Solar USB/DC charger for Li-Ion and Li-Pol batteries - Adafruit 390

Charger for single-cell Li-Ion or Li-Pol batteries powered from a USB type C socket or DC 5.5 / 2.1 mm connector with the possibility of connecting a solar cell . The maximum supply voltage is 6 V , and the set fast charging current of the cell is 500 mA with the possibility of changing it by changing the resistor. It has the MCP73871 system that automatically adjusts the current to achieve higher efficiency. It is also possible to connect an NTC thermistor to monitor the cell temperature.

USB/DC solar charger for Li-Ion and Li-Pol batteries - Adafruit 390.

The user has access to DC 5.5 / 2.1 mm power inputs, USB type C and soldering pads for the photovoltaic cell. The Li-Ion / Li-Pol battery connectors as well as the load connector are 2-pin JST connectors. In order to ensure stable operation, the included THT capacitor should be soldered to the module.

In order to change the value of the maximum battery charging current, replace the 2 kΩ SMD resistor soldered on the board with another one, where the current is calculated from the formula: 1000 V/PROG , where PROG is the value of the soldered resistor. The maximum supported current is 1 A , obtained by using a 1 kΩ resistor. It is possible to replace the SMD resistor with a THT element. For this purpose, the manufacturer used additional solder pads on the board.

The MCP73871 system allows you to monitor the temperature of the connected Li-Ion / Li-Pol battery through a 10 k NTC thermistor . It is not part of the kit and must be purchased separately. Its assembly consists in desoldering the SMD resistor and replacing it with a thermistor. For this purpose, additional THT solder pads have been made available.

• Maximum input voltage: 6V
• Maximum charging current: 500 mA adjustable from 50 mA to 1 A
• Cooperation with 3.7 V / 4.2 V cells
• Charging via USB type C, 2.1 mm Jack connector or 6 V photovoltaic cell
• Power, charging and end of charging signaling via LED
• Low battery indicator
• Ability to monitor battery temperature via thermistor (not included)
• Module dimensions: 41mm x 33mm x 2mm

• Solar charger module
• JST 2-pin cable to battery or load connector
• Stabilizing capacitor for installation in the project

• Manufacturer's website: Adafruit 390
• User Guide
• Documentation of the MCP73871 chip
• Project files on GitHub
• Schematic of the board in EagleCAD