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CPU coolers aluminium versus copper core



 
 
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  #1  
Old January 27th 20, 03:03 AM posted to alt.comp.hardware.pc-homebuilt
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Default CPU coolers aluminium versus copper core

I have an old HP business desktop that seems to have a problem with
overheating. One has to keep the heatsink dust-free in order to survive.
Now this is an aluminium heat sink and the CPU is TDP 95 W.

Looking at some Intel stock coolers, they seem to use aliminium for
65 W CPU, but a copper core for the higher powered products.
So were HP cutting corners?
  #2  
Old January 27th 20, 03:59 AM posted to alt.comp.hardware.pc-homebuilt
Paul[_28_]
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Posts: 1,467
Default CPU coolers aluminium versus copper core

wrote:
I have an old HP business desktop that seems to have a problem with
overheating. One has to keep the heatsink dust-free in order to survive.
Now this is an aluminium heat sink and the CPU is TDP 95 W.

Looking at some Intel stock coolers, they seem to use aliminium for
65 W CPU, but a copper core for the higher powered products.
So were HP cutting corners?


There's the size and composition of the fins.

But there's also air velocity.

Above around 800 linear feet per minute, extra air
velocity doesn't help. 200 linear feet per minute is
a more common value for hardware design. We did do
one high velocity design at work, but you had to wear
protective earphones when in the lab next to it.
Pretty kooky.

Take the Noctua cooler that is cooling my 150W processor
right now. The air through it doesn't move all that fast,
but the heatsink has a *lot* of fins. They tried to make the
heatsink as quiet as possible, by making it bigger.

And you know all the thermal domains by now anyway.

1) THERMTRIP - processor is so hot, a thermal diode
inside the processor triggers a logic signal that
gates off PS_ON# and the ATX supply shuts off.

This protects a CPU when the heatsink falls off. Sometimes
the plastic tabs snap off and the heatsink falls off.

Before this protection was invented, a CPU could shoot up
past 200C in a matter of a couple seconds, after the heatsink
fell off.

2) Throttling - the processor inserts "No OPs" in the instruction
stream. The CPU does no useful work during these cycles, and
the CPU power consumption is reduced (but not eliminated) by
"doing nothing" for a clock cycle. This offers a way for the CPU
to "improve a bad situation" by "not drawing as much power".

Occasionally a CPU enters this state, despite having a very
nice heatsink. CPUs can have the silicon die soldered to the lid
(good) or a crumbly thermal paste is used inside the package, to
mate the CPU die to the cover above it. A void in the paste can
cause the CPU to throttle when running Prime95 for example.

3) All-OK - with a massive enough heatsink, maybe the die temp is
between 40-60C no matter what. And we call that "good enough".
Even if we're running Prime95, the CPU stays within the proper
range and we're happy.

A company like HP can just sit there and try heatsinks, and see
if at 25C or 35C room temperature, the CPU stays out of throttle
country. You don't have to use fancy engineering tools, if you
"cut and try" and stop when you just barely meet the specs.

Now HP *has* made good kit. We had a machine at work, pretty
ordinary looking, that we used to take into the thermal chamber.
It was rated for 50C room temp. We ran it up to 50C... and it
didn't crash! Amazing. So HP can make good gear. You can imagine
in that case, that the CPU would have a decent heatsink.

Some of the machines, put a high static pressure fan right
next to the CPU fins. And that thing runs at reduced voltage
most of the time. The fan can give 110CFM (noisy/lots of air)
if the CPU is too hot. Usually the fan only goes to the max
when the CPU has crashed and is not available to properly
program the fan to a lower setting.

We could use a copper slug aluminum heatsink and a moderate
flow of air, or we could use a cheap pure aluminum heatsink
and a *lot* of air.

And the reason this happens, is the aluminum really doesn't
conduct heat well enough. Maybe only 1" of fin next to the
base block actually transfers heat into the air.

And that's where heatpipes come in. If you go to 2" above the
base and run heatpipes through the fins, you can backfill the
fin and fill the top part of the fin. Now, three inches of fin
does work for us.

Heatpipes are the ultimate solution. Solid copper heat slugs
are pretty and all, but they're inferior to heatpipes.
Heatpipes and heat chambers with a few drops of a phase
change fluid, do an excellent job of moving thermal flux.

The original heatpipes, some of them used to leak. Today,
you're more likely to get most all of the pipes in
working condition. At one time, they didn't do a very
good job of sealing them. And that's a good reason to
use four or five pipes. If one leaked and dried out
and became useless, the others would continue to work.

The thermal transfer mechanism in heatpipes stops working
if you pump too many watts into the heatsink. The heat
transfer is "non-linear". Whereas the plain aluminum or
copper slug aluminum ones, those are "linear" coolers.
When a heatpipe cooler is overwhelmed, the entire heatpipe
is so hot, only vapor is inside the heatpipe and liquid
no longer condenses because the entire pipe is too hot.
If you jacked up the temp high enough, the heatpipe would
burst open from the pressure.

Paul
  #3  
Old January 27th 20, 06:31 PM posted to alt.comp.hardware.pc-homebuilt
Flasherly[_2_]
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Posts: 2,407
Default CPU coolers aluminium versus copper core

On Sun, 26 Jan 2020 18:03:26 -0800 (PST), wrote:

Looking at some Intel stock coolers, they seem to use aliminium for
65 W CPU, but a copper core for the higher powered products.
So were HP cutting corners?


Depends. Coolers can cost, figure $20 before even looking at boutique
$50 and up configurations. And though that $20 cooler is going to be
obviously different than a $10 unit, the $20 unit, for a high to
better efficiency, surrounds itself with a aluminum casing around
copper-core "heatwicking" pipes -- 4, 6, and sometimes more pipes.

Then again, at extremes, the $10 cooler may be fine for a low-wattage
CPU a modest frequencies, as opposed to 12-cores drawing up to 200
watts;- An open-air build can get by without even a fan among lowest
CPU power draws.

As for HP and "cutting corners" I'd personally consider that they
designed the concept: Whatever it takes to get a buyer beyond at
least a representative minimum all-points warrantee offering, all the
sooner to reach that break-even point where a profit-take is realized.

Business, besides stipulating the word for the actual product, means
IT infrastructures;- I'm sure HP would be happy contractually to sell
a "business support" proviso for added services beyond such warrantee
terms aforementioned. After all, averages on computer usage among
average people who haven't a clue what goes on beyond four screws to
the MB's backplane, computers average three and more -- above a retail
strike on build costs -- for support technicians' capacity to unscrew
them.
  #4  
Old January 28th 20, 02:52 AM posted to alt.comp.hardware.pc-homebuilt
Robert[_14_]
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Posts: 6
Default CPU coolers aluminium versus copper core

wrote in part:
I have an old HP business desktop that seems to have a
problem with overheating. One has to keep the heatsink
dust-free in order to survive. Now this is an aluminium
heat sink and the CPU is TDP 95 W.

Looking at some Intel stock coolers, they seem to use
aliminium for 65 W CPU, but a copper core for the higher
powered products. So were HP cutting corners?


Paul has discussed design factors side-thread.
Permit me to add some practical factors:

1) Old is generally a good thing -- at least it has survived.
The design is quite likely adequate or it would not. However,
there is aging. Presumably you've checked all fans are running
and all vents are clear of dust and debris. Follow the
air-path in from the CPU fan 'til it comes out the PSU.

2) HP generally does fully integrated airpath designs
(vs white-box slap-togethers). Make sure shrouds are in
place -- there usually is a black plastic shroud between the
CPU case fan up front forcing flow across the CPU heatsink.
If it is missing, an overheat is likely under ~1h full load.
The heatsink will be unusually warm (check IR).

3) If all this is correct, then check the heatsink (usually
Torx screws). Carefully see if any are loose, then remove
the heatsink and inspect the grease. It can dry out or be
pumped out by thermal cycling. Or the heatsink can become
dislodged by transport. Clean and install your favorite
thermal grease. A bad (dry, cocked) joint generally causes
overheat quickly (minutes) with a cold heatsink.


Hopefully this will fix the problem. But you should be aware
there may be unusual loads (optimized code) that might exceed
TDP if the PSU can provide the current.


-- Robert in Houston

 




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