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  • Electrical circuit help

    I need some help in building a circuit to turn on and off a small motor (115VAC, about 1.25A current) which will be a vibrator for his progressive reloader. The powder dump is not throwing consistent loads, a commercial loader advised us to build a small motor driven vibrator which I have done, it works well. However, we don't want to have it run continuously, it needs to run for 2 or 3 seconds at the bottom of the plate stroke.

    I have a small circuit I drew up, but it needs some kind of relay to turn on and off when the plate hits bottom of the stroke. I think it may be called an "off delay" relay, but I don't know how to integrate it into the circuit.



    Can someone help with this? I need to turn on the motor when the microswitch closes, have it run for 2 to 3 seconds (like a variable length so it can be adjusted for best results), shut off the motor, rearm the circuit when the microswitch opens, and start the series over when the microswitch closes next down stroke.

    Thanks for any help, Merry Christmas!

    Steve

  • #2
    You may want to think about incorporating something like this time delay relay into your solution.
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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    • #3
      Mickey,
      That's sort of what I am looking for. How do you get it to reset itself after running? The microswitch would remain closed. I could get a power supply like this http://www.ebay.com/itm/DC-12V-1A-AC...item3a87035858 to power it with.

      Steve

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      • #4
        After doing some reading on the internet, I think a interval timer might do what I want. Like this one:



        Just how would I hook it up?

        Steve

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        • #5
          You speak of a stroke that has a bottom, so it must also have a top. I imagine this is a vertical stroke, but I could be wrong. Since you want the vibration to be on for a portion of this stroke, the bottom portion, perhaps you could simply use a mechanically activated, normally open push button switch (micro switch?) that is activated with a rod that is spring loaded on the vertical part that is going down and up. When the stroke reaches a certain point in the downward motion, it would be set to activate the switch. After the switch is closed, further motion will bring the activating rod against a stop but the mechanism can continue down because of the spring. When the mechanism rises above that level, the switch rod will lift off the switch and the vibration will cease. No expensive time delay device is needed.
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.

          Comment


          • #6
            Paul,
            A good thought, however, the machine is entirely manual and the time spent at the bottom of the stroke is highly variable, from 15 seconds to several minutes. Since I only want the motor to run for a few seconds, a simple on-off switch wouldn't work.

            I think a interval timer would work, I'm just not sure where it would fit, and if the on and off cycle of the microswitch would work it correctly. I have ordered one of the timers I linked to, will try it out when it gets here.

            Thanks for the help,

            Steve

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            • #7
              I find it really hard to believe that you will get an Omron time delay relay from China for that price. Surplus from US, sure, but ordering from China implies that it's new. My guess is that they use that for the photo but you will not actually get an Omron TDR.

              Whatever, if you replace the motor in your diagram with the coil of a time delay relay then when the microswitch closes, it will activate the relay. The power to the motor would be supplied through the normally closed contacts of the relay in a separate branch.

              What happens then is the microswitch closes, the relay stays on for 2 seconds then the contacts open, shutting off the motor. They relay timer resets when the microswitch opens.

              If you are interested, I have a Potter & Brumfeld adjustable (1-6 seconds, I think) time delay relay with 120VAC coil that you can have for the price of mailing it (hey, it's Christmas). It's at least 15 years old and I have no need for it, but I just tested it a few minutes ago and it still works. Contact me via PM if you want it.

              Lyndon

              Comment


              • #8
                The circuit below uses the Omron timer you chose. Just make sure the timer's coil is 115V ac. Also check that your microswitch can handle the motor current. The way it works: When the microswitch closes it energizes the timer coil and at the same time current flows to the motor through the timer's normally closed contact (pins 1-9). After a set time, the timer switches and the NC contact opens this cutting power to the motor. The timer stays energized until the micro switch opens. At this point the timer deenergizes closing the contact 1-9, but since the microswitch has opened no current flows to the motor.
                Enjoy.

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                • #9
                  Learning from the postings above, I redrew the diagram. Now the relay operates on full voltage, the motor uses the reduced voltage.

                  Will this work?



                  Thanks for the help!

                  Steve

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                  • #10
                    Your circuit will work but not the way you want it to. The timer you have chosen is "On Delay", its contacts operate a preset time after its coil is energized, and they go back to their off state when the coil is de energized. If you use the NO contact as you have shown, the motor will start a few seconds after the microswitch closes and will stay on until the microswitch opens.
                    To incorporate the resistances, use the circuit I drew above and connect the motor with the resistances in series with it to the two points where it says "to motor".

                    Comment


                    • #11
                      Yes, you are right I just read this description on how the relay works.
                      Next we have the normally-closed, timed-open (NCTO) contact. This type of contact is normally closed when the coil is unpowered (de-energized). The contact is opened with the application of power to the relay coil, but only after the coil has been continuously powered for the specified amount of time. In other words, the direction of the contact's motion (either to close or to open) is identical to a regular NC contact, but there is a delay in the opening direction. Because the delay occurs in the direction of coil energization, this type of contact is alternatively known as a normally-closed, on-delay:



                      The following is a timing diagram of this relay contact's operation:

                      Next we have the normally-closed, timed-open (NCTO) contact. This type of contact is normally closed when the coil is unpowered (de-energized). The contact is opened with the application of power to the relay coil, but only after the coil has been continuously powered for the specified amount of time. In other words, the direction of the contact's motion (either to close or to open) is identical to a regular NC contact, but there is a delay in the opening direction. Because the delay occurs in the direction of coil energization, this type of contact is alternatively known as a normally-closed, on-delay:



                      The following is a timing diagram of this relay contact's operation:


                      Dwg won't paste

                      but the contacts are the NC contacts, they open after the delay.

                      Steve

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                      • #12
                        The "normally open" contacts of a relay are open when the relay is not energized. They are closed when the relay energizes. The "normally closed" contacts of a relay are closed when the relay is not energized. They are open when the relay is energized. "Normally" means "coil not energized."

                        Look at the timing chart on page four of the datasheet: http://www.farnell.com/datasheets/204124.pdf - this diagram says what yul m6 has warned about.

                        Be sure to use the pinouts specified by yul m6 in the drawing in post #8.

                        Make sure the 15 ohm resistor and the 25 ohm potentiometer are rated for 20 watts or more.
                        Last edited by Lee Cordochorea; 12-26-2014, 11:57 AM. Reason: spellling

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                        • #13
                          Thanks Lee, I got it now. Both the fixed and variable resistor are high watted values (fixed, 20W, variable 25W). I am a bit concerned about inrush current, but since the duty cycle is low I am hoping it will be enough.

                          Steve

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                          • #14
                            lwalker,
                            I tried to send a PM but it didn't seem to go. Look in PayPal for the $
                            Steve

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                            • #15
                              I got your PM's and the $. Thanks. Make sure to PM me the address!

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