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Latching relay for actuator use?

Discussion in 'Sensors and Actuators' started by Wiggi, Sep 25, 2017.

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  1. Wiggi

    Wiggi

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    Dec 1, 2016
    Hi everybody.

    My current application is as follows:

    A 12V linear actuator is being controlled by either a programmable timer or a photocell. Power source is a 12V, 6A power supply.
    A dpdt relay changes the direction of the actuator motor.
    When the programmable timer switches to "on" the actuator extends. When the timer turns "off" the actuator retracts.
    Same when using the photocell.
    So when the timer /photocell switches "on" the relay/coil is powered the entire time the timer/photocell is in "on" mode which can be between 8-14 hours.
    In some cases it would be extremely helpful if no power is consumed once the actuator reached its internal limit switch.

    A latching relay comes to mind.

    What latching relay would I need and how do I wire it? I guess I would still need a dpdt relay.
    I found several latching relays on ebay but not really sure which one I would need and how to wire it to get the same results as in
    my current setup.

    Thanks a lot for your help!

    Wiggi
     
  2. Tha fios agaibh

    Tha fios agaibh

    2,096
    702
    Aug 11, 2014
    We haven't seen you circuit to know how to wire it.
    Choose your latching relay like you would any relay; Start by defining your load so you can determine the contact ratings. Then coil voltage you need and any current limitations you may have (from the circuit your hooking it up to)
    And physical size restrictions that may apply.
    Also, a description of your application would help us picture what your trying to do.
     
    Wiggi likes this.
  3. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Does the control circuit run on the same 12 V as the actuator?
    What is the peak current being switched?

    ak
     

    Attached Files:

  4. Tha fios agaibh

    Tha fios agaibh

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    702
    Aug 11, 2014
    Screenshot_2017-09-26-00-31-18-1.png
    This one is rated 3 amps @ 220v.
     
  5. Wiggi

    Wiggi

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    0
    Dec 1, 2016
    Thank you all very much for your responses.
    @Tha fios agaibh...thank you...good to know to choose a latching relay the same way I would any other relay.
    @Analog Kid...Thanks for the pdf. Very helpful!

    Thanks again!!!
     
  6. Wiggi

    Wiggi

    14
    0
    Dec 1, 2016
    Well....I sketched the wiring of the actuator application. But I gotta warn you....it's not what you would expect. I am not an electrician or electronics guy so I don't have the knowledge of how to draw a wiring diagram.
    Goal here is that the system won't draw any power after the relay switched and the actuator extends/retracts.
    Thanks again!!!
     

    Attached Files:

  7. Alec_t

    Alec_t

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    Jul 7, 2015
    Latching relays (other than the impulse type) come in two flavours: single coil or double coil.
    Be aware that a single coil type requires a pulse of one polarity to set it and a pulse of the opposite polarity to reset it. A double coil type requires a pulse of one polarity on one coil to set it and a pulse of the same polarity on the other coil to reset it.
     
    Wiggi likes this.
  8. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I can't open the file you attached
     
  9. Wiggi

    Wiggi

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    Dec 1, 2016
    Thank you Alec....Again I learned an important fact. Thanks a lot.

    @Tha fios agaibh....I can open the attachment. I will attach the pdf file again.
     

    Attached Files:

  10. Tha fios agaibh

    Tha fios agaibh

    2,096
    702
    Aug 11, 2014
    I saw your sketch but I'm not sure of your objective. Why is a timer or photocell driving an actuator? Does your actuator have limit switches to prevent overtravel?

    The actuator shouldn't draw any power once its reached its limits. Holding current on a relay coil is rather insignificant especially seeing you are powering it with household 120v.

    Even if relays and actuator are not drawing any power, you still have power being consumed by your power supply, timer or photocell.
     
  11. Wiggi

    Wiggi

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    0
    Dec 1, 2016
    The actuator has to retract/extend at a certain time of the day....that's where the timer/photocell come into play.
    It is true that the actuator does not draw any power once it reached its internal limit switch.
    The power consumption of the timer is very, very little.
    I forgot to mention that I run this setup also on a 12V battery (the battery being recharged by a solar panel) and I am hoping to extend the charge of the battery (and with this using a small solar panel or even run it on a battery pack only for maybe 6 months without solar panel?) if I have a latching relay that does not draw power for 12-14 hours per day as the standard dpdt relay does.
    What do you think?

    Thank you :)
     
  12. Tha fios agaibh

    Tha fios agaibh

    2,096
    702
    Aug 11, 2014
    Can you tell us what its for?
    Your batteries may deplete mostly because of a significant load during the movement of the actuator rather than a coil current of probably less than 100ma for hours.

    You could use a latching relay or H bridge relay but you would need to figure out how to fire two separate coils from a single signal.

    It could be safety concern if you used a fip flop circuit to toggle the up-down (left-right?) motion and power was lost?
     
  13. Wiggi

    Wiggi

    14
    0
    Dec 1, 2016
    The actuator opens/closes a door once a day. The actuator runs for about 50 seconds each time. The current draw of the actuator under load is usually around 1.5A.
    Yeah...that seems to be my problem...how to fire two separate coils in this configuration with a single signal.
     
  14. Tha fios agaibh

    Tha fios agaibh

    2,096
    702
    Aug 11, 2014
    The "How" can be resolved, but your latch proposal may not be the best solution to your problem.
    Adding more battery reserves or another solar panel may be all you need to do.
    There are relays that have very little power requirements to hold a relay. The coil power used may be much less the circuitry used to drive a latching relay.
     
  15. Alec_t

    Alec_t

    2,821
    754
    Jul 7, 2015
    Is this a chicken coop door opener/closer? There are various threads about that which may have useful info for you.
     
  16. Wiggi

    Wiggi

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    Dec 1, 2016
    @Alec_t it is for a coop opener and I read through several threads. My question is not how to make or wire a coop opener/actuator. I have that figured out. It is about possibly conserving energy by using a latching relay and how to wire it. But thanks for your input. Appreciate it.

    @Tha fios agaibh Thanks you. I probably should choose a latching relay and compare the power consumption of the latching relay with the currently used relay to see if it would even make sense to go with a latching relay. Thanks again!
     
  17. Alec_t

    Alec_t

    2,821
    754
    Jul 7, 2015
    Here's a suggested alternative basis for switchng off the relay once the actuator has reached its limit, avoiding the need for a latching relay. It does, however, require a single limit switch external to the actuator to sense when the door is fully open :-
    CoopDoorController.PNG
    This circuit has a photocell plus two (optional) press-buttons to control the operation. A timer with suitable contacts could be connected in parallel with the photocell if required (but unless your hens wear leg-watches I think they'll want to enter/leave the coop at dusk/dawn: not at a certain time of your choosing :) ).
    M1,M2 are N-channel MOSFETS. M1 switches the relay coil and M2 switches both coil and actuator current on/off. It is assumed that limit switches inside the actuator can also switch off the actuator current.
    U1 (a CD4093 quad Schmitt inverter) provides the logic which ensures that :
    (a) at dawn, power is enabled by M2, the relay is energised by M1 and the actuator runs 'up' until the external door-'OPEN' limit switch is activated, causing M2 to shut off the power to the relay (and also to the actuator if the 'Top limit' internal switch hasn't already done so). This changes over the relay contacts, but the actuator now doesn't run.
    (b) at dusk, the logic switches on M2 regardless of the state of the door-'OPEN' limit switch, so the actuator now runs 'down' until stopped by the internal 'Bottom limit' switch.
    C1,C2,D1,R4 decouple the logic supply from relay/actuator transients.
    C3 ensures enough current through the 'OPEN' switch contacts to keep them clean.
    R5,R6 are 'gate-stoppers', very close to the gate connections, to prevent/damp spurious oscillations of M1,M2.
    D4,D5 are assumed limit-switch bypasses inside the actuator.
    Standby current draw of the circuit is ~ 0.2mA.

    Edit:
    .asc file attached, if anyone wants to play.
     

    Attached Files:

    Last edited: Oct 4, 2017
    Tha fios agaibh likes this.
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