Frequently Asked Questions
How do I size a charge controller's current rating?
NEC requires a 1.25× factor for continuous PV current, so controller amps ≥ array Isc × 1.25. A 30 A controller can safely handle an array whose short-circuit current is up to 30 ÷ 1.25 = 24 A.
How do I get charge current from panel Vmp?
For MPPT controllers, output A ≈ (array Vmp × Imp) ÷ battery voltage. A 1,000 W array into a 24 V bank yields roughly 1,000 ÷ 24 ≈ 42 A, so a 50 or 60 A MPPT is appropriate.
PWM vs MPPT - which should I pick?
PWM forces the panel to battery voltage and wastes the extra; MPPT tracks the panel's max-power point and converts. MPPT typically harvests 15–30% more energy and is required when array Vmp ≫ battery V (e.g. 60-cell panels on a 12 V bank).
Why does Voc matter for the controller?
The controller's max PV input voltage must exceed array Voc at the coldest expected temperature (Voc rises ≈0.3%/°C below 25 °C). Exceed it and you instantly destroy the input stage - derate cold-weather Voc by 1.15–1.25×.
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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.