Introduction: Make a Mini-fridge!
This is a good project for anyone getting into electronics or wanting an idea for something cool. This isn't exactly a "cheap" project but its not very expensive either. The total cost for this project was £16.12 (~$25 at current exchange rate), about the same as a new mini fridge from the shops. If you do not have some of the parts mentioned, you will have to buy them. £38.58 is the total cost for all the materials brand new, but almost half my parts were recycled.The space inside the fridge is 10x10x15, big enough for normal sized cans, large cans, chocolate bars, carton drinks, capri suns(you can fit about 2 or 3), chocolate bars, or anything else you might want. I had some trouble finding a material that was cheap, a good heat insulator, strong, and easy to cut without shattering or being too hard. In the end I got a 50x40x0.3cm sheet of PVC from ebay for £5.98 including P+P. The fridge features an adjustable temperature dial (optional), fan cooled peltier plate, magnetic hinged door, and an LED light that comes on when you open the door.
Note: I never actually finished the fridge past step 5, I still have it lying around in my garage somewhere, but it worked as far as cooling. I wrote the instructable ages ago and as I am unlikely to finish it anytime soon, I decided to publish it as is.
Step 1: Materials
Here is a list of the materials you will need, and the UK prices, and UK places to buy.
-500x400x3mm White PVC sheet - £5.98 - Ebay UK (you can actually use a 400x400 sheet, but I would recommend getting a slightly bigger piece incase you make a mistake and so you can sand each piece)
-White Plastic 3 inch cupboard door handle - £1.29 - Ebay UK
-Small Brass hinges - FREE - found in garage
-Small magnetic sheet - £0.69 - Hobbycraft (any thin magnets will do, but I wouldnt recommend the neodymium ones or you probably wont be able to open the door!)
-Small amount of scrap steel - FREE - I found an old sheet of steel in my garage and cut off some 2cmx1cm strips, and let them soak in white spirit and alcohol to clean them. Anything steel works, you could even cut up an empty coke can if you need to. Make sure it is real steel though and not stainless, because it isn't very magnetic and only contains about 2% iron. Real steel contains about 99% iron which is why it is so magnetic. Iron and nickel are also magnetic so they will work too, but may be harder to find and harder to cut.
-Soft touch 6mm knob - £0.55 - Maplin (optional, recommended if you have a potentiometer for better grip and professional finish. I didn't buy one in the end)
-91.2W 40x40mm Peltier cooling unit - £3.37 - Ebay UK
-Akasa chipset cooling kit - £6.96 - Ebay UK (you can also get them for £10 in maplin. All you need is an active chipset heatsink and a small flat passive chipset heatsink. MY heatsinks were actually recycled and the fan was bought for £2.50 on ebay)
-Sub-miniature lever microswitch - £1.29 - Maplin (optional, for door light. Make sure it is a 3 pin one of a push to break one. This was recycled from an old project)
-5mm 12V white LED - £1.29 - Maplin (optional, for door light. You can also use a lower voltage LED if you have a resistor. I actually got mine on ebay for the same price.)
-Miniature Potentiometer 10K - £0.80 - Maplin (optional, but recommended to control temperature. Any large value potentiometer will do really, it just needs to be able to increase/decrease resistance for the peltier unit. I didn't buy one in the end.)
-Single hole 2.1mm DV power jack - £1.69 - Maplin (or any other DC power jack to match your power supply)
-12V DC power supply - This is not included in the parts/price list since I used a recycled computer power supply. You can use anything as long as it is over about 5V and under 12V. The peltier unit uses 7.6A of power, so remember wattage of peltier unit ÷ power supply voltage = Peltier cell amperage. If it is anything lower than 7.6A (which is probably is) Then the peltier unit won't be running as cool as possible, and this is ok, since we are making a fridge, not a freezer, but make sure it isn't too low. I will show you how to convert an old computer power supply (or new one, it probably works out cheaper)
-Wire - This also isn't on the price list because it is too cheap to measure and all good electronics hobbyists should have plenty of it
-Small amount of double sided tape and thermal compound, or thermal tape - not included on the price list since the amount you will use is unmeasurably small. You just need a teeny squirt of compound and a few strips of tape.
-Hacksaw, coping saw, or wood saw (or if you have one, a jigsaw or band saw)
-Drill (preferably a pillar drill, but a handheld drill will work just as well)
-Files (kind of optional but not if you want smooth edges. Alternatively you can use sandpaper)
-Hot glue gun (to stick it together, you could use a drill and screws or araldite/epoxy)
-Ruler, measuring tape, or large vernier caliper to measure the plastic
Step 2: The Power Supply
**If you already have a >100W 12v power supply, skip this step**
The first thing you need to do is make the power supply. If you are reading this, I am assuming you have a computer power supply to convert. Locate and remove the screws on the metal enclosure (sometimes hidden under stickers which will void the warranty). Cut the wire to the mains plug, fan, and switch. Unscrew the ground wire. Now, unscrew the circuit board from the case and remove it. Locate the 20/24 pin motherboard connector. Cut the connector off, and all of the wires from the power supply that go to the motherboard connector except the green wire (if there isn't one or multiple green wires, its the one 4 along from the top left if the clip is on top) and any of the black (ground) wires. Keep those two wires over to one side to avoid cutting them off. Locate the sata/molex power connector, and cut the first connector closest to the power supply off. Then cut off the red, orange, and ONE of the two black wire, or just red and black if its molex only. Now, cut off any other connectors such as the 4-pin 12v motherboard connector or any other connectors the board may have. You should be left with two wires for mains in, two wires for a fan, a green and a black wire to simulate a motherboard being attached, and a yellow and black wire which is your >100W 12v output.
Now, you will need to either mount it back in its old box, or buy a plastic one. (make sure you connect the ground if you mount it in its old box or any metal enclosure). Mount the power connector, switch (optional) and fan on the case. Solder the fan onto the fan wires. If you bought a new fan, cut off the connector, cut off the yellow/white/blue wire and solder the red and black wires to the corresponding red and black wires on the board. Next, solder the power connector and switch (if you have one). Make sure it is connected the right way round or you could blow up the power supply. Cut the green and black wires a bit shorter so they can touch each other but not much more, strip them, solder them together, and coat in insulating tape. Now, strip the remaining yellow and black wires, strip them, and add in an extra length of wire so it is as long as required for your setup. Now, take the 2.1mm dc plug, unscrew it, and solder on the wires. Note which one is positive and negative for when you solder the socket on the fridge itself. Now close the enclosure, plug it in, and test it with a multimeter. If you don't have a multimeter, turn it on, and if it doesn't blow up, it probably works! I also made a cover out of polymorph (a great material that you can put in hot water and mould it, then when it cools down it hardens into a strong plastic) for the power connector since I wired a mains plug straight into it, which is why it looks like there is melted glue all over the back.
Step 3: Cutting the PVC
The next thing you will need to do is to cut the PVC to make the enclosure. You can make your own or use my template. You will probably have to change some things, like the size of the hole to fit your peltier cell or heatsink, power jack, potentiometer knob at the back, magnetic door plates, microswitch, or the size of the LED. Cut out all the pieces of PVC and file/sand them but don't put anything together yet because you need to put in the electronics. Here is the template I used. I have also included a .svg of the template so you can edit it and resize it so it is full scale. I can also give you a .AI file if you message me. I was considering paying £33 to have some guy cut me some acrylic professionally, but in the end I decided it was not worth the money so I bought the PVC instead.
Step 4: The Peltier Unit
first thing I would recommend doing is to attach your power supply to the peltier unit, and make sure it works right, and note which side is cold and which side is hot. Also note which end is positive and which is negative, because most peltier units don't have a polarity. Don't leave it on for too long. Now, you can start attaching your heatsinks. first, take your active (fan cooled) heatsink and attach it with thermal tape or double sided tape and thermal paste to the hot side of the peltier unit. cut the connector off the end of the fan using side cutters or scissors if you don't have any. you can cut the yellow wire all the way back, as you don't need it. Strip the yellow and black wire, and solder them in parallel to the peltier unit, making sure that red (positive) matches with the positive of the peltier, and black matched with black. If you have a potentiometer, mount in on the back panel now. solder the positive wires to the variable output, and solder a wire, preferably red, to either end of the potentiometer. Solder a wire to the negative (black) wires from the peltier unit and heatsink fan. Mount the power jack in the back panel now. solder the black wire to the negative and the red wire to the positive. If you attach the power supply now, the peltier unit should cool down/warm up and the fan should come on, and fan should go quieter and louder and peltier unit should get warmer and cooler when you adjust the potentiometer. If it works fine, move on. If not, check back on your electronics and compare it to the circuit diagrams. If it works, attach the flat passive heatsink with thermal tape to the cold side of the peltier unit. Hot glue the peltier unit into the 10x10cm square with the hole cut out, making sure you only glue the cold part (if you glue the hot part, the glue will probably remelt and it will fall apart). Try and get it so the heatsink is lying flush with the top part of the plastic. Carefully glue the bottom part to the back panel, 4cm up. Measure it each side and make sure it fits perfecty, or the inside of your fridge will be at an angle.
Step 5: More Electronics
Now, you can Start working on the light and magnetic door catch. Find the 10x10cm piece of plastic with a small hole in the top, and hot glue in your LED from the top. If you used a lower voltage LED, solder your resistor on the positive leg now. solder appropriately coloured wires (red for positive, black for negative) to the LED (if you haven't used LEDs before, the long leg is positive, and short leg is negative. You can also tell by the small flat part in the rounded bottom of the LED indicates negative.) Bend the legs of the LED so they are parallel with the plastic. Glue the 1cmx10cm piece of plastic the the edge parallel to the wires, so the wires go off to the right and the plastic stick upwards where the wires are. Glue the back of the 10x10 piece to the back panel, 1cm from the top (again, measure this carefully both sides). Make sure the wires are coming out of the right side, and glue 1 of the two plain 10x10 plates to the top of the back panel and 1x10cm piece at the front. Slide the plain 15x10 piece down the right side, and glue it 1cm in from the edge. Bend the wires down along this piece of plastic. Bend the black wire under the bottom and solder it to the negative of the power jack on the back panel. Find your 15x1cm piece and insert the microswitch. Secure it with hot glue. You may have to do some testing with a multimeter to determine the polarity of the microswitch. Solder the red wire from the LED to common, and another piece of red wire to normally closed. Bend this right round the bottom and solder it to the positive of the power jack. You have now finished all the electronics!
Step 6: Finishing the Enclosure
Okay, now you have got the hardest part out of the way, and you can finish the enclosure. First, glue the metal pieces from the door latch in the 1x15cm piece. You may not have to drill out the holes completely depending on the thickness the metal is and the plastic. Now, glue 1 of the 2 plain 10x20 pieces to the right side of the enclosure. Make sure it lines up with the back panel and top. If it doesn't fit, you may need to make a small hole in the top plastic with the LED hole for the wires to go through. Now you can glue the 1x15 piece (with metal and microswitch) to the front. Glue the last 10x20 piece to the left side, and the last 10x10 piece to the bottom. Glue the 10x4cm piece on the front to cover up the peltier unit and heatsinks. It is nearly complete now.
Step 7: Fitting the Door and Adding Finishing Touches
Your fridge is almost complete now, and you have probably tested it already. Take the remaining 10x15cm piece with two holes in, and attach your door handle with the screws from the back. Make sure it is more than 1cm from the right or it will collide with the door latch. Take the magnetic part for the door latch and glue these in place in the door. glue the hinge to the door on the left side, and then to the left side of the fridge. Make sure it can open and close freely. Your fridge is now complete. You can now add the knob to the back of the potentiometer, adjust the temperature, add any stickers, plug it in and set it up next to your computer, and fill it up with your favorite drink. Enjoy!
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