Solar Charge Controller

Posted by admin on December 30, 2008

A small charge controller usually contains a transistor that shunts the PV charging circuit, terminating the charge at a pre-set high voltage. Once a pre-set reconnect is reached, it opens the shunt, allowing charging to resume.

A more sophisticated charge controller utilizes pulse-width modulation (PWM) or maximum power point tracking (MPPT) to assure the battery is being fully charged. The first 70% to 80% of battery capacity is easily replaced, but it is the last 20% to 30% that requires more attention and therefore
more complexity.

Charge controllers are rated and sized by the solar array current and system voltage.
Most common are 12, 24, and 48-volt controllers. Amperage ratings can run from 1 amp to 60 amps, voltages from 6-60 volts.

Let us take for example:  you have two 12-volt modules that produce 7.0 amps each, Your system will then produce 14.0 amps of current at 12 volts. Because of light reflection and what is called “edge of cloud effect,” it can sporadically increase current levels. For this reason you should increase the controller amperage by a minimum of 25% bringing your minimum controller amperage to 17.5. Your best bet would be to find a 20 amp controller. You should really look into buying a larger controller if you plan to expand your system in the future.