Ok so how much heat are we talking about having to dissipate
Well our chip produces 32.58 watts of heat, and our peltier
produces 66 watts of heat, for a grand total of 98.58 watts of heat.
That is a lot of heat!!!
So what happens if your heat sink
can’t cool your peltier setup well enough?
Well the heat sink will continue to get hotter and hotter,
and pretty soon all of that heat will start traveling through the
peltier and into your chip, heating up the chip and either causing
the computer to lock or in extreme case frying the chip entirely.
Since we don’t want this to happen we have to choose a
really good heat sink.
So what exactly makes a heat sink
“good” well there are a couple of things, a good strong fan
moving lots of air, a large surface area, and the color of the heat
sink (yes the color of the heat sink).
So how do we choose a good heat sink well there is one good
way and that is to look at the C/W rating of the heat sink.
The C/W stands for Celsius per watt, or how many degrees Celsius the
heat sink will raise per watt of heat applied to the heat sink.
The C/W rating is the efficiency rating of a heat sink.
The C/W ratings of heat sinks can usually be found on any
heat sink manufactures web page.
For my example I will be using an Alpha pep66.
Now the Alpha has a C/W ratting of .35
which means for ever watt absorbed it will increase the heat sink
temperature .35ºC that’s with a 60 mm fan moving 19 CFM, which is
very good for a heat sink, compared that to the C/W rating for the
popular Golden Orb which is .98 not bad but not good enough to have
a peltier put on it…
So how hot is the heat sink going
to get? Well here is
another formula for you:
= Tambient + ((C/W)(Wtotal))
= the ambient temperature in ºC
C/W = C/W rating of the heat sink
= the total heat output of the peltier and the CPU in watts
= 25 + ((.35)(98.52))
Theatsink = 25 + 34.5
Theatsink = 59.5ºC
According to this formula the heat
sink will get up to 59.5ºC, which is fairly hot… well at least
hotter than what I would like.
So what is my solution well this heat sinks efficiency rose
from .50 C/W with a 9 CFM fan blowing on it to .35 with a 19 CFM fan
blowing on it so what do I propose?
Stick a 38 CFM fan on it, which should theoretically raise
the efficiency to .23 C/W, which in turn should lower the heat sink
temperature to 47ºC, still hot but a lot cooler than 59.5ºC.
Note: I don’t now for certain if
sticking a higher volume fan will increase the efficiency of the
heat sink by as much as I say, but the more air you have moving
across the surface of the heat sink the more heat can be removed…
The other problem that you will
run into using an air-cooled setup is that the heat sink is putting
a lot more heat into your case (usually double the amount of heat
that would be put into your case without a peltier on it) which in
turn will increase the ambient temperature which in turn will
decrease the ability of the peltier to cool which in turn will raise
your cpu temperature.
So what do you do about that? Well
one make sure you have good air flow in the case, to get rid of all
of the hot air and bring in fresh cool air.
Since you are constantly supplying fresh cool air into your
case, the ambient temperature should raise much in your case, and
your CPU will stay cooler.
Or two, you could go all out and
put in a water cooled system that way you can go way past the limits
of air coolers. If
you’re hoping to run below 0ºC at a load then you have to go this
way. There just
aren’t enough cooling capabilities in an air-cooled system to get
your system running under a load below 0ºC.
Ok so now that we know how, or at least know what we need to cool
the peltier unit what is next?
Well now we need to seal the processor to stop condensation.
Rid of Condensation
how big of a peltier do I need?