Solar Charge Controller Sizing Calculator
Find the minimum MPPT charge-controller amperage for your array and battery voltage, with the NEC 125% safety factor already applied.
rated = 50 A × 1.25 = 62.5 A → 80 A controller
A solar charge controller sits between your panels and your battery bank, and it has to be rated for the current the array can push into it. The operating current is just the array's wattage divided by the battery-bank voltage: the same panels feed far fewer amps into a `48 V` bank than a `12 V` one, which is a big reason larger off-grid systems run at higher voltage.
On top of that operating current, this tool applies the `1.25` factor from the National Electrical Code (NEC 690.8). Solar output is treated as a continuous source, and the code sizes continuous circuits — the controller and its wiring — to `125%` of the array current so nothing runs at its limit on a bright, cold, high-output day. The calculator then rounds up to the next standard MPPT controller amperage so you can match it to a real product.
This is a planning estimate. The controller also has a maximum PV input voltage and wattage per battery-voltage class that you must not exceed, and conductor and fuse sizing follow the same NEC rules. Confirm the full design with the controller's datasheet and a licensed installer before you wire anything.
array current = `1,200 W` ÷ `24 V` = `50 A`
rated = `50 A` × `1.25` = `62.5 A` minimum
next standard controller = `80 A`