Digital temp mod

Discussion in 'Propane Smokers' started by glenwillits, Aug 10, 2015.

  1. glenwillits

    glenwillits Fire Starter

    I've been reading up on the various mods to add digital temperature control.  I've come up with an approach I haven't seen anyone else do, and thought I would explain it and see if anyone sees any hidden flaws.  I have a Camp Chef SV24 that I would use for this mod.

    Design goals:
    1) Automatic temperature control
    2) No pilot light - I get enough wind that I am worried about a pilot blowing out, ruining my Q, and maybe my house!
    3) Cost - around $100

    Split the incoming hose from the tank/regulator into 2 circuits.  Circuit 1 will have a needle valve adjusted to the lowest stable flame my smoker burner will hold.  Circuit 2 will have a solenoid controlled by a PID controller.  The two circuits will rejoin and go into the existing valve on my smoker.  Using a few tees, elbows and other fittings, I think this can be kept fairly compact, and sit under my smoker.

    Essentially this will create a 2-stage flame.  Stage 1 will be low enough to be below the lowest temp I'd want to maintain.  Stage 2 will be full power.  The PID will turn stage 2 on and off as needed to maintain temp.

    Stage 1 will be a much more stable flame than the pilot, and should not have much risk of blowing out. It will also mean that I have less temperature variation, since I won't be switching between full off and full on.  Stage 1 should slow down the temperature drop before Stage 2 kicks back in.

    The PID goes for about $25 on Amazon, and the solenoid is about $25 as well, so I am at $50, plus some fittings and piping to assemble it.  When I add an enclosure for the PID, and power for the solenoid, I may be a bit over $100, but I should be close. 

    Does anyone see a flaw, particularly safety-related, in this approach?

  2. glenwillits

    glenwillits Fire Starter

    Anyone think this will work or not work?
  3. I've been thinking of this feature for a few months now, but I was mentally trying to tackle it from another angle and ultimately decided to forget it because I wasn't sure if it would work and it was going to get really expensive.

    I couldn't find a gas/propane electronically controlled valve (at least with very fine controls), so I started thinking about using a stepper motor to physically adjust a needle valve. The stepper motor could have been driven by something as simple as a PID controller, or a Raspberry Pi2. The potential issues with this approach would be finding a reasonably priced stepper motor with that fine control, and then I'd have to fab up a way for the stepper motor to turn the needle valve.

    I like your approach to this though... Splitting the propane into 2 stages/lines seems pretty easy to do and you could probably find the majority of the parts somewhere locally. What exactly were you thinking of for a solenoid? I have a tiny bit of experience with solenoids (small solenoids for C02 fed with tiny 1/8" ID hose), but I have no idea what you would need in a solenoid holding propane. One question for instance, would the internal seals of the solenoid degrade with exposure to propane?

    I think a PID controller would work, but I personally wouldn't know until it was all hooked up for a test run. I could imagine you might need to incorporate some timing delay in triggering the solenoid because temp changes in your cook chamber aren't going to be instantaneous. If you end up needing to add a timing delay, I'm not sure you could do that with a PID controller. In that case, you would need to upgrade to a "smarter" device and probably have to write or piece together some code for it all to run.
  4. glenwillits

    glenwillits Fire Starter

    I decided to buy the gas parts and solenoid first and test it. If it works well, I'll buy the controller and housing.

    Here's the solenoid I bought :

    It says it's good for propane. Note that the electrical part of the solenoid is outside the fully sealed valve part, so it should be safe.

    I'll post pictures and let you know if it works.


    Sent from my SM-N910V using Tapatalk
  5. glenwillits

    glenwillits Fire Starter

    I tested the valve mechanism, and it works perfectly.  I can get a very low flame with the solenoid closed, and when I open it, it jumps to a full flame.  I ran it for about 1/2 hour and I get full temp in the smoker.  I'm buying the control and mounting parts and will put it all together this weekend.  Below is the prototype version.  I'll make a few changes to simplify the connections.

  6. Just curious, is input on the left side and output on the right?
  7. glenwillits

    glenwillits Fire Starter

    Input is on the right.  If you open the picture larger, you can see an arrow on the bottom of the solenoid.  That is the only directional component.  If that were bi-directional, the whole unit would be as well, and the input/output could be either side.

    I'm eliminating the elbows feeding the needle valve circuit, and just coming out of the tee, into the needle valve, and looping back into the other tee.  I'm putting the elbows onto the ends, so that the input and output come down as well.  That is to make it fit into a space I have to place it.

    I'll post updated pics this weekend when I get it built.

  8. glenwillits

    glenwillits Fire Starter

    I'm also replacing the solenoid with a 110v model, so i don't need a power supply.
  9. jckdanls 07

    jckdanls 07 Master of the Pit Group Lead OTBS Member

    I'm liking your idea... will keep an eye on ya and see how it goes... When I clicked on the link to the solenoid and read the description I was wondering why you were going with 12V. (subscribed) ...
  10. glenwillits

    glenwillits Fire Starter

    I was originally thinking I didn't want 110V out exposed to the elements, and that 12v would be safer.  I have an access panel in my deck right where I have my smoker, and I can lift out the panel and install the solenoid mechanism there where it will be mostly protected from the elements.  However, that wouldn't preclude some water hitting it at some point.  

    But after thinking about it, I realized 2 things.  

    1) The solenoid has a 1/2" threaded port where the wires come out, and I can connect a liquidtight connector to it and run it into my control box, so it should be mostly protected

    2) It's going to be plugged into a GFCI, so it should be safe in any case.

    This is the new solenoid I ordered:

  11. dcarch

    dcarch Smoking Fanatic

    I say never ever play with gas unless you have safety automatic flame out shut off.

    Just my superstition.

  12. glenwillits

    glenwillits Fire Starter

    That's a fair point.  Once I get it working, I may look for a safety shutoff to add to it.  I think with my flame on low, the risk of the flame going out is low, but I understand your point.
  13. jckdanls 07

    jckdanls 07 Master of the Pit Group Lead OTBS Member

  14. dcarch

    dcarch Smoking Fanatic

    I wonder if this would be a simple thing to do:

    Go to you town dump and rip out the burner assembly from a clothes dryer and use that to connect to a PID controlled SSR and your gas supply.

    It has all the safety features built in already.

    Possibly the ignitor system from a gas oven will work fine too.

  15. glenwillits

    glenwillits Fire Starter

    That sounds like a great idea for someone else to try!   I'm already too deep into mine.  [​IMG]   I think I have an approach that will work, and it avoids a pilot light that I think would constantly blow out.

    I ordered this safety valve to see if I can retrofit into my design.  I believe I can.  


    I believe I can unscrew the orifice that comes with it, and use it as a simple safety valve.  It has a push-button override for lighting.

  16. dcarch

    dcarch Smoking Fanatic

    The science of aerodynamics is very sophisticated and complicated. One of the difficult thing in designing any device or structure that has to do with air movement is to predict the end results of what wind can do. It will require high speed computers and most of all, wind tunnel testing.

    Once you have your set up complete, it may be a good idea for you to rent the largest fan you can get to blow on your smoker and see what can happen. The fan test, just like wind tunnel tests for buildings and bridges, needs to be done 360 degrees. You may be surprised that a light breeze can induce a strong tornado turbulence inside a smoker.

    And also try to consider what electric brown outs, black outs and spikes can do to your electronics.

    “A very low chance for bad things to happen” is totally unacceptable. It needs to be “Impossible to happen"

    A propane tank is a bomb.


    BTW, I do recognize you have great skills and knowledge.
  17. glenwillits

    glenwillits Fire Starter

    I finished my build this weekend, and it's working very well.  It maintains a rock-solid temp.  The only issue I'm having is that once it reaches temp, the cycle time is shorter than I'd prefer.  It cycles the heat on and off rapidly.  I'd like to find a way to increase the cycle time, even if that means a slightly larger temperature swing.  A few degrees would be fine.  

    The safety shutoff works great too.  Thanks to dcarch for pushing me to build it in from the beginning.  Here is a picture of the safety shutoff.  

    It's sold by Mr Heater as a safety shutoff to their propane heaters.  It has a thermocouple that senses the heat at the burner, and a push button to bypass the safety for lighting it.  You hold the button in after lighting for about 5 seconds, and then release and it stays on.  If the burner goes out, it shuts off the gas in about 20-30 seconds, once the thermocouple cools. 

    Here's a picture of the solenoid and needle valve mechanism, before and after installation.

    This is the control box.  It's a Carlon weatherproof junction box from Home Depot, and a clear in-use 2-gang outlet cover.  I cut out the divider between the two outlet sides to create one large rectangle.  The PID is cut into the cover for the junction box, and the clear cover is just attached to the junction box so that it sits over the PID and switch.

    Finally, here's a demo video, although it's a bit large:
    dirtsailor2003 likes this.
  18. jckdanls 07

    jckdanls 07 Master of the Pit Group Lead OTBS Member

    Glad to hear that everything works as it's suppose to... Had a feeling that you were going to encounter the rapidly on/off of the PID controlled flame...
  19. glenwillits

    glenwillits Fire Starter

    Does anyone know whether playing with the P, I or D settings will affect the cycle time?

    I found that Auber Instruments makes a PID that has a direct adjustment for cycle time.  If I can't adjust the cycle time with the PID settings, I'll probably get the Auber PID. 

    The basic setup and PID works so well, and holds so stable, if I can fix the cycle time, I think I'll have a great solution.

  20. jckdanls 07

    jckdanls 07 Master of the Pit Group Lead OTBS Member

    I'm not the person to answer that question as I don't know... there are a few PID controller guru's on the board... Dward51 helped me out... PM him and ask questions... get him to look at your thread...


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