Howdy,


Kapton tape is great stuff. It's best to use at least
two full wraps. Some standards for reenforced or double
insulation require three wraps where any two can
withstand the hi-pot. Even where it's not required
the two full wraps minimum is generally a good practice.

The breakdown could be due to insufficient creepage distance
between the windings. If you can build up the bobbin with
tape at both ends to form a barrier which keeps the winding
centered it will help.

Another thing to do is sleeve the wire where it leaves the
winding. A tape "pad" under the lead-out where it crosses
the barrier tape is another option.

Although Kapton is resistant to temperature you're not building
with an insulation system where the components have been aged
with each other at high temperature in oxygen to see if there's
any degredation due to chemical reactions. So the temperature
rise of the transformer should be limited to 65C above ambient.
If it's too hot to hold your finger on for about three seconds
it's too hot. I'd call it a rule of thumb but I'd use the
index finger for that test.

A person should to follow the applicable standards under fear
of fire, injury or death. And as always, all of the above may
be horribly wrong.


73,
Grumpy