75W high efficiency MPPT solar charger, efficiency more than 97%!

After three years of development, this open source project is about to be completed. From its modest start, it has developed into a fairly complex device with USB interface, powerful USB charging port, 20x4 character LCD, rotary encoder with buttons, accurate measurement of all applications from voltage and current to temperature. It has four PWM power outputs and 4MB storage space, which can store one year's real-time clock and calendar data. It connects to desktop applications via USB, and users can monitor and adjust all aspects.

But what's really special about this charger is that it has a very high efficiency of about 97% over a wide power range of 1 to 75 WATTS. And more: this charger doesn't drain your battery when there's no sun. It will enter a very low power consumption state, most of the sub circuits are powered off, while still recording data.


It is suitable for any type of battery with a nominal voltage of 6 to 13 volts.


Multi function independent or as a module


Although the project was originally a separate solar charger, it is now often used as a module for large projects. The main example is meshpoint, a WiFi hotspot for disaster and outdoor areas. The project is about WiFi and 4G mobile networks, not about power collection. Using the solar charger as a module, valent and his team can focus on WiFi connectivity without over decentralizing power management.


Don't reinvent the wheel


Whatever your project is, if there is no wall outlet nearby, you will have to worry about power sooner or later. As has been discovered in the past few years, developing high-quality solar chargers is an important project in itself. It is likely that this charger can meet the specific requirements of your project. It is suitable for various types of batteries, and has a wide power range. Usually, you can meet your needs by simply configuring it. So don't reinvent the wheel. Use this solar charger as a module in the project and focus on what you really want to achieve.


For more participating projects like the meshpoint mentioned above, you can decide to customize the hardware by arranging your own PCB so that it can be physically appropriate, or even peel off some of the features you don't need. Even so, the work involved is only a small part of the work compared to starting from scratch.


If you can use hardware, your life is easier. Just determine if you need a user interface and start configuring the charger. The various interfaces from I2C to I2C make it easy for your application to communicate with this charger.


Independent use


In many cases, people need (or just want) electricity, but there are no wall outlets nearby. Whether it's a camping car, a boat or an outdoor cabin. It has some advantages such as electric lighting, charging mobile phones, etc. Moreover, the availability of affordable solar panels makes solar energy the preferred energy in this case.


Yes, you can buy one of the countless solar chargers there. But if you want to be able to control and configure it, you want to be able to adjust according to your specific needs, and want to be able to connect your laptop to see what it did when you were not. If you're so inclined, this charger is for you.


If your project is about recording environmental data, you may even rely entirely on this project. Two analog inputs originally used for temperature measurement can also be used for other purposes. If you need more, you can connect the external ADC directly to the I2C or SPI interface, allowing the solar charger to do all the work. All you need to do is customize the firmware so that it can handle your additional hardware.


  • beyond solar energy


Even a project to collect wind power decided to use the solar charger as a starting point. Although wind turbines must be different from solar panels, there are many similarities. All of this is to extract as much energy as possible and to transform in an effective way. From this open source design, it has saved countless hours in software and hardware development.


Features and details


High efficiency DC DC voltage reducing converter


The core of the project is an efficient DC-DC switcher with a rated power of 75 WATTS, which is completely controlled by software. It works at 187.5khz and can be operated in synchronous or asynchronous mode. The latter is more efficient in light load. Combined with carefully arranged and carefully selected components, 97% efficiency can be achieved, about 1 to 75 WATTS. This means there is no radiator and fan, which helps to maintain dimensions and costs.


You can connect any size of 12V solar panels. The panel can be more than 75 watt rating of the charger. It's smart enough to absorb more current than it can handle safely. And MPPT (maximum power tracking point) algorithm ensures that the panel operates in the most effective combination of voltage / current when power is required.


Very low standby current


Efficiency is just one side of a coin when it comes to energy harvesting. In many applications, especially in low-power applications, it is also even more important to maintain power without the sun. This is where many other chargers fail. This uses very low static current power and low power microcontrollers. In standby mode, the board voltage is reduced from 3.3 to only 2.2 volts, and any unused sub circuits are completely de energized. The system clock also dropped from 48mhz to 32.768KHz. All of this can reduce power consumption to just about 100 microas while still recording data.


? suitable for any type of battery


Unlike most other solar chargers, this solar charger is suitable for a wide range of sizes of cells. You can use a standard 12V lead-acid battery, but you don't have to. You can also use 3-core lithium-ion batteries, or Libo, or NiMH or any size and technology that suits your project. All parameters, such as maximum charging voltage, maximum charging current, minimum discharge voltage, etc., can be specified, and can even depend on the ambient temperature. It is suitable as long as the nominal voltage of the battery is within 6 to 13 volts.


Precision measurement and data recording


The well designed circuit and 16 bit ADC with a precision 2.048v voltage reference are used to measure the voltage and current of the input and output. In addition, the 12 bit ADC and 2.5V reference voltage sources inside the pic are used to monitor the on-board voltage and up to two external temperatures.

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All of these data and other system parameters are stored in a log file every 5 minutes. There is enough on-board storage to record data for about a year. Real time clocks and calendars serve as time references and provide time stamps for each dataset.


USB interface and bootloader


When connected to the host via USB, the charger acts as a composite HID / MSD (high capacity storage device). The HID interface is connected to a dedicated solarchharger application, allowing users to monitor and control chargers. MSD device classes allow easy firmware upgrades on site without the need for programmers or any host software.


LCD display and rotary encoder


It has a high contrast user interface 4-line 20 character LCD and a rotary encoder with buttons, which can monitor and control the equipment. If your application does not need a user interface, discard it and use another interface.


- SPI and I2C interface


If you integrate this charger into a larger project, you may want to communicate with the device using a protocol simpler than USB. All functions are then accessible through I2C or SPI. These interfaces can run in or from the main mode. In future boot loader versions, firmware can even be upgraded through these interfaces.


USB charging port


There are 2 USB charging ports with a total current of 4 amps. This is enough to charge both tablets at once. Compatible with Samsung, apple and any other devices.

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4 PWM power output


There are four powerful outputs that can be turned on and off separately, and even PWM control can be performed. Therefore, they are very suitable for controlling LEDs or any other equipment you may need.


Fan output


In most applications, fans are not required. If you need one for your project, there is a dedicated output of a temperature control fan on the circuit board.