on 1/11/01 "Mark A. Kippert" <[EMAIL PROTECTED]> wrote:
> I recalled reading a post a while back that mentioned the use of plumbers
> putty as a heat transfer solution. Here it is if anyone is interested.
>
> --------------------Originally sent 11/12/00 ------------------------------
>
> Date: Sun, 12 Nov 2000 08:53:54 -0700
> From: Greg <[EMAIL PROTECTED]>
> Subject: [Duo2400] Re: CPU and heatsink connection to CPU stiffener
>
>> A little while back in response to my questions about the high temperature
>> of my 2300c some people made suggestions about material for replacing the
>> putty-like stuff that joins the processor to the CPU stiffener (magnesium
>> frame). I'm going to have to open my machine up sometime soon and if people
>> wouldn't mind I'd be grateful for your suggestions again as to what I might
>> use to ensure there is a good transfer of heat.
---> BTW, that 2400 CPU stiffener"magnesium" frame is actually faux coated
light green plastic--hate to disappoint you all. Yeah, cheap cheap cheeeep
plastic! It looks real as long as the plating is in place. Probably the same
for all other later Powerbooks. The Titanium might be different because 1"
total thickness eliminates the fat clearances required by cheap plastics, if
improved rigidity/lightness are objectives.
>
> I used "plumbers putty" to replace the MISSING heat sink material on one
> of my 280c's. Later I did a test of my 280c with the standard factory
> heatsink foam material against my other 280c with the putty. Running the
> same program, same OS, same settings, the duo with the putty actually
> run a couple degrees F cooler. This is not a true scientific test. To be
> more scientific I would have switch the putty and foam from one machine
> to the other. Not gonna do it though!
>
> As another experiment, I cut two pieces of aluminum plate about an inch
> square each. Then squeezed a 1/8 inch thick layer of plumbers putty
> between them. Next heated one plate with a soldering iron. Results: the
> heat transfer from one plate to the other is not instant, but the second
> plate does eventually get too hot to touch. The putty does not go limp,
> but remains firm yet pliable even after cooling again.
With the above soldering iron test, even the best 1/8" insulator in the
world will pass heat through to the other aluminum plate (sheet is thin,
plate is much thick(er)). I firmly believe putty, foam and other
non-metallic materials will act less efficiently than pure aluminum as a
heat transfer agent. It actually might even be somewhat insulating, but by
forming a conductive bridge by eliminating the air gap, will still do a
job--albeit much less efficiently. "Thermal caulking", as used on water
heaters, should also be more insulating than conductive. After all, the LAST
thing you want on a water heater is heat loss. (We want MAXXED OUT heat
loss)! The more conservative engineers might have wanted to avoid using a
metallic solution to minimize the possibility of inadvertent contact between
any part of any board and the aluminum sheeting (or to protect the 2400 from
ham-fisted DIYs like us survivalists :-). Gluing aluminum to the aluminum
heat sink also minimizes this likelihood.
The aim is to maximize the CPU heat transfer rate for the speediest
dissipation, thereby (however slightly) also raising the air convection flow
rate through the tube, thereby (however slightly) also raising the ambient
air inflow rate.
The comment about BookEndz probably raising the heat would be correct.
Apple/IBM obviously sought to use the (relatively open) PC card cage orifice
to maximize air venting.
I routinely let the DC power and modem cables run under the backend of my
2400 to provide a (self-contained) slight lift.
Sidney Ho
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