11: Adding the paper at the end of a layer
Here you can see how using the edge of the paper, you make sure that the wire is correctly positioned to start the next layer on top of its last turn. Also try and arrange that the paper joins are as close to the ends as possible. This avoids adding unnecessary bulk to the winding in its centre region. unnecessary bulk to the winding in its centre region.
12: Fitting the paper
There should only be a minimal overlap of the paper's edge (Blue), but there must be at least some, ideally 0.5 inch or 1 cm.
13: Guide lines
On each new layer I marked the extent each side that the winding would extend to. I left a clear half an inch at each end. This is to avoid a flash-over occurring at the edges, which can occur if there is insufficient paper. Do not use a pencil or black marker, both could possibly conduct the HV.
14: Securing the Primary with thread
This is not really needed, but it may stop the primary turns from slipping down.
15: End of secondary wire being anchored
The method I adopted here was to use a simple cable tie taped across the coil. The secondary wire was then wound on top securing it. The raised end of the cable tie (to the right) will stop it from pulling out. I then made a small hole in the cable tie with a hot pin and threaded the wire through it and tied it off. You can then solder a heavier wire for the lead-out onto the magnet wire.
I had the thicker lead-out wire inside a piece of plastic tube, which I was able to slide down over the tapered end of the cable tie. This not only covered the soldered joint, but also made a stiff fixing to stop undue flexing of the delicate connection.
16: Ready to assemble
17: Ready for the oil
I re-used the old transformer oil again. I also had a large 6H oil cooled inductor which also donated some of its oil.
18: The picnic box was a perfect fit
19: The finished transformer.
The primary is a bifilar winding of AWG #14 / SWG #16. The normal current capability of this gauge is around 9 amps under oil. But the bifilar winding means it will carry 18 amps easily, with short runs at around 21 amps.
The maximum output is 10,900 volts at 537 m/amps this gives 5.85 kva. This draws up to ~21 amps at 276 volts (Variac on maximum) on the primary through the current limiting ballast shown above.
The weight of the whole assembly in the box with oil is 31 Kgs or 68 pounds.