The four main components you will need for the electric and control portion are:
1. Digital PID Temperature Controller: These can be found all over the Net. I got mine from EBay for under $28 shipped. You can get them a bit cheaper if you don’t mind waiting for the shipping time. Mine came from an EBAY supplier in the U.S. and I had it in my hands in 5 days. These things are amazing at their versatility. What we are going to do with ours is to monitor the smoker temperatures, and control the power sent to the heating element and can be configured for different preferences, including degrees F or degrees C.
2. Solid State Relay (SSR): These silent little devices are used to provide the power to your heating element. The Controller above can’t handle the amount of current the heating element will require, so the Controller will just be used to turn the SSR on and off when there is a need for heat. Again I got mine from EBay. They can be used to control any line voltages from 24 – 380 VAC.
3. Thermocouple Probe: This is the sensor that will be installed into the wall of your smoker to monitor the inside temperature. Wikipedia says: “A thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage proportional to a temperature difference between either end of the pair of conductors.” Thermocouples are nothing more than two dissimilar metals that are fused at a point (this ‘point’ is at the tip of the probe). When certain fused metals are subjected to temperatures, they act like little batteries and supply a corresponding voltage. This image is a Type-K Thermocouple. This type of thermocouple is made up of Alumel and Chromel metals, and is one of the most common, inexpensive, general purpose thermocouples. How they act with certain temperature changes are predictable and are easily monitored to measure temperature. The Digital PID Controller above can use many types of thermocouples, and some PID’s come with a thermocouple.
4. Heating Element: I purchased a standard hot plate from Amazon. I had to void the warranty, and you will too if you use this type. You will have to disable the on/off knob. You will have no need for using it since the PID will be doing all the work for you. Open up the case and find the wires going to the on/off knob and short them together. I just put an electrical wire nut on them. I also cut off the power plug and stripped the wires bare so I could hook it up to my SSR.
I found this hot plate was way too hot for my insulated refrigerator, so once I had it installed and was testing my setup, I had to rethink the element. I found it was not having to heat up very much at all to maintain lower temperatures in the 120 degree F range, which isn’t good if you expect it to also supply your smudge. I then decided to use a heating element out of a salvaged George Foreman grill I had. It worked perfectly.
Hooking up your circuit is pretty easy. Here is a nice diagram I found on a Smoker website, note that I am using US power 120 VAC:
This guy is using a Terminal Strip to facilitate his wiring. I chose not to include one on my setup instead wiring directly to the SSR and the PID. Here’s what’s going on in this circuit:
The PID is receiving it’s power to turn on via pins 9 and 10. The TC (Thermocouple) is sending a voltage to the PID that corresponds to the temperature it is sensing on pins 4 and 5. Depending on what is programmed into the PID, if it senses the temperature is too low, it will send a signal via pins 7 and 8 to the SSR telling it to close its contacts. The SSR now will pass Line Power on to the Smoker heating element (labeled Power Cord female end), turning it on. With the heating element of your Smoker now getting hot, the temperature will be rising inside and the Thermocouple with it. When the PID senses that the Thermocouple has reached the set temperature, it will turn off the SSR. That’s basically how the operation works. The PID will actually modulate the turning off and on, you will see the light blink on the PID as it does this. It can take about a half hour or so to level out, but once it does it does a good job of maintaining your set temperature.
I built a little wooden box that I mounted my PID and my SSR in. I drilled a hole in the side of my refrigerator smoker to accommodate the thermocouple probe.
I cut a 4” hole in the top of the refrigerator and plumbed it to the outside of my cellar, and cut another 4” hole in the door for intake air, also plumbing that to the outside. My smoker is inside my cellar for convenience. It gets damn cold here at times in the winter, no traipsing outside to check on things for me!
I cut a couple oak mounts and oak rods for my sausages and bolted them to the inside top of the fridge.
This diagram may not correspond exactly to your PID and SSR, so make sure you follow the diagrams included with your controller.
With the George Foreman heating element, I can set my cabinet for 120 degrees F and still get enough heat out of it to provide a nice smudge to my sausages. Programming the PID is a bit confusing, at least mine was. The instructions that came with my PID were in English, but in many places they were a poor translation, but I did figure it out. There is also the ability to wire up an alarm on these, which I haven't used.
Wow!
