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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
At $30 for a 36 yard roll I'm not so sure kapton is the best option. I'll test the dielectric strengths of a couple different hardware store tapes to see what is good.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
I'm not sure it is so expensive ;)
Besides that, the only thing that worries me is inter-layer connections... but if you wire two turns of kapton for each layer, you can make one turn of wire between kapton layers and start over a new layer at the right place
I'm gonna build a flyback with kapton if I have time, and we'll see
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
I got Kapton and Polyester tape from tapecase.com, they have just about every sort of tape you can imagine. The polyester stuff is what commercial toroidal transformers are insulated with. It's nice stuff, similar to packing tape but thicker and slightly stretchy so it conforms better. I got some of the thin solid yellow stuff too but I forget what that was called.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Ok, white tape still burned through at 1.5kV. PVC electrical tape burned through at the same voltage, while masking tape couldn't handle 600V.
3 layers of electrical tape seems to stand up to 4kV, and that ought to be sufficient to insulate between winding layers. Each layer will have maybe only 15 turns of wire anyway. I'll try testing some clear plastic tapes tonight.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Overhead projector transparencies make pretty good insulators too. I've cut them up into strips to insulate HV transformers. Part of the challenge is that high frequency is much harder to insulate than DC.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
I'm well aware of the OHP sheets, the issue is they can't be pulled close to the windings to prevent corona. Hmm...
I got it: A combination of teflon tape and electrical tape. The teflon does the insulating while the electrical tape does the "holding things together" part.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Test results: Three wraps of teflon around a wire stand up to 3kV (AC peak) with very little corona. Five wraps of teflon stand up to 5kV nicely. I think I found my insulator!
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Step 1) Wrap about 23 turns of wire. Step 2) Cover that wire with 5 turns of teflon Step 3) Wrap with one layer of e-tape and repeat step 1
So far I have 9 layers, occupying a space of 1cm. I'm aiming for 25 layers, and if the FBT puts out 20kV then there will be a maximum of 1600V between two layers, certainly enough for 5 teflon layers and 1 e-tape layer to withstand. I don't expect there to be much corona in there because the teflon is pulled tight to the wire, though I'm not sure. As long as I don't expect any spectacular voltages out of this flyback then it'll probably live. I could also go for 40 layers and 30kV output, that would give me a maximum of 1500V between layers.
I used the 28gA so there should be some decent current going on. Hot arcs ftw.
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