Formula used
A real source can be modeled as an ideal EMF E in series with internal resistance r. The terminal voltage depends on current magnitude I and the operating direction.
- Discharging: Vt = E − I·r
- Charging: Vt = E + I·r
- Series load estimate: I ≈ E / (r + RL)
- Load power: P = Vt·I
How to use this calculator
- Select what you want to solve for in the Solve for menu.
- Choose Discharging or Charging to match your setup.
- Pick how to obtain current: enter I directly, or provide RL.
- Enter the known values with correct units, then press Calculate.
- Results appear above the form; export using CSV or PDF buttons.
Example data table
| Case | E (V) | r (Ω) | RL (Ω) | Mode | I (A) | Vt (V) | P (W) |
|---|---|---|---|---|---|---|---|
| Battery under load | 12.0 | 0.15 | 3.60 | Discharging | ≈ 3.24 | ≈ 11.51 | ≈ 37.3 |
| Heavier load | 12.0 | 0.15 | 1.50 | Discharging | ≈ 7.27 | ≈ 10.91 | ≈ 79.3 |
| Charging scenario | 12.0 | 0.15 | 3.60 | Charging | ≈ 3.24 | ≈ 12.49 | ≈ 40.5 |
The series‑load current uses I ≈ E/(r + RL) and then Vt from the selected mode.