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Is someone willing to give me a good amount of technical advice concerning heat dissipation using a Peltier device ?

Ok, I have a laptop that I use to play many videogames with, and as you can imagine, it has an overheating is a problem. I have software that monitors the GPU and CPU temperatures while I play. The GPU and CPU are rated at a 100c max temperature. Now that the summer season has started, my laptop gets hotter and hotter as I play. I am usually forced to Under-volt my computer so that it stays below safe temperatures.

Now, I was digging around online and came across something called a "Peltier device". It is a small ceramic plate (with electrical nodes inside) that when electrified, transfers the heat from one side to the other. The peltier I got is rated at 545 watts, 32 amps, and 18vdc, and gets as cold as -60c, 150c. I ordered a desktop power supply online, along with 2 CPU cooling systems. (I.E.  2x Professional grade heat-sink, and 2x 120mm fan) The Power supply outputs 430watts, 28 amps, and 12vdc.

I planned on taking these parts and simply sandwiching the peltier between 2 heatsinks, having 1 hot heatsink+fan and 1 cold heatsink+fan. I planned on pumping the cold air into the air intake on the bottom of my laptop, and just pump the hot air into the room. 

Unfortunately, the problem I face (and this is a really stupid mistake) was that I did not measure out this whole assembly. It turns out, the peltier face plates are roughly 2.5" x 2.5", whereas the heat-transfer faceplate of the heatsinks are only about 1.5" x 1.5".

Now, I wired this all up, and put it all together, ignoring the parts of the peltier that were hanging off and lo' and behold, the peltier worked as designed, one side got extremely cold, and the other got hot. The only problem is, over time, since nothing was drawing the heat away from the edges of the hot side, it transferred over to the cold side, thus warming it up to about room temperature, negating the entire purpose of the contraption. 

This is the part that I need help on, would simply taking some aluminum plates that are large enough to cover the entire surface of the peltier, smother both sides in my remaining thermal compound, and then connect this aluminum (with more thermal compound) to the heatsink? This contraption is essentially meant to be a laptop cooling pad. Mounted inside of an old computer case. So it needs to be mobile (IE, liquid cooling is not an option). Can anyone think of a better solution to this? 

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You will need a CPU cooler on the Peltier to manage the heat coming off it. Not one of those little stock coolers but one of the larger ones with heat pipes. Consider most of the wattage you are dumping into the cooler is being turned to heat. So you have a 200W or more heater on the back side of that thing.
+1

Heat output of a peltier is Energy Transferred + Energy Added to cause the peltier effect.

@author; yes, you could just 'add heat spreaders' to make the peltier more effective with the smaller heatsinks, but as mpilch says -- Get a big heatsink, you're gonna need it.
schwerlin (author)  frollard4 years ago
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103065
As posted in the other reply, the above cpu cooler is the one i bought 2 of. It has heatpipes, and a 120mm fan. I plan on buying a large ammount of thermal compound to accompany both sides. The problem I cannot find a good solution to, is that the faceplate of the peltier, and the faceplate of the cpu cooler are 2 different sizes. So therefore the edges of the peltier get extremely hot, and might even crack the ceramic its cased in. The heatsinks do a great job at dissapating the hot parts they are pressed against, but its the edges im worried about. The only thing i could think of, was to glue 2 chunks of steel that will cover ALL of the peltier, and share the heat of the edges with the heat of the center, so that at least the whole peltier is the same temperature to prevent cracking due to uneven temperatures. But I was wondering if anyone had a less brute force, more thought out, solution.

Thanks for the quick response!
You won't crack ceramic with heat, unless you impart a force to it, it was fired at a temp far beyond the temp your laptop could ever generate, short of setting it on fire but probably not even then.

What do you mean the peltier is bigger than the CPU cooler? The peltier is 63.5 x 63.5 mm while the cooler is 120 x 79.7 mm. The Peltier unit will fit on the heatsink with room to spare.
Thermal cracking of alumina is actually fairly easy to arrange.....

Peltier cells have a maximum d temp/dt for a reason.
schwerlin (author)  steveastrouk4 years ago
But aluminum is malliable, it can stretch far more easily than ceramic can. I plan on either using aluminum or steel, only because steel is dense, an will therefore transfer heat better.
Put it this way, in 20 years of using Peltiers in professional applications, we've never cracked one because the heatsink expanded.
schwerlin (author)  steveastrouk4 years ago
Ok, thats is good news, I didn't want to make any more mistakes. I'm pretty sure I'm going to a hardware store today, buying 2 small copper plates, and thermal pasting them onto each side of the peltier. That will prevent the edges of it to exceed its maximum rated temperature.
To get GOOD thermal contact you have to squash the heatsinks on VERY, VERY hard. Try and lap the copper pieces perfectly flat on a piece of very fine wet and dry paper on a sheet of glass.

Steve
schwerlin (author)  steveastrouk4 years ago
Ok, I got a 2x 3" x 3" copper plate 1/16" thick, on each side of the peltier, and 2 tubes of arctic 5 silver. I will use half a tube of the compound on each side of the copper, so the order is:
heatsink | Silver | Copper | Silver || Peltier || Silver | Copper | Silver | heatsink

Now that i have these copper plates, should I be worried about them radiating heat over to the other side? The peltier is only maybe 2mm thick, and therefore the hot and cold copper plates will be 2mm from eachother. Would cutting up some oven mitts and sticking them between the 2 plates be better than nothing? Or simply cutting down the copper plates so that they are not hanging over? That seems to be a better solution.
DON'T USE more than a TRACE of compound - get the heatsinks FLAT and well clamped. The cells will die if you insulate them with compound. When the surfaces are flattened, then a translucent film of compound is all you need. Rub the surfaces together as you clamp them,


Ignore radiation losses !! The temperature differences, and absolute temperatures are WAY too low to worry about.
schwerlin (author)  steveastrouk4 years ago
Ok, a trace of compound, and alot of pressure. Does the compound harden over time like apoxy?

Also when I got the peltier and was playing with it, I applied 1 tube of the compound that the cpu heatsinks came with, waited about a min, then powered it on. The hot side turned into a liquid, and the cold side froze. This was really cheap compound I know, but is it something i should worry about? Arctic 5 is rated from –50°C to 130°C. And i doubt I will reach the limits of the peltier.


Also, this entire project is depending on 1 thing:

First, consider this. The way a heatsink works is that it conducts the heat from the thing that it is touching, transmits that heat to the air next to the fins, and constantly replaces this air with a fan.

Does the same apply with the absence of heat? Will the cold side of the peltier, pull heat from the coldside heatsink, and the temperature of the entire system drop, allowing the air between the fins to lower in temperature and be blown into my laptop?

I suppose the question is: Does the absence of heat "flow" much like the presence of heat does?

I think it will; for instance, if you drop an icecube into a drink, the ice pulls heat from its surroundings until it is gone. I think the same principle applies here.
Arctic silver, unless specified as epoxy will never harden fully - it will become less fluid and more goopy/clay like, but will never fully dry.

Remembering that you can never transfer 'cold' - you can only extract energy -- a peltier will always try to pull thermal energy from one side to the other until a stasis of efficiency is reached.
Yes heat flows are symmetrical.
schwerlin (author)  steveastrouk4 years ago
Ok, good. Then it should be all good to go as soon as I put the thing together. Ill post a video on youtube and bring the link here when I finish.

Thank you all for the help, especially you steveastrouk. I hope this all turns out how I imagined :)

Check back in a couple days for the video.
Aluminum actual has a much higher thermal conductivity than low carbon steel. ~250 W/m*K compared to ~54 W/m*k. Your best bet would be copper at around ~400 W/m*K.
schwerlin (author)  bwrussell4 years ago
Ok great! Will do.
Because steel is dense it holds heat. Aluminum is much better at dissipating heat then Steel is. That's why heat syncs are made of aluminum and not steel. If you want better heat dissipation then get an all copper heat sync.
schwerlin (author)  bwrussell4 years ago
I was worried about the ceramic cracking not because it was too hot, but because the edges are so much hotter than the center, and the difference in temperature forces the edges to expand more than the center and (maybe) stresses the ceramic more than it can bare.

The peltier is not connected to the heatsink directly, the heatsink has a small faceplate (and heat pipes) that transfers the heat TO the heatsink from the surface of the faceplate. The faceplate is only about 1.5" x 1.5" whereas the peltier it is sandwiching is 2.5"x2.5". So there is an inch of peltier that is not touching the heatsink. Over about 10 seconds, the cold side of the peltier warms up (past room temperature) because the heat from the hot side is transferring to the cold side. If this heat was dissipated it would not transfer over.
Right, and as I said, YES, you could just add heat spreaders to ...spread...the effectiveness of the smaller heatsink to the entire peltier, but it is BETTER to get a full sized heatsink.
schwerlin (author)  mpilchfamily4 years ago
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103065
This link is the cpu cooler I ordered. It has copper, direct contact, heatpipes. and a 120mm 12vdc, .4 amp, 44.03 CFM (airflow) rating. It is not low end, and should have no problem conducting and dissipating the heat.
lemonie4 years ago
What exactly does "Under-volt my computer" mean in real terms?

L
schwerlin (author)  lemonie4 years ago
Using MSI afturburner, I lower the shader, memory, and core clocks of my gpu. I usually underclock by about 40%, which allows me to hover around 85c.
schwerlin (author)  schwerlin4 years ago
So, I literally am limiting how much power my laptop will send to my GPU and CPU. If you have an excellent cooling system, people often OVERvolt their cards, which offers an increase in performance, whereas UNDERvolting decreases performance (and the card makes less heat). I don't ever plan on overvolting my laptop, just simply running it at standard voltage, at a standard clock speed is my goal.
Hmmm, I though voltage-tweaks were a part of maintaining stability when doing serious over-clocking, most people just slowing the clock for lower wattage.

L
schwerlin (author)  lemonie4 years ago
Well, I'm doing both :)
If your having to go to this extreme to cool your laptop there is something wrong. Laptops will get hot and if you are using it in your lap or on a soft surface where the vents are being blocked it will overheat. If you've had it for a year or more you may have a buildup of dust in the laptop's heat syncs drastically reducing there effectiveness. Get a can of air and try blowing them out really good.

Granted many larger laptops with 17" or larger screens that are considered desktop replacements or gaming laptops are pushing there limits as far as there ability to dissipate heat. But a simple laptop cooling pad with a built in fan should be all that is needed. Even raising the laptop up about 1/2 an inch should help.

Is the monitoring software you are using setting the 100C limit on the CPU and GPU? What temp monitoring software are you using? Has the monitoring software been configured to work with your laptops hardware? Is the laptop case getting hot enough to burn you? What laptop are you using?
schwerlin (author)  mpilchfamily4 years ago
Ive had the laptop for about 6 months, it has never seen summer weather yet.
It is the levono y570, it has a GEforce gt555m GPU (entry gaming level class I card) and i5 2430 CPU. The manufacturer rates the GPU and CPU at 100c max, not the software. I have already opened it up and dedusted. It is simply the warm weather preventing the laptop from cooling efficently, so therefore, i planned on making my own 'cold weather'.

If its worth doing, its worth overdoing.

I use msi afterburner to monitor the gpu temp, and coretemp to monitor the cpu temp. Both are universal software, and read temperatures based on the internal chip sensor.

Thank you for the quick reply!
schwerlin (author)  schwerlin4 years ago
The problem with the laptop is that it has a GPU that gets hotter than the cooling system can handle. Since it is not a 'gaming' laptop, they didn't put anything special into the cooling system. I plan to add what it needs to keep it under 90c.
schwerlin (author)  schwerlin4 years ago
Also, the laptop overheating is not due to the cooling intake being covered. I DO have it on a stand, with a large hole cut out for the intake, and the rest of the bottom of the laptop transfers heat to the stand. I know this system works, because If I get it hot while ON the stand, then take it off and hold it in the air, the temperature increases, because no heat is transferring to the stand.

The contraption Im making now, is simply going to be an addon, blowing cold air up into the intake, cooling the innards, and pumping the heat (from the hot side of the peltier) out into the room.