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How to build a simple solenoid?

Discussion in 'Electronic Basics' started by lukyman, Mar 9, 2005.

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  1. lukyman

    lukyman Guest

    Hi, All:
    I am helping my kid with a school robotic project. One key element is
    to use solenoid to release a latch. The project limits total power
    voltage no more than 9 volts. This solenoid does not need to generate
    strong force, just to pickup weight of an egg will be fine. Can anyone
    please help me by showing one simple example? What gage of wire, how
    many round coil around how big a plastic tube and size of the
    plunger,...,etc. that use only 2 to 3 AA or AAA batteries. Thanks
  2. Methinks you need to specify the throw
    distance for this solenoid. If it just has to
    hold the egg, once thrown, it will consume
    less power than if it must exert that force
    over the whole throw range.

    From your description, I would worry about
    how long that solenoid could be energized
    without depleting the battery. Perhaps that
    should be added to your requirements. You
    may want to devise something with a latch so
    that continuous energizatization is not needed.
  3. lukyman

    lukyman Guest

    Thanks Larry, you're right. I just forgot those things. The throw
    distance is only 1/2 inch. It's not continuous holding. It just release
    the latch that's all. I will use spring to hold the latch. What I need
    is really like an electronic mouse trap, since I am not allowed to
    touch the "trap" by hand, I can only use wire, you know what I mean.
    The force to release the latch is really small. The project requires 2
    AA or AAA batteries only. You think that would work?

  4. Sure. You may need an electrolytic cap to
    supply the pulse current needed to move the
    solenoid plunger. I would get a small permanent
    magnet and experiment with a coil whose axis
    is colinear with the magnet pole. You should
    be able to repel or attract that magnet with a
    short enough pulse to not warrant much worry
    about battery consumption. I would start with
    #32 magnet wire and 40 turns. For your ~3V
    drive, there will be an optimum turns-count
    somewhere if you are willing to find it. Since
    this is a one-shot operation, I would not spend
    much time trying to devise an efficient, closed
    path magnetic circuit unless battery power is
    really precious.
  5. lukyman

    lukyman Guest

    Can I overlap those 40 turns or make it 2-3 layers? Does it have to be
    very neat? Thanks again!
  6. Both. Get the winding into as small a volume
    around the magnet to be moved as you can.
    That could mean even more layers.
    Only if you want a gold star from teacher.
    Welcome again.
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