Build your own refrigerator for $25
Plus the cost of shipping, of course. Before we begin, you folks all understand there's no such thing as cold, right? Just the presence or absence of heat. And you also probably know that a refrigerator (or icebox, in case you grew up in Arkansas) works by removing the heat from the things you put in there. You may have learned a refrigerator (or airconditioner or freezer) needs things like a compressor and freon and coils of copper or aluminum to work as a heat exchanger. But there are other ways to exchange heat and one of those is the Peltier Junction (which is a lot different than the Petticoat Junction, believe me). The Peltier Junction uses dissimilar metals and electricity in what is known as the "thermoelectric effect" to move heat away from one side of the device and to the other side.
Now, you may at this time be asking yourself "why would I want to build my own refrigerator?" I can think of a few reasons...maybe your company has gone paperless and you have a vacant drawer in your desk that once held files. With just a little work you could build a fridge that would fit neatly in there and keep all sorts of things nice and cold. Like beer. I'll bet there are no signs where you work saying "NO DRINKING." So go ahead. If they have a problem with this, look them in the eye and tell them Jon said it would be ok. Remember this is your refrigerator. You can make it any size you want...seriously.
Or maybe you have a son or daughter who is of the age to build a science project and they need a clever idea. Something a little better than the mud volcano 79% of their friends are going to build after they've waited until the last night before it is due. Well, the Peltier is at once simple and then again pretty complex. But the beauty of it is the simplicity and it should be a very good and educational science project. It might stimulate a child to want to learn more about electronics, and that isn't necessarily a bad thing. Actually it is a good thing. After all, they'll be in the workforce before you know it, and they may need to build a beer fridge for their desk, too.
Or you could build an interesting water cooler, maybe a cold tray to keep dips, shrimp, cold cuts, vegetables, etc cool at a party...you're only limited by your imagination. I don't know if they're still being made, but these were once used to build suits to keep firemen cool while working and they're used frequently in medical and manned space applications. What else can you think of that supplies 12 volts DC and plenty of amps? That's right...the alternator in your car.
For $25 plus postage, I'll send you:
(a) a used but working Peltier thermoelectric chip
(b) the aluminum spacer connecting it to the cold sink
(c) the aluminum cold sink
(d) the aluminum heat sink
(e) the electric fan to dissipate heat...a muffin fan I selected because it was quiet and powerful and fit the perimeter of the hot sink well.
You'll need: a 12 volt DC power supply that can deliver anywhere from about 4 to 8 amps of current, something to line your fridge (sheet aluminum is excellent), basic tools like screwdriver, electric drill, maybe plywood or you could use a small insulated cooler. You're basically going to need a relatively airtight box with insulation to keep the heat out. (or the cold in, but remember cold doesn't actually exist so you're already ahead of the game).
I hooked this up to a transformer to check it. The ambient temperature in the room was 80 degrees and in about 10~12 minutes the temperature on the cold exchanger side had dropped to about 50 degrees (f). You can get a temperature differential of about 50 degrees (f) as I recall. Maybe more if you can figure out how to dissipate heat more efficiently from the hot side.
Thermometer and power supply not included.
Questions? Please send them to firstname.lastname@example.org