TheAlgorithms/Python · error · ValueError

Source voltage must be positive.

Error message

Source voltage must be positive.

What it means

Thrown by charging_capacitor() in electronics/charging_capacitor.py when source_voltage <= 0. The function models a step-response charge curve V(t) = Vs*(1 - e^(-t/RC)) and requires a strictly positive driving voltage; a non-positive source makes the model (and its 'charging' semantics) invalid.

Source

Thrown at electronics/charging_capacitor.py:61

    >>> charging_capacitor(source_voltage=0,resistance=10.0,capacitance=.30,time_sec=3)
    Traceback (most recent call last):
        ...
    ValueError: Source voltage must be positive.

    >>> charging_capacitor(source_voltage=20,resistance=-2000,capacitance=30,time_sec=4)
    Traceback (most recent call last):
        ...
    ValueError: Resistance must be positive.

    >>> charging_capacitor(source_voltage=30,resistance=1500,capacitance=0,time_sec=4)
    Traceback (most recent call last):
        ...
    ValueError: Capacitance must be positive.
    """

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


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a strictly positive source voltage (e.g. 5.0 or 20.0).
2. Use abs() only if you deliberately want magnitude of a bipolar source — otherwise fix the sign upstream.
3. Check that you are not passing defaults from an unset config field (0 is the classic default).

Example fix

# before
charging_capacitor(source_voltage=-9, resistance=1500, capacitance=30, time_sec=4)

# after
charging_capacitor(source_voltage=9, resistance=1500, capacitance=30, time_sec=4)

if source_voltage <= 0:
    raise ValueError("source_voltage must be positive")
v = charging_capacitor(source_voltage, resistance, capacitance, time_sec)

When it happens

Trigger: charging_capacitor(source_voltage=0, resistance=1500, capacitance=30, time_sec=4) or any call with a negative source_voltage.

Common situations: Default-initializing voltage to 0 and forgetting to set it; AC or bipolar sources where a signed instantaneous value can be <= 0; parameter-order mix-ups passing time in the voltage slot.

Related errors

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

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/b4c59f4f14f630a6. Report an issue: GitHub.