Rule of thumb #1: case inside temperature will be about 10 degC higher than
the room ambient temperature.
Rule of thumb #2: Rtheta of a GOOD thermal grease gap ~0.1 W/C.
Rule of thumb #3: Rtheta between the CPU die and the CPU case is ~0.1 W/C.
Given: Rtheta_Spire = 0.33 C/W (this spec is for the Spire only, I presume)
Rtheta_Die_Amb = (0.33 + 0.1 +0.1)*C/W = 0.53 C/W
Rtheta_Case_Amb = (0.33 + 0.1)*C/W = 0.43 C/W
These are my estimates from Excel:
Rthet Pd(P4_3.4P) dTC Tamb Tcase Tmax Tspec
Units (C/W) (W) degC) (degC)(degC)(degC)(degC)
Die 0.53 103.0 54.6 25.0 10.0 89.6 73.2
Case 0.43 103.0 44.3 25.0 10.0 79.3 73.2
Rthet Pd(P4_3.0) dTC Tamb Tcase Tmax Tspec
Units (C/W) (W) degC) (degC)(degC)(degC)(degC)
Die 0.53 81.9 43.4 25.0 10.0 78.4 70.0
Case 0.43 81.9 35.2 25.0 10.0 70.2 70.0
Tspec should be <= Tmax or you're out of spec.
So, if the Tspec you are quoting is CPU case temperature, you may already be
borderline with the P4 3.0.
I say, "No Way" that the Spire will cool a P4 3.4P within CPU case spec or
CPU die spec.
If you don't get the thermal grease boundary nearly perfect, you can add
another 0.05 to 0.10 to Rule #2 and add another 5 or 10 C on top of what
Prescott shows above.
_jim
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of Winterlight
Sent: Wednesday, May 11, 2005 2:32 PM
To: [email protected]
Subject: [H] Thermal Resistance ??
I want to get a P4 3.4 Prescott that specs out at
Thermal Spec 73.2C
Thermal Guideline 103W
I currently have a P4 3.0 800FSB 512 that specs out at
Thermal Spec 70C
Thermal Guideline 81.9W
It is using a very nice, and very quiet
a P4 Spire cooler specs
Thermal Resistance = .33 C/W
The case is a large extended case with very good cooling.
the Spire is rated up to 3.4 but not particularly for the Prescott... for
earlier P4s like my model which were a little cooler models.
I don't understand how the Thermal Resistance spec works. Will I be able to
use a 3.4 Prescott with my Spire cooler?
thanks
