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PID Questions

Discussion in 'Smoker Builds' started by pipinchaz, Nov 10, 2013.

  1. My cabinet is uninsulated single thickness. My idea is to use a welders blanket against the cabinet then sew a movers blanket on top of that (or two depending on the insulation) then attach it to the cabinet with snaps that can be removed while preparing everything. I would like to cut the top off so I can access the inside for a rotisserie also.

    Whether hot or cold smoke, I'd like to do both if possible. I was thinking about a detachable hot box for when I do the cold smoke then bolt the cover back on over the opening for when I do the hot smoke, no hotter than 250 degrees F. I have 110V with 20 amp breaker for power source or (this is what I have been pondering) using propane as a source. I was just looking through the threads last night to get ideas which way I'd like to go. It would be easier to control the temp with the PID though.

    So I guess I would like an all around smoker all rolled into one. Haha. I'll see if I can figure out how to post a picture of the cabinet on the thread to give you an idea what it is.

    What type of heating elements do you recommend? I have thought about hot plate burners, electric stove burners. I had place a decent hot plate inside the cabinet (with out insulation inside my garage during the summer) and it barely reached 100 degrees. So that brand hot plate was out.

    Thanks for the help.

  2. dward51

    dward51 Master of the Pit OTBS Member

    Uninsulated cabinet is going to be a challenge.  Metal will wick the heat outside the cabinet (ie, if the air inside is 225* then the smoker's metal cabinet is also 225*) and could also be a hazard if you have kids around.  If you can find a way to insulate it, that would be better.  I'm not sure about the external blanket idea.  I think I would go with installing metal tubing inside to form a space, then a new sheet metal layer with rock wool insulation in the void between them.  Otherwise no matter what your heat source, it will be harder to keep temps stable, especially as winter approaches.

    As to LP vs electric.  Both have their pluses and minuses. I like electric as once you have the cabinet at temp, it is very stable and pretty much a "forget about it until done" type of thing.  LP and charcoal not so much.  Both need to be checked for temp and to make sure the fire did not go out every so often.  Electric is "on" as long as you have electricity and most people would notice the lights just went out in their house no matter what room you are in.

    As to elements....  A hot plate element will have a thermal limiter in the unit.  They do not work in confined spaces without modification.  If you do not remove or bypass the thermal limiter you will top out around 150* from what most have posted.  As to element size, if I recall your PM your dimensions were 32"x48"x48" so that is a good size volume of air to heat (especially when full of cold meat).  You may have to go 220v on this for an electric build, but it may work OK on a 1,500watt brinkman type element.  I know the taller warmer to smoker conversions seem to work on 1,500 watts and would guess the overall volume is close.

    I'm not so certain a cabinet like you describe will work without pretty extensive modifications, but post photos so the group can all chime in.
    Last edited: Nov 10, 2013
  3. Dave,

    Attached are some photos of the metal cabinet and also an old 50's style refrigerator minus the cooling unit that was on top. It had been my first thought of a smoker and it still might be depending on the work on the stainless cabinet.The inside dimensions for the fridge is 16" X 24" 28" tall to the drawer.

    The metal cabinet is 24" X 36" X 32" tall. The doors are the only thing that is double thickness with a air jacket inside. I'd still like to be able to put a rotisserie in the stainless cabinet.

    Where can you purchase "rock wool"? If I was to go with 220V, where can you get an element that would be suitable for the build.

    Your opinion on either?



  4. dward51

    dward51 Master of the Pit OTBS Member

    Both would work for smokers, volume is different (obviously)....

    The old school fridge probably has either a cellulose, wood, or cardboard based insulation in the walls.  A lot of the builds from old fridges seem to have posted they found insulation of that type.  May work for cool temps, but not good for heat and smoking.

    I like the stainless cart myself.  I would see what it would take to install square tubing and skin the inside either with aluminum or thin stainless (aluminum will work just fine as once you start using it, you will have a thin layer of "smoke" that will hide the stainless anyway.  Plus aluminum is much less expensive).   Then you can insulate the void between them.  A well insulated smoker cabinet is the key to consistent and even temps.

    You could make a rotating rack system that would let you either run with flat racks like normal or with rotating racks or rotisserie rods (think like a rib-o-lator but with more or larger racks to fit the large opening. Google it if you have not seen one).  I think you could mount the bearings and hub for the side supports though the shell.  Then you can have removable spokes to the revolving racks.  That way you can disconnect the spokes and then still have regular rack tracks on each side of the smoker above and below the hub so you could slide in regular fixed flat racks when you want it or hanging racks up top when needed (for sausage, etc...).  That way you get the best of both worlds and your drive motor is outside the heated chamber.

    The more I think about this idea for the stainless cabinet, the more I like it.  It would take a little work, but that would be one sweet electric smoker.

    As to elements....  You have several options.

    You could take two of the 1,500 watt brinkman 110v elements and power the cabinet from a 220v 4 wire supply (would require a dedicated outlet run to where you will be operating the smoker).  Inside the smoker circuitry box you would then split the 220v L1 & L2 feed into two 110v feeds from L1 to Neutral, and L2 to Neutral.  You run one brinkman element on the L1 to Neutral circuit and the other on the L2 to Neutral circuit.  Both can be switched by two SSR's which are triggered at the same time by a single PID controller unit.  Two elements let's you space them across the bottom of the cabinet to help even out the heating.

    Or you could look at the myriad of heating elements available online or at places such as Grainger or McMaster Carr.  Wattage, size and designs are many.  But the brinkman elements are proven workers, inexpensive and easy to find.

    Dang, I a chance for a similar cabinet about a year ago and passed because it was not insulated and too wide and short.  Might have to see if I can find another one to make a rotating rack smoker.  Thanks for getting the creative juices flowing on this one.

    Check out this video of a Southern Pride commercial wood fired model and you will get an idea of what I'm talking about with the rotating racks.  This would work great in the size cabinet you have.  I would put it on some sort of a raised stand with storage underneath if it was mine though. 

    Last edited: Nov 11, 2013
  5. Dave,

    Can I use aluminum flashing for the lining of the cabinet or should I use something heavier? Where do I get rock wool? How thick does it come?

    I really like the rotating rack idea, but I'm not sure if I want to get that involved into building it. Haha. I do want to do a rotisserie for turkeys and chickens.

    I also like the idea of the dual element to balance out the heat. Would the Digital F/C PID 25A SSR Thermostat Temperature Controller J S K E Thermocouple work for the dual element?

    I could sink the element below the cabinet in a separate box, and (or) I could build a side box that would be detachable for cold smoking cheese or fish.

    Any opinions on a rotisserie motor or gear box? I know some people use a motor or gear box from a mangle, but they are far and few in between. I stepper motor would probably work but I'm not sure about the gear box.

    Now you got me thinking outside the box!!!


  6. dward51

    dward51 Master of the Pit OTBS Member


    Sorry it has taken me so long to reply.  I've been working overtime and just have not had the time to even turn the home PC on until tonight.

    Yes you can use aluminum. Or plain old sheet metal, or go high end with stainless.  Just stay away from using any galvanized metal or galvanized screws, bolts, etc....  Galvanized metal will emit chemicals when heated and you can get "zinc poisoning" also known as "metal fume fever" (google it).  The stainless looks great, but plain old unfinished sheet metal will work.  As soon as you start using the smoker, you will get a coating of smoke on the interior that will protect the metal.

    Rock Wool is also called mineral wool.  It's made by heating rocks until they melt and it is then spun like fiberglass into a mat.  Mineral wool has a very high temperature resistance usually in the neighborhood of 2,000* or more.  Grainger, McMaster Carr, Lowes, Home Depot, Menards, etc... all usually carry it.  A common brand name is Roxul.  It comes in batts like your home fiberglass insulation and in sheets of varying thickness.  If you find a good deal on sheets that are too thick, you can usually split the sheets easily to make them thinner (may vary by brand and design though).

    I would not go to the trouble of making a separate box, but I would put some sort of grease drip guard over the heating element (can be a simple metal plate held a inch or move above the element by metal stand offs or brackets).  If you are cold smoking you will probably just not turn on the heating element (although cold smoking covers a wide range and can extend into the lower 100* range for cured meats).

    As to the gear box & motor, you are talking about rotating a lot of weight in meat.  I seriously doubt you will find an affordable stepper motor with the torque you need.  I would think about salvaging a DC reduction gear unit from another commercial product (e-Bay is your friend for this sort of stuff).  You have other options though.  A gear reduction drive with a small sprocket that is connected to a much larger sprocket via a chain drive would be the first thing that comes to my mind.  Size the sprockets to get the desired RPM of the meat racks.

    Saved this for last.....

    Digital F/C PID 25A SSR Thermostat Temperature Controller J S K E Thermocouple

    That is a mouth full and actually describes many generic components of a process control system.  This is what you would need.....

    A digital PID controller - This is the "brains" of the temperature control unit.  This module has a temperature probe that provides input and based on the process settings will then provide a triggering voltage to control an external device such as an electric heating element.  Usually the triggering voltage is a low DC voltage that is output when the smoker or "pit" temp is below the desired set point programmed into the PID.  So if you dial a PID controlled system to be set at 225* and the pit temp is 150*, the DC triggering voltage is "ON".

    25A SSR - This is a 25 amp Solid State Relay, which is a switching device that takes a low voltage triggering signal to control or switch a higher voltage and higher amperage electrical circuit controlling a process (ie, it acts like a computer controlled switch turning the 110v AC or 220v AC power to the heating element ON or OFF).  These come in different amperage ratings and need to be sized higher than the maximum possible amp draw of your heating element.  So if you go with large wattage element you may need a SSR rated higher than 25 amps.  The SSR and wiring must be sized to the load for safety.

    J S K E Thermocouple - Ok, pick just one. It will be either a "J" type, "S" type, "K" type, etc..... but not a J S K E.  Most PID units can be set to work with any of them and also with RTD type sensors.   This is the probe that the PID uses to read the pit temperature.   Any of them will work just fine for a smoker.

    A note on PID units.  There are a lot of inexpensive and used Chinese PID units on e-Bay for around $20.   Usually these are MYPIN TA-4 models.  A word of caution about those....  Sometimes that $20 can be a bargain and they work find, but other people have reported Chinese PID's that never worked properly and gave weird readings.   I'm partial to Auber Instruments PID modules.  The are a little more than the e-Bay specials, but Auber Instruments is in the Metro Atlanta Georgia area and they have great customer support.  The Auber units are very popular with smoker builders and the home beer brewing groups.  They are also referred to as "Auberins" PID controllers which is short for AUBER INStruments.  Also I have seen PID units that the spec sheet shows one "pin out" and the schematic on the actual PID shows another "pin out".  Always go with the "pin out" terminal identification on the actual PID if there is a schematic drawing label on the PID.

    There are a lot of threads in this forum on wiring PID units in general.  Main thing you need to decide on is how big of a heating element, or how many smaller elements are you going to use (and what voltage will you be running them at).  From there we can fill in the blanks to give you a wiring diagram.

    Clear as mud yet?
    Last edited: Nov 16, 2013
  7. Dave,
    How thick should I make the insulation for the sides and top? What about the bottom, how about cement board? Is 4" stove pipe big enough for the top vent? Then I was thinking having a series of holes on the opposite side at the bottom for the draw.
  8. dward51

    dward51 Master of the Pit OTBS Member

    With insulation, more is better (up to a point).

    Simplest thing to do is buy some 1" or larger square aluminum stock and screw or blind rivet it into the inside of the cabinet.  This gives you something to attach the new lining to, again either by screws or blind rivets.  I think 1 1/2" would be good and anything over 2" would be overkill. 1 1/2" should not be hard to find either. Don't have any science to back the 1 1/2" figure up, it's a "looks good to me" number.  You could still go with a stainless inner skin if you want.  I would put more spacers on the sides as you will be mounting rack supports as well and that will give the supports something behind the inner skin to mount to.

    I would not be worried so much about the bottom, as heat rises.  Were it not for most people putting their burner or electric element at the very bottom, you could probably get away with no insulation there.  The cement board on the bottom may be all you need. The top would need to be insulated like the sides and door.

    I think a 4" chimney is going to be way too much for an electric smoker.  In a gas smoker you need more draw as you have to be bringing in combustion air for the flames.  In the electric, you just want to keep the smoke flowing and not let it get 'stale'.  If you go with two elements, I would go with two smaller chimney's and would probably want a damper on them to be able to dial the smoke flow in where you want it.  Remember with the smoke going out, you are also loosing heat that the electric element will have to make up.  Basically the air flow will need to be enough to keep the pellet tray/tube or other smoke generator running.  That's not a whole lot.  This also applies to the holes you were talking about.  I would not do that, and would only have fresh air to the smoke source.  If it was a charcoal or gas fired smoker, yes you need that air but not in an electric.

    Besides, it's easy to take a small chimney off and cut the holes a little bigger along with adding inlet holes at the bottom.  It's a lot harder if you cut them big and then find out they should be smaller.  Trying to make them look good shrinking them down and patching the larger opening never seems to work. 
    Last edited: Nov 18, 2013
  9. Dave,

    What kind of Amps do you think those 1500W elements will draw, Would it be safe for 25amp breaker or should I go larger? What do you think about a sliding plate over the holes to control the air intake at the bottom and top? Say like 1 1/2" dia holes maybe 3-4 hole in line.

    Should I get the 25DA SSR or the 40A SSR? and also do I need heat sinks for them?

    I figure I will have one element with a cast iron skillet over it for the wood chips and the other element with a water pan over it when I need water. Not quite sure what I am going to do about a drip tray/pan and maybe some kind of catch pan for it yet.


  10. dward51

    dward51 Master of the Pit OTBS Member

    A single 100% efficient 1,500 watt element would draw 14 amps on 110v (nothing electrical is 100% efficient though).

    If you go with two 1,500 watt elements, you are going to have to run it on 220v and split the 220v feed into two 110v circuits at the smoker (or get 220v 1,500 watt elements).  If you have 220v elements, then the amp draw is 1/4 what it is at 110v which makes that 1,500watt element only 7 amps (each).  I've had a few side conversations in PIDs & elements in the past couple of weeks, were your elements the 208v single phase ones from the 3 phase oven or are you looking at the Brinkmann 1,500 watt 110v type?  Guess I'm showing my age or working to much at the day job <G>

    From your question about 1,500 watts, I'm "assuming" we are talking about the 110v Brinkmann style elements.  If I was going to use two of those, I would bring a 220v 4 wire single phase AC line from a dedicated breaker to a dedicated outlet (ie, the outlet is the only thing on the circuit).  A 20amp double pole breaker (220v breaker) would work, as would a 30 (Generally they come in increments of 10 amps, but if you find a double pole 220v 25 amp one go for it).  Normally you have 220v between L1 and L2 (the red and black wires) in a 220v 4 wire circuit.  The ground still serves as a cabinet ground for safety and in a purely 220v circuit the white neutral wire is not needed.  However, stick with the 4 wire system and if you take the L1 (black) and route the other side of the element back to the white neutral you have a 110v circuit.  You then do the same with the L2 (red) wire and end up with two 110v circuits at what ever amp capacity the wiring and breaker are rated for.  Any amperage breaker in the 20 to 30 amp range should work for a 220v smoker like this.  I would go with 10 gauge wire or larger (smaller numbers like 8 and 6 are actually larger diameters), but 10 gauge is rated for 30 amps so it should be fine (and not too expensive).  Go with copper wire only and don't even think about aluminum.

    As to the PD and SSR's.....  Since you are going to be switching two 110v circuits, you need to think of them as totally separate.  Each element will need it's on SSR and 25 amps is plenty (yes get the heat sink, it is necessary).  However you only need one PID and the low voltage DC triggering signal from a single PID can trigger both SSR's simultaneously. 

    I would go with one of Todd's pellet tube smoke units instead of a cast iron chip pan.  Reason is the pellets will be burning and generating smoke continuously when the chip pan is not keeping hot when your heating element is off.  A well insulated cabinet will not require the heating elements to run as often or as hot, so smoke generation in a chip pan on top of the element may not work that well.  Plus with the pellet tube you get smoke even when you don't want the heating elements on (cold smoking).  This would let you smoke things like cheese, sausage, fish etc...

    As to a water pan.  Not sure you will need it, but a drip pan would be a must.  Easy way is to use the bottom rack to hold a disposable aluminum chafing pan like you get at Sam's Club as a drip pan.    I would also put a sheet metal guard over the heating elements so there is zero chance of any errant drips of grease hitting the hot element directly.   Lessens the chance of a grease fire as with a "set and forget" electric smoker, it's easy to walk away and not pay as much attention to that short of thing.  You can go so far as to make channels and drain any drips away, but the disposable pan is inexpensive and works just fine for most people.

    The sliding damper over/across the holes would work just fine.  As long as you have some way of controlling the air flow (up to the point of cutting it off - if you ever do have a grease fire, kill the heat source and shut down all the air flow in and out of the cabinet to choke the fire out.  Then wait a few minutes before opening the cabinet, as an inrush of fresh air can reignite the blaze if the temps are high enough).
  11. I was the one with the brinkmann 110V inserts. I (assume) figure when your talking 220V 4 wire, you are talking 10-3 with ground Romex wire correct? You split the neutral and take one of the legs to L1( black) and the other neutral leg to L2 ( red) to make both your 110V circuits right?
    You like the tube smoker over the tray version then? It looks like you light it and set inside to smoke. That would be easier to do that then having to throw chips in the pan every once in a while. I did plan on putting some kind of shield over the elements to keep the clean from juices or falling misc. I like the idea of the throw away pans to catch the unwanted mess.
    So the sliding dampers, should I place them on top and bottom diagonally from each other then or do I just need them at the top?
    I'm picking up my square tubing this weekend and my plan is to start putting in into the cabinet next week.
  12. dward51

    dward51 Master of the Pit OTBS Member

    Yep, 10-3 w/ground and split the 220v into two individual 110v circuits each returning to a common neutral.  10 gauge can handle 30 amps 220v which gives you two separate 30 amp 110v circuits if you want to max it out.  Should give you plenty of safety margin as those elements will not draw near that power.  Try to keep the run back to the distribution panel as short as possible, and again the 10 gauge gives you some cushion there as well.

    I have a pellet tray and not a tube.  I think the tubes burn through pellets faster from what I've seen posted, but it looks like they also crank out more smoke as you have a larger cross section of pellets burning at any given time.  In a larger smoker, that should be a good thing.  The tray will burn a long time and I don't think I have ever filled all the channels of the tray.  I think half a tray is the most I've ever used.

    Dampers are  a designers choice sort of thing.  The key is having some sort of adjustability which you have covered in the slide. Depending on where you are going to put the smoker for use, I would still recommend some sort of a exhaust stack.  Reason is it helps with the natural air flow through the cabinet.  Heated air naturally flows up, and having a chimney exhaust lets you take advantage of the "chimney effect" to keep air moving up and out.  I would probably go with a single 3" round chimney in the center of the top.  You probably will not need a damper on the chimney if you can adjust the inflow.

    I'm sure some of the others will jump in here with design comments too!  That's what is great about this site.
  13. Dave,

    So with the tray or tube smoker, I could use the tube for either hot or cold smoking inside the cabinet? Or would the smoker put off to much heat for cold smoking, otherwise I was thinking about the mail box conversion for cold smoking.

    Would the Auber Model SYL-2352P PID work for my 220V dual element set up?

    I decided to play with a cheap PID for my little Brinkmann smoker. I am working the schematic right and as soon as I get it finished and looking presentable to the public, I'll post it on the thread. If you wouldn't mind taking a look at it and tell me what you think I would appreciate it. I will put pictures of the PID and SSR so you see what they are.

    I also purchased a "K" probe.

    I would like to add a on/off switch, indicator light and a fuse.

    Thank you.
  14. I forgot to ask about the size of wire for wiring the PID and SSR? I also have a terminal strip and heat sink.

    Thank you.

  15. dward51

    dward51 Master of the Pit OTBS Member

    That SSR is probably the most commonly used model in both smoker and beer projects! Should work fine (just remember you will need two of them for the final build as you are splitting the L1 and L2 from the 220v into two 110v circuits and they will need to be switched by two separate SSR's).  A single PID can trigger them both in parallel though.

    The Auber Instruments SYL-2352P is also one of the most popular units used.  It will work fine on 220v and can be powered from either the 220v or 110v portions of your circuit.  Since you are splitting it into two 110v circuits, I would just power from one of those.  It makes it simpler if you keep all of the areas of the smoker as 110v.  I know that may sound confusing to some as you are running a 220v power source into the smoker, but you are splitting it into the two 110v components as soon as it enters the cabinet.

    You can use a much smaller gauge wire from the terminal strip fed through a fuse to power the PID.  The SYL-2352P draws less than 5watts of power, so the fuse can be ultra small in amp rating (5 watts at 110v is 50 milliamps or 0.05amps.  You want it to be a fast blow fuse also.  As long as you wire to the PID is rated higher than the fuse that is protecting it, you will be fine.

    Also remember the probe type will need to be set in the PID software to match the probe you have (ie, K, J, etc...).  Every PID I've seen has a way to change the probe setting in the PID setup menu.  And most probes have a positive and negative lead, so if you do not get a temperature reading, try swapping/reversing the leads for the probe on the PID terminals.  The triggering signal to the SSR is also polarity sensitive (and it's DC also, not AC - it is just a triggering voltage to the SSR that causes the SSR output side to close the "switch" so to speak and turn on the load).  So if the LED on the SSR does not light, try reversing the polarity on the triggering wires. 

    ****NOTE: Most SSR's require some load on the output side before they will trigger.  I have seen many that would not "light" the LED to indicate the SSR was triggered when there was nothing hooked up to the output side of the SSR.  Even though SSR stands for Solid State Relay, it does not work exactly like a dry contact switch (ie, light switch) There is basically a small feedback loop that is part of how they work and the digital circuitry needs to see a small resistive load to make the "switch" connection on the load side of the SSR.  If you don't get the triggering LED to light without a load, try connecting a small incandescent light bulb and 110v power to the load side of the SSR and it will probably work.  I had a long discussion with a fellow who was controlling low amperage draw powered valves in a beer brewing setup.  The valve had such a low wattage/amperage draw the SSR did not "see" it as being connected and would not switch on.  He had to add a indicator light to make it switch.  The amp draw of a heating element will not be a problem.  Oh, and as a side issue if you have a 110v LED or neon light they also will probably not be enough of a load for the SSR to "see" them and switch either.  So if the load is very small, try upping it with a plain old filament type light bulb as a load for testing.