Thermo-Cup
From GrinningMonkey
This page describes my project to turn the guts of a thermoelectric fridge into a device that will keep your cup cold (or warm, depending on the polarity d:)
Contents |
History
Sometime in 2005 I bought a Coleman thermoelectric fridge.
What's that, you say? It's a fridge that runs on 12VDC, using thermoelectric cooling (see http://en.wikipedia.org/wiki/Thermoelectric_cooling). The basic idea is that if you take two dissimilar metals, stick them together and apply electricity to them, one side gets hot and the other gets cold. Stick big aluminum fins to each side, and stick fans to run air through the fins. One side goes inside the box, the other goes outside. If you reverse the polarity (go Geordi LaForge!) then the cooler gets hot on the inside and spits out cold air.
When I worked at SiteBrand, at the time we had this tiny bar fridge in the office that wasn't big enough for all the crap everybody had. So I kept my thermoelectric fridge in my office for a long time and put my stuff in there. Because the fridge had a cigarette lighter for its power plug, I had to buy a 120VAC -> 12VDC w/cig. lighter I/F power supply. I couldn't just use any crappy Radio Shack one, because the fridge actually draws quite a lot of power. I got one from Canadian Tire designed for Koolatron fridges (same style thermoelectric fridge, different company).
It was actually quite powerful. I frequently had to stop it and de-ice the aluminum fins. (part of this is because the fridge has a good thermoelectric module, part of it is because our office was kept at 20°C all the time) Eventually I solved the ice problem by (a) sticking a thermometer inside and (b) tuning how far away from a nearby wall I positioned the external air outlet.
At some point, there was a powerfailure. After the powerfailure, the fridge wouldn't turn back on. The fan motor had died.
I ripped the cigarette lighter power plug and its wires out of the fridge and am currently using them to power my Carputer, along with the Koolatron power supply.
Thermo-cup
I plan to rip the thermoelectric module (which I believe is still working) out of the fridge (including the nice monster aluminum fins) and rig up some sort of cup-cooler.
Ideas:
Cool-a-Jug
You know those "contintental breakfasts" that hotels have where they throw a bunch of bagels on a table with some milk and OJ? You know how the milk and OJ jugs have a separated core where they dump icecubes to keep things cold?
Well, this idea involves getting one of those jugs, filling the core with a very heat-conductive material (nice big metal bolt?), attaching the thermoelectric module to the bottom of the bolt, and building a base onto it with big aluminum fins and a fan on the other side of the module.
Thermo-Cup
In this idea, the base contains all the goodies and you put whatever you want on the top. This is my favourite because it's easiest to build.
- Find a metal stove burner protector. I think the dollar store has them. Basically it's a flat metal disc.
- Glue one side of the thermoelectric module to the burner protector using thermo-conducting glue (the same shit they use to stick the aluminum fins to your computer's processor). We'll glue it to the burner slightly off-center (see below).
- Glue a big aluminum fin to the other side.
- In the center, we put an electric motor. On the top of this motor is a small bar magnet (you know, with N at one end, S at the other). This motor will have a potentiometer on it to control its speed
- Another nice, fast electric motor has a fan on it (conveniently, there are two fans already in the fridge, and one of them even more conveniently has a plastic shroud for airflow management!)
The whole thing is enclosed in some sort of base. Room-temperature air comes in one side, goes through the aluminum fins which dissipate heat from the module, and hot air goes out the other side. Meanwhile the burner cover gets cold. You put your glass, or cup, or whatever on the top. Hopefully your cup is about the same diameter as the burner cover.
Here's the fun part: do you remember, in chemistry class, those little spinners you'd drop in your beaker?
Basically, it's a little magnet encased in plastic. It's shaped like a large, tubular pill. You put this in your cup with your favourite liquid, and the motor with the bar magnet on it causes it to spin. It stirs your glass for you. Otherwise you end up with a cup full of juice that's only cold at the bottom.
