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I have questions about an electromagnet coil and the winding technique

  1. Aug 8, 2013 #1
    Hi guys, I am building an electromagnet to use mainly for its reaching properties. I want to have a large air gap. I don't care if the magnet can only lift a paper clip but I do care if it can move it from a 15 to 20 cm distance or more. I only have 1 core to work with so my choices are only with the winding technique
    I am not an engineer nor do I have any electrodynamics background and the basic questions I already figure out from googling it. This is what I cant figure out from the web, please help.

    1.- Can I wind parallel wires in my magnet?, lets say 2, 3 or more at a time? you can see my attachment that shows a red, red/blue, red/blue/green configurations. My reasoning is that if I use 3 I can use 3x the amperage, save winding time and since the length of any individual wire is 1/3 of the traditional winding, it would have less resistance, more electric flow, better magetic field. Does this make sense, and if so, is it regularly done, any pointers in where to look some examples.

    2.- Winding the first layer always looks beautiful!, second coming back not so much, third, ugly, from then on, a horrible mess, with huge gaps and air pockets. The reason is I am doing this by hand and my core is so damn heavy. But I also noticed the grooves between wires from the previous layer are oriented at cross angle from the direction of the current layer. This promotes skiping and bigger air pockets. But if I always wind in the same direction and have the wires just fall onto the groves from the previous layer at the same angle, (see the right side of my second attachment), the air between wires is also much smaller. The issue is that with every turn you end up in the same side and need to bridge to the other side to start the next turn. The figure shows layer 1 blue going from left to right, then bridges outside the coil to layer 2 green, then the layer 3 red. The second row of figures shows an exaggerated view of how layers lay onto each other with this and the usual technique and the third row shows a cross section of the wires and the difference in air pockets (in green). Also the wires are closer to the core with each turn in this method. I did this, I am not sure I see a difference, I will troubleshoot this but I wanted to ask smarter people than me to see if some theory will save me some of the time and money I spend doing this empirically.
     

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    Last edited: Aug 8, 2013
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  3. Aug 9, 2013 #2

    Baluncore

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    The problem you may encounter is voltage breakdown of the wire insulation. When powered normally with a DC voltage that may not be a problem. But when the power is disconnected there will be a flyback voltage spike. Unless that spike is caught by a power diode across the coil it may breakdown the internal insulation.

    Consider winding several coils on formers that can then slide onto your core. That will separate the different voltage sections. It will also mean that voltage changes are minimised between layers inside each winding. The inner terminal wire of each winding should have an insulation sleeve to keep it clear of the core, or the other windings. The formers can be wound on a lathe or hand drill which will make a much neater winding. If you hand feed the wire from the right direction with the right tension it will remain neat.
     
  4. Aug 21, 2013 #3
    Thank you for your advice. What can I use as a former? Can I get the custom made for the dimentions I need? Any tutorial you may point me to?
     
  5. Aug 21, 2013 #4

    Baluncore

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    I do not have any idea of your coil former dimensions or sectional profile....
    In effect you make bobbins out of card joined with glue.

    Start by making one short test sleeve that will slide over the core. You will be using several of that size. Next find some tool to wind your coils on, (a drill, lathe or whatever), make a mounting jig on that tool to hold the sleeves while you wind them. Now make more sleeves to fit the jig.

    Knowing the depth of the windings you can now make end plates with a hole to fit the sleeves, they will prevent the windings spreading. Glue these end plates onto the sleeves, at right angles to make neat winding bobbins. Lacquer or paint could be used to harden card bobbins, or you could be using a different non-magnetic material such as thin plywood or plastic, get creative.

    When set, you mount a bobbin on the jig and then carefully wind that bobbin. The start of the winding will have a short length of wire passing out through a very small hole in the end plate. That will have an insulated sleeve to protect it. Wind neat layers until the required number of turns, then tape, glue of tie off the free end and cut it to length. Put a protective sleeve on that wire also.

    Once you have made several windings on bobbins you can slide them onto the core. It will pay to wedge them tightly in position so they don't move. I would use hand carved wooden wedges fixed in place with lacquer. Then join the coils together in series or parallel to satisfy the voltage and current available from your power supply. Make sure you know which way the coils are wound so they can all be arranged to work together in the same direction.

    If the bobbins are going to be wired in parallel make sure they each have about the same resistance or length of wire, which if they are neat will be the same number of turns. If they will always be in series then they can all be different.

    If you cannot work out what to do, ask a specific question.
    You could google “coil winding tutorial” or similar.
     
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