dumbwaiter control system

Discussion in 'The Projects Forum' started by shafam, Oct 26, 2009.

  1. shafam

    shafam Thread Starter New Member

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    I am trying to build a control system for a 3 stop dumbwaiter. I would like to use latching relays and magnetic contacts for simplicity. The lift motor is a 120V reversible hoist that draws 7A. The wall switches I have are Leviton LVS-003. I need help with the circuitry design and sourcing of materials. The open door safety and the slack cable safety are in place, as is a 24V DC power supply for the relays. There are basically three circuits 1 to 2 / 2 to 1, 1 to 3 / 3 to 1, and 2 to 3 / 3 to 2 . If it were only two floors it would be quite simple. My difficulty is how to bypass the middle floor when needed. I want to stay away from electronics that because of my remote location would be unserviceable. Just simple relays and contacts. Can anyone help with a schematic and parts list. Thanks . BOB S.
  2. SgtWookie

    SgtWookie Expert

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    Bob,
    Are you talking about this switch:
    http://www.leviton.com/OA_HTML/ibeCCtpItmDspRte.jsp?sitex=10021:22372:US&item=409013
    The LVS-3W was the only reference I found to that on Leviton's site.

    Are you in the USA, or elsewhere? It helps a great deal to know your approximate location when attempting to find suitable parts.

    A motor that draws 7A @ 120V will probably draw several times that current when it's starting up. Is it a DC or AC motor?
  3. shafam

    shafam Thread Starter New Member

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    Yes that is the switch that i have. The motor is 120V AC. It is a geared reduction motor and an ammeter showed no extra startup amps. I'm in WV in the mountains 2 hours from anywhere, but I do get UPS and Fedex deliveries. In fact I order 80% of everything and have it deleivered. Its cheaper than a 3 or 4 hour round trip to town, and I probably won't find what I need anyway. I can put together relays, limit swithces, etc. from a schemetic, but designing the circuit is something else altogether. Thanks in advance. Bob S.
  4. SgtWookie

    SgtWookie Expert

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    OK, you're going to have to tell us more about the motor wiring.

    Do you have the instructions on how to make the motor reversible?

    Providing a wiring diagram would be very helpful. If you don't have that, the manufacturer's name and the model number of the motor could be used to find a datasheet for it.
  5. williamj

    williamj Active Member

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    Bob S.,

    Not knowing your experience with electrical circuits I feel that I must state the obvious. Not only can 120VAC kill (and has killed) it can also burn down you house. The job you want to do is not an easy one, be careful and thorough.

    An instructor I had once said, “Always assume that the person who drew this diagram up was drunk, hung over or just plain having a bad hair day and made some serious life threatening mistakes. Your life is in “YOUR” hands. Act accordingly.”

    I have attached a ladder diagram, which I believe will accomplish the task at hand. I also believe that it is error free but you never know. If anyone else reading this thread sees any errors by all means... please speak out!

    Do not take this ladder diagram and start wiring up your project. Take the time and make the effort to do a test mockup on a sheet of plywood using a light bulb in place of the motor. Once it is wired correctly and fully tested, then and only then begin work on the dumb waiter itself.

    Not only will the mockup test the validity of the circuit but it will also give added and valuable experience.

    Good Luck,

    williamj

    Attached Files:

  6. williamj

    williamj Active Member

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    Bad hair day ALERT!! Bad hair day ALERT!!

    The 24V portion of diagram will not work. Apparently a relay for each floor is required. Don't know why I missed that. (bummers) Will revise...

    See what I mean about mistakes on drawings and schematics?

    Apologies and Mia Copas,

    williamj
  7. williamj

    williamj Active Member

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    Attached are the revised diagrams. Please check thoroughly.

    [​IMG]

    williamj

    Attached Files:

  8. shafam

    shafam Thread Starter New Member

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    thanks sgt...the motor is already reversible...it is a hoist motor...the type you might see lifting an engine from a car...880# capacity...16 ft +/- per min cable speed...it has a hand control that i will remove and splice my control circuit to...120v ac comes into the control and goes to two momentary contact push buttons...if you push up power goes back to the motor through one wire...if you push down power goes back to the motor through a different wire...the neutral does not come to the hand control but there is a ground wire for safety...very basic...I am very familiar with AC voltage...I wired the whole house myself...bob s.

    williamj...I will print the wiring diagrams and see if I understand them...as I mentioned above, I wired the whole house myself so I understand AC and the risks...whenever possible I kill the power to a circuit before working on any wires in it...thank you very much for your time...bob s.
  9. shafam

    shafam Thread Starter New Member

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    won't it will take at least 6 ( maybe 9 ) relays???...from any floor you have two send options to the other floors, and 1 call option if the car is not on your floor...????just thinking out loud...bob s.
  10. shafam

    shafam Thread Starter New Member

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    and won't 2 limit swithches be required at each floor (possibly 3 on the second floor)?..one limit switch to stop travel, and one as a proximity sensor...for example...if you are on the first floor, to call the car down from upstairs you would press 1, which would activate the motor down...but if the car were already on the first floor and you pressed 1, there has to be something to prevent the motor from going down further...the same for the other floors????headache!!!thanks...bob s.
  11. williamj

    williamj Active Member

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    Bob S

    A new circuit design is an evolutionary proccess (always do your basics first, power and safety/limiters first, then "start/stop", "up/down", and then your particulars, "Call" buttons) and I believe we are almost there.

    This latest revision now has the "Call" buttons to summon the dumbwaiter to your floor. Pay particular attention to the second floor (2nd Floor) "Call" button, it must be double pole double throw (dpdt) where as rest of the push buttons and the other two "Call" buttons can be single pole single throw (spst). That being said, each floor would require a three (3) button station and I don't know if your Leviton switch will work as the second floor "Call" button.

    The three (3) floor limit switches (LS) switches have been relocated in the diagram. The door switches (DrSw) and floor switches can be the same, makes things a little simpler.

    To date five (5) control relays and atleast one, possibly two (2) motor relays (dependent on how you motor is wired for reverse), eleven (11) push buttons, one (1) keyed selector switch, one (1) transformer, one (1) circuit breaker and assorted fuses are needed.

    If you could post a wiring diagram or schematic on the motor we may be able to trim this down a bit and maybe even eliminate a component or two.

    williamj

    Attached Files:

  12. shafam

    shafam Thread Starter New Member

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    thank you william... I am somewhat understanding the schematic...I am assuming the AC wiring is not shown but indicated by connection points?
    I do not have a schematic readily available (i'm 900 miles away presently)... the motor has 3 wires...a white neutral, a black forward, and a black/white stripe reverse...the casing has a ground terminal in the connection block...
    could the second floor call button output be routed through the existing (or additional)first and third floor door switches to determine motor direction? if calling to the second floor one of those circuits is closed and the other open...
    again...THANK YOU for your time...I have been trying to find help with this project for two years...bob s.
  13. williamj

    williamj Active Member

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    Bob S.

    Yes, you are correct. In a ladder diagram it is the path that electricity takes that is shown, not component or wire placement. It is also important to understand that in a ladder diagram everything is shown in a "de-energized" state. That is, without electrical or physical force being applied.

    I have revised the 120V part of the diagram, I labeled a few of the paths for a clearer picture of that portion of the circuit.

    Again, you are correct about the limit switches. Physically, if the dumbwaiter is at the third floor, and you were to call it to the second floor, the third floor limit switch there would be "made" and the contacts in the limit switch would go through a change of state. The "normally closed" side of the switch would open and the "normally open" side of the switch would close changing the electrical path, allowing the dumbwaiter to move downward. If at the first floor the same change of state would occur at the first floor limit switch and the dumbwaiter would then move upward.

    I've noticed, looking at the file attachments themselves, that the images appear blurred and are a little difficult to follow. I make these diagram in a cad program called DeltaCad. If you happened to have this program I would be happy to send the files directly to you and it may be a little easier to see and understand it all.

    williamj

    Attached Files:

  14. shafam

    shafam Thread Starter New Member

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    william...I downloaded a trial version of deltacad...if you have a chance email me a copy of the schematic r_shaffer@bellsouth.net... maybe the resolution will be better...thanks so much...bob s
  15. williamj

    williamj Active Member

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    Bob S.

    Sent dc files as email attachments, hope it works.

    williamj
  16. shafam

    shafam Thread Starter New Member

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    william...got the files , but I have deltacad 4 so I will try to update to dc7...thanks so much...I think I have a pretty good handle on the schematic...what about sourcing the relays..will they be latching relays?...magnetic?...i was going to use magnetic alarm contacts for the limits and doors...bob s.
  17. williamj

    williamj Active Member

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    Bob S.

    Glad ou're getting a handle on the diagrams. Just to be a nit picker, schematics show component connection and sometimes component placement as well as electrical paths, where as ladder diagrams just show the electrical paths. Picky I know, though they both maybe fruit, an apple is an apple not an orange.

    At any rate, the diagram isn't quite finished, evolution, remember? Not knowing what particular motor you'll be using, I must assume that it doesn't come with a brake, most don't, one will have to be incorporated into the system.

    Now, depending on the pulley system you plan to use, do NOT plan on using the brake to hold the dumbwaiter in place. Brakes wear out and sooner or later they fail, and when that happens your dumbwaiter will becoming down in no time at all.

    I strongly suggest a right angle worm gear drive attached to your motor. (motor, worm gear, pulley system) The worm gear will hold the dumbwaiter in "place" and all that the brake will do is stop the dumbwaiter at the desired location.

    Also, I suggest a "slow down/start up" period just before stopping/starting to reducewear and tear on the equipment and on the contents of the dumbwaiter. This will require an additonal speed reduction circuit, (single speed, perhaps one third (1/3) of motor rpm), in additon to what we already have. I wouldn't be of much help here but you could find additional help elsewhere in this forum.

    I've been working on incorporating both the brake and speed control connections into the diagram. Will post when complete.

    Bet ya didn't think it was gonna get this complicated this quickly did ya?

    williamj
  18. williamj

    williamj Active Member

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    Bob S.

    I'm not familiar with the magnetic alarm contacts but the limit switches here must have both normally open and normally closed positions.

    williamj
  19. williamj

    williamj Active Member

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    Bob S.

    Sorry for the multiple posts but it's real early and I haven't had any coffee in over a decade. (bummers man)

    In reference to "latching relays" we just take regular relays with multiple contacts and turn them into latching relays as required.

    A "regular" or non-latching relay would just have a on/off button or switch to energize and de-energize the coil. When the button is pushed, current flows through the button and relay coil and the coil is then energized, closing the normally open contacts and opening the normally closed contacts. And when the button is released current flow stops and the coil is then de-energized, opening the closed normally open contacts and closing the open normally closed contacts.

    A "latching" relay requires a "holding" contact (and comes with a latching contact pre-wired) to maintain current flow throught the coil when the "on" button is released.

    The circuit would be something like this...

    --On Button----------------|-------Off Button-----Relay Coil--
    --normally open contact ---|

    When the On Button is pushed the Relay Coil (in series with the On and Off Buttons) is energized and the normally open contact (in parralell with the On Button) closes.

    --On Button---------------|-------Off Button-----Relay Coil--
    --held/closed contact -----|

    The held closed contact keeps the Relay Coil energized, which in turn keeps the normally open contact held closed. When the Off Button (in series with the On Button) is pushed current flow to the relay coil stops the held closed contact returns to a normally open contact and everything returns to a de-energized state.

    --On Button---------------|-------Off Button-----Relay Coil--
    --normally open contact ---|

    So we just put in our own lactch circuit into the relay, latching relays generally cost more, why pay more when you don't have to.

    williamj
  20. williamj

    williamj Active Member

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    Bob S.

    I've been rereading the posts and I need a little clearification... is it just the hoist motor that you have or is it the complete hoist package?

    williamj
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