Understanding Litz Wire Coil Design
Litz wire helps reduce high frequency losses. It uses many small insulated strands. Each strand carries part of the current. The goal is lower skin effect loss. A coil still needs careful sizing. Turns, diameter, strand count, and strand size all matter.
Why Strand Size Matters
At high frequency, current crowds near conductor surfaces. This is called skin effect. Skin depth becomes smaller as frequency rises. A strand should often be near or below two skin depths. Smaller strands can help. They also raise strand count and cost. This calculator checks strand diameter against skin depth.
Resistance And Heating
Copper resistance grows with length and temperature. More turns increase total wire length. More copper area lowers resistance. Temperature also raises resistance. The calculator adjusts resistivity with a copper temperature coefficient. It then estimates direct current resistance. It adds skin and proximity allowances for an alternating current estimate.
Inductance And Quality Factor
The coil inductance is estimated with Wheeler's air core solenoid formula. It works best for normal single layer coils. Very short, shielded, ferrite, or multilayer coils need deeper modeling. The quality factor compares inductive reactance with ac resistance. A higher Q can mean lower loss. It can also narrow bandwidth.
Using Results In Real Builds
Use the output as an engineering estimate. Check winding fit before ordering wire. The occupied length value shows if turns can fit in one layer. A value above one hundred percent suggests overlap or multilayer winding. Review copper loss against cooling limits. Also compare voltage drop with your circuit margin.
Design Limits
Litz wire performance depends on twisting pattern. Real bundles have strand transposition, insulation, tension, and spacing effects. Proximity loss can dominate near other conductors. Magnetic cores can add loss and change inductance. Use lab measurements for final work. Measure resistance, temperature rise, and resonant frequency after winding.
Good Workflow
Start with target inductance and frequency. Choose a strand size from skin depth. Increase strand count for current capacity. Adjust turns and diameter for inductance. Then review loss, Q, and winding fit. Repeat the process until the coil meets electrical and physical limits. Document assumptions clearly. Save each trial, so later comparisons stay simple and traceable before selection.