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temp controller

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  • Aaron Smith
    thanx Mike and Dave for you circuits, IMPORTANT READ FIRST DO NOT ATTEMPT TO BUILD THIS CIRCUIT UNLESS YOU ARE QUALIFIED OR EXPERIENCED WITH MAINS VOLTAGE.
    Message 1 of 1 , May 7, 2000
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      thanx Mike and Dave for you circuits,
       
      IMPORTANT
      READ FIRST
      DO NOT ATTEMPT TO BUILD THIS CIRCUIT UNLESS YOU ARE QUALIFIED
      OR EXPERIENCED WITH MAINS VOLTAGE. THIS CIRCUIT INVOLVES SWITCHING
      AN EARTH TO AN ELEMENT THAT CAN DRAW 10AMPS, THIS WILL KILL YOU.
      YOU CAN BUY CONTROLLERS LIKE THESE (COMMERCIAL) FROM ELECTRONIC
      SUPPLY SHOPS, SO WHY RISK YOUR LIFE.
       
      now where was I, oh yeah
       
      I ran with the I.C controlled (TDA1023) without using a temp probe.
      the specs on this (and application data) can be found at
       
      you will need to download the above PDF file (page 14,15) to understand what I am
      talking about below.
       
      there were a few changes that I made for safety and to compensate for the
      240V 10Amp supply that we have.
       
      they are as follows
       
      D1   1N4007
      RD   6.8Kohm 10W
      RS   180Kohm
      RG   110ohm (100 and a 10)
      Triac was a BT-139-800
      heater (load) is a 1380Watt element  in theory this circuit could handle 2.4KW
      Ct   1uF 63V
      Rntc  I replaced this with a 22kohm resister as I didn't require temp feedback
      R1    18kohm
      pin 5 of TDA1023 goes to earth to give you 400mV range control
       
      I played around with resistors between pin 11 and Rp (40kohm) and also between Rp and
      Neutral (37kohm), this was only to trim the potentiometer into the range that I wanted.
       
      I also place a neon indicator across the load to give me a visual on when power
      was applied to the element
       
      Cooling,
      the Triac requires a fair amount of cooling, I used a finned heatsink (100mm x 45mm x 45mm)
      this keeps it reletively cool, I also used plastic screws, heat compound and a mica washer to
      electricly insulate the triac from the heatsink
      the Resister RD dissipates approx 5W, so I advise that you heat sink this as well, this item does
      get to hot to touch if you don't, this is my next mod.
      Mount it all in a well ventilated preferrably plastic box
       
      that is about all I have to say about that.
      it worked really well on the first batch (25lt) yesterday.
      the neon indicator is a good idea and lets you know everything is working ok.
       
      for the future,
      1.  I'm going to have a water flow sensor that will switch heater power off if water stops.
      2.  I'm going to have my laptop do all of temp ,water control  and failure monitoring
       
      cheers
      Smithers
       
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