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Coil Winding Trouble

Discussion in 'Electronic Basics' started by W. Watson, Mar 29, 2005.

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  1. W. Watson

    W. Watson Guest

    We have an exhibit at our local science museum that is a 3-4' 1" diameter tube
    with about 150' of wire wrapped around 8" of one end. First 75' were wound, and
    then another 75'. An LED is connected across the wires. When a cow magnet is
    dropped down the tube, the LED lights momentarily. Some time ago someone
    deliberately broke the exhibit. I had to unwind the last 75' to make some
    repairs. When I try the new configuration out, the LED doesn't light. I'm sure
    the connections are correct. At least a continuity check at the leads shows a
    connection. I would think if 1/2 the wire is wound the opposite way from the
    other 1/2 that maybe no current would appear. Is that right?
    --
    Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
    (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
    Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

    "I know that defies the law of gravity, but, you see, I never
    studied the law of gravity." -- Bugs Bunny

    Web Page: <home.earthlink.net/~mtnviews>
     
  2. Rich Grise

    Rich Grise Guest

    At this point in time, my best suggestion is, unwind the broken 75', and
    wind it back the other way, and see what happens.

    In the interim, please do some googling on basic electricity and magnetism.

    Good Luck!
    Rich
     
  3. If the two halves are in series, that is correct. The wire has to all
    wrap around the magnets the same way, since each turn makes a
    contribution to the total voltage.

    Have you checked the LEDS to make sure they have not been damaged?

    By the way, another neat magnet - generated current demo is to drop a
    neodymium iron boron or samarium cobalt magnet down a copper pipe not
    much larger than the magnet. It falls very slowly because of the
    interaction with the magnetic field produced by the high currents that
    are generated around the magnet. The forces also keep the magnet away
    from the pipe. I even got this to work just rolling a cylindrical
    magnet down an aluminum flat strip. It rolled slowly, and when the
    magnet got near the edge, the drag forces dropped, that end sped up,
    and the magnet was steered away from the edge. It zig zagged all
    across the strip as it crawled to the bottom but never went over the
    side. An example of a gravity powered mechanical negative feed back
    loop.
     
  4. W. Watson

    W. Watson Guest

    Google? What's Google? :) Suppose I had virtually no knowledge of electricity
    and magnetism. Would you make the same suggestion? Then too I'll bet you've
    never seen the inside of my garage and the exciting time I had unwinding the
    coil and rewinding it. I'll bet ... Oh, well.

    --
    Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
    (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
    Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

    "I know that defies the law of gravity, but, you see, I never
    studied the law of gravity." -- Bugs Bunny

    Web Page: <home.earthlink.net/~mtnviews>
     
  5. W. Watson

    W. Watson Guest

    I tried 5-6 LEDs. Sounds right to me. Thanks. Weather permitting, I think I'll
    do the rewinding outside. I just had to check before facing the confines of my
    garage again. It takes about an hour in my garage. Alice-in-Wonderland would
    feel happy there.

    Yes, I'm familiar with those demos. Eddie's currents. :) I always liked that
    guy. Fun stuff.

    --
    Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
    (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
    Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

    "I know that defies the law of gravity, but, you see, I never
    studied the law of gravity." -- Bugs Bunny

    Web Page: <home.earthlink.net/~mtnviews>
     
  6. Eric R Snow

    Eric R Snow Guest

    This trick with super magnets works well with flat ones too. Take a
    strip of aluminum canted at about 15 degrees from vertical and slide a
    washer down it. It will stay on the aluminum and zip down the length
    of it. Next, lay a flat super magnet on it and let go. It just crawls
    down. It really is a good show. BTW, this is how mechanical
    speedometers work.
    ERS
     
  7. If you can get to the ends of that half, you can just cut it and swap
    the ends.
     
  8. Rich Grise

    Rich Grise Guest

    I could have been more specific: http://www.google.com ;-P
    Well, notwithstanding "virtually" means "not really", I'd say, of course.
    We all have to start somewhere, and as Commander Spock said just before
    the thin Vulcan Kirstie Alley ("Mister Savik") drove the Enterprise out of
    Space Dock, "For everything, there is a first time."
    This is a sucker bet. I've never seen the inside of your garage and don't
    expect to. ;-p

    If winding coils is giving you pains in the neck, you might need some kind
    of spool or fixture to manage the lengths of wire. Once, I needed to wind
    a fairly large toroid (1.5" OD) with some teflon-insulated wire. I made
    a shuttle out of a stick about 2' long, with notches in the ends. Loaded
    it with a passel of wire, and it only took a couple of hours to get it
    wound. But winding on a cylinder should be trivial.

    If the PITA you're having has to do with getting the exact length of wire
    wound on the coil, let that whole idea go. Go by number of turns, and
    let the length of the wire be whatever it needs to be. I used to hold
    a pencil between my knees to mount the source spool on, but the point
    kept sticking into my knee, until I figured out that I should use
    something blunt.

    When do I get the opportunity to say, "Elementary, ..." ;-P

    (what did Mr. Holmes say about the digestive system? "Alimentary, my
    dear Watson".)

    Good Luck!
    Rich
     
  9. Terry

    Terry Guest

    It's too late at night here, but a suggestion. Before you rewind try
    reversing the end connections of one of windings! Might work?
    Logic being that if one coil is reversed in winding direction to the other
    reversing connections to one of them MIGHT put the induced voltage back in
    series?
    Terry in Canada.
     
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