Home / Blog / MPPT chargers

How to size an MPPT charger for your panels and battery

Three checks tell you whether an MPPT controller suits your system: current, voltage and battery type.

Check 1: charging current

Charging current ≈ total panel watts ÷ battery voltage. Add about 25% margin.

Includes 25% margin. A higher battery voltage means lower current and a smaller controller.

Check 2: maximum panel voltage

Every MPPT controller has a maximum PV input voltage, such as 100 V, 150 V or 250 V. Add up the open-circuit voltage (Voc) of the panels you connect in series. The total must stay below the controller's limit, with some safety margin, because panel voltage rises on cool mornings.

Check 3: battery compatibility

• The controller must support your battery voltage (12, 24 or 48 V).
• For LiFePO4, choose a controller with a lithium charging profile, or one where you can set the charge voltage. Using a lead-acid profile on lithium can undercharge or stress the battery.
• Some lithium batteries can talk to the controller through a communication cable. This gives the most accurate charging.

Quick checklist

1. Current rating ≥ panel watts ÷ battery voltage × 1.25
2. Max PV voltage above series Voc, with margin
3. Supports your battery voltage and lithium profile
4. Installed with correct cable size, fuses and earthing

More articles