The PD.Charger-GSM v2.5 is an industrial-grade solar and LiFePo4 charger/controller with MPPT support, designed for 2–4 cell Li-Ion/LiFePo4 batteries. With various connectivity options and a cryptographic co-processor, it’s ideal for IoT, remote solar power systems, and battery-powered industrial applications.
The device features a dual-MCU architecture where the STM32 handles battery charging and monitoring, and an ESP32 manages WiFi and Bluetooth connectivity, as well as LTE/NB-IoT GSM/GPS, and RS-485 with ModBUS support. The board also offers two solar inputs with MPPT, a DC adapter input, automatic buck/boost control, SMA connectors for all RF interfaces, a USB Type-C for programming, and expansion headers for prototyping. A hardware crypto co-processor handles secure key storage, TLS encryption, and secure boot.
PD.Charger-GSM v2.5 specifications:
- SoCs
- STM32L051xx MCU for battery management and monitoring
- ESP32-D0WDQ6-V3 dual-core Xtensa LX6 processor, 240 MHz, 16MB Flash, 8MB PSRAM
- Display – Supports optional PD.Screen / PD.Screen_PRO modules for real-time display of battery status
- Connectivity
- Wi-Fi 802.11 b/g/n and Bluetooth via ESP32
- LTE/NB-IoT GSM/GPS module (SIM7080G-M) with onboard SIM card slot(X13)
- RS-485 interface with ModBUS protocol support
- Antennas – 3x SMA connectors for Wi-Fi, Bluetooth, GSM, and GPS antennas (X4, X10, X11)
- USB – USB Type-C for programming and data exchange (X12)
- Debug
- SWD STM32 flash header (X5)
- I2C EXT connector, for connecting external I2C devices for debug (X6)
- Expansion – GPIO extension connector from both ESP32 and SIM7080G subblocks (X15)
- Security
- ATECC608A Crypto-Authentication co-processor
- Hardware support for SHA-256, HMAC, AES-128, ECDSA, and ECDH
- Secure boot, TLS 1.2/1.3, small message encryption
- Misc
- NTC connector (X7, X8) – Supports 10k NTC for battery temperature monitorng
- Input, balancer cable input from the LiFePo external battery pack (X42)
- Optional connector for changing I2c address (X3)
- RS-485 bus connector, connected to the XR33038IDTR-F RS-485 chip (X14)
- Status and power LED in the front
- Voltage, current, SoC (state of charge), and per-cell voltage monitoring
- Add-on breadboard-style PCB available for prototyping
- Power
- Inputs
- 3.6-V to 40-V wide input from Solar panel or external DC (X1 and X2)
- X1: up to 7A (18V recommended)
- X2: up to 8A (18V recommended)
- Combined input current: up to 14A
- XT30 connector for battery input (X41)
- 3.6-V to 40-V wide input from Solar panel or external DC (X1 and X2)
- Outputs
- Charger output also battery input(X41) – up to 12A (7A recommended)
- Load(X9) – 12V default (10–14.4V), up to 14A (8A recommended)
- Supports 2, 3, or 4-cell Li-Ion and LiFePo4 batteries (up to 500+ Ah)
- TI BQ25756 dual MPPT solar panel or DC inputs (up to 40V)
- Automatic buck, boost, or buck-boost power management
- Max charging current – 15A (API controlled)
- BMS/charger subblock idle current ~1mA
- Inputs
- Mechanical
- Dimensions – 113.2 x 98.5 mm, including SMA connectors
- 11 mounting holes for M3 screws, 3.2 mm diameter
- Weight – 82 grams (module only)
- Temperature
- Operating – -40°C to +85°C
- Storage – -55°C to +150°C
- ESD rating – CDM ±250 V per JEDEC JESD22‑C101
The ESP32 in the model can be programmed using Arduino IDE, PlatformIO, and ESP-IDF. As for the STM32, the firmware can be updated via the SWD interface using the STM32CubeProgrammer. It provides an I2C/UART-based API for controlling and monitoring the charger, gauge, and BMS chips, with communication speeds up to 1 Mbps. Additionally, the module comes with ready-to-use Arduino examples for I2C commands, battery monitoring, and sensor integration, for quick prototyping and integration with external controllers or SoCs.
The module enforces strict LiFePO₄ balancer rules (5-wire pinout) and requires disabling the onboard balancer if the battery pack already includes one. There are 11 mounting holes (Ø3.2 mm for M3) and outdoor installation guidelines, including lightning, waterproofing, and cooling measures. Previously, we wrote about the Waveshare Solar Power Manager Module, which supports 6V to 24V input, MPTT support, and battery charging functionality, but it was not as feature-rich as this one.
The solar MPPT charger module is available on ProtoDevs GmbH’s Tindie store for $190. More information, including datasheet design files, source code BOM can also be found on that same page.
Debashis Das is a technical content writer and embedded engineer with over five years of experience in the industry. With expertise in Embedded C, PCB Design, and SEO optimization, he effectively blends difficult technical topics with clear communication
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