Timed relay Problem!

Discussion in 'General Electronics Chat' started by gavin1987, Apr 14, 2016.

  1. gavin1987

    Thread Starter New Member

    Apr 14, 2016
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    afternoon all,

    i have started a new project in my workplace with the aim of reducing our carbon footprint, the plan is to have a 24V lightgate control a timed relay, which when trigger will start a 5 minute cycle of power to our 415V motors with the theory of instead of running them needlessly for an hour with one box, the box can pass and 5 mins later the relay switches off the motor, only problem is if there is more than one box (we process on average 9000 per day) the lightgate is constantly cycling through high and low states which in turn has the relays coil cycling at the same rate which has the motors on and off jumping every time a box passes, anyone know if there is a way to delay the signal from the lightgate to the relay to ensure there is a large enough gap in the on off sequence?

    cheers

    >
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Welcome to AAC!

    There are many ways to do what you want. Post a schematic or block diagram of your relay control circuit for more specific suggestions.
     
  3. gavin1987

    Thread Starter New Member

    Apr 14, 2016
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    forgive the horrid drawing.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    What voltages are available in the system?

    What is the polarity of the signal on the black wire?

    Do you want the delay to keep the relay energized longer?
     
  5. gavin1987

    Thread Starter New Member

    Apr 14, 2016
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    available voltages are 24V for control of both timed and standard relays

    black wire is 24V +

    the timed relay seems to hold for the time required if the lightgate is broken once however if the lightgate is blocked twice for example from two boxes passing within 30cm of each other the relay coil will stutter and turn off, my workplace has a conveyor system hence the close proximity of the boxes.
     
  6. mcasale

    Member

    Jul 18, 2011
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    It sounds like if the relay has been activated by the "first" box, and a "second" one comes along quickly, the relay does not catch it. Correct?

    There used to be "time-delay" relays back in the old days - both NO and NC. Perhaps the simplest thing is to lengthen the time the relay is actuated. At least the duty-cycle of the relays and motors would be reduced.

    If you want to do some electronics, a simple, cheap MCU, like an Arduino can make the whole system a lot more flexible. The toughest part would be interfacing the Arduino to your relay. You would also have to generate +5VDC.

    Sounds interesting.
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
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    The black wire is 24V when the relay is supposed to be energized? How long is the relay normally energized when triggered? How long do you want it to be on?

    Post your circuit ideas. Members here will help, but few will do free work for commercial applications.
     
  8. gavin1987

    Thread Starter New Member

    Apr 14, 2016
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    yes the black wire is 24v, the relay is supposed to stay on for 5 minutes when the lightgate goes dark (box in front) but as soon as the box clears the lightgate the relay switches back off as if to start the sequence again, it seems as if because the lightgate is active it breaks the power to the relay.
     
  9. mcasale

    Member

    Jul 18, 2011
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    Sounds like the N/O timer relay isn't doing its job. Have you tested it?
     
  10. dl324

    Distinguished Member

    Mar 30, 2015
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    Or the controller isn't working.
     
  11. Tonyr1084

    Active Member

    Sep 24, 2015
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    I wonder if it's just me, but are you saying the motor runs a belt, and when a box is sensed the motor runs until the box is no longer sensed. Then five seconds later another box comes down and the motor has to start up again. Sounds like you want the motor to run for a set minimum period of time after a box is sensed, AND the time is reset every time a box is sensed. So that if (and this is just an example) the first box comes down, the motor turns on and runs the belt for 30 seconds. If no more boxes are sensed in that time the motor shuts down. But if a second box comes down in 29 seconds you still want the motor to run up to 30 seconds past the last time the box was sensed.

    Is that what you're asking for? A resettable timer that is reset every time a box is sensed. If no box is sensed the motor / conveyor shuts down after 30 seconds.
     
  12. gavin1987

    Thread Starter New Member

    Apr 14, 2016
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    yup that's what i'm looking to do with the aim of, once the last box has passed the sensor 30 seconds later the motors will shut down and save energy, however so far the sensor is doing a double action, when the front end of the box breaks the lightgate the relay activates as it should but when the box's rear end passes the lightgate sees the reflector again and the coil opens , stopping the motor.
     
  13. Tonyr1084

    Active Member

    Sep 24, 2015
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    Went on Amazon and found this page:

    http://www.amazon.com/s/ref=nb_sb_s...words=timer+relay&sprefix=timed+relay,aps,186

    I don't see anywhere that says the countdown timer can be retriggered during an already in-progress countdown. In other words, it's counting down from 30 to 0 and at 5 seconds to go another box is sensed and the countdown starts over. But at least this may be a start.

    The alternative would be to build a capacitor based timer. Every time the box is sensed the capacitor is charged up. As its voltage decays (depending on your RC circuit) the relay cuts out at a certain point. But if a box breaks the beam again the capacitor is recharged and the decay time starts over.

    One way or the other, that's what you want to do.
     
  14. Tonyr1084

    Active Member

    Sep 24, 2015
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    One of the units I'm looking at has a link to a PDF of the users manual. It's written in China-English. In other words it's written in English but is somewhat difficult to understand because something is being lost in translation. Nevertheless, it seems like programs 11, 12, 13 or 14 are most likely to do what you want. There are 18 available programs. The first nine start with the relay in the active mode, meaning the NO and C contacts are closed.

    http://www.easydiag.cz/fotky29604/fotov/_ps_202Timer-Relay-Module--FRM01--User-Manual.pdf
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
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    The circuit is called a retriggerable monostable multivibrator (RMMV). A monostable makes one pulse (mono) of fixed duration (stable) when it gets a trigger input. For a true monostable, if a second trigger input arrives while the circuit is still timing out the first one, the second one is ignored. With a retriggerable circuit, the second trigger restarts the timing function without the output changing state. So the output of a 30-second RMMV returns to the off state 30 seconds after the *last* trigger input, not the first trigger input. Of course, if another box comes along 31 seconds after the end of a previous one, the output will bounce.

    If this sounds like what you want, then it comes down to make or buy. We love make around here, but *some* people want to just get on with their lives...

    ak
     
  16. Tonyr1084

    Active Member

    Sep 24, 2015
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    I asked (on Amazon - of the timer relay) "If triggered for 30 seconds, can the countdown be reset BEFORE the initial 30 seconds is completed? Time resettable during countdown?"
    JD Axxxx answered:
    "One of mine is set for an input that counts down and it will reset before the count finishes"

    But if you want to build: Here's a "RMMV" circuit. All you need to do is supplement R1 / C1 to get the time delay you wish. Pins 11 & 13 are unused.

    Retrig MonoStable MultiVib.png
     
  17. gavin1987

    Thread Starter New Member

    Apr 14, 2016
    6
    0
    thanks all sorted the problem.
     
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