Inductor Calculator

Calculate total inductance for series and parallel combinations. Enter 2-4 inductor values and optional current/frequency to calculate energy storage and inductive reactance.

Series Inductors: L_total = L₁ + L₂ + L₃ + ... + Lₙ Where: • L_total = Total inductance (H) • L₁, L₂, L₃, ... = Individual inductances (H) • Current is same through all • Voltage sums: V_total = V₁ + V₂ + V₃ + ... Parallel Inductors: 1/L_total = 1/L₁ + 1/L₂ + 1/L₃ + ... + 1/Lₙ Or for two inductors: L_total = (L₁ × L₂) / (L₁ + L₂) Where: • Voltage is same across all • Current divides Energy Storage: E = ½ L I² Where: • E = Energy stored (Joules) • L = Inductance (Henries) • I = Current (Amperes) Inductive Reactance: X_L = 2πfL = ωL Where: • X_L = Inductive reactance (Ω) • f = Frequency (Hz) • ω = Angular frequency = 2πf (rad/s) • L = Inductance (H) Unit Conversions: • 1 H = 1,000 mH = 1,000,000 µH = 10⁹ nH • 1 mH = 1,000 µH = 1,000,000 nH
Example 1 - Series Inductors (Filter): L₁ = 10mH, L₂ = 22mH, L₃ = 47mH, I = 0.5A L_total = 10 + 22 + 47 = 79mH = 0.079 H E_total = ½ × 0.079 × 0.5² = 0.00988 J (9.88 mJ) E₁ = ½ × 0.01 × 0.5² = 1.25 mJ E₂ = ½ × 0.022 × 0.5² = 2.75 mJ E₃ = ½ × 0.047 × 0.5² = 5.88 mJ Example 2 - Parallel Inductors: L₁ = 100µH, L₂ = 100µH, f = 1 MHz 1/L_total = 1/100 + 1/100 = 2/100 L_total = 50µH = 0.00005 H X_L = 2π × 1,000,000 × 0.00005 = 314.16 Ω (At 1 MHz, presents 314Ω reactance) Example 3 - Buck Converter Inductor: L = 100µH, I_peak = 3A E = ½ × 0.0001 × 3² = 0.00045 J (450 µJ) (This energy is transferred to output each cycle) Example 4 - Two Different Parallel Inductors: L₁ = 10mH, L₂ = 22mH, f = 1 kHz L_total = (10 × 22)/(10 + 22) = 220/32 = 6.875 mH X_L = 2π × 1000 × 0.006875 = 43.2 Ω Example 5 - RF Choke (Series): L₁ = 100µH, L₂ = 220µH, f = 100 kHz, I = 0.1A L_total = 100 + 220 = 320µH = 0.00032 H X_L = 2π × 100,000 × 0.00032 = 201 Ω E = ½ × 0.00032 × 0.1² = 0.0000016 J (1.6 µJ) Example 6 - Audio Crossover: L₁ = 2.2mH, L₂ = 3.3mH (series), f = 2 kHz L_total = 2.2 + 3.3 = 5.5 mH X_L = 2π × 2000 × 0.0055 = 69.1 Ω (Used with speakers for frequency filtering)

What is the formula for inductors in series?

For inductors in series, total inductance is the sum: L_total = L₁ + L₂ + L₃ + ... (assuming no mutual coupling). Like resistors in series, inductances add directly. Current is the same through all inductors.

What is the formula for inductors in parallel?

For inductors in parallel: 1/L_total = 1/L₁ + 1/L₂ + 1/L₃ + ... (like resistors in parallel). For two inductors: L_total = (L₁ × L₂)/(L₁ + L₂). Total inductance decreases. Voltage is the same across all parallel inductors.

How do I calculate energy stored in an inductor?

Energy stored in an inductor is E = ½LI², where L is inductance (Henries) and I is current (Amperes). Energy is stored in the magnetic field around the inductor. This energy is released when current stops, potentially creating voltage spikes.

What is inductive reactance?

Inductive reactance X_L = 2πfL = ωL, where f is frequency (Hz), L is inductance (H), and ω = 2πf is angular frequency. Reactance is opposition to AC current, measured in ohms. Higher frequency or inductance increases reactance.

Why do inductors oppose changes in current?

By Lenz's Law, an inductor generates a back-EMF (voltage) that opposes current changes: V = -L(dI/dt). This makes inductors resist sudden current changes, acting as "electrical inertia". They pass DC easily but oppose AC, especially high frequencies.

What are common inductor units?

Henry (H) is the SI unit. Common units: millihenry (mH) = 10⁻³ H, microhenry (µH) = 10⁻⁶ H, nanohenry (nH) = 10⁻⁹ H. Typical values: power supplies (1µH-1mH), RF circuits (1nH-1µH), audio (1mH-10H for transformers).

How does frequency affect inductor impedance?

Inductor impedance Z_L = jωL = j2πfL increases linearly with frequency. At DC (f=0), impedance is zero (short circuit). At high frequencies, impedance is high (blocks AC). This makes inductors useful for filters: block high frequencies, pass low frequencies.

What is the quality factor (Q) of an inductor?

Quality factor Q = X_L/R = ωL/R, where R is series resistance. Q measures inductor efficiency: higher Q means less energy loss. Ideal inductor has Q = ∞. Real inductors: Q = 20-200. Important for tuned circuits, filters, and resonant applications.

Can inductors be used for energy storage like capacitors?

Yes, inductors store energy in magnetic fields (E = ½LI²) while capacitors use electric fields (E = ½CV²). Inductors: store energy as current flow, release slowly. Used in switching regulators, flyback converters, and power supplies for efficient energy transfer.

What happens when you break current through an inductor?

Breaking current suddenly creates very high voltage spikes because V = -L(dI/dt). Large dI/dt creates large voltage that can arc across switch contacts or damage components. Use flyback diodes or snubbers to safely dissipate inductor energy in switching circuits.

How do I calculate time constant for an inductor?

Inductor time constant τ = L/R, where L is inductance (H) and R is series resistance (Ω). Current reaches 63% of final value in one τ, and 99% after 5τ. Current: I(t) = I_final(1 - e^(-t/τ)) for rising, I(t) = I₀e^(-t/τ) for falling.

What are typical applications for inductor calculations?

Applications: switching power supplies (buck/boost converters), filter circuits (low-pass, band-pass), RF circuits, impedance matching, transformers, motor windings, energy storage, EMI suppression, ballasts, and resonant circuits (LC oscillators).

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