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This is a picture of the first secondary I made. The top turns are covered with electrical tape for corona suppression, which works pretty well.

The coil is wrapped by hand with 14" of 22 gauge magnet wire giving it, if I remember correctly, around 600 turns. The form is 3" thin wall PVC sewer pipe. I didn't dry it or do anything fancy do prep it. I coated the turns with 6 or so coats of spray shellac. This thing has sucked up more abuse than I ever would have thought possible. It has been powered by everything from a single ignition coil to a 15kV/120mA NST. It has put out streamers approaching 3', and has often put out 24". It does have at least one fatal construction flaw, which is that the wire is led through the interior of the coil and the ends aren't sealed.

As you can see, arc over occurred inside the form. Surprisingly, it still works although it is easy to tell that the carbon tracks are shorting out a number of turns during operation, as it tunes as a coil of less turns would. Amazing though, to see 18" of spark from such an abused piece of equipment!

This is a secondary wrapped by hand with 7" of 30 gauge magnet wire on a HDPE dishsoap bottle.

Once again, I led the wire through the inside of the form. I hadn't blown the first coil yet when I wrapped this one! I don't really push it, as this is the one I use for classroom demonstrations. Powered with a 7kV/23mA OBIT, it puts out 6" streamers. One of these days I'm gonna hook it up to an NST...

This is my latest secondary. It has 48" of 20 gauge double polymide coated magnet wire, for close to 1,300 turns, wrapped on a 6.5" PVC form. I kept the PVC indoors for a few months, then sanded and acetone washed it inside and out, taking care to remove all lettering.

For this coil I made a winding jig, Hillbilly style. The first job was to give the form an axis to spin on. I took a 5' piece of 3/8" all thread stock and two irrigation covers (the green thing on the end of the form) . I drilled a 3/8" hole in the center of the covers, and placed them on the ends of the form. Then I ran the all thread through the whole affair, tightening it down with nylock nuts. I also used loctite to prevent the nuts backing off. I cut the all thread so that one end was about 4" long and the other around 2".

I took two 8" angle brackets, and drilled out the upper hole on one side of each to accept the 3/8" all thread with a little room to spare. I mounted them on a piece of 4" by 8".

The picture above shows the jig being powered by a 42 rpm gear motor. As you can see, it is professionally attached to the board using tie wraps. I attached a 1" belt drive pulley to the motor and to the shaft of the jig. The small bungie cord visible is used to tension the belt. This is the setup I used to coat the coil. The gear motor was not hefty enough to turn the form during wrapping, so I used a 1/2" drive angle drill on a variac to perform this operation. I used a milk crate for a wire dispensing device, putting the spool on a dowel run through the sides of the crate. A bungie cord was used to tension the spool. I would advise making sure you have a good adjustable tensioning system set up, loose wraps will make you cry, as we will see later.

Contrary to what one might think, it took less time to actually wrap the wire than it did to set up and test the jig. Once I got going, it all went quite well, although next time I think I would round up an assistant. Kicking the variac switch on and off with your toe is a pain! I used a credit card to push the wire tight, and tried to keep even pressure on the turns. I think it took about 2 hours of nonstop wrapping to complete the job.

And then came the Great Aquarium Disaster of 2001. I awoke in the middle of the night to the sound of a pump sucking air, and discovered that a 30 gallon aquarium had blown a hose and tossed nearly all of its contents on the floor. Since I was enjoying myself so much, I decided to drop a 5 gallon container of water on the floor to add to the fun! Lucky it was plastic. Anyway, the long and short of it is that the secondary was uncoated and underneath the aquarium. And got soaked. And when I dried it out, it got too warm, and some of the wraps loosened up and didn't return to their former shape when cooled. Ugh.

So, I had to loosen the upper section of the coil carefully, and work all of the slack out of the coil. This process took considerable longer than wrapping it originally and setting up the jig combined. The lesson to be gained here: Tension the wire well and evenly when wrapping, and coat the dang thing ASAP! Luckily, the end result was quite nice. I coated it with 8 thick coats of polyurethane, using the set up pictured above. The plastic tent is to keep dust off, although some still got in.

I was determined to have a sealed secondary with no wires inside this time. On the ground end of the coil I made an inletted contact, using a dremel tool to do the carving. The contact is heavy copper, rolled to the curve of the form and glued in place. The secondary wire is soldered to the back, full length along the contact. I saw this idea on someone's web site, and now can't find it. If anyone knows who this is, please let me know so I can properly credit them. I went this route not only to avoid interior wires, but for easy coupling adjustment. The socket that holds the coil will have the ground connection. The ground end of the coil is sealed with an acrylic disc glued inside of the form.

On the output end of the coil, I sealed the end as I did the other, with a 5/16" acrylic disc glued in place flush with the end of the coil. Then I took a disc of 1/2" acrylic the size of the outside diameter of the form, and cut a slot in it from the edge to the center, and drilled a hole in the center. I used a 1" forstner type bit to make a inlet to accommodate the head of the bolt. A 5/16" toilet bolt with the head ground flat is employed here, and the disc is threaded to accept it.