Solar calculator

Solar Charge Controller Size Calculator

A controller must pass two different limits: battery-side charging current and the PV array's highest possible open-circuit voltage. This tool checks both.

Minimum controller output current62.5 AEntered controller fails at least one limit check

Calculation breakdown

Calculation breakdown
Cold-corrected PV open-circuit voltageMust remain below 100 V	98.4 V
Entered controller current limit	60 A
Voltage check	Pass
Current check	Fail

Output A = array W ÷ battery V × margin; cold Voc = panel Voc × series × cold factor
= 1200 ÷ 24 × 1.25; 41 × 2 × 1.2
= 62.5 A; 98.4 V

The controller's published PV open-circuit-voltage limit is absolute; do not use operating Vmp in its place.

Before you rely on this

PV open-circuit voltage can be lethal and must never exceed the controller's absolute limit in the coldest credible condition. Verify module coefficients, protection and wiring with manufacturer and code requirements.

Method

How the number is reached

MPPT output current is approximately array power divided by battery voltage, with a design margin. Separately, panel Voc rises in cold conditions and every series panel adds voltage.

Victron controller names encode both maximum PV voltage and battery charge current; neither rating substitutes for the other.

Controller A = array W ÷ battery V × current margin
Cold Voc = panel Voc × series count × cold factor

Symbols

Voc: Panel open-circuit voltage
Vmp: Operating voltage; not used for the absolute input limit

Worked examples

The same maths, applied

Example

1,200 W array on a 24 V bank

Two 41 V Voc panels per series string, 1.2 cold factor, 25% current margin and a 100/60 controller.

Current = 1,200 ÷ 24 × 1.25 = 62.5 A
Cold Voc = 41 × 2 × 1.2 = 98.4 V

Result: 62.5 A and 98.4 V; the entered 60 A controller fails current while 100 V barely passes voltage.

Limits of the model

What it assumes, and where it stops

Assumptions

Array watts are nameplate DC power and the cold factor comes from appropriate module/location data.

Not covered

Does not check short-circuit current, controller-specific oversizing rules or code-required conductor sizing.

Sources

Where these figures come from

SmartSolar MPPT — Battery voltage, PV voltage and current ratingVictron EnergyDefines controller maximum PV voltage, maximum battery charge current and compatible battery voltages.
SmartSolar MPPT — Installation and PV array limitsVictron EnergyManufacturer installation guidance requiring array open-circuit voltage to remain below the controller maximum and directing designers to verify array configuration.

Next steps

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Last meaningful update: 2026-08-19. This date changes only when the model, the sources or the guidance change.