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Release Type Solenoid

  1. Jan 2, 2008 #1
    Hi All,

    I have a project and was hoping for some help here. I need to build a type of solenoid that will move a 3/4 inch diameter rod vertically about four inches and hold it there for a minute plus. This will have to be powered by a battery so energy use is a concern. I have an idea on how to do this but need some input regarding the feasibility (not an engineering major). This will not require any additional linear energy beyond just extending the rod itself. Since this would be outdoors with space limitations, I want to avoid using a motor.

    Would it be possible to:
    Use a permanent magnet (tube or disc) to hold the rod in the retracted (bottom) position with a compressed coil spring below suitable to lift the rod.

    Wind the permanent magnet to cancel the permanent magnets field and release/extend the rod using a DC pulse to the windings. Momentum of the released rod would carry the rod beyond the tube magnet (and spring) to a second smaller "holding" permanent magnet (also wound).

    To retract, a second DC pulse to the "holding" magnet would release the rod and allow it to drop into the lower permanent magnets field and be drawn all the way down and recompress the spring for the next cycle.

    The rod can be sectional (metal/plastic) and the target weight of the rod is about 3 ounces.

  2. jcsd
  3. Jan 2, 2008 #2
    What do you mean by "Wind the permanent magnet to cancel the permanent magnets field" How do you wind a magnet?

    Have you looked into magnetic latching solenoids? Company called Ledex sells them (among others), you can buy one and benchmark, or just apply it??
  4. Jan 2, 2008 #3
    What I mean is wire wound around a regular permanent magnet. I want to cancel the field of the permanent magnet to allow the rod to release. If energizing a coil around the permanent magnet wont do it, is there a method of doing this?

    I understand that a latching solenoid would do the trick but I have looked at a lot of off the shelf items (including Ledex) and none of them have the travel that I need (not even close).
  5. Jan 2, 2008 #4


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    If space and power allow it, you could add a levered linkage to increase the travel.
  6. Jan 2, 2008 #5
    It seems to me that you need to start with "energy in = energy out" equations since you are using a battery. Creating a magnetic field with a winding to overcome a permanent magnet may take more juice than you can afford. Unless the magnet is a weak ferrite which may not have enough force. What you may need is a clever magnetic ciorcuit with proper pole pieces, etc.
    You can Google "electro-magnetic valve actuator" to see some examples of magnetic circuits in patents or articles.
    I am not sure what is your strategy / flexibility. Do you want to ( can afford to ) have a custom design, or should you leverage a proven technology (like a latching solenoid ) and find a way to adopt it.
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