Temperature control help.

Discussion in 'The Projects Forum' started by tee2, May 7, 2009.

  1. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    I need help with an electric smoker that I have been making. I'm still working on the prototype with a garbage can, and it is working good. The problem that I was having is the heat source is an electric heat plate, and I could set the heat control and get 200deg to hold for a few hours then it would drop to maybe 150deg then jump to 214, it was all over the place. I am looking for 250deg. So I took it apart and looked for some type of over load breaker or high limit switch but didn't see anything. I took the Temperature control and disconnected it and ran power straight to the heating coil. That worked better but I got to 300+ deg. I looked to get a dimmer switch but a 1000w dimmer is $40.

    Is there a way to build a dimmer switch that would be less? I'm looking to 1000w at 120v. I have looked into using controls from and electric stove but I would need to go with 220v. Witch is doable but I would rather keep it 120v.

    Once I get this to work this is where I would like to go with version 2.

    A Temperature control that would work like an oven, set 250 deg and forget about it for 12 hours. Ideally I would use more smaller heating elements like a 600w that would make the smoke and the base heat, then a 2-200w or 400w element that would hold the set temperature.

    How could I do this on a budget? I know I can but something but it is way to expensive since I am out of work now. Like always I have the time but not the money.:(

    Thanks, This forum has always come through for me.
     
  2. gryskop

    Member

    Mar 1, 2008
    26
    0
    Please clarify one thing for me :confused:

    What is your domestic voltage running at? (120 or 220V)

    Why I'm asking. You mention that a stove controller works on 220, but you'd rather stay with 120. Does that mean your supply is at 220V but the heating element you have for the smoke machine is a 120V element?
     
  3. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3

    I'm in the U.S. so domestic is 120V. I could go 220V because my AC disconnect is about 10 feet from my smoker. But it would make it hard it take it somewhere else to use. But that might be a good thing. It would be harder for some to borrow.:D
     
  4. gryskop

    Member

    Mar 1, 2008
    26
    0
    From what I now about stove control switches, (Low, Med, High) or the more modern ones (ranging from pos 0-7 (or 9)) the voltage rating shown on the switch is only to indicate MAX operating voltage. That 240V switch will work 100% for 120V supply.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    This circuit has few parts ,If you wished to build it. Themister around 10k @ your op. temp. Most stove heat controls do not measure burner temp, just open loop time control. There are other ways with more parts.
     
  6. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Thanks Bernard, I looked at at your diagram and it is a little over my head, I googled the parts and can't find many of them.

    I did find these circuits that looks like it would work, and I have most of the parts for. The only thing is it is it is rated up to 125degC that is around 257degF, I am looking for 250degF. I would be at the upper limit.

    It shows a relay but could I use a triac instead? I have not used them and have a few other project that they could use them too.

    http://www.craig.copperleife.com/tech/thermo/
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    A triac can be used with a few more parts, I'm short of time today. Seems there should be a thermister with higher temp rating, microwave temp probe must go to 300 deg. F. Diodes also make good temp senaors, need to confirm temp range. I've used both over the years.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There used to be a series of thermostatic switches made by Klixon that might handle the heater and maintain a temp around 250 deg F.
     
  9. tkng211

    Well-Known Member

    Jan 4, 2008
    65
    2
    You can buy a cheap low power dimmer and a Triac with proper rating, then modify it as the attached figure. Add a heatsink to the new Triac ( or use the heatsink of the triac in the dimmer for the new Triac) if required.
     
    Last edited: May 8, 2009
  10. Andrew Leigh

    Well-Known Member

    Sep 8, 2008
    92
    2
    Hi tee2

    That circuit you posted http://www.craig.copperleife.com/tech/thermo/ is not bad at all. I use it to control the element on an absorption fridge. When you study the article you will find that it needs a little tweaking for each temperature range. This is not an issue.

    The problem you will always have with a conventional oven controller / stoveplate controller is that the hysteresis (range) is always far too wide. You have already experienced those large temperature swings. You need a controller that controls hysteresis, this one does.

    What craig does not show is a smooth supply which is included in the board as well as decoupling and smoothing caps.

    You will need to change the transformer value from 220V to 120V but with the same output. I have used 12V for ease of relay selection.

    Relays are not a problem, you will not be using this smoker 24/7 will you? The relay I used only handles 5A but for me this was adequate. I have included the schematic and the PCB for you. I have adapted the schematic and the PCB to turn it into a heating circuit for you (as per Craig's writeup) but unless you get a suitable relay then perhaps one of the clever boy's here can change the relay for an SCR, that is beyond my assemble by numbers ability.

    Note that you need to download Eagle, the free version will not allow you to have a larger board than the one shown so a larger relay will be a problem, you really will need the same pin dimensions.

    You will also notice that I have kept the HV side away from the LV side.

    Cheers
    Andrew
     
  11. tee2

    Thread Starter Active Member

    Nov 19, 2004
    46
    3
    Thanks everyone, I'm I think I will have this working soon. :)

    Todd
     
Loading...