High-Performance Litz Wires for Modern Induction Cooktops

As part of a joint development project, PACK LitzWire supported a manufacturer of induction cooktops in implementing flat, spiral-shaped planar coils. These coils carried very high currents and were located directly beneath the glass ceramic; therefore, particularly high requirements applied to power density, temperature resistance, and electrical safety.

Technical Specifications

For the project, the customer and PACK LitzWire defined the litz wire specifications: primary material copper, alternatively aluminum or copper-clad aluminum (CCA); single wire diameters in the range of 0.10–0.4 mm; number of single strands per litz wire depending on coil size and operating conditions; use of high-temperature enamels with a temperature resistance of ≥ 200 °C; profiling of the litz wire to increase the fill factor.

The Challenge

The key development questions were:

• Fill Factor and Installation Height: The coils were to be constructed as flat and compact as possible with a very high fill factor (profiling), without compromising electrical dielectric strength.
• Dielectric Strength and Insulation: Enamel layers and insulation concepts had to guarantee high dielectric strength even after mechanical pressing and during continuous heating.
• Temperature Resistance: The selected enamel systems had to withstand temperatures and radiation from the cookware over the long term without emitting odor-active decomposition products.
• Material and Processing Issues: The choice between Cu, Al, and CCA required coordination regarding contacting, solderability, corrosion behavior, and mechanical behavior during profiling.