How to size your PWM charge controller?
The main function of a charge controller (sometimes called ‘charge regulator’) is fully to charge the battery in a solar system but also to prevent it both from overcharging in hot sunny days and from deep discharging in days of scarce sunlight. If you connect a solar array directly to a battery, with no charge controller, this will eventually result in shortening the battery life.
The most common charge controllers are ‘pulse-width modulation’ (PWM) ones. A PWM controller senses small voltage drops and reacts by sending pulses of charge to the battery. The duration of such pulses vary depending on the battery’s state of charge.
A battery in a low state of charge gets a long pulse, while a battery in a higher state of charge gets shorter charging pulses. Therefore the duration of a charging pulse is adjusted on the measured state of charge.
As a rule, charge controllers are sized according to the current and the voltage of the solar system they are connected to. Since system voltages are typically 12V, 24V or 48V, 12V, 24V and 48V-charge controllers are most common. Amps ratings usually vary from 1 to 100 A, and you should size your charge controller depending on the value of the current flowing through your solar array.
‘To size’ actually means ‘to select’ your charge controller according to the voltage and current of your solar array. It commonly recommended to ‘oversize’ a charge controller by at least 25 % for safety and reliability reasons, which means to find a charge controller of maximum current that is 25% more of the calculated maximum current.
By trying our new mini calculator here:
you will be able to solve two kinds of important tasks:
- PWM charge controller of what maximum current to select for a PV array that will produced the desired solar generated electricity, and visa versa,
- A solar array of what size (that is, of what maximum current and voltage) you will need to build, if you already have a charge controller available. In this case, you will eventually find out whether such a charge controller will fit a solar system of desired output.
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