Extra-Small Mini Fridge

Details

I decided on using a TEC, as I have no familiarity with using them, and condensers can be loud, which is unappealing. The noise from a fan is acceptable. I don't need it to be large, and a simple cooler associated with shipping chemicals should be more than sufficient. The 3cm thick walls realistically should provide enough insulation to allow the TEC to get it cold. Of course, as the cooling is a function of the air temperature (e.g. if an ideal 40°C gradient, the cold side could get below zero), if the room temperature is too warm the cooling effect will not be significant.

A standard ATX PSU is being used to supply power to the fan and the TEC, as the 12V *rail* can provide as much as 22A. The TEC can handle as much as 200W, but for safety concerns, I'll limit the TEC to 100W, and see the results. Currently with my benchtop supply, 36W (12V, 3A) does not provide much for cooling, maybe 3-4°C below room temperature.

For the temperature display, I decided to go archaic and not use any MCU for an A->D converter to display. I will be using a comparator network with closely matched resistors, and display the current temperature in C on 2 7 segment displays, and 1 LED to indicate negative (although I do not expect to drop below freezing).

Components

1 × TEC 12715 TEX capable of using 230W

1 × CPU Heat Sync Used to pull heat away from the TEC

1 × Styrofoam Cooler Cooler designed for packaging. 3CM think styrofoam with 21x19x22cm size. (L,W,H)

1 × 500W ATX Power Supply Scrapping the 12V lines for powering the fans and the TEC. 5V available for more information.

1 × Thermal Paste To adhere the heat sync to the TEC

Project Logs

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New PSU, New Problems
Lucas Rolfes • 09/25/2015 at 05:26 • 0 comments

So, to attempt to make the TEC run even cooler, I decided a standard bench PSU won't be able to provide enough power (12V, 3A). In addition, a bench PSU is not a good long term solution, and a dedicated PSU is probably a much better and cheaper solution. For this matter, I ordered a couple (ruined my 500W by shorting Green -> Black with no load attached) of 350W ATX PSU's, the one of which pictured a server grade. I know the 12V lines can provide as much as 16A so it should be more than sufficient to power the TEC. However, an unfortunate side effect is I do not have sufficient heat dissipation to get the cold side colder than room temperature. The connectors are standard screw terminals, which can support up to 6A or 12A, I do not recall.
The next step is to attempt to find a heat sync/fan combination to pull away as much heat as I can. I do have an overly large heat sync lying around, which might be nice just to test the heat dissipation, but it is too large for mounting on the side of the Styrofoam container.
First Cut & Assembly
Lucas Rolfes • 09/04/2015 at 14:17 • 0 comments

Well, the first cut was put into the Styrofoam cooler. It is going to be exactly the same size as the TEC's cool side radiator, in order to ensure the insulation works the best. The ATX PSU was modified to allow screw connections to the fans and TEC and a switch to enable the PSU (Forcing an ATX PSU on is as easy as tying the green wire to any ground wire),but it appears something is broken as the PSU no longer turns on. When I turn on the external switch, I hear a single *click* in the PSU, but no power or fan movement.
Once this issue has been diagnosed, the next step is to ensure the insulation is complete; possibly with caulk.