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Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Hello, does any one try to use kapton tape or film for Flyback transformer insulation ? I need to make two transformers with 30KV output capability, and started to search for insulation. Idea is to use U core, , wind secondary dipped in epoxy, and use kapton tape in between layers. U cores: Or maybe some one know where to buy larger U shaped cores, since not much winding space left...
Registered Member #3908
Joined: Tue May 24 2011, 09:40PM
Location: Gilbert, Arizona USA
Posts: 68
Good question. I've learned some lessons with this already. I have used 1mil Kapton successfully, with P221 acrylic adhesive for this exact task. Beware, there are two adhesive choices; acrylic and silicone. The silicone may affect and/or contaminate an epoxy encapsulation afterward. Often resulting in epoxy voids during catalyzation. If you're potting, you'll have better success with the acrylic adhesive.
The manufacturer identification is: P221 for Acrylic based adhesive (permanent), and P222 Silicone based adhesive for high temp (500f) operation (removable).
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
i guess i will stick with plexyglass insulation. Idea shown in picture: Blue is windings Red is Ferrite core Green is plexy glass, made from 1mm and 2mm sheets, and all void space would be willed with epoxy.
I really need bigger U shape , but i have 6mm of plexy glass for 30Kv, and 4mm for 3.3kV in between windings, where epoxy should be, again, no problem.And quite low parasitic capacitance, witch is good
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
You can buy bigger cores. You can also sandwich cores together. Another alternative that is popular with HV'ers is to arrange four sets of cores in a X shape, with the primary around the intersection, and secondaries mounted on the extremities. This creates a core with four times the power of one set and aids insulation on the secondaries, It also helps with reducing capacitance problems (I think). It also aids cooling.
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Patrick wrote ...
how much insulation do you have between the primary and high side secondary? ill you vacuum draw the epoxy in?
I have "special" copper wire, 10KV rated, it will be submersed in epoxy while i will wind it. i will have at least 4mm of Plexiglas to core, and another one 2mm for primary coil so in short: 8mm of Plexiglas between first and last turn to with respect to core, and 6mm respect to primary. and in between windings i should get 4mm of Plexiglas and 1mm of epoxy for 3.3KV I guess i will leave ferrite core floating, or maybe use >1M resistor to ground, so it will not drift to far from zero.
Or even better idea, i will use two resistors like 100M in series in secondary, and connect core to middle voltage, so i will get 4mm of Plexiglas for 15KV for secondary, and 15KV for 3mm of 1capton+2Plexiglas for primary just will resistors be able to keep transformer ferrite core under that voltage ?
NO, i don't have equipment to do vacuum filling, i just going to heat epoxy, it will be like water, and fill it, best i can do in my mind. Figures looks like right, with lot of place for error, but what i don't like that maybe i can't get enough voltage from transformer
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Kapton Insulation
