What Is A Charge Control?
A charge controller is an electronic component that goes between your solar panel array and your battery bank in an online or off grid system. Depending on the model, the charge controller provides both overcharge protection, so that your batteries do not receive more than the proper charge during any given day, and can also provide additional functions like automatic on and off for lighting at night (like outdoor lights) and load diversion (like taking excess energy from a full charge and a number of other uses including remote monitoring.
Why a Charge Controller is necessary Since the brighter the sunlight, the more voltage the solar cells produce, the excessive voltage could damage the batteries. A charge controller is used to maintain the proper charging voltage on the batteries. As the input voltage from the solar array rises, the charge controller regulates the charge to the batteries preventing any over charging. Modern multi-stage charge controllers Most quality charge controller units have what is known as a 3 stage charge cycle that goes like this :
|During the Bulk phase of the charge cycle, the voltage gradually rises to the Bulk level (usually 14.4 to 14.6 volts) while the batteries draw maximum current. When Bulk level voltage is reached the absorption stage begins.|
|During this phase the voltage is maintained at Bulk voltage level for a specified time (usually an hour) while the current gradually tapers off as the batteries charge up.|
|After the absorption time passes the voltage is lowered to float level (usually 13.4 to 13.7 volts) and the batteries draw a small maintenance current until the next cycle.
A charge control must be able to handle the extra or excess current that can be produced by the solar panels. Reflected sunlight and high temperature conditions can increase the output current of a solar panel by as much as 25% above it’s rated output current. The charge control must be sized to handle the increased current.
For instance: An 160W 12V solar panel has a rated output current of about 9.5 Amps and a rated short circuit current of about 10 Amps.
Minimum solar regulator size for a single 160W solar panel should be:
Joepascalsolarworld recommends that the charge control selected is even slightly larger than this figure to ensure that it is not constantly operating at 100% of its rating, particularly in regions with higher ambient temperatures.
A good rule of thumb is a margin of between 20 and 30%.