Sorry, but I think those are both normal transformers. Maybe someone misinterpreted the outside copper band...?
It would be fun to have someone compare some of the foil output transformers to other decent transformers.
Compare leakage inductance and overall behavior.
I am guessing the foil transformers might have poor interleaving leading to overall poor behavior.
Compare leakage inductance and overall behavior.
I am guessing the foil transformers might have poor interleaving leading to overall poor behavior.
I would think that given their nature one turn of foil would occupy one entire layer whereas in a conventional magnet wire based design a primary can have perhaps 40-50 (or more) turns on a layer and a secondary could have 10-20 (or more) turns per layer. A foil based transformer would be huge even with thin foil. Add to that it would be a bear to wind if the foil was made as thin as needed to equate to the wire size. Foil the thickness of 1 oz copper is 1.4mils (.0014") thick. At 1/2" wide it's similar in cross sectional are to AWG 20 wire. If we were to work with smaller wire equivalents the foil might be too thin to manage.
Foil secondary windings are commonly used on AC line distribution transformers, commonly called "pole pigs" . The primaries are wound of conventional wire and sized for the local distribution system. In my area, the line distribution is at 14.4 KV. with 240 volts out; there is roughly a 60;1 ratio, so there are relatively few secondary turns. It is convenient and easy to wind, and with foil the full width of the core, and it is relatively straightforward to get the required cross-sectional area in the conductors to handle 200 AMPs or so.
There will be significant self-capacitance in the secondary windings, but at 60HZ, it is not a big problem. For a wide-range transformer that requires many turns, though, this situation would be drastically different.
There will be significant self-capacitance in the secondary windings, but at 60HZ, it is not a big problem. For a wide-range transformer that requires many turns, though, this situation would be drastically different.