Off delay timer for two contactors

Discussion in 'Power Electronics' started by mztrordinary, Jun 13, 2017.

  1. mztrordinary

    Thread Starter New Member

    May 25, 2016
    16
    0
    Hi guys
    I have two contactors (forward and reverse) that are being used to open and close a sliding door. There is a stop button fitted and e stop also but what is happening is that when people are pressing the open or close button they are sometimes forgetting to press the stop button so the contactor keeps running in the open or closed position depending on if it has been left open or closed. So what i want to do it put an off delay timer in so that if they forget to press the stop the contactors will still shut off. The only problem is im not 100% on the type i know i need an off delay timer but do i need two? one for each contactor? Or can i get one with 2 outputs that will do both? i have attached link of where i will be buying timer from if anyone could recommend which one would be best. Contactor coils are 230vac

    Thanks guys

    http://ie.rs-online.com/web/c/autom...Term=time delay&applied-dimensions=4294569661
     
  2. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
    546
    34
    Firstly you need an ON delay... bear with me.
    I dont think I can give you a circuit because it would briech forum rules with respect to none isolated power supplies, and for good reason.

    I strongly recomend you get an electrician to do this for you but, it is simple and only requires a single timer...

    From here on in I will be describing functions and not telling you what to connect where, lest I get a vertual slap.

    You have two controllers, up and down, that actually switch the door motor.
    You have 3 buttons,
    one is a common stop that turns off both controllers.
    One turns on the up controller, and one turns on the down controller.
    The controllers, stay on, once started, until stopped, without the need for the button that started them to be held in.
    Only one controller can be on at once, they are interlocked (At least I would hope so)

    If you add a timer that either controller can start, and have it perform a stop when it times out, things will work as you invisage.
    (The timer is turned on - there is an ON delay - a stop function is performed, which turns off the controllers and thus the timer)

    That said I wouldn't use a timer, I would use limit switches on the door so it never stalls.

    No oiffence but if yiou dont know this, which is a relativly simple and common sort of thing to do with industrial controls, you shouldn't be mucking about with it as it could literally kill you or burn down the property if done incorrectly.

    Youe electrician should supply a universal timer and connect it to the existing contactors. You may need additional contact blocks that fit them.

    PLEASE do not be tempted to try this, it isnt safe, which is why you need a qualified installer.

    Sorry to be blunt,
    Al
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    16,220
    4,758
    @mztrordinary do you have a schematic of the present setup?
    Max.
     
  4. mztrordinary

    Thread Starter New Member

    May 25, 2016
    16
    0
    attached is image of current setup the 24volt supply in the diagram should be 230v but everything else is as per drawing. And @Dyslexicbloke the supply is isolated through a swtiched isolator and an MCB and yes the contactors are interlocked. As for myself i am an apprentice electrician trying to work this out and ALL my work will be checked over before anything is switched on and handed over. Full-voltage-reversing-3-phase-motors.jpg Full-voltage-reversing-3-phase-motors.jpg

     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    16,220
    4,758
    Could you not fit a L.S. on either end for a positive result? A timer is a rather indefinite solution due to variation in open/close times.
    That is the method used typically.
    Max.
     
  6. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
    546
    34
    If its OK with Max I guess I will be OK telling you then...
    I apriciaqte the clarification RE your circumstance.

    As I said I would use limits on the door if at all possible but none the less...

    Timer,
    any on delay with a normally closed output contact and a 24VDC coil will work.
    I would probably buy a universal timer which will have several functions to choose from and will operate over a wide voltage range, AC and DC
    This or simmilar, I usually have a few on hand which is why I use universal types.
    You will find it easier if you number the wires but I think we will manage.

    As is, there is no common place in the circuit that is on when either contactor is on you are either going to need to create one or use two timers.

    There may be an additional, normally open, contacts available on the contactors or you may be able to add a block, you could even use relays but that is messy an no better than two timers given the relative cost.

    There is one place on your circuit that is both common and switched with both contactors, L2, but using it would not be good practice and I wouldn't. The existing control system is SELV and you should keep it that way.

    If you add or use additional contacts connect 24V, from the fuse, to one side of each new normally open, one on each contactor.
    Connect the coil, B1, of the timer in this case, to the other side of both new contacts and connect timer A2 to 0V.
    Some timers only have A1 which is both supply and signal... Using the one. suggest A1 is 24V whilst B1 is the signal.
    Now thew timer will run if either contactor is closed and 15/16 will open when the time is up.
    Connect 15 to the stop button and 16 back to 96 on the overload where the button used to go.

    The timer is now a stop button that operates some seconds after either contactor closes.

    If you are using two timers connect the A1's to 24V, B1 & 15 of each to (54 / PB) on each contactor, disconnect the contactor A1's
    Connect the 16 of each timer to A1 on each contactor.
    Each timer will run when its start button is pressed or its contactor is closed. When the time has elapsed it will open the contactor, turning its self off in the process.

    Set the timer/s to 'on delay function' with a run time that is the longest you want to the door to run.
    Note that with two timers up can be diferent from down if you need it to be.

    Two timers is probably the easiest and best option.
    There are many ways to do this sort of thing and should considder what will happen if the timer times out when the button is still pressed.
    It all depends on what you want. A better circuit would only start timing when the button was released, creating a 'jog' function but running the door if the button is held. in fact you could simply remove the latch so that the button need to be held to move the door and forget the timers all together.

    The propper way to do the job is to write an FDS, Functional Design Spec, which states what needs to happen in all possible circumstances.
    Possibly overkill for a door but a good learning tool

    Your door mechanisme may have internal limits in which case there is no issue simply leaving the up or down supply on but if it doesn't your existing system, and the timer solution will stall the door motor which is a very bad idea.
    Using the single timer solution will cause the contactor to bang in and out if the up or down button is held longer than the time delay, also not a great plan.
    The two timer solution avoids this because the timer runs when the button is pressed or the contactor is closed so holding the button keeps the timer energised even if the contactor has opened, but, holding the button will not force the door to run. If the time is not long enough to do a full stroke the button will have to be pressed again.

    As I said earlier I would use limit switches not timers.

    This sort of problem is a good learning opertunity, its not too complex but there are still things to considder that are not imidiatly obvious.
    I can give you a complete solution with all the bugs and issues worked out but I would need to know more about the equipment and your requirements.
    Quick and dirty you now have but I strongly recomend taking the time to fully considder the system because it will give you a better outcome and be a good learning tool.

    What you have now looks wrong, or at least incomplete, are you sure the door simply stalls, if so you should fix it by designing a better solution from the ground up.
    In addition there is no electrical interlock so pushing the down button when up is running, for example, is likely to damage the interlock and or contactor. Mechanical interlocks should be used for safety not functional control.

    Hope that helps,
    Al
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    16,220
    4,758
    You might find these useful, Telemecanique wiring diagrams
    Except there is one practice shown that is not recommended any more, this is the use of O/L's on the neutral side of a contactor coil.
    Max.
     
    EM Fields likes this.
  8. EM Fields

    Active Member

    Jun 8, 2016
    583
    154
    WOW!!!
     
Loading...