Latching relay

Discussion in 'The Projects Forum' started by jls667, Jul 29, 2013.

  1. jls667

    Thread Starter Member

    Jun 5, 2013
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    I bought a Magnecraft latching relay 755xbxcd-12c. Before I build my project, I wanted to test this relay. This is a DPDT two coil latching relay that works on 12vdc. My userstanding is that when I put 12 vdc on the set coil, the contacts move in one direction and when I put 12 vdc on the reset coil, the contacts move back. What actually happens is that the reset coil only moves the contacts temporarily when voltage is applied. What could be the problem?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The normal operation is the main coil is activated or pulsed, the relay armature will move over and will stay latched, the release voltage should unlatch or release it, at least this is the way the ones I have used in the past have worked.
    Make sure the latching voltage is no longer present.
    Max.
     
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
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    I'm with Max. My understanding is you apply a DC pulse to set the relay and a DC pulse to reset the relay. Is this what you've tried?
     
  4. jls667

    Thread Starter Member

    Jun 5, 2013
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    Yes. That is exactly what I tried. Could I need a load for the latching to work?
     
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
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    You are removing the voltage from the set before applying the reset?
     
  6. jls667

    Thread Starter Member

    Jun 5, 2013
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    Yes. I did the coils one at a time to test the latching.
     
  7. MaxHeadRoom

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  8. JohnInTX

    Moderator

    Jun 26, 2012
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    Max and the others agree with my experience with these; energize the set coil to make, energize the reset coil to release. There is some additional info here (4-wire circuit at bottom). They show current going in specific directions but its not called out in the catalog as to current directions and these are not really rocket science so -meh. You might play with it but one possibility is that the thing is just broken. Applying the reset current pulls on the armature like it should but its mechanically unable to move over center or the contacts are welded. What do you see through the clear case when you try it? Does it break the contact when you apply reset?

    I don't know why it would matter as far as switching but do you have catch diodes across the coils?

    BTW I think the PN is 755XBXCD-12D. -12c is not listed.
     
  9. jls667

    Thread Starter Member

    Jun 5, 2013
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    You are probably right regarding the part number. I typed it in from memory.

    When I energize the reset coil, the contacts do move to the reset position, but only until I remove the 12vdc. Then the contacts move back to the set position.

    To make matters more confusing, I bought two of these relays and both work this way. That means to me I must be doing something wrong.
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    So the set coil does nothing?
     
  11. jls667

    Thread Starter Member

    Jun 5, 2013
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    A pulse does nothing lasting.
     
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I think you are referring to the reset coil.
    What I'm saying is, if the relay always returns to the set position, then apparently, pulsing the set coil does nothing.
     
  13. jls667

    Thread Starter Member

    Jun 5, 2013
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    That is correct. The set coil just makes a nice click, but the contacts do not move.
     
  14. MaxHeadRoom

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    Jul 18, 2013
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    If the armature does not move in order to close the contacts, then something apparently is preventing it from moving.
    The way it works is the core has a small P.M. but not strong enough to attract the armature, when you pulse the main coil, the armature (should) pull in, it is a known phenomenon that once a DC relay or solenoid armature is energized it now only requires a much small magnetic field to keep it attracted.
    This is done by the small P.M.
    On pulsing the release, the reverse magnetic field counter acts the small magnetic field and releases the armature.

    If the armature clicks and the contacts do not operate, then it sounds like it is pulling in but contacts are welded closed?
    Max.
     
    Last edited: Jul 30, 2013
  15. jls667

    Thread Starter Member

    Jun 5, 2013
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    The contacts cannot be welded shut, because I see them move when I pulse the reset coil. The problem is that the connection only lasts as long as 12vdc is on the reset coil.
     
  16. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Are you sure you have a relays with 12V coils? It sounds like you might have received units with higher voltage coils.
    Are the part numbers printed on the relays?
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Power/pulse on the reset coil should Open it??
    Explain in detail what the scenario is?
    When you apply a pulse to the main coil what does the armature and contacts do?
    When you apply a pulse to the reset coil, what happens?
    When you say 'Connection' do you mean armature & contacts closed?
    Beginning to sound as though you still have power on the pull-in coil instead of a short pulse?
    Max.
     
  18. jls667

    Thread Starter Member

    Jun 5, 2013
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    The model number 755xbxcd-12d is printed on the front of the relays. This is supposed to be a 12vdc relay. I attached a pin diagram to make this discussion easier.


    This is a DPDT relay as in the attachment.

    When I power/pulse the reset coil, pin 1 and pin 4 temporarily connect. Pin 11 and pin 9 also temporarily connect together. When I remove the power/pulse from the reset coil, pin 1 connects to pin 5 and pin 11 connects to pin 8.

    Whether or not I power/pulse the set coil, pin 1 connects to pin 5 and pin 11 connects to pin 8.

    I am testing the relay with a plug-in transformer that is giving me 9vdc and 300mA. The specs told me the minimum voltage is 5vdc and 100ma. I earlier tested with a true 12vdc transformer, so I know the lower voltage is not the problem.

    When I use the word connection, I mean the armature moves so one pin makes contact to another.
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The normal sequence is first pulse the main coil 2 & 10 to latch it in? 1&4 and 9&11 should be closed at this point.
    It should then remain latched until the reset coil pulse.
    It sound as though for some reason you are initially pulsing it with the reset coil, as I read your post?
    Max.
     
  20. jls667

    Thread Starter Member

    Jun 5, 2013
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    No. I pulse the set coil first.
     
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