Inductor Time Constant Calculator Formula
Understand the math behind the inductor time constant calculator. Each variable explained with a worked example.
Formulas Used
Time Constant (tau)
tau = l_h / resistanceTime Constant (ms)
tau_ms = l_h / resistance * 1000Settling Time (5 tau)
settle_5tau = 5 * l_h / resistance * 1000Variables
| Variable | Description | Default |
|---|---|---|
inductance_mh | Inductance(mH) | 100 |
resistance | Resistance(Ω) | 100 |
l_h | Derived value= inductance_mh / 1000 | calculated |
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
- 01tau = 0.1 / 100 = 0.001 s = 1 ms
- 025 tau = 5 ms to reach steady state
Frequently Asked Questions
Why L/R and not LR?
Units: henrys/ohms = seconds. The inductor opposes current change; higher R dissipates energy faster.
RL vs RC time constant?
RC = R x C. RL = L / R. Both describe exponential approach to steady state.
What is 5 tau?
After 5 time constants, the circuit is within 0.7% of final value, considered fully settled.
Ready to run the numbers?
Open Inductor Time Constant Calculator