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Help with Triac based Temerature Controller

Discussion in 'Electronic Design' started by Antony N. Lord, May 20, 2007.

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  1. I've built a kit (Silicon Chip June 2005 "Tempmaster Temperature
    Controller") to run my a fridge as a wine fridge.

    The fridge is a 240v (Australia) commercial "cool drink" type fridge
    drawing about 600W. I've replaced the old 'mechanical' thermostat with
    this new electronic one to run is at a higher and more accurate
    temperature.

    The "output" is essentially a MOC3021 opto coupler driving a BT137F
    triac.

    However when the controller switches on the condenser / fan it often
    clicks a few times (like its taking a few attempts to start it).

    I've already tried incorporating a LC line filter without luck. A TVR
    fitted between the active / switched active gets really hot (obviously
    dissipating quite some power).

    Any ideas what else I should be looking at?

    Cheers, Antony
     
  2. Can you post a link to a schematic? It's almost surely electrical
    noise getting back into the control circuitry, although if the power
    supply is not robust enough it could also be the dip in supply voltage
    due to the surge when the compressor turns on.

    This kind of thing is not good for the compressor.


    Best regards,
    Spehro Pefhany
     
  3. DaveM

    DaveM Guest


    You should probably use a mechanical relay to switch the refrigerator. Triacs
    are rather poor choices for highly inductive loads.
    If you're intent on using solid state switching, I recommend that you switch
    from a triac to an alternistor, which is essentially a couple of
    inverse-parallel connected SCRs, which avoid the commutating problems of the
    triac.

    --
    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
    address)

    Life is like a roll of toilet paper; the closer to the end, the faster it goes.
     
  4. Check the magazine web site for updates.
     
  5. Phil Allison

    Phil Allison Guest

    "Homer J Simpson"


    ** Nothing in the notes and errata of interest.

    BTW
    The article is called:

    " Coolmaster Fridge/Freezer Temperature Controller ".




    ........ Phil
     
  6. Donald

    Donald Guest

    Oh yea, the alternistor !!

    Never made it in the market place, I wonder why ??

    http://en.wikipedia.org/wiki/Alternistor
     
  7. Phil Allison

    Phil Allison Guest

    "Donald" <

    ** Called " snubberless triacs " by many makers.




    ....... Phil
     
  8. You should probably use a mechanical relay to switch the refrigerator.

    That's easily tested.

    How do I prevent contact arcing?

    Cheers, Antony.
     
  9. Rich Grise

    Rich Grise Guest

    With a snubber. Designing an actual snubber is somewhat of an arcane black
    art - I've seen people just pick values out of the air, but I've also
    heard that the resistance should be equal to the inductive reactance of
    the load, but I'm not sure how to choose a cap value - I'm sure someone
    will chime in here.

    Cheers!
    Rich
     
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