Plywood Smoker with PID Controller

Discussion in 'Smoker Builds' started by quackerspaniel, Jan 15, 2013.

  1. Just started my build this weekend.

    Here are a couple teaser pics.

    I am adding shingles to the roof.

    I need to cut out bottom door for access to heating elements.

    It will be hot plate warmed.



    Let me know what you think.
     
  2. dutch

    dutch Smoking Guru Staff Member Administrator Group Lead OTBS Member SMF Premier Member

    What are you dimensions?  Looks fairly deep~plenty of space for hanging stuff.
     
    Last edited: Jan 16, 2013
  3. I'm using Calphalon cooling racks for my racks which are about 12"x17" so I will put 2 per level making it 24"x17" on the interior. Total height is about 50" tall plus the legs.

    Right now there will only be 3 rack levels and then the top level will have 1" bars across of hanging bacon or sausages.
     
     
  4. roger shoaf

    roger shoaf Fire Starter

    A few points.

    The door looks to be smaller than the racks.  Picture a smoker full of jerky where you have to reach inside and pull each piece off the racks rather than hauling the racks into the kitchen to package.

    Insulation.  When you are smoking, the temperature is something you want to control rather than letting fate be the guide.  With out insulation the unit could get too hot or too cool to give you what you want.  Also if you are paying to heat the box, an un-insulated box is going to cost you more to maintain heat than an insulated box will.

    What if you get some sort of grease fire inside the wood box?   Looks like it is going to be close to your home so if something goes wrong it could go very wrong.
     
  5. Roger,

    Thanks for the tips and points.

    The door is smaller than the racks by just a little bit. I just tilt the rack a touch to get it out. So i don't think it should be a problem but I it is something I will think about now as I'm finishing it. I can replace the door and cut a bigger hole if I would like.

    Insulation:

    My original design did use insulation by creating an inner and outer wall but I decided to scrap that idea and move to 3/4" plywood single wall instead.  My thought here was that the 3/4" plywood should do a good enough job insulating. I might be wrong. We will see.

    Regarding a fire, I am very concerned about this. This is actually on my rooftop(I live in Chicago). When using it it will be moved away from the side of the house (seen in the picture). I am going to try and hook up a siren to the PID controller on the upper temperature limit if I can to alert me of excess temperature. I will also obviously have a drip tray to catch most of the drippings.
     
  6. I also want to reinforce that I appreciate the feedback. This is my first smoker build and I fully expect to make some mistakes, so please keep the questions/comments coming, they are very helpful. 
     
  7. As I mentioned in this post:

    http://www.smokingmeatforums.com/forum/newestpost/83549

    I am having some trouble with getting the temperature to where I need it.

    I have two hot plates 1000W and 900W and without modification they don't seem to be able to do the job.

    I think my options are:

    1. Insulate

    2. Override the hotplate thermostat and let my PID controller do its thing.

    Obstacles:

    1.How? I could add a double wall but that seems like a pain in the butt and will it really get the job done?

    2. Will the burner overheat? Should i do both or just one?
     
  8. dirtsailor2003

    dirtsailor2003 Smoking Guru OTBS Member

    I am interested to see how this turns out. I am not a electricly inclined person, so I hope someone comes along to help you out there. One member that has posted quite a bit on wiring PID's is Dward51. I have learned a ton from his posts. If he doesn't chime in you might pm him.

    Along the lines of insulation, you could easily add a layer of rigid insulation to the exterior of what you have. you could leave it like that, or sheath it with plywood. It will help you out a bunch. I personally would sheath it after insulating. You could go cheap and use as light as 1/4" ply. You will need to move your door out, so plan on support around the original opening for that. I would just screw the insulation and new ply to the original ply and only put furring strips of wood around the door.
     
  9. Here are some more pictures with some close ups of what I have done.

    The Roof


    View of the Front


    The inside. Three levels of racks with 2 11x17 cooling racks on each level.


    1" dowel slots to hang sausages from.


    1000W hot plate


    900 W hot plate


    RTV Silicone caulk to seal the doors. Also Diffuser is removable as you can see.


    The vents (Closed)


    Vents (Open)


    3 Vents on the back


    I have also sealed the bottom.

     
  10. link

    link Smoking Fanatic SMF Premier Member

    I like what you did there it looks great. I want to do one like it but use it just for cold smoking so I think this would be a great setup for that and I would not need to worry about keeping temp.
     
  11. I am actually hoping to do some cold smoking as well as some hot smoking with this one. The chimney out the top has a removable cap and I was going to try and run a dryer vent hose form it to another box to cold smoke.

    I have to get this one to work first though.
     
  12. Apparently the issue is related to the Thermal limit switch.

    I'm going to try and override this and see if I can get some higher temps.
     
     
  13. dward51

    dward51 Master of the Pit OTBS Member

    Ben,

    I got your PM and here is my take on the two threads in which you describe your issues.  I'm not the know all and end all source and this is just my opinion.

    Insulation would help with heat retention and also let you run the smoker with a smaller wattage element.  I don't know if a 1000 and a 900 would work together very well and you would probably have better results with a single 1,500 watt element like the brinkmann model that runs about $39 on Amazon.com.

    Since you indicated the SSR is never shutting off and the hot plates are both cycling - your main problem is the thermal limit switch in the hot plate bodies.  Each of them should have a small "switch" that opens at a set temperature cutting the power the the plate to prevent overheating and a possible fire.  Due to the enclosed environment, this switch is kicking in and cutting the power to your heating elements.  In essence the thermal limiter is setting your temps and not the PID (which is why the SSR never shuts off).  Having both hot plates in the smaller enclosed area below the plywood with the vent holes exaggerates this effect.  I bet if you took the temp of that chamber (the hot plate chamber) you would find it is a lot hotter than the temps in the meat chamber.

    I'm leery of having that dividing sheet of plywood with the holes between the two chambers.  I would be more comfortable seeing either large ceramic tile squares or cut cement board (Hardie board or similar) lining the bottom and sides around the hot plates.  I would then think about a sheet metal tent you could foil and keep food drips off the hot plate(s) and your smoke source.  I would rather see a metal grate (like meat grates) if you want to put a drip pan where the plywood divider with holes is now.  It will allow better heat and smoke flow and not be prone to combustion/charring.

    Try taking the plywood sheet with holes out, remove the thermal limit from the 1,000 element and see what sort of temps you get then (and I still really think you need tile or cement board to protect the plywood around the heating element, no matter what the wattage is).

    Another suggestion I would make is since this is a plywood box and you are talking about having it on or close to your home, I would add a 2nd PID controller to act as a safety cut off if the temps go above a certain point (add a smart thermal limiter of your own).  This would be a fail safe if the SSR or PID failed and the electric elements were in a run-a-way "on" type situation.  In essence it's a 2nd PID and SSR who's temp sensor must see chamber temps below the "fail safe" set point.  If the temps are below the fail safe point, the rest of the circuit (the smoking PID, SSR & heating element(s) have power and can do their thing).  If it goes above the fail safe point (ie, something is wrong), it kills all the power to those parts of the smoker and prevents your house from burning down after the wooden smoker catches fire due to a run-a-way temp situation.  This would also kill the power if you had a grease fire.  I would not put out the grease fire, but it would kill the electric current and take the primary source of ignition away.  It might still be self sustaining, but it will have limited air supply and will probably choke down quickly.  You could still use the alarm function on the smoker PID, but having a fail safe set above the other PID's alarm point would be a good idea IMO.

    I know there are quite a few wooden smoker owners on SMF, but I'm just leery of an unlined wooden smoker if you are going to warm smoke above say 170-180* (and I would not even consider going above the low and slow temps in the 225* range - forget about poultry at 375*).
     
    dirtsailor2003 likes this.
  14. I tested it with the thermal limit switch soldered shut last night. It got up to 170 in 20 min. After another 25 min it only ever reached 175 deg.

    So I am in need of additional heat.

    I looked at the brinkmann element you mentioned. That might work but I am wondering if I need more than an additional 500 watts.

    What about using a hot water heater element? I have found 2000 Watt 120V hot water heater elements.

    I am also going to pick up some fire bricks to mount or set it on.

    I also ran it without the wood diffuser. I am going to probably replace that with some additional metal cooling racks.

    My goal is 225 for temp. I was not going to run the wood smoker in the 300 range.

    When I smoke Poultry I will finish on the grill (located conveniently next to the smoker) or oven.
     
  15. dward51

    dward51 Master of the Pit OTBS Member

    Couple of thoughts....

    1) There are a lot of INSULATED smokers that run great on the 1,500 watt brinkman element.  If you look at photos on SMF you will see there are smokers with a good bit more volume than yours that run on the 1,500 watt element.  I think it may be time to think of adding a liner and insulation to your smoker.

    2) 2,000 watts is possibly beyond the limits of typical household electrical wiring.  You are looking at nearly 19amps just to power the element. Even on a 20 amp 110v circuit that's pushing it.  Once you go above about 1,700 watts it's time to move up to 220v elements.  The majority of household outlet circuits are only 15amp and you can't just swap out a bigger breaker as the wiring must also be matched to the breaker.

    I would give thought to adding some more wood blocking like your corners already have as spacers to your interior.  You could then put some insulation in and attach a new inner liner to the spacers and corner blocking.  Roxul is good, but for the temps you are talking about plain old household fiberglass insulation would be fine.  Just use unfaced insulation. Fiberglass would be inexpensive and would compress to fit the void. If the weight is not going to be an issue (ie, you don't plan on moving it around once it is put into place) you could use 1/4" Hardi-board or similar cement board as your liner material to also add thermal mass and some measure of fire resistance.  I would just line the entire interior like that.  It might take a few minutes more to get the interior up to running temp due to the mass of the Hardi-board, but it would be very stable once there.  You could might be able to use a "ziz wheel" or grinder blade to cut one side of the grates you have to shorten them to fit the new liner.  You could take it a step further and get thin sheet aluminum (or stainless, but it's expensive) and wrap the hardi-board before you screw it in place.  That would give you a metal, easy to clean liner while adding thermal mass and fire resistance.
     
  16. iowa josh83

    iowa josh83 Smoke Blower

    So I'm thinking...This smoker is being operated on your roof, how long of an extension cord are you running? Because I think you may be seeing a lot of drop which could effect the amount of heat your hot plates can produce.
     
     
  17. I bought some firebricks to line the bottom of the smoker then I picked up some radiant barrier insulation that is A/1 fire rated. I was going to look at adding this to the inside of the smoker box on the bottom and possible lining the outside with it. I'm not sure exactly. I will see once it arrives how best to use it.

    I am using a 30 or 40ft heavy gauge extension cord right now I think. I don't need to use one that long. I have an outlet 5 ft away I was just using that one because my other heavy gauge one (8') was in use. Do you think I'm seeing that big of a drop across 30 or 40ft?
     
  18. iowa josh83

    iowa josh83 Smoke Blower

    At 30-40ft...I would say yes. Use the closest outlet with the least amount of cord. See if your hot plates run warmer.

    Also if you are running the both hot plates off the same cord be aware of the combine wattage. At 1900 watts your drawing almost 18 amps, you would need to have a 14ga cord if not 12.
     
  19. I will try shorter cord. I did not run both plates on one cord I would run them off two. I have an extra SSR hanging around and I have another cord that I was using in test.

    I believe both cords are 14g. I highly doubt they are 12. I will see if it is printed on either cord. Maybe it is a 16 and that is why.
     
  20. iowa josh83

    iowa josh83 Smoke Blower

    If your using 2 separate cords 14ga should be ok.
     
     

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