Terminal Voltage Calculator
Calculate the terminal voltage of a battery or generator using EMF, internal resistance, and load current with this simple tool and formula.

internal resistance voltage calculator
The real voltage on the terminals of a battery or generator is referred to as terminal voltage. Formula: Vt = E - I × r.
Formula & Table Summary:
| Formula | Description |
|---|---|
| Vt = E - I × r | Terminal voltage formula |
| Vt = E | No load condition |
| Vt < E | Under load condition |
emf and terminal voltage formula
Terminal Voltage Calculator assists in determining the actual output voltage of a battery or generator with reference to EMF, load-current, and internal resistance.
generator terminal voltage
| EMF (E) (V) | Internal Resistance (Ω) | Current (A) | Terminal Voltage (V) |
|---|---|---|---|
| 12 | 0.2 | 5 | 11 |
| 24 | 0.1 | 10 | 23 |
| 48 | 0.5 | 20 | 38 |
| 6 | 0.05 | 2 | 5.9 |
Frequently Asked Questions - Terminal Voltage Calculator:
What is terminal voltage?
Terminal voltage is the actual voltage available at the terminals of a source when current flows through it.
How do you calculate terminal voltage?
Use Vt = E - I × r, where E is EMF, I is current, and r is internal resistance.
What is the difference between EMF and terminal voltage?
EMF is the ideal source voltage, while terminal voltage is the practical output under load.
When is terminal voltage equal to EMF?
When no current flows (open circuit), terminal voltage equals EMF.
Why is terminal voltage less than EMF under load?
Because of the voltage drop across the source's internal resistance.
Can terminal voltage be higher than EMF?
Yes, in charging conditions, terminal voltage can exceed EMF.
What units are used?
Voltage is measured in volts (V), current in amperes (A), resistance in ohms (Ω).
Is internal resistance important?
Yes, it affects battery efficiency and output voltage under load.
Can this calculator be used for generators?
Yes, it works for both batteries and generators.
Why does battery voltage drop under load?
Because internal resistance consumes part of the EMF, reducing the output.
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