Wire Adviser¶

The Wire Adviser selects optimal wire types and dimensions for a given operating frequency and current, minimizing AC resistance while considering manufacturing constraints.

Overview¶

Wire selection significantly impacts winding losses at high frequencies due to skin and proximity effects. The Wire Adviser evaluates different wire types and finds the best match for your requirements.

flowchart TD
    subgraph "Input"
        A([Start]) --> B[Receive frequency and current requirements]
        B --> C[Load temperature constraints]
        C --> D[Get wire type preferences from settings]
    end

    subgraph "Wire Type Selection"
        D --> E{Include Round?}
        E -->|Yes| F[Add round wire candidates]
        E -->|No| G{Include Litz?}
        F --> G
        G -->|Yes| H[Add litz wire candidates]
        G -->|No| I{Include Rectangular?}
        H --> I
        I -->|Yes| J[Add rectangular candidates]
        I -->|No| K{Include Foil?}
        J --> K
        K -->|Yes| L[Add foil candidates]
        K -->|No| M[Candidate pool ready]
        L --> M
    end

    subgraph "Evaluation"
        M --> N[Calculate skin depth at frequency]
        N --> O[For each wire candidate]
        O --> P[Calculate DC resistance/m]
        P --> Q[Calculate AC resistance factor]
        Q --> R[Calculate effective resistance]
        R --> S[Score based on losses]
        S --> T{More candidates?}
        T -->|Yes| O
        T -->|No| U[Rank by score]
    end

    subgraph "Output"
        U --> V[Apply current capacity filter]
        V --> W[Return ranked wire list]
        W --> X([End])
    end

Wire Types¶

Round Wire¶

Standard solid copper wire. Best for: - Low frequencies (< 50 kHz) - Low current applications - Cost-sensitive designs

Skin depth consideration: $$\delta = \sqrt{\frac{\rho}{\pi \mu f}}$$

Effective when wire radius < 2δ.

Litz Wire¶

Multiple individually insulated strands twisted together. Best for: - Medium to high frequencies (50 kHz - 2 MHz) - Moderate to high currents - Applications requiring low AC resistance

Strand selection: - Strand diameter should be < 2δ - More strands = better high-frequency performance - Trade-off with fill factor and cost

Rectangular Wire¶

Flat copper conductors. Best for: - High current, low frequency - Planar transformers - Applications requiring high fill factor

Considerations: - Higher proximity effect than round wire - Better thermal performance - Limited flexibility for toroidal cores

Foil Wire¶

Thin copper foil. Best for: - Very high currents - Planar inductors - Single-layer windings

Configuration¶

Settings¶

auto& settings = OpenMagnetics::Settings::GetInstance();

// Enable/disable wire types
settings.set_wire_adviser_include_round(true);
settings.set_wire_adviser_include_litz(true);
settings.set_wire_adviser_include_rectangular(true);
settings.set_wire_adviser_include_foil(false);
settings.set_wire_adviser_include_planar(false);

// Allow rectangular wire in toroidal cores
settings.set_wire_adviser_allow_rectangular_in_toroidal_cores(false);

Usage Example¶

#include "OpenMagnetics.h"

int main() {
    // Operating conditions
    double frequency = 200000;  // 200 kHz
    double rms_current = 5.0;   // 5 A RMS
    double temperature = 40;    // 40°C

    // Run wire adviser
    OpenMagnetics::WireAdviser adviser;
    auto wires = adviser.get_advised_wire(frequency, rms_current, temperature, 20);

    std::cout << "Wire recommendations for " << frequency/1000 << " kHz, "
              << rms_current << " A:" << std::endl;

    for (size_t i = 0; i < std::min(wires.size(), size_t(5)); ++i) {
        auto& wire = wires[i];
        std::cout << i+1 << ". " << wire.get_name();

        auto type = wire.get_type();
        if (type == MAS::WireType::LITZ) {
            std::cout << " (Litz, " << wire.get_number_conductors().value()
                      << " x " << wire.get_strand_diameter().value() * 1e6 << " µm)";
        } else if (type == MAS::WireType::ROUND) {
            std::cout << " (Round, " << wire.get_conducting_diameter().value() * 1e3 << " mm)";
        }
        std::cout << std::endl;
    }

    return 0;
}

Skin Depth Reference¶

Litz Wire Selection Guide¶

For optimal litz wire selection:

1. Strand diameter: Should be approximately equal to skin depth
2. Number of strands: Based on current capacity
3. Construction: Consider twist pitch and bundle configuration

// Example: Finding optimal litz configuration
double frequency = 100000;  // 100 kHz
double skin_depth = OpenMagnetics::calculate_skin_depth(frequency, 25.0);

// Strand diameter should be ~2x skin depth for round strands
double optimal_strand_diameter = 2 * skin_depth;

std::cout << "Optimal strand diameter: " << optimal_strand_diameter * 1e6 << " µm" << std::endl;

AC Resistance Factor¶

The AC resistance factor (Fr) represents the increase in resistance due to skin and proximity effects:

$$F_r = \frac{R_{AC}}{R_{DC}} = F_{skin} + F_{proximity}$$

Typical values: - Well-designed litz: Fr ≈ 1.1 - 1.5 - Round wire at f > skin depth: Fr ≈ 2 - 10 - Foil with proper thickness: Fr ≈ 1.5 - 3