What does a battery need protection from, and what does a charge controller do?

A charge controller serves several purposes:

It reduces the voltage of the solar panels to match the battery's level, which prevents the battery from heating up due to direct connection to higher voltage panels. Overheating can decrease battery lifespan or even cause an explosion.

It prevents overcharging, which can cause temperature rises and damage to the battery's capacity and lifespan.

It prevents deep discharge, which reduces the number of charge cycles a battery can handle.

It blocks reverse currents, which can lead to temperature rises and fires in PV modules when electricity flows back to panels from the battery at night.

It allows for monitoring of the panels and battery's state.

PWM and MPPT controllers handle panel voltage differently. PWM controllers simply reduce the voltage to the battery level, while MPPT controllers utilize extra panel voltage to generate more electricity. While either can be used with slightly higher voltage panels and a corresponding battery, MPPT controllers can harvest an additional 20-25% of energy, particularly in winter when panels reach peak voltage.

How to Properly Size a Charge Controller

 To properly size a charge controller for your solar panel system, you should look for the maximum volts and amps. The crucial parameter is the maximum amps, which must be greater than the combined power of all solar panels divided by the voltage of the battery.

For example, if you have two 300W panels and a 12V battery, you can calculate the required amps as follows:

300W * 2 panels / 12 V = 50 A

To be on the safe side, you should add 25% to account for potential increases in current during cold weather:

50 A * 1.25 = 62.5 A

Therefore, the controller should be sized to handle at least 62.5 A.

Connecting battery, controller and panels

Whether you have a PWM-controller or an MPPT-regulator, the process of connecting it to the battery and panels is the same. Typically, a charge controller has three wiring sections: one for the panels, one for the battery, and one for DC loads.

To make the connection, you will need a simple stranded copper core wire. Use the black wire to connect the charge controller's "minus" to the battery's "minus," and use the red wire to connect the charge controller's "plus" to the battery's "plus." Make sure to screw the wires tightly into the charge controller.

After making the connections, turn the charge controller on. It should be able to measure the battery's charge. If you are unsure about the wiring, consult the user manual of the charge controller, which should have a wiring diagram.

1.Once the battery is connected to the charge controller, it is safe to connect the panels. From the junction box of each panel, you will find two cables - a positive and a negative. In some cases, there may only be two wires that connect directly to the controller. However, typically, there will be MC4 connectors at each end, with a "male" connector for the positive cable and a "female" connector for the negative one.

2.If you have two wires that come out of the junction box, connect them to a complementary pair of connectors that have wires on the other ends. If you have MC4 connectors, simply plug the connectors into the corresponding ports on the charge controller.

3.Once the panels are connected to the controller, it should recognize them. You can verify this by checking the status of your array on the charge controller screen.

4.As soon as the PV modules are exposed to sunlight, they will start generating electricity.

Here's a diagram that shows how to connect the various components of a solar panel system together.