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thermostat for kettle water heater!

Discussion in 'General Electronics Discussion' started by luke.w.pc, Apr 3, 2012.

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  1. luke.w.pc

    luke.w.pc

    6
    0
    Apr 3, 2012
    Hi
    I am trying to build a stirred hot water bath with thermostat using a picaxe type micro controller a thermistor with some kind of transistor or relay on the power input of a kettle with the switch and original thermostat bypassed for my easter project but im having trouble finding the transistor or relay to control it, as it has to switch on and off at least once every 2 seconds or so, to keep water temperature stable once the target temprature has been reached and also cope with uk mains (240 volt, 50 hertz) with about a 12 amp load.
    LUKE
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    240 V / 12 A is a tough requirement. I think a triac would be the right component to switch this load. You will also need galvanic isolation between the mains circuit and the microcontroller for safety. Here http://www.electronics-tutorials.ws/blog/optocoupler.html is a usefull description which hopefully helps you along the way.

    Happy easter

    Harald
     
  3. luke.w.pc

    luke.w.pc

    6
    0
    Apr 3, 2012
    Triac

    So do you mean have the Optocoupler attached to the picaxe then going through a power supply into a triac to switch the mains power, and also would this triac be suitable triac.
    Thanks
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    This triac could do the job. You will probably need a heatsink to avoid thermal overload.

    Note: handling 240 V is very dangerous and can be lethal in case of a fault. If you're not familiar with high voltage, I would not recommend that you build the high voltage / high current part yourself. Get expert help.

    Harald
     
  5. luke.w.pc

    luke.w.pc

    6
    0
    Apr 3, 2012
    Thanks for replies, i will use a relay then a triac and be carefull.
     
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