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What Size MPPT Charge Controller for Van Solar?

An MPPT charge controller is rated by output amps, and you size it from your array watts and battery voltage. The formula is amps = (array watts ÷ system volts) × 1.25, then round up to the next standard controller (20, 30, 40, 50, 60, 80, 100 A). The 1.25 factor is NEC 690.8's continuous-current margin, and using the nominal battery voltage (12 or 24V) rather than panel voltage keeps the result conservative.

Worked example

A 400 W array on a 12V system: (400 ÷ 12) × 1.25 = 41.7 A. Round up to the next standard size and you need a 50 A MPPT controller. Switch that same array to 24V and the current roughly halves to (400 ÷ 24) × 1.25 = 20.8 A, so a 30 A controller does the job — one reason larger builds move to 24V.

Array12V controller24V controller
200 W 30 A 20 A
300 W 40 A 20 A
400 W 50 A 30 A
600 W 80 A 40 A
800 W 100 A 50 A
1,000 W 100 A (split array) 60 A

Above roughly 100 A of output it is common to split the array across two controllers, which also adds redundancy. Always confirm the controller's maximum PV input voltage against your panels wired in series.

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