TheAlgorithms/Python · error · ValueError

Source voltage must be positive.

Error message

Source voltage must be positive.

What it means

Thrown by charging_inductor() in electronics/charging_inductor.py when source_voltage <= 0. The function computes the RL step response I(t) = (Vs/R)*(1 - e^(-Rt/L)) and requires a strictly positive source voltage; non-positive values are rejected as invalid for a charging model.

Source

Thrown at electronics/charging_inductor.py:84

    >>> charging_inductor(source_voltage=0,resistance=200,inductance=20,time=5)
    Traceback (most recent call last):
        ...
    ValueError: Source voltage must be positive.

    >>> charging_inductor(source_voltage=10,resistance=0,inductance=20,time=5)
    Traceback (most recent call last):
        ...
    ValueError: Resistance must be positive.

    >>> charging_inductor(source_voltage=15, resistance=25, inductance=0, time=5)
    Traceback (most recent call last):
        ...
    ValueError: Inductance must be positive.
    """

    if source_voltage <= 0:
        raise ValueError("Source voltage must be positive.")
    if resistance <= 0:
        raise ValueError("Resistance must be positive.")
    if inductance <= 0:
        raise ValueError("Inductance must be positive.")
    return round(
        source_voltage / resistance * (1 - exp((-time * resistance) / inductance)), 3
    )


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a strictly positive DC source voltage.
2. If modeling magnitude of a bipolar source, apply abs() deliberately at the call site.
3. Use keyword arguments (source_voltage=, resistance=, inductance=, time=) to avoid positional mix-ups.

Example fix

# before
charging_inductor(source_voltage=0, resistance=10, inductance=20, time=5)

# after
charging_inductor(source_voltage=12, resistance=10, inductance=20, time=5)

if source_voltage <= 0:
    raise ValueError("source_voltage must be positive")
i = charging_inductor(source_voltage, resistance, inductance, time)

When it happens

Trigger: charging_inductor(source_voltage=0, resistance=10, inductance=20, time=5) or any negative source_voltage. Note the parameter is named time (not time_sec).

Common situations: Unset config defaults of 0; swapping the positional order of source_voltage and time; feeding signed AC samples into a DC step-response model.

Related errors

• Capacitor at index {index} has a negative or zero value!
• You cannot supply more or less than 2 values
• Source voltage must be positive.
• Resistance must be positive.
• Inductance must be positive.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/3fbd3bf8979ac05c. Report an issue: GitHub.