Battery Models: Open-Circuit Voltage & Internal Resistance
Battery models using open-circuit voltage and internal resistance provide a simplified way to represent real batteries in electrical circuits. The open-circuit voltage is the potential difference across the battery terminals when no current flows, reflecting the battery’s maximum voltage. Internal resistance represents energy losses within the battery as it supplies current. Together, these parameters help predict battery performance, voltage drop under load, and efficiency in practical circuit applications.
Battery Models: Open-Circuit Voltage & Internal Resistance
Battery models using open-circuit voltage and internal resistance provide a simplified way to represent real batteries in electrical circuits. The open-circuit voltage is the potential difference across the battery terminals when no current flows, reflecting the battery’s maximum voltage. Internal resistance represents energy losses within the battery as it supplies current. Together, these parameters help predict battery performance, voltage drop under load, and efficiency in practical circuit applications.
💡 Key Takeaways
- Understand what open-circuit voltage (OCV) is and why it matters when no current is drawn.
- Learn what internal resistance is and how it causes a voltage drop under load (V = OCV − I·Rint).
- Recognize how a simple Thevenin battery model represents a cell as an OCV source in series with Rint.
- Know that OCV and internal resistance change with state of charge and aging, affecting performance.
- Learn practical ways to estimate OCV and internal resistance from basic tests and how to interpret the results.
❓ Frequently Asked Questions
What is open-circuit voltage (OCV) in battery models?
OCV is the voltage of the cell when no current flows. It represents the electromotive force and is modeled as an ideal voltage source in the Thevenin model. OCV depends on state of charge and temperature and is independent of the internal resistance.
What is internal resistance in a battery, and how does it affect performance?
Internal resistance is the resistance inside the cell that causes voltage drop when current flows. In the Thevenin model it sits in series with the OCV; under load the terminal voltage is V = OCV − I·R_int, and power loss is I^2·R_int, which causes heating.
How do open-circuit voltage and internal resistance relate to state of charge and aging?
OCV correlates with state of charge (specific OCV–SoC curve for the chemistry). Internal resistance changes with SoC, temperature, and aging; higher R_int means larger voltage sag under load and more heat, and aging generally increases R_int.
How are OCV and internal resistance measured or estimated?
OCV is measured after the cell rests with no current. Internal resistance can be estimated from the voltage drop under a known load (R_int ≈ ΔV/ΔI) or via current interruption/AC impedance methods; ensure safe procedures.