Insulate the secondary of the Tesla coil with a PET plastic bottle

[thedark]

It is possible to do it with a plastic bottle made of PET material such as a soda water bottle, etc., since the polyurethane paint is out of my budget, I have thought about using that bottle and after having the exact dimensions with a hot air gun, shrink the plastic in the secondary and if it does not reach the height, a joint would be made between the two layers with about 5 cm above the other, would it affect anything if I use this plastic?

[MRMILSTAR]

The primary purpose of the varnish is to hold the windings together so that they will not fall apart during big temperature changes. The varnish does little to increase the insulation. The coating on the wire does that job. If the wire is double-build or heavy-build, the breakdown voltage can be up to about 10 KV. Since using plastic bottle material won't do anything to secure the windings against temperature changes, I don't see much point in using it. Brush-on varnish isn't expensive. A single small can will easily give you two coats on a secondary coil.

[davekni]

I have thought about using that bottle and after having the exact dimensions with a hot air gun, shrink the plastic in the secondary and if it does not reach the height, a joint would be made between the two layers with about 5 cm above the other, would it affect anything if I use this plastic?

Interesting idea.  If it would shrink only radially as heat-shrink tubing does, might work well for both insulation and to hold windings in place.  My concern is that I think PET bottles will shrink axially too, which may or may not create a problem.  I could imagine axial shrinking pulling windings out of place and creating overlap.

The varnish does little to increase the insulation. The coating on the wire does that job.

Depends on thickness.  I'd probably agree for standard air-dry varnish.  Two-part epoxy coatings can be thicker and provide useful insulation.  My DRSSTC has 7 coats of epoxy about 1mm thick each.  Initially had only two coats.  Additional five was a big help in minimizing racing sparks along secondary.

[Michelle_]

You can just wrap it with kapton tape, it’s cheap, insulates, and will hold it together. PET has a pretty high melting temperature, so depending on what the secondary is wound on (I’m guessing PVC since that’s what everyone is using) it might degrade that by the time anything happens to the PET.