1. What is Internal Resistance?

Internal resistance (r) is the opposition to current flow within a power source itself. It causes voltage drop when current is drawn from the source and represents energy lost as heat within the source.

2. How Does the Calculator Work?

The calculator uses the internal resistance formula:

Where:

• \( v_{oc} \) — Open circuit voltage (no load) in volts
• \( v_{load} \) — Voltage under load in volts
• \( i_{load} \) — Current under load in amperes
• \( r \) — Internal resistance in ohms (Ω)

Explanation: The voltage drop (V_oc - V_load) divided by the current gives the internal resistance.

3. Importance of Internal Resistance

Details: Internal resistance affects battery performance, power delivery efficiency, and causes voltage sag under load. Lower internal resistance generally means better performance.

4. Using the Calculator

Tips: Measure V_oc with no load, then measure V_load and I_load under known load. All values must be positive and I_load must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: Why does internal resistance matter?
A: It determines how much voltage drops under load and affects maximum power transfer capability.

Q2: What are typical internal resistance values?
A: Alkaline AA batteries: ~0.1-0.3Ω, Lithium-ion: ~0.05-0.1Ω, Car batteries: ~0.01Ω (varies with state of charge).

Q3: How does temperature affect internal resistance?
A: Generally decreases with higher temperature (except in some lithium chemistries).

Q4: Can internal resistance be too low?
A: Extremely low internal resistance can lead to dangerous short-circuit currents.

Q5: How does internal resistance change over time?
A: Typically increases as batteries age and degrade.