Instead of cutting apart a perfectly good Crock Pot this build will show you how to build a controller your appliance you can plug into. This modular approach means you do not need to buy a second appliance. If you have an old rice cooker in the cabinet you can make it a sous vide oven.
The tricky part of sous vide cooking is keeping the water at a precisely regulated temperature. Most cooking appliances have the ability to turn the heat down but regulating it with any accuracy is not possible without automation. Fortunately temperature controllers are not expensive and they are as easy to use as a regular oven. An eBay search for temperature controller 58 194 should give options under fifteen dollars ($15USD). Amazon also has the same controllers. The advantage these devices have over a dial on the side of a slow cooker is that the temperature controllers use a thermometer to monitor the temperature.
The versatility of these controllers is also impressive and since this build is being made very modular it is possible to use this appliance for things other than cooking, such as automating a window fan. A short list to get the brain gears turning is shown at the end of the instructions.
The goal of these instructions is to help you build a device that is highly functional, rugged, and looks good on your counter. All the wires are hidden away and sealed up so a few errant splashes from the sink are not cause for an emergency.
*Alternatives to these devices are given on the last page
Step 1: Electrical Cable Preparation
The PVC enclosure will have three holes. The easiest to cut is the 7/8 inch hole for the cord-tight connector. The second easiest to cut is a rectangular hole for the receptacle. The most difficult to cut is the rectangular hole for the temperature controller.
Step 2: Power Cord Entry
The only hole drilled into the base of the enclosure is to let the electrical power cord into the box. I like to keep this cord coming out the back of the enclosure so it is hidden but it also makes sense to have it come out the side so the control box can be pushed up against a wall while cooking.
Step 3: Receptacle Hole
The holes in the enclosure lid are marked and cut from the inside so all the scratching and abrasions from the tools are on the inside and not visible once the unit is sealed up. The hole for the receptacle should not be a stressful step because the receptacle cover will be large enough that any imperfections will be hidden. The most important thing is to make sure the receptacle is squared up to the edge of the enclosure lid. A crooked receptacle will look sloppy more than a few scratches.
Step 4: Temperature Controller Hole Part One
The hole for the temperature controller is the trickiest step in this project. Any large imperfection in the hole may become visible around the lip of the controller face. Sloppy measurements will be the most obvious with this hole. Be careful when using a saw on this hole because a line that is not true may be an eyesore later. Give yourself as much time as you need to do this step neatly.
Step 5: Temperature Controller Hole Part Two
Step 6: Electrical Wiring
A quick couple of notes about wiring. I have a diploma as a Construction Electrician so I have training and experience with wiring. If you do not feel comfortable wiring ask for help. The second note is an anecdote from those college days. My electrician teacher would identify amateurs who tried to do their electrical work by how much wire slack they afforded themselves in the boxes. Amateurs would only give themselves a few inches to conserve a precious scraps of wire. Electricians would pull a generous amount into the electrical box and give themselves enough to work with and to have some extra for the future. He charged stingy amateurs more because it was a hassle. Lesson: give yourself enough wire inside the box.
Step 7: Thermometer Protection
To keep the thermometer off the heated bottom and away from cool food it has been enclosed in a small stainless steel whisk. The whisk is a great shape since water can freely flow through the tines without obstruction. Strictly speaking it is not necessary but since precision is the name of the game it is recommend to keep the thermometer probe protected.
Step 8: Thermometer Connection Outside the Box
The NTC (Negative Temperature Coefficient) thermometer is not a polarity sensitive device which means it cannot be hooked up backwards. The wires on the temperature probe may need to be clipped and stripped so that wire are able to be soldered. These instruction makes the assumption that the builder knows how to solder. If not, there are many fine tutorials and YouTube videos which can assist.
Step 9: Thermometer Connection inside the box
The modularity of the project will hopefully give people other ideas for how to use this controller. All kinds of home automation is based on temperature sensing. It is possible to hook up a different NTC thermometer using the 3.5mm jack and have a different application altogether. One temperature probe could go outside to see what the temperature is outside and turn on a light bulb when there is a risk of the garden being frostbit.
Step 10: Testing
At this point the unit is ready for testing. Since the temperature controller does not use a digital thermometer it is possible that the readings may not be 100% accurate so it is important to verify the readings against an accurate thermometer. If the temperature controller allows the water to remain too cool when cooking food may be undercooked and hazardous. If this is the case it would be prudent to make a note of how much hotter the oven should be set in order to maintain sufficient temperature.
A note about how the temperature controller works. The relay closes when the temperature is below the set point then opens when the desired temperature is reached. If the temperature falls below two degrees of the set point the relay closes again and remains closed until the desired temperature is reached.
Step 11: Closing Thoughts and STUFF
This unit can be used for other automation projects in the home. It can heat a room with a space heater or cool a room with a fan whenever it is temperate outside. It could be used to control an alcohol still but check your local laws first. I think it is legal to distill alcohol if it is ONLY used to power vehicles but better check just to be safe.
Alternatives to some of the devices used in this example
**Whatever device is selected it needs to have simple controls. Analog controls, often the less expensive model, are compatible with this controller. To test, plug in your appliance and turn it on, it should get warm. Unplug the device for a few seconds and plug it back in, if it continues to heat without touching the controls again it will work with this controller. The reason is that the temperature controller cuts all power to the device and digitally controlled devices will lose their memory.
This build took me less than fourteen days and almost that many trips to the hardware stores and thrift stores. I was inspired by other people and their builds but I did not like the enclosures they chose. Some people had the temperature controller sitting on the counter while a water bath was inches away. Please do not do that. An enclosure is less than fifteen dollars and an ambulance ride is more expensive.
I run a blog where I talk incessantly about the things I build, including an unabridged version of this project where I talk about all the things I did wrong as well as what I did right and what I plan to do with it after the build. There is also a day I talk about how to calibrate the thermometer to get very accurate readings from these inexpensive controllers. There are other neat things there like a device that lets you hear temperatures and a keyboard you can use from inside your pockets.