Monday, Jan 20, 2013
Peltier Junctions, or How to Do It Right
People can get pretty excited about thermoelectric coolers, also known as Peltier junctions. At first glance they look pretty great: electrically powered refrigerators! Plus they are pretty cheap and widely available: some surplus sources can be amazingly inexpensive.
While you can think of a lot of super-neat applications (USB beer coolers! Gnarly heatsinks for overclocked CPUs! A micro-fridge for Burning Man!) it turns out that they are not quite as magical as they look. In fact, using gratuitous Peltier junctions is often a warning sign that someone doesn't really understand what they are doing.
There is a simple reason why: Peltier junctions are simply inefficient at cooling. Typically they are between 5% and 10% efficient, which means that to move a watt of heat you need to put something like 20 watts of electricity into the unit. The problem is that those watts also turn into heat, which you also need to remove! In fact, if you want to burn up a Peltier cooler pretty fast, just run it without a big honking heatsink and a fan! Since the whole point was likely to avoid something like that, it is rarely a win.
OK, so how do you do it right, then? Well, a big gnarly heatsink and a fan should take care of most electronic cooling problems. If you want to be badass about it you can try liquid cooling.
If you need to cool something below the ambient temperature, you really need a refrigerator of some sort. Consider hacking a dorm fridge, or you can buy a commercial unit. If you really need a microfridge for desert conditions, consider this Stirling cooler.