Need to know what would be best way of tensioning 120ac to 12v DC for a gear motor

Discussion in 'The Projects Forum' started by Herndon7468, Mar 6, 2016.

  1. Herndon7468

    Thread Starter New Member

    Mar 2, 2016
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    I'm currently building an auto chicken coop door and have very little experience in low voltage design. I have a GE 15132 digital timer (dpdt) that I plan to use to power the set up. I have a 120v AC line to the shed in using and plan to use this motor to open a window I use as chicken door. I need to know some ideas to transform to 12v to kick a relay to reverse motor and stop it at limit switches.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are numerous previous 'Chicken Door' projects here in the past.
    A couple only just very recent.
    Max.
     
  3. Herndon7468

    Thread Starter New Member

    Mar 2, 2016
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    1
    Max,
    Would a regulated switching power supply be best way of doing this? I'm not using solar or battery... Just powering some kind of transformer from mains.... But am stupid on how to do it. Thanks for any reply!
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What type are you using for a motor? DC? AC ? if using DC you do not necessarily need a regulated switching supply, the simple linear style will do it and far more rugged.
    Oops I see you are using a DC motor so go with a simple linear supply, only two basic components needed,
    Max.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    This is an example, for motor the cap and resistor is not needed.
    [​IMG]

    Max.
     
  6. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Here's http://www.trcelectronics.com/View/Mean-Well/LRS-50-12.shtml an example of something that should work.

    Some Switching power supplies have a minimum load requirement. This one does not. It also has a low "no load" power consumption which is what you want.

    You should have an idea of the current requirements of the motor. The starting current is somewhat higher. Counter-weighing the door, depending on the design, will reduce running requirements. The "window" is likely counter weighted already.

    Are you considering "rack and pinion"?

    A PTC fuse, self resetting (sized properly) is a good type of fuse for motor protection.

    You will also likely need 2 SPDT relays and two to four diodes and two SPDT limit switches rated for low current DC. The BASIC circuit is here: http://www.parts-express.com/resources-automotive-relays, one of the last two on the page.

    You have a choice of positive or negative trigger. One of the diodes will go across each relay coil.

    The SPDT automotive relay here http://www.parts-express.com/12-vdc...relay-spdt-30-40a-with-metal-bracket--330-079 is a good choice with the dual or single socket. I'd suggest dual.

    The diodes can be a 1N4002 or 1N4003 (preferred).

    The design (not shown yet) allows the motor to stop instantly.

    You will also need a SPDT relay (120 VAC coil) to turn your 120 VAC timer ON/OFF signal into a OPEN/CLOSE.


    The way it would work is that the OPEN signal (to the OPEN relay) gets routed through the OPEN Limit Switch which opens when it reaches that limit thus preventing from turning in the open direction. Similarly for the close direction.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    One application I personally would not use a SMPS in is DC motor control, One, it is not needed, Two, can be difficult to repair in the case of failure.
    Initially it may be cheaper, but in the long run, not, if failures occur.
    Max.
     
  8. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    In the end, you have to pick a few things:

    1) Overload protection
    2) Positive (+12 does stuff) or negative logic (grounding does stuff)
    3) How do you open the window when it's dark and no power?
    4) Upgrade paths - if any.
    5) regulated or unregulated power supply
    6) Construction (e.g. NEMA 1 cabinet with backing plate)

    An adjustable friction clutch is an easy method. So might removing a chain or belt. Urethane might be the easiest.
    Brass tipped set screws are often used as overload protection too.
     
  9. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    To go over the design again:

    1) Will assume Negative logic ~OPEN is OPEN Door

    The basic idea is to use two 12 V coil SPDT relays where the NC (Normally closed) connections are grounded. The Normally Open (NO) connections goto the motor supply of 12V.

    One end of each of the relay coils goes to +12 (logic). For protection, the relay coils should have a 1N4002 diode across the coil. The band goes to +12 (logic). At this point you will have two signals (~OPEN) and (~CLOSED). When grounded, the door will either open or close.
    When both are energized or de-energised the door will stop.

    If the directions are wrong at this point, flip the motor leads.

    Now with SPDT limit switches installed at full open and full closed wire the common contacts individually to ~OPEN and ~CLOSE.

    Make the ~OPEN signal go through the NC (Normally Closed contact of the FULL OPEN limit switch.
    do the same for ~CLOSE
    i.e. Make the ~CLOSE signal go through the NC (Normally Closed contact of the FULL CLOSED limit switch.

    Grounding the new ~CLOSE signal will cause the door to move to the closed position.
    Activating the FULL CLOSED limit switch will stop the door.
    Grounding the new ~OPEN signal will cause the door to move to the closed position.
    Activating the FULL OPEN limit switch will stop the door.

    Now you can use one pole of your DPDT relay for open/close and choose either off for open or off for closed.
    I'll choose normally Normally closed side to be = ~CLOSE
    Ground the center contact and connect the NO contact to ~CLOSE.
    Connect the NC contact to ~OPEN.

    SO, OFF on your timer means close and ON on your timer means open.

    You have to "chicken proof" your wiring.

    I don't care either way whether a switcher is used or a transformer is used, the rules in your case would be that 1.4*(AC secondary voltage)-1.2 V = 12 with a full wave bridge rectifier. The capacitor chosen would be 1000 uF/amp of motor current or more.

    You will be following the "full wave bridge, resistive load" here": http://www.hammondmfg.com/pdf/5c007.pdf

    I(AC) of the transformer secondary should be greater than or equal to 1/0.9 (Motor load). Torrodial transformers will be smaller.

    So, ideally you need a 7.4 VAC transformer at (1/0.9) * the motor current. I'd probably make that 2-3x the motor no load current.

    So while transformers may seem like a good idea, it might be difficult to get one sized properly. The meanwell series is pretty cheap to consider keeping a spare or even wiring two in a redundancy mode.

    The automotive relays is not a done deal, because there are other techniques.

    An industry standard construction technique involves a NEMA1 enclosure which has a plate in the rear. DIN rail is mounted on the plate and stuff is either mounted to the rail or tapped holes in the plate. Terminals can be mix or match. The technique works best if you have a strip of "outside connections". 120 VAC has to be physically separated and/or all wire ratings have to be for 120 VAC,

    DIN rail mounted power supplies are also available.

    These http://www.alliedelec.com/images/products/datasheets/bm/Hoffman/70066842.pdf or similar are used in industry with a rear panel. Warning - they are expensive.
    IP ratings are Ingress Protection. See: https://en.wikipedia.org/wiki/IP_Code

    Here's https://www.polycase.com/yq-141206? an example of a plastic case. Remider, the metal bottom plate is extra.
     
    Last edited: Mar 6, 2016
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    In the case of simple motor control, the secondary can be the motor rated voltage when no capacitor is used or needed.
    (e.g. SCR bridge controllers do not use any capacitor and they are phase controlled yet).
    Max.
     
    Last edited: Mar 6, 2016
  11. Herndon7468

    Thread Starter New Member

    Mar 2, 2016
    26
    1
    Thank you both! I'm very appreciative for your in depth explanation!! I've actually got my mechanism all made up for the window to open/close & was just down to the wiring. I have made bracketry to attach to the window so that this motor will turn a threaded rod and the window has a female thread fixed to it, allowing it to travel up and down to the limit switches. The timer I have is a dpdt timer that will have power both at night as well as during the day. At 7am the LED lighting inside of the coop turns on and that will be when window opens.... At 9pm, the timer switches contractors and night light kicks on (led goes off) and this will be when window closes.
     
  12. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Good! I just hope my explanations make sense?

    I hope you will have an easy to use contingency plan if the power fails? To make it interesting, the power fails and it's raining.

    In the "chicken coop" threads, I always mention "Astronomical Timers". These calculate dusk and dawn. So you can set them for like (1 hour after "Dawn" ) and 9:00 PM or whatever.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    One source I have used in the past for multi-output real-time clock timers is the fairly cheap zone timer for lawn sprinkler systems.
    They use 24vac output for control, which can either operate a relay or a small motor.
    Each 'Zone' can be programmed independently.
    An automotive block heater timer is also a source of outside timer, which has 120v switched outlet.
    Max.
     
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