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HELP needed with relay bounce

Discussion in 'Hobby Electronics' started by [email protected], Jul 13, 2005.

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  1. Guest

    Hi All


    I've been trying to construct a pressure regulating device, using a 12v



    latching solenoid and conventional valve, to protect a filter in a home



    irrigation system. I am using a pressure switch which goes contacts
    open at high pressure/contacts close at falling pressure. These two
    states in turn trigger 555 timers which in turn drive small 12v SPDT
    relays.


    The relays are configured so that in the relaxed state the circuit
    connects to the 0v line and when exited by the pulse from the 555,
    switches to supply 12v for each relay in turn. The purpose of this
    switching configuration is so that the 12v latching solenoid, which
    operates the valve, can be switched to close the valve when pressure
    reaches a high threshold, but then by reversing the supply voltage, is
    switched to open the valve at a low threshold.


    This all works perfectly - until the latching solenoid is connected,
    whereupon the action of the solenoid causes the relays to bounce
    erratically.


    I have tried various combinations of (non polarised) capacitors and R/C



    combinations across the terminals of the solenoid, and/or across the
    relay. I have also tried using seperate 12v power supplies to power
    the two sides of the device (timing - relay activation side and power
    supply for solenoid side)but the action of the solenoid still causes
    the relays to bounce erretically.


    I feel I am running out of options to solve this dilema, but am now
    considering the use of switching transistors or solid state relays.
    Only I'm not sure how to switch such devices on and off to give the
    necessary pulse to switch the solenoid on then off etc.


    Any help would be greatly appreciated
     
  2. Chas

    Chas Guest

    You could try shunting the solenoid with a suitable diode to damp any
    reverse polarity pulses. This is also a good idea across the relay coils.
     
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