #2 of 6
Temperature is an effect of power consumption.


So high temps don't mean high power consumption, just insufficient cooling. A 45w mobile CPU can get up to 80c and still spend much less power than a 1100T running @ 4.2GHz 1.5v under 40c.
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post #3 of 6
it matters enough that i cant get stable above 85C but if i knock the vcore down a bunch and Prime95 rides at 77C it is stable

you can calculate it yourself. vcore * 125 amps is the wattage. most of it goes as heat. A MUGEN-2 has like 140W dissipation and my cpu kills it without push/pull at 1.36v
Edited by AMD HATER - 1/8/11 at 4:18pm
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post #4 of 6
Thread Starter 
Not quite the answers I was looking for, but I may have found something interesting, I had assumed that resistance increase with temperature, then I thought that for Silicon it might not actually change much (thus not be a factor), but low and behold, I find:

That apparently the resistivity of Si decreases as temperature increases.

So running your chip at a higher temperature, should in theory be more efficient?


Wasn't expecting that... haven't had much luck finding a resistivity/temp graph either, which is disappointing.
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post #5 of 6
Quote:
Originally Posted by Crabid View Post
Not quite the answers I was looking for, but I may have found something interesting, I had assumed that resistance increase with temperature, then I thought that for Silicon it might not actually change much (thus not be a factor), but low and behold, I find:

That apparently the resistivity of Si decreases as temperature increases.

So running your chip at a higher temperature, should in theory be more efficient?


Wasn't expecting that... haven't had much luck finding a resistivity/temp graph either, which is disappointing.
No, the electrical resistance decreases as temperature decreases, in general. Thus at the same OC a cooler CPU should be noticeably more efficient that is use less electricity. Noticeably probably being up to a dozen Watt of electricity or so, depending on the temperature difference.

Some light reading for you, from a 200-level collegiate physics class that came up on a quick Google:

http://spiff.rit.edu/classes/phys273...emp_coeff.html
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post #6 of 6
PM the user cdolphin and ask if he has anything to contribute with. He seems like he knows a lot of stuff on these subjects. Check the link in my sig, that's some awesome reading although more or less irrelevant to your question.
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