Engineering Tools for Precise Litz Wire Design

Electrical and mechanical characteristics must be perfectly coordinated to minimize losses and maximize service life. Precise calculations are the foundation of successful engineering.

Selecting the right litz wire depends primarily on the requirements of the component or power electronics in question. Key factors include the conductor cross-section, the specific construction (number and diameter of single wires), the conductor material, and the type of insulation. Current carrying capacity, bending radius, temperature range, and skin and proximity effects also play critical roles.

LiWiCalc® is a high-frequency calculator developed by the Fraunhofer Institute IISB. In collaboration with Fraunhofer, PACK LitzWire has created a specialized environment to calculate power losses and current densities of PACK HF litz wires in real time.

Designing passive components for power electronics requires balancing a variety of parameters. Engineers must harmonize electrical, mechanical, and thermal requirements to ensure optimal function. Selecting the appropriate HF litz wire is a complex task, as numerous factors influence the conductor's performance. Inherent trade-offs exist between different litz wire configurations and their impact on performance.

The configurator allows users to enter two of the following three core parameters: single wire diameter, number of strands, or desired copper cross-section; the system then calculates the third parameter. Additionally, specifying the type of outer insulation is a mandatory requirement.

Engineers typically start with the electrical specifications of the power converter, such as input/output voltage and current, switching frequency, and target efficiency. Winding design involves determining the number of turns and the type of wire. For high-frequency applications, the selection of litz wire becomes paramount. Engineers must account for constraints like available winding space, thermal management, and cost. Litz wire selection is not an isolated step but is deeply integrated into the entire design process of inductors and transformers. Tools like RuPaFox® and LiWiCalc® provide essential support in this process.

We use standard metric units: millimeters (mm) for diameter, square millimeters (mm²) for cross-section, and amperes (A) for current intensity.

This value indicates how many meters of a specific litz wire weigh one kilogram. It is calculated from the cross-section and material density – essential for both technical calculations and logistics.

Cross-section = Number of single wires × (π × (wire diameter/2)²). 
The result determines the current carrying capacity and the total resistance.

Lay length is the distance a conductor travels to complete one full (360°) turn around the litz wire circumference. It is typically specified in mm or cm.

In addition to our flagship HF calculators, we provide diameter, cross-section, lay length, and length-to-weight ratio calculators – available directly online or as technical PDF tables.

Generally, longer lay lengths increase flexibility, while shorter ones reduce it.

To calculate the outer diameter, please use the RuPaFox® product configurator. For every calculation, the configurator prominently displays the following results:

• Total Diameter: The calculated outer diameter of the litz wire, determined both with and without outer insulation.
• Copper Cross-section: The total conductive copper area of all strands in the litz wire, convertible to AWG.
• DC Resistance (min): The minimum DC resistance of the litz wire at 20°C, based on minimum single wire resistance.
• DC Resistance (nom): The nominal DC resistance at 20°C, a fundamental property for evaluating ohmic losses.
• DC Resistance (max): The maximum DC resistance at 20°C, which accounts for potential wire breaks in configurations with more than 25 strands.
• Meters/kg: The total length of litz wire per kilogram of finished product, essential for material and weight estimations.
• Number of Strands: The total number of individual wires, explicitly displayed when derived from a target cross-section or diameter.

Please use our RuPaFox® configurator for this calculation.

Yes. Our compendium includes reference tables for typical cross-sections, resistances, and weight data. Additionally, our online tools offer interactive calculation capabilities.

Conventional calculations are indispensable in power electronic design for approximating electrical losses, current displacement (skin and proximity effects), temperature rise, and current carrying capacity. These models provide an essential basis for the pre-selection of conductor cross-sections and stranding concepts.

However, their limits lie in the fact that they are based on idealized assumptions. In practice, numerous factors influence the real behavior of a litz wire that cannot always be calculated with absolute precision. These include:

• The specific stranding geometry and manufacturing tolerances.
• The interaction between litz wire, insulation, and the specific application.
• Mechanical influences during processing (bending, winding, pressing).
• Thermal conditions during real-world operation.
• Interactions with adjacent conductors, cores, or shielding.

Especially at high frequencies and power levels, these effects can cause calculated values to deviate from actual performance. Therefore, alongside theoretical design, experience in litz wire manufacturing is crucial for an optimal result. We view calculations as one part of a holistic design process, combining theoretical know-how with decades of practical expertise.

No. Current calculations are based on the specific material parameters of copper.

Any change in parameters (frequency, temperature, construction) should trigger a recalculation, as small changes can have significant impacts on losses and thermal performance.