Solar Charge Controller from dddd's blog

A solar charge controller( or regulator, as they are sometimes known) is an essential part of every solar charging kit. The main role of a controller is to protect and automate the charging of the battery. It does this in several ways:

• Without a controller between a solar panel and a battery, the panel would overcharge the battery by generating too much voltage for the battery to process, seriously damaging the battery.
• Overcharging a battery could result in the battery exploding!

• The controller detects when the battery’s voltage is too low. When the battery drops below a certain level of voltage, the controller disconnects the load from the battery in order to prevent the battery from being drained.
• A completely drained battery will lose some of its overall capacity.
• Low voltage can still damage the battery if the load is connected.

• The controller stops any current from flowing back into the solar panel at night.
• This prevents any damage to your solar charging kit.

NOTE: The controller can also regulate current from the load when the load is connected to the controller. The load terminal on the controller is for direct connection of the load to the controller - unlike a wind turbine controller, it is NOT a load dump. The controller can still operate as normal if there is no load directly connected to it. 

This diagram illustrates the connectivity of a typical solar power kit, including a solar panel, a solar charge controller, a battery and the load (e.g. a light bulb). The solar panel connects to the controller through positive and negative leads, only creating a charging function when the controller is connected to a battery. The load is then responsible for the discharging function from the controller (if it is connected to the controller).