MPPT amps ≈ panel watts ÷ battery volts × 1.25. PWM amps = panel Isc × parallel strings × 1.25. The 1.25 factor covers bright, cold days when panels beat their rating. For MPPT, the open-circuit voltage of a series string rises in the cold, so add about 10–25% to Voc and stay below the controller's max input voltage.
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
On a 12 V battery about 42 A, so a 40–50 A MPPT; on 24 V about 21 A.
MPPT is 10–30% more efficient, especially in cold weather and with series panels. PWM is cheaper and fine for one or two small panels.
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