Solar Charge Controllers Alison Ray and Scott Hamshaw

Basic Functions Prevents battery overcharge Blocks reverse current Prevent over-discharge from batteries (some models) Prevent electrical overload (some models) Displays battery status

Blocking Reverse Current To prevent night discharging of batteries, controllers pass current through a semi-conductor only allowing current to flow in one direction. Some controllers use a relay to switch off at night Very small systems can use a simple diode to prevent discharge.

One and Two Stage Charge Controllers Most basic form of charge controller Work by simply switching current fully on/off (1 stage) or reducing current in two steps (2 stage) Utilize relays to act as a simple disconnect

Pulse-Width Modulation (PWM) Controllers Battery is charged using pulses of energy that can vary in length and speed according to battery condition. As the battery reaches capacity, the flow of energy is slowly tapered off as opposed to sudden cut off to reduce battery overcharging Ideal for situations where excess energy is often present higher charging efficiency rapid recharging healthy battery at full capacity

Maximum Power Point Tracking Controllers A MPPT controller adjusts the voltage output to take advantage of the Vpp and charge the battery more Peak Power Voltage (Vpp) is the maximum power point that a PV system can deliver; varies with temperature and sunlight intensity Vpp is higher in colder and sunnier conditions therefore, MPPT controllers are ideal for cold climate use where battery use is high

Prices for Typical Charge Controllers Brand/ModelTypeAmperagePrice Xantrex C40 PWM40$159. Blue Sky Energy Solar Boost 3024i MPPT30$299 MorningstarSHSPWM10$40 For a list of Charge Controller Manufacturers visit