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Reed switch fails within a few operations

Discussion in 'General Electronics Discussion' started by j37prakash, Aug 2, 2011.

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  1. j37prakash

    j37prakash

    4
    0
    Jul 15, 2011
    I need to design a circuit to switch on a warning lamp or sound a hooter when a door is opened and the reed switch is activated by the magnet. I have herewith attached the circuit diagram of the test setup. My problem is that the reed switch fails within a few (3 or 4) operations though the current measured is in very small units.
    Kindly advise me how to go about it to solve the problem.
     

    Attached Files:

  2. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    What is MIC DB107? Is this a bridge rectifier?
    A reed switch can only switch a very low current at a low voltage. You are switching a 10uF capacitor and probably more capacitance in the PSU. This will blast the reed switch contacts as they charge.
    Possible solutions
    1. Use the reed switch to control a FET to switch the main current.
    2. Use a microswitch instead of the reed switch.
     
  3. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    :)
    I like the microswitch idea. But I wonder if the microswitch should control a contactor designed for the very inductive load - the hooter.
     
  4. daddles

    daddles

    443
    3
    Jun 10, 2011
    It's possible the magnet/reed switch might be already installed in a door -- and changing to a different switch would be difficult (OP help us here please).

    Note that a switch that is used outside its design area can have its contacts permanently damaged for even just one mis-operation. You probably would be wise to replace your reed switch.

    The main thing to realize is that reed switch contacts are intended for switching low currents. I'd be concerned about your application; but from your diagram, we can't tell how it works because you haven't explained what the DB107 device is.

    Note that there are switches that are made to be mounted in doors that can switch line voltages -- my sister has one in her walk-in pantry: when the door opens, the pantry's overhead light goes on. Very convenient. Of course, a microswitch could be adapted for this service too.
     
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