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This instructable details how to assemble an automated temperature controller for a Weber Smokey Mountain (WSM) smoker. Total cost was around 72$. This should free up lots of time wasted on constantly adjusting the lower air vents during the cook.

The inspiration came from the instructable "Universal controller for sous vide cooking" by abefetterman.

I am not an electrician, far from it. If you do not feel comfortable wiring/soldering electronics please do not attempt.



Step 1: Parts List

Lightobject.com
EFAN-D12032 12cm DC12V Blower Cooling fan - $8.50
Note: 12cm fan is plenty strong. If possible buy a less powerful fan (e.g. 6cm or 5cm).
ETC-CB-K3M 10ft (3M) K type Thermocouple - $4.50
ETC-JLD612-A JLD612 Dual Display PID Temperature Controller - $32.50

Home depot
5" duct end cap
carriage bolt
3/4 " pipe
3/4" conduit housing -grey housing for fan
silicone
3-prong extension cord with 15 amp circuit breaker
3/4" conduit connector (very important, holds 120V ext. cord in project box
outlet with cover
HVAC tape (can withstand heat)
various nuts/bolts/screws

You will also need a plug for the fan. I repurposed a 12VDC plug from an old portable DVD player. Make sure (if you wire same as I did) that the plug/fan pulls below 3 Amps (all the relay on my PID device could do). The combo here pulls 0.8 amps.

Step 2: Assemble

Smoker fan attachment
Using a metal bit drill a hole in the duct end cap offset from center for the carriage bolt. This bolt will go through an air vent on the bottom of the smoker to hold the fan in place. Then drill a hole for the 3/4 inch thread pipe (held on the inside of the duct end cap with a nut). Place a strip of styrofoam on the bottom of the 3/4" conduit housing so the fan is not flush with the bottom of the housing. Place fan in the 3/4" conduit housing and seal with silicone.

PID controller
The temp control type depicted in the wiring diagram does not utilize the PID portion of the controller. It is a simple on/off relay. The device allows the user to set a lower temperature bound (i.e. 225 F) that when the TC reads <225 the controller supplies power to the outlet (fan), thus increasing the smoker temperature.

You will need solder the circuit breaker from the ext. cord. If you don't feel comfortable soldering just leave it out. First cut out all the holes in the project box and wire everything up. Tape off any exposed wire and wire screw cap connectors.

Step 3: Test

The PID controller has various settings. There are several good tutorials on youtube explaining the different settings. I highly suggest you watch similar tutorials.

I tested my controller using the "PID" algorithm to control temperature. I experienced considerable over and undershoot of the target temperatures. After further internet research, I found people suggest that fire/charcoal smokers are not ideal for PID control. This is due to the PID requiring variables that are relatively constant. Charcoal smokers have variables that change (amount charcoal, air intake, etc.). This is why I changed to the simple on/off relay. If the temp drops below the set point (e.g. 225 F) the fan kicks on, when the smoker reaches 226 F the fan stops.

I suggest taping off the two other air vents on the bottom and leaving the top vent at about 15-20% open.

7-15-13.
Enjoy.

Step 4: 1st Cook

Today I cooked a 3 lb boston butt (pork, no bone). I am loving the temperature controller.

I filled the smoker bottom with unlit charcoal. I then added ~10 white hot coals on the side furthest from the fan. Three hickory wood chunks were placed from side to side on top of the charcoal. I set the PID controller to 250 F (SV value). The lower boundary was set to 255 F. This boundary temp turns on the relay controlling the fan. I had to change it several times as I dialed in the temperature that left the smoker closest to 250 F.

There was considerable overshoot at the beginning of the cook. The temp got up to 300 F at one point. I think the fan was put on the smoker to early and really got the coals going. Next time I will leave the fan off longer and allow the smoker to come to temp on its own before placing the fan on the mount. Additionally, I covered half of the 3/4" pipe, which the fan mounts to, with tape to limit the airflow while the fan is "off" and set the top air vent open ~10%. This was the ideal setting for this cook.

Additional cooks are needed to really hone in on the proper settings, but for the first trial with food I am very pleased.

Step 5: Final Update (Ribs!)

I bought a pt100 temperature probe.  It appears to work faster than the K type I originally used.  

I decided to try baby back ribs today.  I started with 10 white hot coals placed on the side of a full basket of unlit charcoal.  I used two chunks of hickory for the smoke.  The temperature controller is great, provided you are a little patient.  The key to maintaining the target temperature is letting the smoker come up to temperature before attaching the fan to the smoker.  The initial white hot coals are plenty hot to bring the WSM smoker to ~250-275 deg F without extra air provided by the fan.  Once target temp is reached, attach the fan and step away.

Also, after removing the lid when checking the meat or applying rub/sauce the smoker temp with drop.  Once the lid is replaced, remove the fan and let the temperature slowly rise back up.  Once the smoker is near your target temp re-attach the fan.  I had to wait by the smoker for about 10 minutes every time I opened the lid before i could attach the fan.  If you don't remove the fan after opening the smoker the temperature will over shoot your target by about 50 deg F.

I am thrilled with this setup and don't expect many tweaks will be needed in the future. The ribs turned out great https://www.instructables.com/id/Smoked-baby-back-ribs/.  Restaurant quality if not better.

Enjoy. 09/01/2013 
I'd imagine a timer relay between the temp controller and the fan would help the overshoot. It might save some baby sitting (for an added cost and level of complexity)
<p>Since you are using the pid as a simple on/off relay, do you think a stc-1000, or the single stage Fahrenheit equivalent, would work instead? You could save some bucks going this route.</p>
<p>I not terribly familiar with stc-1000 but a simple on/off temperature switch should work fine. </p><p>Side note: the 12cfm fan is more than enough. I smaller fan would be preferable as the 12 cfm can blow ash onto the meat if the bottom isn't cleaned regularly.</p><p>-D</p>
What's the housing for the fan? What's it siting in?? Any suggestions?
It is the gray &quot;box&quot; see in the top picture of step two. The picture has a description of how to mount the fan in the conduit housing.
The fan is sitting in the 3/4&quot; conduit housing. This is a standard electrical component. It has two holes in it, one needs to be plugged.

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