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Charge Controller

The purpose of the charge controller is to charge batteries without overcharging them. The most basic charge controller disconnect the PV array when the battery is fully charged and keeps the battery fully charged without damage.


Different charging regimen are required is different for battery types. Within lead acid batteries different charging is required for Lead Acid (liquid), GEL AGM or VRLA and yes Lithium Ion batteries.


Controller Types: 

  • 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 requirement at the current for this stage within the charging cycle. The most efficient technique used in MPPT is 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 e.g a heating coil.  This technique is mandatory for wind and water turbines as these would be damaged if operated without a load.  Many charge controllers have ability 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 e.g. charging another battery, turning on a light at dusk or timer.


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. The advantage of higher voltages is that Amps are lower, avoiding power loss if the panels are not close to the charge controller.

  • Current:   Simple controllers have the same input and output amperage.  MPPT charge controllers, because can convert incoming power have lower output voltage to match the battery's charge requirement.  Charge controllers are rated by the Volts and Amps they are able to 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. If these are beyond your budget consider a PWM based charter. Read the manufacturer's specification. Efficiencies range up to 98% power conversion.

  • Expandability:    First comes capacity, if you think you may want more solar panels in the future, consider purchasing the additional capacity now.  Unless you invest in a charge controller that can communicate to another expanding later will require the original charge controller to be replaced.  Two controllers that don't communicate with each other cause one to fool the other as one will start sooner and will fool the second one to 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 Solar), others require special wiring and additional equipment (e.g. Outback).  MidNite Solar has a 30A and 90A MPPT charge controllers that are able to share the incoming power from PV.

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Last modified: January 12, 2023