MPPT charger (20A)

Development Stage Prototype built, development ongoing (major issues might still be open).

The Libre Solar project started with the development of this flexible and hackable MPPT charge controller. After a few prototypes using Arduino boards and AVR 8-bit microcontrollers, the current version is based on 32-bit STM32 ARM MCU with lots of free computing power to allow your own additions in software and communication features.

Charge controller PCB

Unique features

There are lots of charge controllers on the market. So you might ask yourself why this one is special?

Extensible hardware

The PCB of the Libre Solar charge controller contains lots of interfaces which could be useful for applications not yet thought about. Especially the UEXT connector is useful to add features like displays, wireless communication, etc.

Creativity by software

Though the primary function of the charge controller is to charge a battery using solar panels, the hardware behind the charge controller is just a high-power DC/DC buck converter. With some tiny software changes it can be used for numerous other applications.

Some examples:

  • Small wind turbines with AC generators can be easily connected to the charge controller using some diodes for rectification. Now you can develop a Maximum Power Point Tracking algorithm for your wind turbine.

  • As a synchronous buck converter, the DCDC power stage can be changed into a boost converter by software. In this case, current flow goes from the battery output to the solar input. This feature can be used to charge an electric bike battery pack with 36V nominal voltage using a 12V solar pannel. Sounds strange, but works and has been tested already. The 5V output is needed to switch on the bicycle battery (e.g. Bosch or Specialized).

Fully Open Source

Software and hardware are fully open source and can be used even for commercial applications. You are free to change whatever you want as long as you publish your changes and contribute to the open source hardware community.

Hard facts

If you want to know the core specifications…

  • Maximum Power Point Tracking (MPPT)
  • 12V or 24V battery output
  • 20A peak charging current
  • 55V max PV input
  • 32bit ARM MCU (STM32F072)
  • CAN communication interface with standard RJ45 jacks (CANopen pinout)
  • USB interface for firmware update and serial monitor
  • Expandable via Olimex Universal Extension Connector (UEXT) featuring I2C, Serial and SPI interface (e.g. used for display, WIFI communication, etc.)
  • Built-in protection:
    • Overvoltage
    • Undervoltage
    • Overcurrent
    • PV short circuit
    • PV reverse polarity (for max. module open circuit voltage of around 40V)
    • Battery reverse polarity (destructive, fuse is blown)


The charge controller is under active development and you are welcome to participate.

Visit the GitHub page for schematics and board layout.