RL Time Constant (τ = L/R)
Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!
Learning zone
Close a switch on an inductor and the current doesn't jump — it climbs toward its final value, covering 63% of the remaining gap every τ = L/R seconds and essentially settling after 5τ. A 100 mH relay coil with 50 Ω of resistance has τ = 2 ms, so it clicks in about 10 ms. The same constant governs the decay when power is cut, which is why inductive loads need flyback diodes: give that stubborn current nowhere to go and it will arc across the opening switch.
RL Time Constant (τ = L/R)
Where
- = Time constant
- = Inductance
- = Resistance
Missing one of these? Work it out first, then come back
- Time constant — RC Time Constant, RC Capacitor Discharge
- Inductance — Energy Stored in an Inductor, Inductive Reactance (X_L = 2πfL)
- Resistance — Ohm's Law, Electrical Power (P = I²R)