Is there a way to make a NC thermistor work as a NO one?

Discussion in 'The Projects Forum' started by j4e8a16n, Mar 24, 2014.

  1. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    Hi,

    Is there a way to make a NC thermistor work as a NO one?

    -----
    Normally opened
    Normally closed
     
    Last edited: Mar 24, 2014
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    theremistors vary their resistance with temprature, not act as switches.
     
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  3. crutschow

    Expert

    Mar 14, 2008
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    Are you referring to surge-limiting type thermisors?
     
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  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Do you mean Ntc and Ptc ?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Or is this a N.C. thermal bi-metal sw?
    Max.
     
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  6. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    See attachment

    thermal Normally Closed cantherm_r53.bmp
     
    Last edited: Mar 24, 2014
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    From the data sheet it appears to be bi-metal, if so there is no way to invert it without a external device, relay etc.
    What is the application?
    Max.
     
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  8. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    To start a 3v motor with a fan when the transistors heatsink reaches 100°C .
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
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    Like Max posted.

    Use a relay to invert.

    Or for your small load you could use a transistor between sensor and motor.

    Seems a large device for your purpose. They are generally slow and have a large differential.
     
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  10. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    I just connected the two poles of the thermistor to the 2 poles of the motor. This creates a bypass when the thermistor is closed.
    When it opens the current run the motor. :eek:)
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Buy a NO (normally open) thermal switch.
     
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  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    So what prevents that bypass short-circuiting the supply?
     
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  13. BillB3857

    Senior Member

    Feb 28, 2009
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    That's great as long as your power supply can accept a full short circuit while the motor is supposed to be off. Also, lets call it what it is.... THERMOSTAT, not thermistor.
     
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  14. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    What would be a better component?
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The current will probably open the Bi-metal switch :eek:
    Heck of a way to control a motor on/off.:confused:

    What are you trying to do exactly?
    Max.
     
    Last edited: Mar 26, 2014
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  16. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    I agree EEK!

    When the heatsink is too hot , the fan starts; when it cools down, the fan stops.
     
  17. j4e8a16n

    Thread Starter Member

    May 1, 2013
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  18. MaxHeadRoom

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    Jul 18, 2013
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    Show how you have the circuit wired right now?
    Max.
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    What you want is a KSD9700 thermal switch which is available as NO (normally open) or NC (normally closed) with temperature set points 25-180°C in steps of 5°C.

    KSD9700 NO 100°C
    http://www.sourcingmap.co.uk/ksd9700-100-bimetal-normal-open-type-temperature-control-switch-pcs-p-121743.html

    KSD9700 NO 60°C
    http://www.frozencpu.com/products/16492/tmp-68/Fully_Automated_KSD9700_Series_Thermal_Switch_-_60_Threshold_On_at_60C_Off_at_40C_.html

    Data Sheet:
    http://www.ic-world.com.cn/pdf/20120724220954.pdf

    Edit: Reading the description from the supplier it is not clear that these are NO (normally open) switches.
     
    Last edited: Mar 26, 2014
  20. j4e8a16n

    Thread Starter Member

    May 1, 2013
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    What would be the advantage of putting the motor at the emitter?
     
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