Linear Actuator automatic open/close not quite working

Discussion in 'The Projects Forum' started by mattrofe, Dec 19, 2017.

  1. mattrofe

    Thread Starter New Member

    Dec 16, 2017
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    Hi all -

    apologies upfront - I have next to no experience/knowledge with electrical design etc - i'm a complete rookie!

    I've followed the diagram supplied by MikeML that outlines how to wire up a linear actuator with a 12V timer and power source to automatically open/close a chicken coop door and it looks like it does work - but i'm having a slight issue and wondering if anybody could suggest what is wrong.

    I initially power the circuit and activating the timer the actuator extends fully, and switching off the timer the actuator closes. After that, at approximately every 2 secs the DTDP seems to want to engage the circuit but instantly opens the circuit again - i can hear the actuator's motor receive power but immediately loses it again.

    My actuator has built in limit switches and appears to work fine. The entire circuit is 12V.
     
  2. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    I vaguely remember the discussions that led to this circuit. Can you share a datasheet, part number, etc. for the timer?

    It looks like the timer directly controls the coil of the DPDT relay, so if it's flipping on/off for a split second every few seconds, it seems likely to be a timer problem.

    Is the relay coil 12V or 120V? I remember there being some doubt about how to wire the timer, and I don't remember if it was configured with 12V output or 120V output.
     
  3. mattrofe

    Thread Starter New Member

    Dec 16, 2017
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    The timer is a TP109A and the relay is 12V (i've attached pics). I am yet to get the timer to turn on and off using its actual timer function - i've only been testing it by manually turning it on and off etc.

    I think you are correct - the timer does control the relay.
    I have tested this a few times by disconnecting and reconnecting the power source, and every time i reconnect, i can successfully extend and retract the actuator once only.

    I have noticed on a couple of tests, the 'pulsing' of the relay is strong enough to actually start driving the motor of the actuator briefly as well - i can only assume this is related to the amount of load in the circuit????

    Thanks for your help.
     
  4. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    First off, I was thinking of a different circuit, different conversation, different relay. Sorry for any confusion.

    Are you saying that right now, when you turn on the 12V power supply, you can only get one cycle, open and close, out of the actuator? After that first cycle, no amount of manually switching the timer output on or off makes the actuator move? But then, if you turn off the 12V supply and turn it back on, you can get another cycle out of the actuator?

    If so, that's truly bizarre! Can you measure the voltage at the relay coil when you have the 12V supply active, with the timer both on and off, and then when it should be on again for a second go around.

    It's hard to imagine that your wiring is wrong, cause if you can open and close the actuator once by turning the timer on and off, that would seem to indicate good wiring. I would assume this is some sort of timer issue, but it'll be easier to confirm with voltage readings.
     
  5. LesJones

    Well-Known Member

    Jan 8, 2017
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    Have you monitored the 12 volts first when it is a working state and then when it is the none working state. I am thinking that the power supply protection circuit shuts down the power supply until the mains input to it is switched off and on. Also you talk about the relay clicking on and off. As the coil is operated from mains voltage connect a mains voltage lamp DIRECTLY to the relay coil terminals. Then see if that flickers on and of at the time when the relay is clicking. When you say "switching off the timer" do you mean removing the mains supply to the input of the timer, Removing the connection between the timer and the realy coil or using the manual on/off button on the timer ? All of your pictures are poorly focused so the data on the timer is unreadable. Try using manual focus on your camera.

    Les.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The timer is a YP109A (not TP109A) and it requires a 12V power input. The coop.gif image shows a "Plug into timer". What are you plugging it into? (If 120V then the timer is dead).
     
  7. mattrofe

    Thread Starter New Member

    Dec 16, 2017
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    I'm providing power to the timer, as well as hooking it up to pins 7,8 on the DPDT. Please remember that i could be (and suspect) that i'm plugging things into the wrong inputs.
     
  8. mattrofe

    Thread Starter New Member

    Dec 16, 2017
    8
    1
    Ok - i've taken Les's advise and completely removed the timer from the circuit, and manually supplying power to the relay coil terminals. Here's my findings:

    1 - no power supplied to the coil terminals, the actuator fully extends and stays extended with no further movement.
    2 - supply power to the coil terminals, the actuator retracts and when fully retracted, it starts its frequent 'pulsing'. To explain this in further detail, i'm pretty sure i hear a tiny click coming from inside the actuator, which is then immediately followed by the DPDT relay quickly going on/off.

    I've supplied a video to hopefully help explain what is happening:
    https://www.dropbox.com/s/qtbs767b6sp1fg7/chick door.mov?dl=0

    Thanks again!
     
    Last edited: Dec 21, 2017
  9. mattrofe

    Thread Starter New Member

    Dec 16, 2017
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    I thought i'd supply you the relay specs as well - i was told it was a 12V relay and assume the following confirms that?

    Device Type Cradle Mounting Relay
    Input DC
    Contact format DPDT
    DC Switching Voltage 24V
    DC Switching Current (Opening) 10A
    Nominal Voltage 12V
    AC Switching Current (Opening) 10A
    AC Switching Voltage 240V
    Coil Resistance 160Ω
    Coil Current 75mA
    DC Voltage 12V
    DC Max current 75mA
    Item connection Spade Terminals
    Mounting Method Cradle/Socket Mount
    Product Height 35mm
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I guess what could be happening is that when the actuator retracts fully its motor stalls just before the limit switch opens, or else the limit switch is failing to open. The stall current exceeds what the supply is rated to provide, so the supply goes into shut-down mode. This causes the relay to drop out. The supply comes out of shutdown, but the current is still excessive, so it shuts down again. Rinse and repeat.
     
  11. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    Here's my theory/guess:

    The limit switch for retracting the actuator isn't working for some reason. Without a working limit switch, as the actuator reaches the end of its travel, it will start drawing a lot more current (stall current of the motor,) and if that's me current than the power supply can provide, the power supply may shut down as a self protection. Many power supplies automatically try to restart quite regularly when they auto-shutdown (hiccup mode,) which is why it pulses regularly. Possible explanations:
    • There are no limit switches. Do you know if your actuator has built-in limit switches? If you're not sure, provide part numbers and/or datasheets. If it doesn't, you'll need to add your own.
    • Something is stopping the actuator before it can reach the limit switch. Perhaps the door doesn't slide freely all the way to the top, and as it starts binding on its way up, the motor draws too much current?
    • The limit switch is simply defective. I think this is relatively unlikely, but if you investigate and rule out all the other possibilities, it's one to consider.
    Ways to test this and see if this is really what's happening:
    • Try running the actuator circuit with the door disconnected so that the actuator can move freely without doing any real work. If there's still clicking/pulsing at the end, then it's not the door mechanism's fault.
    • Does your power supply have an indicator LED? If so, watch it during the pulsing. Does the light stay on until the actuator stalls, then go dark except for brief momentarily pulses? This would confirm that the power supply is cutting out in hiccup mode (and that the motor is drawing too much current for the supply.) If the supply doesn't have an indicator, but you have LEDs and resistors, you could simply add your own indicator in parallel with the power supply.
    • Measure current. If you have an amp meter that can handle the maximum current your power supply will put out, you could run the power (12V side) through your meter and watch current draw. I'd expect a low, reasonable number when the actuator is moving freely in either direction, then a spike of high current as it stalls, followed by alternating zero current and stall current while it's pulsing.
     
  12. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    Dang. I always spend too long writing - @Alec_t beat me to it!
     
  13. mattrofe

    Thread Starter New Member

    Dec 16, 2017
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    1
    Ok - well i'e considered your points and basically have removed the relay the the door mechanism from the scenario altogether... interestingly that full retraction seems to also have this 'pulse' in the actuator. So potentially the adjustment of the inbuilt limit switch is not 100% correct causing this issue?

    I've uploaded a detailed pic of the actuator motor - thats all the info i have... it definitely has internal limit switches though.
     
  14. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    Yeah, if it's got internal limit switches, but it tries to draw current when it's fully retracted, then it seems like something must be wrong with the limit switch.

    It's possible that measuring current draw or watching indicator lights from a power supply would provide some other clue, but from what you describe, I don't really expect it.

    I'm not sure what your options are at this point. Hopefully someone else with more linear actuator experience can help. I don't know if the actuator is really serviceable. I'm guessing you either need a new actuator, or you could wire up your own external limit switch to get this actuator working.
     
  15. LesJones

    Well-Known Member

    Jan 8, 2017
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    Have you tried the actuator with it not mechanically connected to you gate system in case your gate is not allowing it to reach the point where the limit switch operates. If you had made it clear from the start that the time switch and relay were powered from the same 12 volt supply as the actuator then your problem would have been solved much more quickly. I and I suspect others assumed the time switch and the relay coil worked from mains voltage. If your actuator is the same as those used to move satellite dishes then there is a cam on the gearbox that rotates less than one revolution for the full travel of the ram. This operates the limit switches. There may be some way to adjust the position of the switches or the cam. You can normally see this cam in the connection box. A GOOD FOCUSED picture of the inside of the connection box may help.

    Les.
     
  16. mattrofe

    Thread Starter New Member

    Dec 16, 2017
    8
    1
    Post #13 states that i disconnected the gate system.
    Post #1 states that the entire circuit is 12V. I didn't realise it could be misleading at all. I simply see 1 power source in the circuit so I interpret that as gospel. Is that not the case?
    I'm not keen on pulling apart this actuator - might be easier for me to hook up an external limit switch.

    Please remember that electronics is not my thing at all and have had next to no background in this. I'm doing the best I can to explain my problem.
     
  17. LesJones

    Well-Known Member

    Jan 8, 2017
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    I had used the information on the diagram in post #1 which shows a relay with a 120 volt AC coil. I missed your comment in post #13

    Les.
     
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Ah, but you explained it better :).
     
  19. mattrofe

    Thread Starter New Member

    Dec 16, 2017
    8
    1
    OK so its working now.

    I decided to pull apart the actuator and like some previous posters said, the retraction limit switch was not set correctly. At the end of the worm drive is a spring - i assume to assist in propelling the cog back up when polarity is reversed. The limit switch there was positioned slightly too late which caused too much tension on the spring which in turn pushed the the cog up the shaft again, disengaging the limit switch, which in turn engaged the motor.

    I have managed to move the switch up the shaft slightly by packing it out 2mm using some wire sheath. Once that was done everything started working perfectly.

    Thanks to everybody for your assistance.
     
    ebeowulf17 likes this.
  20. ebeowulf17

    Well-Known Member

    Aug 12, 2014
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    Awesome! Congrats.
     
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