Sous Vide System With STC-1000 Temperature Controller

This instructable seeks to show you how easy it is to build and use your own Sous Vide at home. Commercial Sous Vide cookers often cost several hundred dollars [1], but this unit under $50, particularly if you already own the right kind of slow cooker.

Before starting on the build, we'll first go over the components and theory operation. There are two components to this build. First is the enclosure that contains the temperature controller. The controller takes AC power in from the wall, measures the temperature of the water, and decides whether to power the plugged in slow cooker. By powering on and off the second component, the slow cooker, the temperature controller heats the water temperature until it hits the target temperature.

For those unaware of this cooking style, sous-vide is a method of slow cooking in which a sealed piece of food (meat, vegetable, etc) is placed into a bath of water that is both temperature regulated and at a lower temperature than is typically associated with cooking. The intent is to cook the food evenly, retain moisture and ensure that the inside is cooked to a desired temperature without overcooking the outside. In addition, food texture can be easily controlled based on how long the food is kept in the water bath.

Step 1: Warning!

Before starting on this project, you need to be aware of related electrical hazards and how to keep yourself safe. 120V AC can lead to fires and, although not commonly, kill.

1. Always disconnect (not just turn off) your unit from the wall before getting anywhere near the electrodes or other exposed wires.
2. Make sure no electrodes are exposed. Anything dangerous should always be enclosed or shielded with electrical tape, electrical terminals, etc.
3. Always use a fuse with this device. In addition, make sure you size the fuse for your application. Check the power load of your desired device to determine your fuse size. Amps (current) = Power (watts) / volts. If uncertain, err on having smaller fuse that you need. If it repeatedly blows under normal operation, slowly increment up until the fuse stops blowing. Never go any higher than you absolutely have to.
4. Use the correct wire size/gauge. The unit is rated for 10 A, and it is recommended that you use 12 gauge wire at 10 A. Smaller power/current requirements means to you get away with smaller diameter wire. There are plenty of tables on the internet to tell you which wire gauge to use for any current.
5. Always connect the ground between your two sockets. If you're using a metal enclosure for this project (which is safer than plastic), make sure your also connect it directly to ground.

Step 2: Order Parts

There are two parts to build: the enclosure containing the temperature controller and the slow cooker. This build focuses on the enclosure and temperature controller, but I also include some suggestions on determining if your slow cooker will work or buying one from elsewhere.

1. Enclosure

Assuming you are building a similar enclosure as mine, start buy acquiring the following parts:

1. Acrylic sheet, cast, 1/4" thick, clear. I recommend 2 square feet. Amazon, Ebay, and Inventables are good suppliers.
2. M3 square nuts. Hex is also ok. 4-40 works just as well.
3. M3 bolts m3x12mm. 4-40 works just as well.
4. Wire. 12 to 16 gauge depending on power load of your slow cooker. Your local hardware store may sell it by the foot. If so, buy at least 3 feet. I find stranded easier to work with (it's more pliable), but it's rated for lower current.
5. Terminal set, particularly the spade female terminal. Ebay is a cheaper (but slower) supplier
6. STC-1000* temperature controller with sensor
7. 3 pin power socket, female. This part will need to be modified slightly to fit inside on the 1/8" case.
8. Fused male power socket. I have an older instructable covering wiring, safety, and mounting this unit.

* A few notes on the temperature controller: The STC-1000 is a decent temperature controller. It works by turning on the heater when the temperature is below a certain threshold and off when above. It's primary advantages are its cost and ease of operation, but it takes a while to achieve a steady state temperature. If you watch it while its working, the temperature will rise quickly, overshoot the desired value, and then oscillate around that temperature before finally settling some time later. Nicer controllers, such as PID temperature controllers, use more sophisticated algorithms to achieve steady state temperatures much faster and better maintain them when the temperature unexpectedly changes (such as when you put in your food). The downsides is that they cost more, typically require an external relay to operate, and have a more complicated interface. In the future, I plan to write up another temperature controller instructable using this unit.

2. Slow cooker

Before buying a unit or deciding if your unit is good enough, consider these 3 constraints on the slow cooker. For the record, this is the unit I bought, and while it worked just fine, some people may not find it ideal in their applications.

First, the slow cooker must be an "analog" unit. An "analog" slow cooker typically has a few coarse settings (e.g. high, low, warm, off) and no digital display. Most importantly, it retains its settings when if it is repeated turned on and off (which is how the temperature controller will operate the cooker). In contrast, the nicer, "digital" slow cookers have a fancier digital interface and additional features. The deal breaker is that these digital units lose their settings when turned on and off, and therefore they won't work with this build. Conveniently for us, the analog slow cookers are typically cheaper than digital. See pictures for details.

Second, make sure you get a unit that meets your volumetric needs. The unit I list above is a 4 quart cooker, and it seems to work just fine for medium and small sized items. For example, I cooked two vacuum sealed steaks in it last night without much trouble. I don't think it would work well for a large roast.

Third, make sure your unit puts out enough power. Without impressive thermal heat transfer calculations, it's hard to determine exactly what you need ahead of time. I recommend reading reviews of any unit you buy and make sure that there are no complaints that it's slow to heat. My unit is a 180 W unit for 4 quarts, and I find it struggles a little to heat up initially. I help it along by pouring in already hot water and even once wrapping it in towels to conserve heat. The towels weren't required, but it did heat faster.

Step 3: Build Enclosure

There are many ways to make an enclosure for your temperature controller, and it's entirely up to you what you choose. I do however, recommend that you make an enclosure that contains all electrical leads, is relatively water tight, and has a fuse. In my design shown here, I make a laser-cut, acrylic enclosure.

1. Design

In one of my previous instructables, I go into detail about how to make generic acrylic electronics enclosures. If you choose to follow my design, you'll need to start with that instructable. I've also attached my CAD files, and you're welcome to use them verbatim or as a starting point for your design.

2. Cut

Load the design and your acrylic sheet into a laser cutter and cut out the enclosure. If you don't have access to a laser cutter, I recommend looking into joining your local makespace.

3. Modify female ac socket.

The female socket is intended to be mounted in 1/16" thick panels. Being that the acrylic pieces are 1/8" thick, this is a problem. I took a dremel tool and "shaved off" roughly 1/16" of the locking ear. See picture. A pair of snippers likely could have done the job as well.

4. Mount components

Go ahead and mount both ac sockets and the stc-1000 unit to their respective sides.

5. Assemble sides

Excluding the top, connect all 5 sides together and secure them with screws and nuts.

6. Wire the enclosure

Finish wiring the enclosure. See my previous instructable on the Male AC socket for details on wiring it to the temperature controller. Connect ground from the male socket to the female socket. Connect the neutral wire from the male socket to both the controller and female socket. Connect the hot wire from the male socket through the temperature controller relay to the female socket. As previously mentioned, use appropriately sized wires for the current.

Note that the female socket has 3 plug holes. The round one on the bottom is always the ground. The narrower plug on top is the "hot", and the wider plug is the "neutral"

7. Top.

Feed the temperature sensor through the hole in the top. Then secure top before testing.

Step 4: Test

The next step is to test that your setup works.

Plug in your slow cooker in the controller box, fill the slow cooker with water, place the temperature sensor into the water in your slow cooker, and turn on the box. To program the controller, hold "S" on the unit until "F1" pops up. Press and hold "S". Press up and down to set the temperature. Release "S" when you're done. Ideally, your slow cooker should heat up the water until the set temperature is reached. "F2", one click up from "F1", sets the window about the set temperature where the turns on and off. I set mine to the minimum setting, 0.3 deg. C. Finally wait and make sure your system heats up appropriately. If the system is slow to heat, I have a few suggestions on the previous "choosing a slow cooker" section.

There are more detailed directions on youtube on how to operate the STC-1000.

Step 5: Calibrate

Next, we need to test if how accurate the temperature sensor is. To start, fill a cup 3/4 full of ice, and then top it off with cold water. Stir for at least half a minute to ensure that the water temperature is uniform and ideally around the freezing point. Stick the meter into the ice/water mix, and wait for it to reach steady state. This may take a few minutes. In my case (see picture), my ice water read 1.0 deg. C in the ice water bath. I then calibrated my STC-1000 unit by setting "F4", three clicks above "F1", to -1.0 deg. C.

Step 6: Cook!

My first recipe was steak [1]. My local grocery store sells vacuum sealed frozen steak which is perfect for the sous vide system as you need to seal the food anyway. There are ample recipes and sous vide tips out on the internet to help you. Good luck!

[1] http://www.seriouseats.com/2015/06/food-lab-comple...