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Charge Controller

The most basic charge controller disconnects the array when the battery is fully charged and keeps the battery fully charged without damage.

Charging regimen required is different for each battery type. Different charge are required for Lead Acid (liquid), GEL AGM or VRLA and yes Lithium Ion batteries.




  • Series controllers stop the flow of current by opening the circuit between the battery and the PV array. The more advanced version of this is called Pulse Width Modulation (PWM)

  • MPPT (Maximum power point tracking) charge controllers use both PWM and MPPT.  MPPT charge controllers frequently and continually sample the incoming voltage and amperage then convert the input to the voltage and amperage required by the batteries at the current requirement for this stage within the charging cycle. The most efficient technique used in MPPT sis called Perturb and observe. It essentially means that the incoming volts and amps are interrupted, analyzed and reconfigured for optimum output at this stage of charging. (you really don't need to know this bit but you can search "MPPT Perturb and Observe" on the internet if you're so inclined).

  • Shunt controllers divert the PV array, hydro or wind current from the battery to an electrical load.  This technique is mandatory for wind and water turbines as these would be damaged if operated without a load.  Many charge controllers have facility to provide power to a load based on voltage, time and power coming in from the solar panels. These are not shunt loads to divert power in order to avoid over charging batteries.


Selection criteria: 

  • Input voltage:  Solar panels operate at higher voltages than batteries and most PV allows even higher voltages by wiring several panels in series.

  • Current:           Simple, series controllers have the same input and output amperage.  MPPT charge controllers, because the convert incoming power will have lower output voltage to match the battery's charge requirement but because of the equation Watts=V*A as voltage is reduced Amperage goes up. Charge controllers are rated by the Volts and Amps they can handle.  Make sure that with a MPPT charge controller that you calculate output amps.    

  • Battery type:     Each battery type from Flooded Lead Acid to Lithium Ion has different charge requirements and restrictions. 

  • Battery voltage: Currently system battery voltages range from 12 to 72V.  The most popular off-grid system voltages are 24 and 48 volt.

  • Efficiency:         In general the least expensive charge controllers are the least efficient.  Look for an MPPT charge controller for more efficiency. Read the manufacturer's specification. Efficiencies range up to 98% power conversion.

  • Expandability:    First comes capacity, if you think you will want more solar panels later, consider purchasing the additional capacity now.  Two controllers that don't communicate with each other will cause one to fool the other as one will be fooled by the other's charging.  Many top tier controllers have methods of connecting to each other.  Some of these connections require nothing more than a telephone jacked cord (e.g. Midnite), others require special wiring and additional equipment (e.g. Outback).  MidNite Solar has a 30A MPPT charge controller that is able to share the incoming power from PV on the same wire.

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Last modified: March 07, 2021