Day and night heater controller

Discussion in 'The Projects Forum' started by Andrew Leigh, Jun 7, 2014.

  1. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Hi,

    I keep scorpions and would like to simulate natural conditions in their enclosures. My scorpions come from an environment with a large day night temperature differential. Currently I have a commercial controller that drives one ceramic heater at a constant temperature of 30°C.

    My wish is to have a different day and night temperature. To this end I have found two circuits on the net. The first is day night controller and the second a heater controller. I am hoping to merge the two;

    In the heater control circuit the temperature is set via a potentiometer. I would like to insert another potentiometer in the existing control circuit making one for the day and one for night. The potentiometer brought into the circuits will be determined by the relay output from the day / night circuit.

    I have included the schematic of the original circuit along with the schematic including the addition pot and the relay from the other circuit.

    Could someone confirm that the addition of the pot will not alter the circuit functioning.

    I did note that the LV ground and the HV ground are tied together, is this OK?
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
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    The .sch extension is messing up the application when opening the file. Can you post the link instead, or else extract the schematic and post it as a .png or .jpg?
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    Why not use a programmable domestic central heating thermostat? The one I have can be set from 5C to 35C.
     
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  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    On the surface your concept seems solid, but we can't see your schematic. Bitmaps work better, as do PDF's.
     
  5. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Apologies here goes.
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
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    The LM35 is connected incorrectly in both of your schematics. Add some hysteresis to the 2nd schematic, and you're getting there. You might also want to voltage amplify the LM35 output so you can use the full range of your controller adjustment.
     
  7. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
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    2
    I could not find an LM35 in Eagle so used another package with the same pin outs. Please ignore the naming of the pins ....... is it still incorrect given this?
     
  8. crutschow

    Expert

    Mar 14, 2008
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    No, you don't want the LV and HV grounds connected together. You must have isolation between the two to avoid a serious shock hazard, such as a regular or solid-state relay.

    We need to see the schematic of your temperature controller to know if you can safely hack into it.
     
    Last edited: Jun 7, 2014
  9. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
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    I couldn't really say. If I were to ignore pin names, I have nothing else to reference. In the TI datasheet, it only gives names for the to-92 package, so numbers are arbitrary.
     
  10. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Here is the circuit as requested. The mains loop on the outside will be omitted and the relay will drive the LV side at the pots.
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,993
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    You need to put some hysteresis on the op amp, or it wont switch on and off cleanly, also better to use an Optocoupler to drive the triac.

    Here is a fridge thermostat, to see how to connect the mains.
     
  12. crutschow

    Expert

    Mar 14, 2008
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    That circuit does not appear to be correct. It shows an LDR controlling the circuit and I see no pot.
     
  13. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    OK Dave get the gist of the opto isolator.

    Crutschow, this is the problem I have. My interest and enthusiasm far exceed my ability. I trawl the net looking for something that would appear to be a solution for my problem but I simply do not have the electronic aptitude or intellect to see if a circuit is good or bad or indeed if it will work.

    Very much paint by numbers for me so if it is a working circuit I can solder and test well enough to be successful.

    My understanding on the day night circuits was that the trigger was the 10k pot which is next to the cap. It is a poor drawing.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    I'm was referring to the temperature controller you have that you want to modify. I need the circuit schematic/diagram for that.
     
  15. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
  16. samuel.whiskers

    Member

    Mar 17, 2014
    95
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    How about just using a commercial timer to cut off the heater at night??
     
  17. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    In winter temperatures here plummet (as with you chaps) and we do no have central heating due to the long summers. Last night was 6°C and it was rather fresh. Scorpion husbandry books suggest a day time temperature of 30-32°C dropping to 26-28°C in the evening. In having the correct day night cycle (and they are nocturnal) it is important to have the correct temperature for hunting, at 6°C they will not have a feed.

    The reason for looking for a home built solution is that my large female is pregnant and soon I will require multiple enclosures. I was hoping not to fork out for 30+ commercial units and was hoping for a simpler solution.

    Two timers would work, set out of phase time wise but would still require another heating controller, it get too expensive.
     
  18. crutschow

    Expert

    Mar 14, 2008
    13,016
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    We seem to have a communication problem. ;) I'm referring to the commercial heat controller you said you already have that's controlled by a pot (at least that's what I understood from your first post). Isn't that what you want to modify with an added pot?
     
  19. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Indeed a communication problem, apologies.

    I had intended discontinuing using the commercial controller in lieu of a homebrew unit consisting of a hybrid between the two internet circuits I found. The controller I found I wanted to modify to include a further pot for a second temperature setting and then using the control relay of the day night switch circuit I found to move between pots to give the day and then night temperature.

    The commercial unit is sealed and did not come with a schematic so unfortunately a little stymied there.

    Thanks for the patience.
     
  20. samuel.whiskers

    Member

    Mar 17, 2014
    95
    2
    This kit from Jaycar here would be tweakable for your purposes - you could do what you wanted - relay switch between set point pots for different settings at different times of day....
    http://www.jaycar.com.au/productView.asp?ID=KC5381
    I have one, not built yet though, would be happy to email you the schematic/etc from the kit, might give you some ideas..... just PM if you want....
     
    Last edited: Jun 8, 2014
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