Secondary Coil Construction
I purchased an eight inch diameter acrylic tube from McMaster Carr. Other
materials would do but I wanted the look and dielectric performance of
the acrylic. I purchased the wire from Wiretron at http://www.wiretron.com/magnet.html
I purchased about ten pounds of #22 enameled wire.
I set up a simple lathe arrangement,shown above, using a battery drill as a power source. I used a piece of all-thread rod through the center of two wood plugs that fit in the ends of the tube. A larger disk of ¼ inch plywood acted as a large pulley which was driven by a friction tire fitted to the drill. The drive tire was a piece of ¼ inch fuel line cut to about an inch long and pushed onto a 2 inch ¼-20 bolt. I put on a couple of nuts to compress the tubing to hold it in place. This arrangement worked well. I built a separate holder for the spool of wire so I could slid it along as I went guiding the wire with my hands.
In this close-up you can see how I applied pressure on the drill to maintain friction. The block the drill is mounted on, pivots on the pin to the right of the drill. The spring maintains some pressure.
My wife worked the drill as I guided the wire. Periodically I would tape the wire in place when we wanted a break. I wound about 25" of wire for about 900 turns. At the top I gradually spread out the windings to feed the top load. I took about two hours to wind it. I then taped the ends securely and applied a few layers of thin epoxy resin followed by about 5 layers of thicker epoxy. The thin resin soaked into the winding nicely. I obtained the two-part epoxy at West Marine.
I finished the ends with Disks made of ¼ inch polycarbonate. I cut a smaller disk to fit inside the tube and a larger disk that matched the outside diameter. I epoxied the two pieces together then I epoxied the ends onto the secondary tube. I did not drill the tube or the ends. This was to avoid the possibility of arcing inside the tube. This is a very good idea. It is recommended that nonflammable glue be used to fasten the end caps since you could trap an explosive mixture of volatile fumes and air.
Here are some photos of the finished coil:
This photo shows the top end of the finished coil with the small toroid attached. The toroid is formed on two cake pans pop-riveted together. The pans are attached to the top of the coil with the two ends of a pvc flange union. The two parts of the union are joined with a short length of pvc pipe. One of the flanges is glued to the top cap of the coil using "Goop"
The coil is connected to the toroid with a tapering strip of sheet copper.
Here you can see a detail of the connection at the top of the coil. The end of the winding gradually separates and connects to the copper strip in a smooth helical line so that no sharp bends are formed where an unwanted discharge might occur. The wide end of the copper strip is soldered to the inside of the cake pan.
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