A solar module converts sunlight into direct current. So the current from the solar module could be directly fed into the battery which also stores the electricity as direct current which in turn could be used to serve DC consumers.
The solar modules’ voltage, however, is higher than the voltage of a fully charged battery and can therefore damage a battery when it is directly charged. Moreover, a deep discharge of the battery may considerably impair its durability when the loads are used excessively.
The charge controller protects the battery from deep discharge, overload and short circuits. It extends the durability of the batteries considerably and should be on principle applied with self-sustaining solar systems.
When the end of charge voltage is reached, a series controller interrupts the module power using relay or power conductor and switches it back on after a defined voltage drop. It disables further current flow into batteries when they are full.
MPPT solar controllers make the solar panels operate at their optimum power output voltage. The current is regulated by the battery voltage, therefore they make the system accept high input voltages from the solar array. The generated power is able to be used more efficiently.
Duo charge controllers
For the caravan area so-called duo charge controllers are offered, which have two charging outputs. One for the automatic charge and charge maintenance of the (main) on-board supply battery and a charging output for the charge as well as charge retention of the vehicle starter battery.
A shunt controller continuously reduces the module power when the end of charge voltage is reached. But since the module continues producing power, the unneeded part of the module´s power is used as a short-circuit current without any problems. This method is ideal for the battery as charging is safe and swift.
What means PWM?
Pulse Wide Modulation is a special charging algorithm that is used in most charge controllers and also in other electric devices.
It is the most effective means to achieve constant voltage battery charging by switching the solar system controller´s power devices.
When a battery voltage reaches the regulation set point, the PMW algorithm reduces the charging urrent to avoid heating and gassing of the battery. The result is a higher charging efficiency, rapid recharging, and a healthy battery at full capacity.