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2 Channel timer project

Discussion in 'General Electronics Discussion' started by richardthistle, Apr 27, 2013.

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  1. richardthistle

    richardthistle

    2
    0
    Apr 27, 2013
    I am in the need for 3 units that will do the following. Would like a programable unit but not sure where to look or what to use........

    I have an electric motor that drives a hydrolic pump, and then an electric valve that causes hydrolic drive motor to start or stop after pump is running. Would like a circuit that can upon pressing a start button via an input turn on one relay to start the hydrolic pump wait 5 seconds for the pump to get to full speed and then turns on the second relay to the valve for say 2 min. Unit would also need a stop input for emergencies.And then if no input on start button is received within 5 min shut off the relay that runs the pump. If start button pressed again unit starts over. Any ideas? I am pretty technical but not aware of what is out there to use.

    Thanks
     
  2. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    What's the voltage of electric motor? Is it dc or ac motor?
     
  3. richardthistle

    richardthistle

    2
    0
    Apr 27, 2013
    Both are AC. The valve is 110 motor is 3 phase but I have enough knowledge to get it to work if the timer is single phase. Just put a contactor in line ahead of this device. If low current I can use a relay for the valve as well.
     
  4. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    I have worked before in a knitting company 43 years ago and we use 3 phase motor, I know there's a wiring configuration for slow and high torque for the ac motor then a timer switch the magnetic contactor to another 3 phase wiring configuration for higher speed or once inertia was reduced. I forget which of the "Y" or " Delta" connection. Do you need this kind of switching connection?

    Timers can easily be built using NE555 to activate the solenoid of 3 phase magnectic contactor.
     
    Last edited: Apr 28, 2013
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Here's a circuit that should do what you want.

    [​IMG]

    Here's a circuit description.

    The circuit requires a 12V DC power supply. Current consumption will be 500 mA maximum so I recommend a power supply rated for 1A.

    SW2 is a normally closed pushbutton for Emergency Stop. Pressing it breaks the circuit and causes the relays to drop out. SW1, the Start pushbutton, must then be pressed to start the circuit again.

    When SW1 is pressed, current through DPS energises K1 which starts the pump and connects the 12V supply to the circuit's main 12V power rail.

    On power-up, CROT is discharged, and U3's output (pin 3) is high. Current flows through DPK and keeps K1 energised, keeping the whole circuit running. U3 is described in more detail below.

    Upon power-up of the circuit, CPSD begins to charge through VR1. After about five seconds (set by VR1), the voltage on CPSD reaches 2/3 of the supply voltage and U1's output (pin 3) goes low, and stays low until the circuit is powered off and restarted again. This state (U1 pin 3 low) indicates that the pump is (presumably) running at full speed.

    While SW1 is pressed, Q1 is biased ON, and discharges CVOT, the timing capacitor for the valve open timer. This causes U2's output (pin 3) to go high, and if U1 pin 3 is low (pump is up to speed), current flows through DV and energises K2, which activates (opens, I assume) the hydraulic valve.

    When SW1 is released, Q1 turns OFF and CVOT begins to charge through VR2. After a delay of about 120 seconds (set by VR2), the voltage on CVOT reaches 2/3 of the supply voltage and U2's output (pin 3) goes low, closing the hydraulic valve.

    Every time SW1 is pressed, CVOT is discharged. While CVOT's voltage is less than 2/3 of the power supply rail, K2 remains energised, and the hydraulic valve remains open. Pressing SW1 again while the valve is active will discharge CVOT and reset the timeout. If SW1 is held closed, the hydraulic valve will remain open indefinitely.

    U3 provides an overall timeout and shutdown for the circuit. It activates when the pump is running and the valve has been closed constantly for about three minutes. At startup, CROT is discharged. While the valve is open, the bottom contacts on K2 keep CROT fully discharged. If the valve is closed, CROT charges up through VR3. If the valve remains closed, after about 180 seconds (set by VR3) the voltage on CROT will reach 2/3 of the supply voltage and U3's output (pin 3) will go low. Assuming SW1 is not being held in, there will be no source of current for K1's coil, and the whole circuit will shut down until SW1 is subsequently pressed.

    RPD is connected across the circuit's main 12V rail to ensure it falls to zero when K1 opens. This ensures that CPSD and CROT will discharge to close to 0V quickly, through their respective discharge diodes DPSD and DROT.

    Safety notes and disclaimer

    If you use this circuit to control mains voltages and heavy equipment, you must take full responsibility for all safety implications, including the ones I list below, but also including any other safety requirements that relate to your application, the details of which I do not know.

    As designed, the circuit can switch mains voltages directly. These mains voltages may be present on one set of contacts of K1, and one set of contacts on K2, and on CN1 (if used). These connections must be fully insulated and isolated from the other circuitry. If you are constructing the circuit on stripboard, remove all copper around the relevant pins, connect to them with mains-rated wire, and cover all live points with epoxy or hot melt glue.

    Relays K1 and K2 are rated to switch up to 8A and up to 250VAC. You can substitute any safe relay with a 12V coil and DPDT or SPDT contacts. You may prefer to use smaller, low-voltage relays, and have them switch the 12V supply to the coils of larger interposing relays. That would keep the mains voltages out of the circuit and improve safety and reliability.

    It is up to you to determine that the critical components (SW2, K1 and K2) are suitable from a safety point of view. It is also your responsibility to comply with any applicable safety regulations, especially those relating to the accessibility and reliability of SW2, the Emergency Stop switch. I explicitly disclaim knowledge of, and responsibility for complying with, these safety regulations.

    Special and safety-critical components:

    My recommendation for SW1 is a green SPNO pushbutton made by E-Switch and available from Digikey: http://www.digikey.com/product-detail/en/RP3502MAGRN/EG1934-ND/280452 for USD 2.79.

    My recommendation for SW2 is a Honeywell high-quality Stop pushbutton with SPDT contacts. You use the normally closed contact for this application. It's available from Digikey: http://www.digikey.com/product-detail/en/87943-08/480-2082-ND/1162812. Price is USD 20.76. You can of course substitute any fully insulated pushbutton with a normally closed contact but this is the one I recommend.

    Relays K1 and K2 are heavy duty PCB-mount DPDT relays, part number RT424012 from TE Connectivity, available from Digikey: http://www.digikey.com/product-detail/en/RT424012/PB967-ND/1095291. Despite their impressive specifications (8A contacts) they cost only USD 2.59. See the note on using interposing relays, above.

    If you construct this circuit, please post photographs of your board, and any mains-voltage wiring. This may enable me, or others who use these forums, to recognise any possibly dangerous construction you have used, although we make no guarantee.

    This design is provided with no warranty whatsoever. It is your responsibility to ensure that it works to your satisfaction, and it is your responsibility to ensure that all safe practices are used when constructing the circuit and when using it. You should also check with your insurance company to see whether using this design will (or may) have any implications.

    By using this design you agree to take full responsibility for its safety and its safe use.
     

    Attached Files:

    Last edited: Apr 28, 2013
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