The alpha winding method: eliminating internal lead-out wires

The hazards of the internal crossing strand

To connect a conventional coil to an external interface, the crossing wire path introduces three primary engineering risks:

• Axial protrusion: The crossing wire creates an asymmetrical bulge on the end face of the coil, increasing its total axial length.
• Dielectric breakdown risk: The start lead (at 0 V potential) directly crosses over the outermost layers (at maximum potential Vmax). This creates an extreme voltage gradient (ΔV = Vmax) across a single layer of wire insulation, making the coil vulnerable to electrical short circuits.
• Winding asymmetry: The space occupied by the crossing strand disrupts the winding pattern of subsequent turns, preventing a clean, high-density orthocyclic layout.

The alpha winding solution

The alpha winding method is a specialized manufacturing process that completely eliminates the internal crossing strand. It ensures that both the start lead and the finish lead exit exclusively from the outermost layer (OD) of the coil structure. The alpha method modifies the traditional winding sequence using one of two distinct techniques:

1. Dual-spool center-start method: The winding process starts from the center of a continuous wire length. The wire is split, and two independent winding heads simultaneously or sequentially wind outward from the inside. The inner connection remains protected as a flat, continuous loop at the base of the coil, allowing both ends to finish cleanly on the outside.
2. Reverse folding layer progression: The first layer is laid down with a precise, pre-calculated axial pitch change. When reaching the layer boundary, the machine performs a reverse fold, utilizing specialized nozzle kinematics to route subsequent layers without passing over the initial start strand.

Geometric and electrical advantages

• Absolute minimization of envelopes: Without an asymmetrical exit strand crossing the end faces, the coil maintains a completely flat, symmetrical profile. This allows mechanical designers to work with tight tolerances, maximizing the spatial fill factor within narrow enclosures.
• Optimized dielectric insulation profile: Because both leads exit from the outermost layer, the maximum voltage difference between adjacent wire paths is minimized. The start and finish potentials are physically separated across the outer circumference, eliminating high-voltage stress points and reducing internal parasitic capacitance (Cp).
• Planar surface integration: Alpha-wound coils feature completely unobstructed top and bottom surfaces. This allows them to be mounted perfectly flush against flat surfaces, which is ideal for direct surface-mount technology (SMT) integration on PCBs or automated handling with vacuum pick-and-place systems.

Technical comparison mapping