Ok so how much heat are we talking about having to dissipate here? 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:
Theatsink = Tambient + ((C/W)(Wtotal))
Tambient = the ambient temperature in ºC
C/W = C/W rating of the heat sink
Wtotal = the total heat output of the peltier and the CPU in watts
Theatsink = 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.