24V DC solenoid valve

Discussion in 'The Projects Forum' started by caffeineboy14, Jan 18, 2012.

  1. caffeineboy14

    Thread Starter New Member

    Jan 18, 2012
    2
    0
    Hi,

    I have an application where I need to control a solenoid valve. It takes a 24 V DC input and it's connected to a switch and a 120AC to 24VDC power. I want to add a controller or timer which I can program it such that when I can start the program / push on the switch, it will turn on for say 8 mins then turn off, and turn back on after 20 mins, then off, and on after say 2 hours and off. The duration / time should be easily changeable if needed. What are my options here? Can time switches do the job? or do i need a controller? A microcontroller? or a PLC type controller? and how do I hook them up ( what the circuit diagram looks like) and what other components do I need?


    Thanks you for the advice.
     
  2. mcasale

    Member

    Jul 18, 2011
    210
    12
    There are many ways to do this, but the best for YOU depends on how comfortable and confident you are with various technologies.

    I would NEVER touch a PLC. I have been forced to use them against my better judgement.

    Probably the best way to go is an MPU like the Arduino or Basic Stamp driving a MOSFET, which in turn drives the valve. How much current does the valve require at turn on?

    Using an MPU you can also power down the valve coil after it turns on. Many DC valves will stay ON with only half the rated supply voltage. This will save energy.

    Hope this helps.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    Your description sounds a lot like a sprinkler controller, which you can buy at a local hardware store. On sale, they're under $10 and can control something like 4 channels.
     
  4. caffeineboy14

    Thread Starter New Member

    Jan 18, 2012
    2
    0
    Which mosfet do i need? and how the circuit is going to look like? I am not sure about the current, I can go double check on that. Right now there's another a limit switch connected to the valve, which takes 120V ac to operate. I am wonder if it is easier to implement a switch + a controller that just take a 120v ac from the wall and output 120v ac to the limit switch according to the programmed schedule but I am not sure how to connect all these stuff together and which controller / switch to use. I do have some experience with plc programming and microcontrollers like arduino. I probably prefer programming with something like assembly, c , vhdl than plc ladder logic.

    Thanks!
     
    Last edited: Jan 18, 2012
  5. mcasale

    Member

    Jul 18, 2011
    210
    12
    You need to determine the required valve current. It all depends on that.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    For the current you likely need (less than 2A?), almost any N-channel MOSFET in the TO-220 package will work. I have a bunch of IRF540N and would use one of them. You'll want to be sure the max current rating of the MOSFET far exceeds (by >2X) the current demand of your solenoid. There's almost no penalty or cost for over-specifying. If your control circuit is at 5v, choose a logic level fet that is fully on at 5v. A "regular" fet such as my IRF540N requires 10v or more to be fully on.

    Your control signal will go to the gate pin of the MOSFET, whose source pin will be at DC ground. The low-voltage side of the solenoid will connect to the drain pin of the MOSFET. Voltage at the gate opens a path to ground for the current coming through the solenoid.

    The beauty of the MOSFET is that it needs almost no current - just a voltage - at its gate in order to control the drain-to-source current flow.
     
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