I recently became interested in sous vide cooking since the price of meat has skyrocketed and I want to get the most flavor from each and every ounce. I considered building my own to use with a crock pot but problem is I love my steaks cooked medium-rare and my wife enjoys a well-done pork chop. Hmmmmmh! Four hours or better cooking for each of two different cuts of meat then you're looking at a minimum of eight hours cooking time since they cook at vastly different temperatures. Well, why not make a controller which will control two cooking vessels independently at different temperatures?
Step 1: Materials & Equipment Needed
1 - Project Box
For my project box I chose aluminum for a few different reasons:
***Electrically conductive - Because the box is metal, it is easy to provide a common ground for the components
***Conducts heat - This is important in order to wick the heat away from the solid state relays to prevent damage
I measured my components to make sure that they will all fit when installed so take this in consideration when choosing your box because your components may be of different dimensions than the ones I used.
2 - C14 Inlet Module
I chose this for the power inlet because the matching C13 cords for it are easy to come by (used on desktop computers and some monitors) and this particular one is fused and has an integrated power switch.
3 - 5 Position Screw Terminal Strip
I used this to facilitate making circuit connections.
4 - Heat Sink
Used to dissipate heat generated by the solid state relays (SSRs).
5 - Solid State Relays (2)
Since most of the components here are from things I had lying around my shop, the SSRs I used are rated to switch 50A @ 240VAC with a 3-32VDC input. This is way more than enough capacity to handle most crock pots or hot plates.
6 - Proportional-Integral-Derivative (PID) Temperature Controllers (2)
This is the microprocessor controller used to monitor and control cooking temperatures. Once again, I had two of these lying about and used them for this project. They were salvaged (along with the SSRs) from an old junk laminating machine.
7 - K-Type Thermocouples (2)
My PIDs can be calibrated for several types of temperature sensor inputs but for the sake of saving a few bucks, I went with these.
8 - Banana Jacks / Binding Posts
I bought these from Radio Shack, making sure to get the ones that are color coded in order to maintain proper polarity with my thermocouples.
9 - Banana Plugs
Plugs for the thermocouple leads to facilitate connection to the controller. With the binding posts I'm using these aren't exactly essential but they add a nice touch.
10 - Silicone Thermal Grease Paste Compound
Normally used on CPUs but works well between the SSRs and project box on the inside and between the heat sink and the project box on the outside.
11 - Wire and crimp terminals to make connections
12 - Solder and soldering iron
Step 2: Planning the Cuts
Before actually drilling, cutting, and filing holes in my project box, I made templates from some scrap poster board I had lying about. Once I measured the components and drew them out, I cut them with a knife and scissors then traced them onto my project box. Then, using the needle-sharp scribe which stows in my combination square / level, I scribed over the pencil tracings on my project box. Next step now is to cut and fit the holes.
Step 3: Making the Cuts and Drilling the Holes...
Using the templates, I cut the holes for my PIDs, my Edison outlet sockets, my banana jacks/binding posts, the terminal board, and the C14 power inlet module. For proper placement of my heat sinks and SSRs, I first drilled holes between the fins of the heat sink to match with my SSRs leaving a bit of space between the SSRs. I used the heat sink as a template to drill the holes in the top of my project box. As a note here, I intentionally placed my SSRs in the top of my project box to aid in heat dissipation from the SSRs. Now you must remember, I'm using as many on-hand parts as possible to complete this project. The heads of the screws that I intended to use to secure the heat sink and SSRs to the box wouldn't fit between the fins. I simply chucked them into my Dremel tool, turned it on, and ground the heads down on my bench grinder until they would fit between the fins.
Step 4: Install the Components...
Maybe it was overkill to ensure heat transfer, but I didn't want to leave anything to chance, so I used a liberal amount of heat transferring paste like that used on CPU cooling fans in computers. I put it on both the SSRs and on the heat sink to ensure proper heat transfer on each side of the project box. One of my crock pots is rated at 200W and the other is rated at 240W and my SSRs are rated at 50A (50A X 120V = 6000W, I don't see too much of a probability of an overload here). This allows me a considerable amount of "wiggle room" in case I want to swap my crock pot for a hot plate or something. As long as the combined current of my two channels doesn't exceed the 10A capacity of the fuse in my C14 power inlet module. I mounted my PIDs, my banana jacks/binding posts, my Edison outlet sockets, and my C14 power inlet module. Now I need to wire everything together...
Step 5: Wiring It All Together...
I am a fan of crimp type terminals as long as I can solder them as well as crimp them. I also love the durability and neat look of heat-shrink tubing. Although I drew my schematic using different colors for the wiring, I had only a limited number of colors of wire in my shop so I couldn't color code the different circuits in my controller. When I installed the Edison outlet sockets, I had a slight hiccup. If the plug I used in it fit very tightly it tended to pull the socket from my project box when unhooking because of the thickness of the aluminum project box's wall not allowing the retaining tabs on the sockets to lock properly. I fixed this by driving a small screw between the socket and the tabs to add more tension to prevent this from happening. One other note, I can't emphasize safety enough so please observe polarity with the socket and plug connections and by all means, use an Ohmmeter to ensure that you have good ground connections between the inlet module, the outlets, and the aluminum project box. The control circuits of my controller are low voltage and low current so I used 18 gage wire for them, but the power circuits, once again, I overkilled it (partly of necessity because of my limited variety of wire sizes on-hand in my shop) by using 12 gage wire. I'm pretty certain I could have gone with as small as 16 gage, but I have no qualms using the heavier. Upon finishing wiring, I placed heavy vinyl electrical tape over the PID connections in the event vibration over time may rub through the wire insulation. Before inserting the wires into the PID screw terminals, I tinned them to strengthen the connection and lower resistance . I clipped the terminals from the thermocouple leads leaving the crimped portion which I soldered to improve the strength. I then bound them to the banana plugs observing polarity to the colors (red +, black -).
Step 6: Install Thermocouples...
I made sure to buy thermocouples long enough to stick through the crock pot lid and go about halfway down into the water. Luckily my larger crock pot lid had a handle that once removed was the perfect size for mounting the probe. My other crock pot had a plastic lid which I easily drilled through the center and mounted the probe.
Step 7: Let's Fire This Baby Up!!!
I connected my C13 power cable into the C14 inlet module, connected my thermocouple banana jacks, plugged my crock pots into the Edison sockets, switched it on, and we were up and running. The PIDs I used are Fuji PXR3 models. I went online and downloaded the data sheets for them where I discovered that my PIDs have an autotune feature on them which allows easy setting of the parameters automatically. After autotuning them I had to tweak the ramp and soak times a bit to maintain better temperature control with less temperature overshoot and undershoot.