Flyback Winding

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Dunn by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mdunn-at-wmwmeyer-dot-com>


Gentlemen:

I am new to the "List", but I've been building HV units for some time to
power Plasma Globes and Jacobs Ladders with old Flybacks and Ignition Coils.
I haven't yet graduated to Tesla Coils.

Currently, I'm trying to wind my own flyback secondary(I do this instead of
sleeping) to improve performance and have a number of questions specifically
related to that.  Old flyback secondaries were short axially and big in
diameter.  In many cases there is plenty of room on the core above and below
the secondary to use.  Why not make them tall and big in diameter?  Is the
danger that they will arc to the ferrite core?   If  I carefully wind the
first course right hand and run the second course back the other way over
the top(left hand), then the last winding in the second course is directly
over the first winding in the first course(If I wind 10 courses then this
same issue is present in every other course on either side)  Are these apt
to arc because of the differential voltage between these windings?  Someone
told me a rule of thumb that the flyback will generate about 2-4
volts/winding in resonance with a 12 Volt primary.  Thus if I put 100 turns
in each course, then the subject windings will be 400-800 volts apart.  Any
comments?  Does the 4 volt/winding rule make any sense or is it strictly
dependent on the gain associate with the system's resonance?

I am using 30 ga enameled magnet wire.  Is another film coating better?  I
seal each course in epoxy and wrap with epoxy impregnated brown paper to
give a guaranteed gap between courses.  Any suggestions on the thickness for
that gap or a superior construction method?  It seems to me that the
dielectric constants aren't that far apart for these insulating materials.
Since I am embedding in epoxy anyway, a 1 mil coating on the wire is not
important.

So far I've been lucky enough not to blow any of my prized old disc shaped
secondaries.  Therefore, I've never disassembled one.  I've been told they
typically have 1200 turns, but they don't seem to be big enough to support
that number.  Anybody have different information?  I've sawed in half the
potted newer style flybacks(circa 1970) and find nowhere near 1200 turns in
their secondaries.

Thanks for any help

Mark D.