Resources / Calculators

MPPT Controller Size Calculator

Enter your panels and battery voltage to find the controller amps you need and the cold-morning voltage it must handle.

An MPPT controller is sized two ways: the current it delivers to the battery, and the highest voltage the panels can put into it. Both are checked here. Everything is worked out in your browser. Nothing is saved or sent anywhere.

1. Your panels

Take these from the label on the back of the panel or its data sheet. Voc is the open-circuit voltage, Vmp the voltage at maximum power, and Isc the short-circuit current. The examples are a typical 400W panel.

Series adds the voltages.
Parallel adds the currents.

2. Battery and conditions

Panel voltage rises as it gets colder.
On the data sheet. About -0.25 to -0.35 is common.
Extra allowance on the controller amps (0 to 100%).

3. Results

How it was worked out

    Before you rely on it

    • MPPT controllers are often named by their two limits, for example 150/45: up to 150V from the panels and 45A to the battery. Both numbers must suit your result.
    • The controller's maximum PV input voltage is an absolute limit. Going over it on a cold morning can destroy the controller. Use the maker's own string-sizing tool if one is offered.
    • Also check the controller's maximum PV short-circuit current, and that it has a charging profile for your battery chemistry, such as lithium (LiFePO4) or AGM.
    • The panel voltage check here is rough. The string's Vmp must stay well above the battery's charging voltage on hot days, so check the controller manual.
    • A string over 120V DC is no longer extra-low voltage and can give a dangerous shock. Panel wiring at that voltage, and any 240V AC work, must be done by a licensed electrician.
    • This is a planning estimate only, not a system design, wiring specification or safety assessment. Real results depend on your location, weather, shading and the gear you choose. Check the manuals and specifications for your panels, battery, inverter and charge controller.
    • Safety: in Australia, any work on 240V AC wiring, including connecting an inverter, battery or solar system to a home's switchboard or fixed wiring, must be done by a licensed electrician. Grid-connected systems also need approval from your electricity network.

    Next steps

    Not sure which type you need? Read PWM vs MPPT Charge Controllers. Then protect the wiring: see Fuses, Breakers and Isolators for 12V to 48V Solar.

    ↑