Inductor Time Constant Calculator Formula

Understand the math behind the inductor time constant calculator. Each variable explained with a worked example.

Use the Inductor Time Constant Calculator

Formulas Used

Time Constant (tau)

tau = l_h / resistance

Time Constant (ms)

tau_ms = l_h / resistance * 1000

Settling Time (5 tau)

settle_5tau = 5 * l_h / resistance * 1000

Variables

VariableDescriptionDefault
inductance_mhInductance(mH)100
resistanceResistance(Ω)100
l_hDerived value= inductance_mh / 1000calculated

How It Works

RL Time Constant

tau = L / R

Current in an RL circuit rises to 63.2% of final value in one tau. After 5 tau, current is at ~99.3% of steady state.

Worked Example

100 mH inductor with 100 ohm resistance.

inductance_mh = 100resistance = 100
  1. 01tau = 0.1 / 100 = 0.001 s = 1 ms
  2. 025 tau = 5 ms to reach steady state

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