High much higher should cpu temp be than case?

[Nakamori]

Hey guys, my cpu idles at 44-46 C and my case is a steady 30C. My specs are in my signature, and I have a Silentboost using AS5. Is this 15 degree difference normal?

Also, whats the normal difference in temperature between load and idle? I run prime95 overnight and my high is 60C.

 

[clownvomit]

My case actually runs the same or a degree or two more at idle in a room with ambient of 79F.

My idle is 32c and with prime95 running for hours it'll go up to somewhere between 43 and 47c tops. my case will then be around 40c

So your 44-46 idle jumping to 60 sounds about right to me, but then again I've only built this one system. All the rest of mine have been stock.

 

[Ice Czar]

depends on the C/W rating of the heatsink
the ambient temperature in the case
and the amount of heat generated by the CPU


Delta = CPU temp - Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt the CPU radiates, each system will cool the core by the (C/W x watts) plus ambient temp. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU core temp will be 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

the more work the CPU does the more watts it pulls and converts to heat
the higher the ambient the less temperature differential there is and the less heat can be transfered for the same volume of air\water

 

[Nakamori]

depends on the C/W rating of the heatsink
the ambient temperature in the case
and the amount of heat generated by the CPU


Delta = CPU temp - Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt the CPU radiates, each system will cool the core by the (C/W x watts) plus ambient temp. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that the CPU core temp will be 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

the more work the CPU does the more watts it pulls and converts to heat
the higher the ambient the less temperature differential there is and the less heat can be transfered for the same volume of air\water

Ok, I'm not too sure what is meant by CPU watts, and I don't know my HSF's C/W rating.
what is the CPU wattage output of an Athlon xp barton core?

going back to my orignal question, what is an acceptable diff in cpu and case temps for air cooling? I know it differs from fan to fan, but a lot of people here seem to be running their cpu's well below 10c higher than their case, and only have a 6-8 difference in temperature between idle and load.

 

[Nidhogg]

my cpu idle is 40c and system idle is 32c
my cpu load is 51-52c and system load is 37c on prima95 max heat test.
in socal the normal indoor day temp is around 85f+ now.

i got an old crappy hsf thats just alittle better then stock, but i have a 7 fan case.

 

[Ice Czar]

Ok, I'm not too sure what is meant by CPU watts, and I don't know my HSF's C/W rating.
what is the CPU wattage output of an Athlon xp barton core?

going back to my orignal question, what is an acceptable diff in cpu and case temps for air cooling? I know it differs from fan to fan, but a lot of people here seem to be running their cpu's well below 10c higher than their case, and only have a 6-8 difference in temperature between idle and load.

1. http://users.erols.com/chare/elec.htm
2. find the C/W for the heatsink
3. measure your case ambient

a few other things to consider
the SYS temp in the BIOS or software is a poorly calibrated sensor that measures just one spot on the mobo

the actual answer to your question is on a sliding scale
critical information to attempt to answer the question isnt included in your post
for instance the model of silent boost
http://www.thermaltake.com/coolers/volcano/rs/a1889.htm
is it the stock fan ect (since the volume of air is another variable)


Heat transfer is all about temperature differentials. Conduction through materials and convection away from surfaces is proportional to the temperature differential that exists. Basically the thermal resistance of a given solution changes with the temperature differential, which is why thermal solutions are rated in °C/W which leaves that variable ambient open but gives you a formula

General Heat Transfer Guide

We can draw some interesting conclusions from this equation. First, heat transfer is proportional to the temperature difference on the object. If the temperature differential doubles, the heat transferred doubles. Second, the conduction coefficient "k" is proportional to heat transfer. If the conduction coefficient doubles, the heat transfer doubles Alternatively, for the same differential temperature, twice as much heat may be transferred. The final observation is "L". As thickness increases, heat transfer decreases. Alternatively, to maintain the same heat transfer through a material twice as thick requires twice the temperature differential.

thats for conduction or convection its Newtons Law of Cooling that addresses the same thing

its been so hot here recently in the afternoon my AC simply doesnt have a big enough condensor air interface to dump all the heat with that small of a temperature differential and Ive been overwhelming my thermal solution, Thus ambient temperature has everything to do with the difference between the CPU and SYS temp as its not a set figure

regarding watts, it a measure of energy generally for electrical power, but it can be converted to calories, BTU, horsepower ect
http://www.onlineconversion.com/power.htm

 

[Nakamori]

Sorry, didnt know there were multiple Socket A silent boost models. mine is the
A1889-01 completely stock.

I'm pretty confident in my case temps because I have a temp probe that is usually 1c cooler than the mobo.

 

[Worminater]

with rig in my sig on a cool night my cpu was consistently lower then ambient case temp tjhx to 80mm fan on side of case blwoign directly into xp90 fan. 6800gt raises cambient case temp alot

 

[Ice Czar]

still looking for an actual C\W rating

http://www.frostytech.com/articleview.cfm?articleid=1551&page=5

with rig in my sig on a cool night my cpu was consistently lower then ambient case temp tjhx to 80mm fan on side of case blwoign directly into xp90 fan. 6800gt raises cambient case temp alot

which is patently impossible you cant drop below ambient with air cooling alone

and just goes to show that a single spot on a mobo is no real indicator of a case temp, there is a gradient and currents at different temperature, your mobo sensor was in a "hot spot" and the intake air for the CPU was likely in a cool spot

 

[Nakamori]

Thanks for the sites, definately bookmark material

Here is my math. My result is slightly high I think.

C/W=Delta/Watt output
Sample wattage ouput 50W
Delta=17.6C
C/W=.324C/W for thermaltake silentboost A1889-01

Athlonxp 2500+ barton typical wattage output: 53.7W
C/W=.324C/W
Delta=53.7Wx.324C/W=18.9C

Does this mean that the minimum cpu temp attainible by a silentboost at 30C case is 49 degrees? that doesnt seem right, but w/e.