Selecting the Right Size Controller To size a solar charge controller, take the total watts of your solar array and divide it by the voltage of your battery bank, then multiply by a safety factor of 1.25. This calculation will give you the output current of the charge controller.
Depending on the number and power of the solar panels to be paired with the number and voltage of the battery bank, a selection of the best size charge controller can be made. Charge controllers are rated according to amperage.
That’ll give you your solar charge controller’s necessary minimum capacity in amps. Let’s say you have a 400W solar panel system and a 12V battery bank. You would divide 400 by 12, giving you a minimum of 33.33 Amps. This means your solar charge controller should be at least 34 or 35 Amps. How Big a Solar Charge Controller Do You Need?
Block Reverse Currents: Solar panels pump current through your battery in one direction. At night, panels may naturally pass some of that current in the reverse direction. This can cause a slight discharge from the battery. Charge controllers prevent this from happening by acting as a valve. DO YOU ALWAYS NEED A SOLAR CHARGE CONTROLLER?
Charge controllers are sized depending on your solar array's current and the solar system’s voltage. You typically want to make sure you have a charge controller that is large enough to handle the amount of power and current produced by your panels. Typically, charge controllers come in 12, 24 and 48 volts.
To calculate the required rating of the Charge Controller for a 100W solar panel charging a 12V battery bank: 1. Watt Rating: The power rating of the panel is 100W. 2. Current Rating: Let the system voltage be 12V, so current = 100W / 12V = 8.33A. 3. Consider Safety Margin: