latching relay

Discussion in 'The Projects Forum' started by kirkyj78, Jan 19, 2008.

  1. kirkyj78

    Thread Starter New Member

    Jan 19, 2008
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    hi, has anyone got any ideas on how to latch a relay using a pushswitch from a negative supply???

    thanks
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    By the term "latching" do you mean to have the relay go to the closed state when the switch is pressed and then stay in the position when the switch is released?

    hgmjr
     
  3. kirkyj78

    Thread Starter New Member

    Jan 19, 2008
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    hi yes that's exactly what i need to do, it is basically to remove the power from a relay, i thought by latching another relay this could work. maybe there is an easier way???
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    There is such a thing as a "latching" relay. It will stay in its last state even if power is removed. They are not cheap as relays go. These relays are most often driven using an H-Bridge.

    Does that sound like what you would want to use?

    hgmjr
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Not necessarily - I an using a P & B latching relay to control lights in my basement from four locations. It just takes 12 VAC - P & B # S89R11DAC1-12. But they are $36.77 from Digi-Key.
     
  6. hgmjr

    Moderator

    Jan 28, 2005
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    That sounds like just the thing for kirkyj78's application.

    Is that a mechanically latching relay?

    hgmjr
     
  7. mrmeval

    Distinguished Member

    Jun 30, 2006
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  8. hgmjr

    Moderator

    Jan 28, 2005
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    No doubt about it. The relay that beenthere put forward and mrmeval kindly provided a link to is far simplier than the solution I had in mind.

    I would like to join beenthere and mrmeval in recommending this as a proposed solution to kirkyj78's relay question.

    hgmjr
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    See the attached schematic.

    S2 through S4 are optional; simply there to show how you could connect a large number of switches to control whether the relay was ON or OFF.

    If the coil voltage is the same as Vin, you can use a SPST relay. Otherwise, you'll need two sets of contacts.
     
  10. kirkyj78

    Thread Starter New Member

    Jan 19, 2008
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    hi, thanks for all the reply's,
    I guess what i really need is some way of disconnecting power to a 12v dc relay using a one press of a push button supplied from the negative rail.

    My problem is a latching relay needs to be switched between states manually.

    But i need it to reset when the power is disconnected.

    Hope this makes more sense.

    thanks
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    So let me see if I can understand what you are seeking to do

    You already have a 12V relay that you want to be able to energize whenever power is applied by manually pressing a push-button. Then you want the relay to disconnect when power is removed but you don't want it to re-energize when power is re-applied until you press the button again.

    Is that correct?

    hgmjr
     
  12. beenthere

    Retired Moderator

    Apr 20, 2004
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    Then you use a DPST relay and use one set of contacts in parallel with the pushbutton. That way, the relay is self-energizing, and will drop out when power is removed.
     
  13. John Luciani

    Active Member

    Apr 3, 2007
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    A latching relay maintains its state when the power is removed.
    Some relays have two coils others have a single coil. The two
    coil variety has a set and reset coil. To set/reset the single
    coil variety you need to reverse the polarity of the coil.

    The polarity of the supply doesn't matter as long as you connect
    the positive terminal of the relay to the more positive potential
    in your circuit (for the two coil version).

    I have been using the NAIS DSP1-L2-DC5V two coil latching
    relay. It is apx $7 from Digikey. You can also get a single version.

    (* jcl *)
     
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