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Design a small disconnect cicuit

Discussion in 'Electronic Design' started by [email protected], Sep 13, 2007.

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  1. Guest

    I need a small circuit that can disconnect AC power (means will have a
    relay) when it detects freezing on coil. I have a non working
    appliance that I want to power up but also include a antifreeze
    circuit design so that when it senses ice or freezing on the coils it
    powers off/disconnects. can anyone help ? is there any such circuits
    available that can do this job ?
     
  2. JeffM

    JeffM Guest

    http://www .google.com/search?q=temperature.controller&num=100
    Set it to limit at 33F.
     
  3. ecp

    ecp Guest

    Some form of direct frost detector perhaps.
    Polish a section of the coil to a mirror finish, and then
    use an optical reflectance sensor to detect frost formation.

    Eric
     
  4. D from BC

    D from BC Guest

    Thermistor + comparator + relay
    D from BC
     
  5. John Fields

    John Fields Guest

     
  6. John Fields

    John Fields Guest


    ---
    View in Courier:


    +12V>-----+-------+---------+--------+----+-----+
    | | | | | |
    | | | [10k] |K | O------C
    [47k] [30k] | | [CR1] [COIL]- - -|
    | | +---|--[1M]--+ | | O--> |<--O--NC
    | | | | | +-----+ |
    | | | | | | +-----------NO
    +---+---------+--|+\ | D
    | | | | >------+--+-----G 2N7000
    [RTH] | [10k]<--+--|-/ U1A | S
    | | | | | LM393 | |
    +---+ | | | | |K |
    | | | | | | [Z15V] +---|+\
    | [39k] | [30k][0.1µF]| | | | >
    | | | | | | | +---|-/ U1B
    [0.1µF]|[0.1µF]| | | | |
    | | | | | | | |
    GND>--+---+---+---+-----+---+-----------+-------+

    RTH is a thermistor with a resistance of 10K at 0C.
     
  7. No need to reinvent the wheel.

    http://www.sensata.com/products/controls/ptherm-7bt2.htm

    [8~{} Uncle Monster
     
  8. Fred Bloggs

    Fred Bloggs Guest

    Those may not work very well with the +/-5oF tolerance on setpoint, not
    too mention no standard part number is suitable.
     
  9. Fred Bloggs

    Fred Bloggs Guest

    There may be but they will be junk. The best way is to modify the
    "sealed system" by including an evaporator pressure regulator set for a
    refrigerant saturation pressure corresponding to 33oF. You will need to
    know how to pump the system down, make proper flare connections, install
    pressure access ports and other fittings, and read something called a
    pressure gauge and something called a thermometer. Something like
    this:https://pgw100.portal.gases.boc.com...ts/DANFOSS_Evaporator_Pressure_Regulators.asp
    The thermostat cutoff is the pussy weakling half-assed wimp way of
    handling the problem: the sissy nerd method IOW.
     
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