Charge Controllers
Charge controllers
are needed in off-grid solar systems to control the flow of electricity from the panels to the batteries at a safe voltage and rate of charge. This is essential because the solar panels operate at a voltage that is higher than the maximum the batteries can handle and a direct panel-to-battery connection will damage the batteries.
The less expensive controllers simply monitor the battery voltage and stop the flow of electricity when the battery reaches its maximum safe voltage, generally considered to be about 13.7 volts. They can be used where the panel voltage is only slightly higher than the maximum battery voltage and the panel current cannot exceed the safe charging rate.
More expensive and more capable charge controllers, known as Maximum Power Point Tracking (MPPT) controllers, are needed in systems where the panel voltages are much higher than the battery voltage, as they are able to convert from high to low voltage as well as control the rate of charge at the maximum the batteries can accept. They also are available in a broad range of power handling capacities.
Some charge controllers include a battery protection feature that disconnects loads from the batteries if the battery voltage drops below the maximum safe range, generally considered to be about 11.7 volts. This feature is highly desirable because it protects the batteries against damage or significantly shortened life caused by over-discharge.
Some charge controllers provide built-in battery voltage and charging current meters and most controllers provide charging status and battery status lights.
