Seeking Basic Non-Electronic Gate Opener Circuit

Discussion in 'The Projects Forum' started by frank1492, May 21, 2015.

  1. frank1492

    Thread Starter Active Member

    Dec 7, 2010
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    I have an old swing gate opener with a bad control board, no longer available. I would like to design a circuit using the present motor and other parts that would allow the gate opener to function without an electronic control board. This circuit would be similar to the ones used in very early (70's or earlier) garage door openers having no "bells or whistles" (e.g. automatic timed closing, electronically-controlled auto-reverse, etc.)
    The motor is a 1/2 horsepower capacitor-start reversible 110v ac motor with four leads. The opener employs micro-switches ("limit" switches) to stop the gate at its excursion limits (open or closed). The gate is activated by a standard single-button Liftmaster remote control unit which is "momentary on." I am looking for a circuit similar if not identical to what I see when I look at the circuitry inside my old 70's era Liftmaster garage door opener. This design has no control electronics, but naturally employs what I assume is a double-pole double throw latching relay(???) and a transformer is also present. Unfortunately I have no schematic, otherwise I could probably replicate the design myself.
    The design I am seeking is obviously quite simple but I don't quite have the expertise to put it all together. Your help would be very much appreciated. Thanks very much.
     
  2. MikeML

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    Oct 2, 2009
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    So what happens when you trap a child or animal in the closing gate??? There is a reason why your '70s Liftmaster can no longer be installed...

    I recently built a gate operator (Arduino-controlled), and included current-sensing, and auto-reverse if an obstacle is detected. It is not that hard...
     
  3. crutschow

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    Mar 14, 2008
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    It's electronic, but how about using a cheap remote control relay board?
    For example, I used this device to replace a failed controller in a TV lift mechanism and it works well.
    It has two DPDT relays to provide the reverse function with inputs for two limit switches.
    It has a latch mode where the activated relay stays energized until its corresponding limit switch closes.
    It uses a two button remote controller, one for open and one for close. Pushing either button again will reset its respective relay, so will stop the opening or closing if an emergency stop is needed.
    I power it with a small 12VDC wallwart (it draws a maximum of only 70mA).
     
    Last edited: May 21, 2015
  4. frank1492

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    Dec 7, 2010
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    The gate opener has a slip mechanism that can be adjusted so that when it strikes something it exerts little or no force. The old mechanical reverse mechanism in the 70's Liftmaster garage door opener could be adjusted too but in my experience never so it would reverse soon enough to avoid injury. Thanks. Will look into your operator.
     
  5. frank1492

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    Dec 7, 2010
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    Thank you, will look into this. The question is is it robust enough to handle a 1/2 hp motor.
     
  6. frank1492

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    Dec 7, 2010
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    I see that it is. It looks like it may be the perfect answer to my problem! I will keep you posted!
    The gate opener in question is a 20 yr old Allister Twist'r, a device that is in perfect shape mechanically. Seems a shame to dump a $2000 device for lack of a control board.
     
  7. crutschow

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    Mar 14, 2008
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    That could be a concern.
    10A relays can have an inductive rating of only 5A or less and motors can have a large startup current many times their running current.
    To be on the safe side and for good reliability you may want to add some larger slave relays, such as some 12V coil, 20A to 25A units.
    Make sure you add a snubber diode (1N4148 or similar) in reverse direction (cathode to positive) across the relay coil to protect the contacts on the board relays if you do.

    Do you know how the motor is connected to run in each direction?
     
    Last edited: May 21, 2015
  8. frank1492

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    Dec 7, 2010
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    I was just looking at this. I was trying to determine what kind of reversible motor it is from the schematic. It has four leads with a non-electrolytic capacitor across two of them. I have an image of the entire circuit on my smartphone which I would like to post for you, but this is being composed on my laptop. I don't suppose you would share your email address. Obviously it is very important that I determine which leads go where when I use the motor with the board you have suggested. Do I have a motor with two separate windings and how to identify these, for example. Somehow, I would like you to see this schematic and wiring diagram.
     
  9. MaxHeadRoom

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    Jul 18, 2013
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    You would normally have two windings, one start and one run, they can be checked with an ohm meter to identify, one, the start or phase shifted winding will have the capacitor connected in series with it.
    to reverse the motor, you just need to reverse one pair WRT the other pair.
    Both pair are connected across the AC supply, (one with a series cap).
    Max.
     
  10. frank1492

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    Dec 7, 2010
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    IMG_20150521_224336_806.jpg
     
  11. frank1492

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    Dec 7, 2010
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    Thank you MHR. Could you or Crutschow please take a look at the posted schematic and see how it jibes with MHR's motor explanation, making reference to the lead colors? Let's say I removed the motor from this circuit (as planned), leaving the capacitor in place. I assume if I connected white and brown directly to the a/c, the motor would run but I'm a little unclear what I would then do to reverse it, simply reverse the capacitor connections? And is this properly called a capacitor start single phase induction motor?
     
  12. MikeML

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  13. MaxHeadRoom

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    As posted by MikeML you appear to have a motor where the start and run windings are identical, on these motors, the reversal can be done as in #12 which essentially reverses the winding usage between main and phase shift winding.
    In this case both windings should show identical resistance.
    Max.
     
  14. MikeML

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    I got the wire colors in post #12 off the schematic posted by Frank. I have played with garage door operators, and those only had three wires going to the motor, so the capacitor is switched in-series with one winding or the other. In Frank's four wire motor, I cannot figure how it is wired internally?
     
  15. frank1492

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    Dec 7, 2010
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    Hi Mike. That is the schematic that came with the opener. The actual unit is at my other house right now so cannot examine it. I am aware that all the garage door openers I have seen have 3 wires. Does this concern invalidate your posted schematic?
     
  16. MikeML

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    Not if you intend to use the four wire motor depicted in the schematic you posted.
     
  17. frank1492

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    Dec 7, 2010
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    As to first issue, I assume any DPST relay with contacts rated at 20a 120v ac will work, but is it necessary? Tables show different starting watts for different type 1/2 hp motors so I still need to know what type of motor this is: split phase, capacitor start or induction. (Is the capacitor used here for starting purposes or for isolation or some other purpose? Not savvy enough to know.) If the motor is pure induction, 1300w, for capacitor start, 1800w, according to tables. If induction, I wouldn't be so concerned with directly connecting the relays in the kit. Your thoughts?

    Please refer to my posted schematic for answer to second question.
     
  18. frank1492

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    Dec 7, 2010
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    I will be using it. I just thought you might not be sure because you wondered how it was wired internally.
    Thank you so much for this information! Your circuit makes this all much simpler for me!
     
  19. MaxHeadRoom

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    I would do a resistance check of the motor, I suspect that at least a pair of the conductors entering the motor may be common to each other?
    Max.
     
  20. frank1492

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    Dec 7, 2010
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    Thank you Max, will do.
     
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