Inductive device with precision wound coil

Abstract

An improved inductive device such as a transformer of the type containing a closed magnetic core, typically formed of magnetic laminations, with at least one coil-receiving core window and an electrical coil winding mounted on a core leg fitting through the core window, said coil being of a multilayer precision wound bobbinless construction in which the coil side to which a winding start lead extends faces an adjacent core leg, the improvement therein wherein the first turn of the first layer of the coil winding is interleaved between two turns of an overlying layer of winding turns and wherein the last turn of said first layer is also interleaved between two other turns of said overlying layer, whereby the spacing between the coil and magnetic iron core elements is increased to enhance electrical insulation. A novel expandable arbor of the type containing two coupled arbor blocks each containing two longitudinally extending edges, each said edge having a plurality of wire receiving grooves extending transverse the edge between the ends of the arbor block and which in section view defines a sawtooth-like series of peaks and valleys, wherein the bottom of the first groove is located a distance from one said arbor end equal to the wire diameter and the first peak adjoins the arbor end and is a height greater than the other peaks for providing a slide surface into the first groove and the bottom of the last groove is located a distance from the other arbor end equal to a wire diameter.