Automatic Temp Controller

[Winz]

I have been searching for a used DigiQ DX2 or Rock's Stoker for a little while.  The focus has been on a used unit because the $300 - $400 price tag for a new one just is not in the cards.  In the meantime, I decided to build one from scratch.  Given my pathetic electrical skills, I though I just may learn a few things along the way.

Like all projects of mine, it starts with multiple trips to home depot, radio shack, and a few visits from the UPS dude:



This is the brains of the system.  It is controlled by a PID controller, which measures temperature and compares it to the target temp.  If the measured temperature is lower than the desired value, it opens a relay which (in this case) drives a blower fan to stoke the coals.  If the temperature is higher than the desired value, it shuts the fan off, reducing oxygen and as a result the temp falls.  The system is programed to learn how fast your smoker temperature fluctuates and adjusts itself accordingly.  I installed two switches - a main power switch (off/on), and an on-off-on switch.  This capability is needed to compensate for big temp drops when I lift the lid, and also allows me to run the blower manually as well.  The indicator light at the bottom right goes on when the fan is running.




Here is my motor set up.  I need to do some finish work on it to make it look nice, but right now its functional.  I decided to put a ball valve in so I can completely shut off the air into the smoker, thus saving some charcoal when I shut it down.  I bought two fans as they were only $9.  This one is rated to 10 CFM.



The air is directed right at the fire box.  I plan to plug the other holes with some 1" metal plugs.  This mounting position required no drilling in the SJP.  I may add a diffuser to redirect the air down if needed.  I can control the airflow by adjusting the fan, or by partially closing the ball valve:



I had to install a probe to measure the ambient temperature in the smoker.  I chose to order a female K-type thermocouple unit and attached it to the PID.  This allows me to use all of my existing thermoworks probes which saved quite a bit of money.  Probes are not cheap!  This one has an alligator clip installed on it so I can position the probe where I need to:



For power, I wanted to be able to plug the unit in the wall, but also wanted it to be portable.  The system is 12V DC, so I bought a small ac to dc adaptor to plug in.  Shown here is the portable option - a 12V battery that I had used to power an automatic door on my chicken coop.  Since a bear ate the chickens, I no longer needed a chicken door     The fan and PID draw a total of 500 MA, so this battery would last about 16 hours with the fan running constantly.  It should provide plenty of power for smoked pork butts!



The next step is to figure out a good installation spot on Wapiti's cart:







Hoping for a free day early next week to do a low and slow cook.  With any luck at all, I can finally get some sleep on those overnight smoke sessions.

Winz

[1911Ron]

Nice work!

[Nate]

Nice work Winz. I built a PID controller to control a 1000 watt element in my electric smoker.  I might need to see if it can control a fan now.

[Lerxst]

Nice - and nice Martin photobombing most of the pics too! 

[MrHoss]

Wow - I am more than a little impressed Winz. Thinking of attempting something like that is way beyond what I would ever even think to do. Knowing a little of your other projects though leaves me not really surprised that you would be on this as you are.

[Troy]

holy crap, that is awesome!!

[1buckie]

Reminiscent of Killswitch's make up from Smoke Ring.....

http://www.thesmokering.com/forum/viewtopic.php?t=37975

I started reading thru his post & realized I already had a bunch of the stuff.....even the exact same fans......I probably could have saved you a few bucks on things.....the stuff's just laying around !!!!


Anyways, good show !!!!!

[Winz]

Reminiscent of Killswitch's make up from Smoke Ring.....http://www.thesmokering.com/forum/viewtopic.php?t=37975

Wow - wish I had seen that thread before I started.  Some good info there.  I searched high and low for a box to put the PID in (project box) with a DIN 1/16 opening, but ended up going with a 4 X 4 X 4 conduit box, much like the one "skeeter" went with. 

I also went DC power 1) for portability, and 2) so when I shock myself while putting the project together is does not hurt as much 

Winz

[1buckie]

" 2) so when I shock myself while putting the project together is does not hurt as much  "


It's DC that kills......ask Tesla........

Speak up when you get a harebrained idea.....maybe some of us can help !!!!

[saxart]

Are you freaking kidding me?   Wow, this is amazing!  Great work man...

[argentflame]

Very nice work. I just got a freebie DigiQ DX from a garage sale. Tried it Thanksgiving day. It turns on but does not read grill and food temp. Hopefully it's an easy fix.

[pbe gummi bear]

Nice job, Winz. Do you mind if i ask what the total cost on the BOM was?

[Winz]

Speak up when you get a harebrained idea.....maybe some of us can help !!!!

Its a good point.  But you know me - I live in the woods away from humanity and harebrained ideas are a frequent occurrence. 

I just got a freebie DigiQ DX from a garage sale.

Why does that not surprise me....  I swear, on a $ expended per Kettle owned (or given away to others) basis, no one can touch you.

Do you mind if i ask what the total cost on the BOM was?

Total cost was about $100: $28 PID, $10 conduit box, $9 fan, $18 ball valve, $7 thermocouple connections, $6 toggle switches, $2 light, $2 power plug adaptor, $5 power supply, $10 misc wiring, connectors, etc.  The fun I had and new knowledge gained doing the project = priceless 

The above does not include the probe and 12v battery for portable power, both of which I already had.

___________________________________________________________________________________________________


2 hours in on a test cook.  So far so good!




Winz

[SixZeroFour]

OK, what the heck! I KNOW I responded to this thread via tapatalk when you first posted but I see nothing!?.. Very weird..

Anyways - Another amazing project out of the top secret Winz Laboratories! It's incredible that you were able to learn how to make this essentially all on your own!

I'm reasonably handy when it comes to most things but electrical is NOT one of those things

[Winz]

It's incredible that you were able to learn how to make this essentially all on your own!

While I certainly appreciate the complement, the reality is that this idea has been done before - I simply learned from others to apply it to my own situation.

I did a second test cook - this time targeting a lower temperature of 160.  After an initial overshoot to 170, Wapiti settled in nicely.  This would be a perfect temp to smoke some jerky:




What I find amazing about this project is the consistency of temperature in the smoker.  I have used my Thermoworks TW8060 to monitor the temp in my Wolf propane stove (I have a weird obsession with measuring temperatures while I cook, but I digress).  My observation is that the temperature of my oven swings by 20 - 30 degrees from the target temperature.  Here is a graph I found of a Viking stove - it pretty much reflects the way my oven works as well:




One of the contributing factors to this wide fluctuation is that the thermocouple used to measure the ambient temp in the oven, is located in the walls or in the roof of the oven.  In essence, the "control input" is located in one of the most volatile areas of the oven.  With the unit I built for Wapiti, I am able to locate the ambient temp probe right next to whatever I am cooking.  This means 1) a much more stable measurement for the control unit, and 2) you can see the actual temperature the food is being exposed to.  Pretty amazing that a smoker with an automatic temp controller can be more accurate that a stove costing thousands of dollars.

Winz