Hi, Scott,Modern flybacks are wound on a slotted bobbin of PVC. The ones I worked on were for TV sets and had 16 slots on a bobbin about 1.6"dia, 2" long. The slots were about 1mm wide and 5 or 6 mm deep. This resulted in a set of 16 little pancake coils embedded in the bobbin. There was at least 4 or 5 mm of material between the inside of the slot and the ID of the bobbin. There were slanted passes between the slots for the wire to go to the next slot, although a longitudinal groove milled through all the slots works fine and is easy to do. The wire was #39 (almost visible) and there were 300 turns per slot. Having many slots like this greatly reduces the interturn capacitance and is much easier to wind than one with paper layers--you can do it on a lathe or even an electric drill. The whole coil assembly was in a shell and was potted in epoxy under vacuum to eliminate voids.
The core was rectangular. Its diameter was about 5/8 inch and was made in two halves spaced with two 0.019 thick nonmagnetic spacers to avoid core saturation. If I were making one today, I would make the bobbin from polypropylene. The TV co. used vinyl because it was cheap. The secondary was interrupted every four slots by a HV diode, again to reduce capacitance. If these diodes were moved to the top end of the coil, the voltage was reduced by about 20%. I wouldn't try to put the diodes on the coil--it's hard to do.
The primary was 110 turns, #26 if I remember correctly, on a mylar form between the bobbin and the core. There were also several low-voltage secondaries working in normal transformer mode. The operating voltage was 160V, with normal TV NTSC timing.
A pix is worth 10^3 words, but I don't have one and I couldn't find one on the web. In the remote chance that this description is not entirely clear, write with questions. The dimensions are as I remember them from 1983, but pretty close. I have a few cores with mounting hardware if you need them.
---Carl
Greetings all,
Contemplating winding a few flybacks for high power operation (28 awg
secondary) does anybody have any experience with this, I'm looking to make
several identical ones for my plasma drivers, what should I use to separate
the windings, paper, poly, mylar? How may layers can I do? What do I pot
them in? Google is turning up fairly little information, just wondered if
anybody on list has tackled this, please note I am aware this will require
patience... Thanks in advance! Oh and where can I get cores, I've found
some on information unlimited but I've heard unsavory things about them,
and am hesitant to order...
Scott Bogard.
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