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How to compute RL current rise time in Python using UliEngineering

You can easily compute the RL current rise time to reach a target current using the UliEngineering Python library:

rl_current_rise_time.py
from UliEngineering.Electronics.RL import rl_current_rise_time
from UliEngineering.EngineerIO import *

# Compute time to reach 90% of final current
time = rl_current_rise_time("10", "100mH", 0.90)
print(f"Time to 90% current (10Ω, 100mH): {format_value(time, 's')}")

# Compute time to reach 99% of final current
time = rl_current_rise_time("1k", "1mH", 0.99)
print(f"Time to 99% current (1kΩ, 1mH): {format_value(time, 's')}")

Example output

rl_current_rise_time_output.txt
Time to 90% current (10Ω, 100mH): 23.0 ms
Time to 99% current (1kΩ, 1mH): 4.61 µs

The RL current rise time represents the time required for current through an inductor to rise to a specific percentage of its final value when voltage is applied. This calculation is essential for understanding inrush currents, relay activation times, and the transient response of RL networks. The current rise follows an exponential curve, with the current never truly reaching 100% of its final value in finite time.

The rise time is computed using the formula: $t = -\tau \ln(1 - \text{ratio})$, where $\tau = \frac{L}{R}$ is the time constant and the ratio is the target current as a fraction of the final current (e.g., 0.90 for 90%). For example, reaching 90% of final current takes approximately 2.3 time constants, while reaching 99% takes approximately 4.6 time constants.

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