Rl Time Constant
Calculator
Results
- Time constant (s)
- 0.002
- Time constant (ms)
- 2
- Steady-state current (A)
- 0.48
- Current after one time constant (A)
- 0.303417
Electrical results
| Time constant (s) | 0.002 |
| Time constant (ms) | 2 |
| Steady-state current (A) | 0.48 |
| Current after one time constant (A) | 0.303417 |
formula-map diagram
- Time constant (s)
- 0.002
- Time constant (ms)
- 2
- Steady-state current (A)
- 0.48
- Current after one time constant (A)
- 0.303417
Electrical relationship
Formula
τ = L / R= 0.002
Note
This is a simplified model: it applies the textbook relationship to the numbers you entered and assumes ideal components, steady-state sinusoidal conditions, balanced loads and copper resistivity of 0.0172 Ω·mm²/m at 20 °C. It ignores component tolerances, temperature drift, skin effect, harmonics, inrush, transformer and battery losses, and it is not a substitute for the wiring code that applies where you are. Have any installation sized and verified by a licensed electrician or engineer.
More in Electrical engineering
See all →Frequently asked questions
What is the RL time constant and what does it measure?+
Tau = L / R is the time for current in an inductor-resistor circuit to reach about 63.2% of its final steady-state value after a voltage step. It plays the same role for inductors that RC plays for capacitors.
Why does a larger inductance make the circuit slower, but a larger resistance make it faster?+
A bigger inductor opposes changes in current more strongly, so it takes longer to reach the final value — while a bigger resistance limits the final current itself, letting the circuit settle proportionally faster. That's why L is on top and R is on the bottom of the formula.
How many time constants until the inductor current is essentially steady?+
As with RC circuits, about 5 time constants (5 x L/R) gets you to over 99% of the final current, which is the usual rule of thumb for considering the transient 'finished'.
Where does the RL time constant matter in practice?+
It's important whenever you switch inductive loads like motors, solenoids, or relay coils — the current doesn't stop or start instantly, and that delay determines things like how fast a relay opens or how much voltage spike appears when current is interrupted.
What happens to the energy in the inductor during this transient?+
As current builds toward steady state, energy is being stored in the inductor's magnetic field; when the circuit is switched off, that stored energy has to go somewhere, which is why inductive circuits often need a flyback diode or snubber to protect other components.