Passively cooled 2500k possible?

Borden · 7 Apr 2012 at 13:12

I'm looking to move my system over from my Lian Li q07 to a Streacom FC8 fanless case (http://www.streacom.com/products/fc8-fanless-chassis/) and am having difficulty deciding what to do in terms of processors.

Currently I have a 2500k in my system, it is probably overkill as I only use my pc for browsing and music/movies. I don't play games any more so the processor is rarely stressed. Now the case in question states that it can handle a cpu with a max TDP of 65w. The 2500k is a 95w TDP processor, however if I will never be stressing it too much then surely this should not be a problem as it will use only marginally more power and produce marginally more heat than lower power processors. For this reason I think it should work fine but would like to verify this. The way I see it I have two options:

1) Keep the 2500k - saves hassle of selling and buying replacement, may overheat (or will it)
2) Sell the 2500k and buy a lower power i5 or i3

This leads me onto my other question. How noticeable will it be for day to day usage if I downgrade to an i3? I don't want it to feel slow in comparison, however it's hard to gauge how it will perform for my needs as most reviews comparing i5/i3 tend to focus on gaming rather than desktop usage.

Another option is that I could wait for Ivy Bridge and make do with the 2500k for now?

jamesfreddie · 7 Apr 2012 at 14:05

Don't run the 2500K in that case.

You could underclock and undervolt it and it may be OK, however i would strongly suggest getting a 2400S or below.

Tuppy_Glossop · 7 Apr 2012 at 17:21

Don't forget that some motherboards allow you to override a CPU's TDP. My GA Z68AP-D3 allows me to do this. Check the mobo docs.

Justintime · 7 Apr 2012 at 23:29

Tuppy_Glossop said:
Don't forget that some motherboards allow you to override a CPU's TDP. My GA Z68AP-D3 allows me to do this. Check the mobo docs.

And what will that accomplish? That allows you to exceed the rated tdp not bring it down.

I reckon a decent undervolt will bring that heat output down a whole lot. I run mine in a silverstone HTPC with a big shuriken at 5v (dead silent) @ 1.0v stock speed and it barely breaks 63C under ibt. At a guess i'd say it was in the 60w area at most for TDP.

Tuppy_Glossop · 8 Apr 2012 at 00:10

You can lower it too

Justintime · 8 Apr 2012 at 01:39

Tuppy_Glossop said:
You can lower it too

The only way to lower a tdp is to underclock or undervolt it or both, but most cpus will run their rated speed at much lower voltage. Not used your board but if it has a setting for that, or you mean you can reduce the core current limit or turbo power limit instead of increasing etc.. its just going to do the same thing i assume, and i reckon its going to limit the clock moreso than the voltage, thus defeating the purpose of getting max speed at reduced tdp.

Borden · 8 Apr 2012 at 08:25

Tuppy_Glossop said:
Don't forget that some motherboards allow you to override a CPU's TDP. My GA Z68AP-D3 allows me to do this. Check the mobo docs.

Aha! I'd forgotten about that. Yes my motherboard does have that option 'Sustained mode power limit' which is currently set at 95W. I'll do some tests today and see how lowering it to 65W will effect the load temperatures.

Justintime said:
And what will that accomplish? That allows you to exceed the rated tdp not bring it down.

I reckon a decent undervolt will bring that heat output down a whole lot. I run mine in a silverstone HTPC with a big shuriken at 5v (dead silent) @ 1.0v stock speed and it barely breaks 63C under ibt. At a guess i'd say it was in the 60w area at most for TDP.

This is what I'm trying to say, yours only gets to that temperature under IBT. I will never be using it at anywhere near the demand that IBT will stress it to.

Justintime said:
The only way to lower a tdp is to underclock or undervolt it or both, but most cpus will run their rated speed at much lower voltage. Not used your board but if it has a setting for that, or you mean you can reduce the core current limit or turbo power limit instead of increasing etc.. its just going to do the same thing i assume, and i reckon its going to limit the clock moreso than the voltage, thus defeating the purpose of getting max speed at reduced tdp.

Unfortunately being a H67 chipset there are no undervolting options for the cpu, only for the integrated graphics chip. That would just be too easy!

Tuppy_Glossop · 8 Apr 2012 at 11:54

Justintime said:
and i reckon its going to limit the clock moreso than the voltage

It can only reduce TDP by reducing volts (W=VA my physics teacher would be amazed :cool:

). I agree it achieves this by reducing frequency and that it will be harder on the freq cut back than you, op, or I would be but it doesn't have the benefit of trial and error and has to work on the hoof. This solution certainly brings lower speed but has the advantage that the mobo is controlling the TDP.

OP, best solution is probably to buy a lower power chip. Will you notice the difference ? If all you do is surf and watch vids then probably not much, if at all.

JonJ678 · 8 Apr 2012 at 12:06

As a first point- TDP is a rather crude worst possible case figure intended to allow fan & case manufacturers to roughly size things. It isn't the power the processor uses. In particular, you can't change it any more than you can change the name of the processor.

As a similarly crude approximation, power under full load = TDP * (current frequency / stock frequency) * (current voltage / stock voltage) ^2. Undervolting goes a long way towards reducing power consumption, shame if it isn't an option. Otherwise, your 2500k sitting near idle is going to do exactly the same work a lower power dual core chip would do, and can reasonably be expected to draw roughly the same current to do so. Under any task that cant push the dual core to 100% load, I believe the quad core and dual core chips should be within a couple of degrees of each other (I partly base this on a distant memory that Intel chips switch off cores that aren't in use).

And if it all goes wrong, and you accidentally run the chip at 100% load for long enough to overwhelm the case's cooling, well, your computer will switch off. Which doesn't usually matter a great deal.

Buying a lower power chip would be madness- don't do it!

Justintime · 8 Apr 2012 at 14:12

Tuppy_Glossop said:
It can only reduce TDP by reducing volts (W=VA my physics teacher would be amazed ). .

You are confusing TDP with power draw, TDP is the thermal design power, i.e to cool a 2500K you need a cooling mechanism that can handle 95w of dissipated power. A 2500K @ 3.4Ghz 1.2v (for example) will not be dissipating the same heat when its at 2Ghz 1.2v. Though the TDP of a cpu is roughly related with its powerdraw as a guidline, its not what TDP means.

JonJ678 said:
, shame if it isn't an option.

Haven't tried it but maybe throttlestop works for SB cpus now, last i looked it didn't but that was a loong time ago.

SupermotoMX · 8 Apr 2012 at 14:42

if you only use the PC for browsing / watching movies, even an I3 would be overkill, and also be able to be used in that passive case

Borden · 8 Apr 2012 at 20:49

Tuppy_Glossop said:
It can only reduce TDP by reducing volts (W=VA my physics teacher would be amazed ). I agree it achieves this by reducing frequency and that it will be harder on the freq cut back than you, op, or I would be but it doesn't have the benefit of trial and error and has to work on the hoof. This solution certainly brings lower speed but has the advantage that the mobo is controlling the TDP.

OP, best solution is probably to buy a lower power chip. Will you notice the difference ? If all you do is surf and watch vids then probably not much, if at all.

Lowering the TDP in the BIOS worked to an extent, but there was a delay before it kicked in to throttle down the processor. This was with Turbo enabled.

With turbo disabled it worked much better, but obviously I'd lose the extra instantaneous speed.

JonJ678 said:
As a first point- TDP is a rather crude worst possible case figure intended to allow fan & case manufacturers to roughly size things. It isn't the power the processor uses. In particular, you can't change it any more than you can change the name of the processor.

As a similarly crude approximation, power under full load = TDP * (current frequency / stock frequency) * (current voltage / stock voltage) ^2. Undervolting goes a long way towards reducing power consumption, shame if it isn't an option. Otherwise, your 2500k sitting near idle is going to do exactly the same work a lower power dual core chip would do, and can reasonably be expected to draw roughly the same current to do so. Under any task that cant push the dual core to 100% load, I believe the quad core and dual core chips should be within a couple of degrees of each other (I partly base this on a distant memory that Intel chips switch off cores that aren't in use).

And if it all goes wrong, and you accidentally run the chip at 100% load for long enough to overwhelm the case's cooling, well, your computer will switch off. Which doesn't usually matter a great deal.

Buying a lower power chip would be madness- don't do it!

Justintime said:
You are confusing TDP with power draw, TDP is the thermal design power, i.e to cool a 2500K you need a cooling mechanism that can handle 95w of dissipated power. A 2500K @ 3.4Ghz 1.2v (for example) will not be dissipating the same heat when its at 2Ghz 1.2v. Though the TDP of a cpu is roughly related with its powerdraw as a guidline, its not what TDP means.

Haven't tried it but maybe throttlestop works for SB cpus now, last i looked it didn't but that was a loong time ago.

This is what I thought. TDP is only the maximum and realistically at idle or lower speeds it won't be dissipating much more heat than a low power chip.

Ideally I would like to move to a lower power chip as I feel as though I'm wasting this one a it is. If I can find a second hand Core i3 I might go for it. Either that or I may wait for the new Ivy Bridge ones along with Intel's new H77 ITX motherboard.

Scougar · 8 Apr 2012 at 21:10

You already have the 2500k, so why don't you just suck it and see?

Justintime · 8 Apr 2012 at 21:55

Have you tried throttlestop? http://www.techinferno.com/downloads/

sehcure · 8 Apr 2012 at 22:01

You could probably sell it and buy a £50 g8xx and pocket £120+?

Purgatory · 9 Apr 2012 at 03:38

Many types here low profile and passive 1155 cpu.

http://lmgtfy.com/?q=low+profile+passive+cpu+cooler+1155

Borden · 9 Apr 2012 at 10:19

Scougar said:
You already have the 2500k, so why don't you just suck it and see?

It will be a couple of weeks at least until I get the case so gives me some time to consider my options before coming to that.

sehcure said:
You could probably sell it and buy a £50 g8xx and pocket £120+?

I hadn't realised these were so cheap and offered such good performance for the price! I've just managed to bag a G860 for £55. I won't be pocketing £120 after the sale of the 2500k though, more like £70, but it's still something.

If I end up finding the Pentium a little underpowered then I'll put it in my brothers pc, and by then the Ivy Bridge processors should be out for me to pick up a low power i3 or similar.

Justintime said:
Have you tried throttlestop? http://www.techinferno.com/downloads/

No I haven't, but this is now not needed re my above post!

Purgatory said:
Many types here low profile and passive 1155 cpu.

http://lmgtfy.com/?q=low+profile+pas...pu+cooler+1155

Thank you for gracing me with your wisdom, what would I have done without this helpful and relevant post?

new boy · 9 Apr 2012 at 10:49

edit - i see the problem is solved

Martini1991 · 9 Apr 2012 at 11:07

MSConfig set to 3 or a 2 core?
Should go someway to lowering TDP.

chipachap · 9 Apr 2012 at 13:31

Sorry can I ask why you want this specific fanless case? Is there a reason you couldn't just get a half decent midi tower which would be relatively silent anyway?