A lot of people in this forum and others seem to be asking the same questions about peltier use lately, so I'm going to try and answer some of the obvious questions and outline some of the basic theory. Firstly, what is a peltier/TEC? A peltier is an active heat pump. By ACTIVE I mean that the peltier consumes power to move heat from the cold side to the hot side. The first point worth mentioning now is, You must ensure that how ever you cool the hot side of the pelt, you are able to control the heat dissipated by the cooled component AND the heat dissipated by the pelt itself. Moving on, When buying a pelt, you will be confronted by a number of ratings as follows. Qmax The MAXIMUM heat load the peltier can dissipate. deltaTmax The MAXIMUM temperature difference between the hot side and the cold side of the peltier. BUT, it is a little more complicated than that. Qmax only occurs when deltaT = 0, and deltaTmax only occurs when Q = 0. Consider the 226W pelt as sold by dangerden. Imax = 24 Amps Qmax = 226.1 Watts Vmax = 15.2 Volts Delta Tmax = >67 (C) This pelt can dissipate up to 226W, but it will only do this if the hot side and cold side are at the same temperature. Equally, it can create a temperature differential of up to 67degrees, but only if the pelt is not dissipating any thermal energy. What does this mean for us? When choosing a pelt, it is important that Qmax is considerably greater than the expected thermal load dissipated by the cooled component. The greater the Qmax of pelt used for a given heat load, the closer deltaT will get to the deltaTmax of that pelt. However, the more powerful the pelt, the better it needs to be cooled, for obvious reasons, since it will be dissipating more thermal energy. Consider a cooling system with a combined C/W of 0.25. This means that if your waterblock is having to dissipate 100W from a processor, then the temp difference between the processor and the ambient air will be 25 degrees. Now if we cool it with a pelt, it is quite likely, that we will be dissipating closer to 300W. So, using the same cooling system, the hot side of the pelt will be 75 degrees hotter than the ambient air. So, you can see that the pelt is only worthwile if it can dissipate the 100W heat load generated by the processor with a delta T of more than 50deg. The more efficient the cooling system, ie the lower it's C/W, the less this will matter. For example, if the cooling system is now upgraded, and the C/W reduced to 0.2, then the pelt must now only dissipate 100W at a deltaT of 40 degrees or more. And it gets more complicated than that. The figures quoted above are when running at Vmax. As Vmax is dropped, for example, if you wanted to run it from a 12V power supply, then the potential Qmax and deltaTmax are also reduced. Also, the current draw for a given voltage varies with the heatload dissipated by the pelt. And to make matters worse, ALL of the characteristics are altered by the temperature of the hot side of the pelt. Finally, there is the hidden cost of additional electricity. Roughly equivalent to 3-5 60W bulbs while ever the pelt is on. A real problem for thos who leave there computer on 24/7 So, common questions. Can I use a pelt with my heatsink? In theory, yes. However, your HSF will struggle to keep the hot side of the pelt cool enough to see any real benefit, and more likely, your processor will actually run hotter. Will this X watt pelt be Ok with X processor? Chances are, if you need to ask, then the answer is likely to be no. For current generation processors, you should be looking at 172W pelts as a minimum, with 226W being recommended. Can I use my computer power supply? Again, yes in theory, provided your powersupply can cater for the ~20A the pelt will need on the 12V line plus the 12V requirements of your computer. Plus, the lifespan of the pelt will be affected by the quality of the line signal. Oscillations in voltage result in oscillating changes temperature of the pelt. Not good for ceramics! If nothing else, I hope this has made some people realise that there is a LOT more to pelts than first meets the eye. Granted, it's a nice idea, but pelts are hugely inefficient and require a LOT of cooling if you are to expect decent results. Please feel free to add any other useful information as I got a little bored of writing this and have probably missed stuff out. 8-ball
Fantastic guide 8-Ball and a great source of info i think the mods should start putting this type of work to good use though as a lot of hard work is just getting wasted
To be honest, I'm still not entirely happy with it as a guide. I consider it more a collection of info, since a guide by definition would be well organised and take everything into account. I'll probably have another go once I've got this degree out of the way (I'm really ready to move on now ) Besides, I stil don't properly understand all of the relevent information myself, though plenty enough to write a guide for beginners. 8-ball
That's kind of what I had in the back of my mind when I wrote this, except it kind of got lost amidst all the theory. If people add any other useful info or questions they want answering, then I should be able to write it up properly in a couple of months once I've handed my thesis in. 8-ball
Voltage Curve... There is also a curve to a peltiers effeciency. Say, max rated is 16 volts at 5 amps (water cooler like drink peltier) will actually run a tiny bit warmer at 12 volts 3 amps, and will extend life and consume a lot less power. the temp change is extremely subtle. I suggest play with voltages and a themometer to see where your particular pelt's curve is from drastic cooling to not worth the effort. It can be 2 of the exact same type of pelt, but the curve will still vary. Also, ducting is a must. Take a 120mm PVC, and fit it OVER your heat sink. Cut out a space for a 120mm fan above it, pushing air out of the pipe out of your case. Place another fan at the top, further sucking out. It being over the heat sinl keeps heat from being able to escape out of the sides and also helps to create enough convection so that condensation will hopefuly be sucked out. The have 130 CFM 120mm fans for i think $5 USD at allelectronics, and the are at a decent 49db (less loud than my box fan cooler - by a lot.)
