Solar & battery
Solar Charge Controller Size Calculator
Charge controller current for an array, with the safety margin that stops nuisance shutdowns.
Result
MPPT controllers convert excess panel voltage into extra charge current, so they deliver considerably more from the same array than PWM, particularly in cold weather and with higher-voltage panels. Array voltage must also stay within the controller's maximum input, and cold raises panel voltage, so the check is made at the lowest expected temperature.
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About this calculator
MPPT or PWM?
MPPT for anything beyond a small system. It harvests 20% to 30% more in most conditions and lets you wire panels in series, which cuts cable size. PWM only makes sense for tiny, cheap systems.
Why the safety margin?
Edge-of-cloud effects can briefly push an array above its rating when sunlight reflects off cloud edges. A controller sized exactly to the calculation will shut down on those spikes.
The formula
charge amps = array watts x efficiency / battery voltage, plus a safety margin
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