Open Circuit Voltage Calculator

Calculator

Calculation mode

Loaded terminal voltage V

Source or internal resistance Ω

Measured load resistance Ω

Divider supply voltage V

Upper divider resistance Ω

Lower divider resistance Ω

Norton current A

Equivalent resistance Ω

Meter measured voltage V

Meter input resistance Ω

Series cells

Parallel strings

Cell open circuit voltage V

Cell temperature °C

Reference temperature °C

Temperature coefficient mV/°C/cell

Output load estimate Ω

Target load current A

Tolerance percent

Safety margin percent

Notes for export

Example Data Table

Method	Key inputs	Open circuit voltage	Use case
Loaded terminal	Vload 11.80 V, Rs 0.20 Ω, Rload 10 Ω	12.036 V	Battery or supply load test
Voltage divider	Vin 24 V, Rtop 10 kΩ, Rbottom 5 kΩ	8 V	Divider output check
Norton equivalent	IN 0.12 A, Rth 150 Ω	18 V	Equivalent circuit conversion
Meter correction	Vmeter 9.60 V, Rmeter 10 MΩ, Rs 500 kΩ	10.08 V	High impedance measurement
Cell string	6 cells, 2.10 V each, 25 °C	12.6 V	Battery string estimate

Formula Used

Loaded source: V_oc = V_loaded × (R_load + R_source) / R_load.

Voltage divider: V_oc = V_in × R_bottom / (R_top + R_bottom).

Norton equivalent: V_oc = I_N × R_th.

Meter correction: V_oc = V_meter × (R_meter + R_source) / R_meter.

Cell string: V_oc = series cells × adjusted cell voltage.

How to Use This Calculator

Select the calculation mode that matches your circuit.
Enter only the values needed for that method.
Add tolerance and safety margin if needed.
Use output load resistance to estimate loaded voltage.
Press Calculate to show results above the form.
Use CSV or PDF buttons to save the report.

Open Circuit Voltage Guide

Open circuit voltage is the terminal voltage measured when no external load is connected. It shows the available electrical pressure before current is drawn. This value helps compare batteries, power supplies, dividers, solar strings, sensors, and equivalent circuits. It is useful because loaded voltage often hides internal losses.

Why This Calculator Helps

The calculator supports several practical methods. You can estimate source voltage from a loaded reading, a divider network, a Norton equivalent, a meter corrected reading, or a series cell string. These modes cover bench tests and design checks. They also help when direct measurement is not possible.

Loaded Source Method

Real sources have internal resistance. When a load draws current, part of the voltage is lost inside the source. The calculator adds that internal drop back to the measured load voltage. This gives a closer estimate of the true open circuit value. It is helpful for batteries, supplies, coils, and test fixtures.

Voltage Divider Method

A divider creates an output from two resistors. With no load attached, the output depends on the supply and the resistor ratio. The calculator also estimates Thevenin resistance. That value predicts how much the output will sag when a load is connected.

Meter Correction

A voltmeter is not always invisible. Lower input resistance can pull a weak source down. The meter correction mode estimates the unloaded voltage by accounting for meter resistance. This is useful for high impedance sensors and leakage tests.

Cell String Estimate

Cells in series add voltage. Temperature can change each cell open circuit value. The cell mode adjusts voltage using a temperature coefficient. It then multiplies by the series cell count. Parallel strings do not raise voltage, but they matter for current capacity.

Practical Use

Use realistic resistance values. Choose ohms, kilohms, or megohms consistently after conversion. For field work, add tolerance and safety margin. Compare calculated values with safe meter readings. Do not open live equipment unless you are qualified. Always follow local electrical rules and use rated instruments.

Review each result as an estimate, not a certification. Small contact resistance, aging, heat, and instrument accuracy can change readings. Record conditions with every export, especially during troubleshooting or acceptance testing for clear later comparison.

FAQs

What is open circuit voltage?

Open circuit voltage is the voltage across two terminals when no external load is connected. It represents the unloaded source voltage.

Is open circuit voltage the same as loaded voltage?

No. Loaded voltage is usually lower because current causes voltage drop across internal resistance, wiring, and contacts.

Which mode should I choose?

Use loaded terminal mode for load tests. Use divider mode for resistor networks. Use Norton mode for equivalent circuits. Use meter correction for high impedance readings.

Why does meter resistance matter?

A meter draws a small current. In high impedance circuits, that current can reduce the measured voltage and cause reading error.

Does parallel cell count increase voltage?

No. Parallel strings increase current capacity. Series cells increase voltage. This calculator notes parallel strings but does not multiply voltage by them.

Can this calculator replace a real measurement?

No. It gives an estimate from entered values. Use rated instruments and safe procedures for real electrical work.

What does Thevenin resistance mean?

Thevenin resistance is the equivalent resistance seen from the output terminals. It helps predict voltage sag under load.

Why add tolerance percent?

Tolerance shows a likely high and low range. It helps account for component variation, aging, heat, and measurement uncertainty.