Project Overview

Up-cycling industrial equipment provides a sustainable way to reuse highly reliable components. Mobile-network cell-tower gear is built for 24 × 7 operation in harsh environments, so it is compact, efficient and remarkably resilient.

This project centres on the Huawei R4875G1 48 V Rectifier Module. Designed to power base-station loads and battery banks, it can be trimmed from 45 V to 58 V and happily tolerates a “dirty” AC generator or weak grid. The module is 97 % efficient, delivers up to 4 kW, includes short-circuit and surge protection, speaks CAN bus, and boasts an MTBF of 500 000 h.

A well-designed and powerful battery charger.

View the R4875G1 datasheet

The ESPHome firmware presented here runs on an ESP32 development board linked to the rectifier through a VP230 (SN65HVD230) CAN-bus transceiver.

Key Features

NEW: MQTT support in web-app, see latest release.

Supported Hardware

R4875G
R4850G
R4830G

Parallel Operation (up to three r48xx units, one ESP32 controller)

Join CAN-H lines
Join CAN-L lines
Wire DC outputs in parallel

Supported Sensors

Power State — ON / Hibernate / Error
AC Power In
DC Power Out
Grid Frequency
Input Current
Output Current
Input Grid Voltage
Output Voltage
Set Maximum Output Current
Set Maximum Output Voltage
Output Temperature
FAN RPM (model-dependent)
Total Operating Hours

Configuration Settings

CAN Voltage Set
CAN Amp Set
Fallback Amp Set
Fallback Voltage Set
Simple Daily Charge Timer
CAN Max AC Amp Set (model-dependent)
Cooling-Fan PWM Control (model-dependent)
Low / High Voltage Set (auto wake / hibernate)

Control Buttons

CAN ON (wake-up)
CAN OFF (hibernate)
Fan Full Speed
Fan Auto Mode

Additional Features

Over-temperature Shutdown — YAML-configurable, no Home Assistant required
Daily kWh Energy Meter supplied DC energy
Board-Type Auto-Detect
Manufacturing-Date Auto-Detect
Serial-Number Auto-Detect
Scaling-Factor Auto-Set

🔋 Soft-Charge (balance charging)

Charger tapers max current smoothly to avoid high-current BMS trips
Balance phase current and duration are adjustable
Auto-hibernate once balancing completes

Conventional charging of an unbalanced pack	Soft-Charge of an unbalanced pack
Full current right up to 100 % SOC → repeated disconnects	Current tapers, e.g. 25 A → 15 A → 10 A → 2 A
Cells get only minutes of balance time	Final stage at e.g. 0.5 A for up to 300 min
Bad vibes & stress to BMS and Battery	Safely restore pack balance

The voltages in the "soft-charge" section act as triggers that reduce the charge current when the battery approaches full capacity.

The actual final charge voltage is set here: "10 Set Voltage Limit".

For example, if you set 54.75V as your "Set Voltage Limit", the charger will work towards that voltage at the configured current (12 Set DC Current Limit).

As the output voltage approaches the steep end of the voltage curve, it triggers the "soft-charge" algorithm at the specified voltages to gradually reduce the charge current.

The final trigger also starts a timer, allowing you to define how long the battery should remain in the balancing phase. Once that period has elapsed, the charger switches off.

It is important to note that drawing power from the battery during soft charge is not ideal. While it won’t damage the battery, it is recommended to disable soft-charge if the battery is in use while charging.

For optimal results, perform soft charging when the battery is not under load.

Use Cases

Ideal for 15 s/16 s LiFePO₄ and 14 s NMC home battery systems, generator-backed solar, fast e-bike charging, marine DC systems and even clean-supply HAM-radio amplifiers. Turn your ESS into a double conversion UPS and achieve true zero grid backfeed. Eliminate the need for a transfer switch. Here is Node-RED flow that modulates R48XX charge power depending on surplus solar power. The R4875G can also accept high voltage DC (~400VDC) as input voltage, so could be used to feed a 48V inverter from a high voltage traction battery. The project could also be used as a starting point for an EVSE-facing onboard charger.

Commercial products such as the EG4 Chargeverter are essentially two telecom rectifiers in a box—this project offers an open, automation-friendly alternative.

Hardware Setup

Bill of materials

Item	Notes
ESP32-WROOM dev board	On-board CAN controller
VP230 (SN65HVD230) CAN-bus transceiver	3.3 V logic
R4875G1/G5 edge connector	Available via AliExpress
8 AWG silicone DC leads	40 A continuous
16 A-rated AC leads	230 V single-phase
CAN bus twisted pair	White = CAN-L, Black = CAN-H

Powering the ESP32

Supply via USB or a 60 V → 5 V buck regulator if the battery is permanently connected.

Quick Start

Flash the latest pre-compiled .bin from the releases page using the ESPHome web-flasher, power up, and follow the on-device wizard.

Manual Pad-Jump Start (without adapter board)

Pin 1 → Pin 5
Pin 1 → Pins 11 & 12 (connect Pin 11 and Pin 12 to DC-)
Pin 9 ↔ Pin 10 connecting these two pins enables the full 75 A limit (otherwise limited to 53 A)

PCB adapter reference

Software Configuration

Create a new ESPHome device in Home Assistant (or use standalone web control). Uncomment the mqtt:, api: or webserver: blocks as required. Multi-unit and three-phase YAML examples are provided in the repo.

Latest YAML sample: v0.98.YAML

2x R4875G1 YAML sample: R48xx_autoSet_fullFanCTRL_AC_currentCTRL.YAML

The easy way: Ready-compiled .BIN file and instructions on how to upload to the ESP32 are here.

If you are totally off-grid, no wifi, no cellular connection, no internet, use this version.

If you are developing a portable or on-board fast-charger, this version is also suitable.

MQTT Topics

Click to expand topic listings

Text Sensors

r48xx-off-grid/sensor/003_power_state/state — Charger ON/OFF/Error
can-bus01/text_sensor/charger_power_state2/state

Sensors

can-bus01/sensor/ac_power_in/state — AC Power In
can-bus01/sensor/dc_power_out/state — DC Power Out
…and many more, see full list in repository

Numbers

can-bus01/number/can_voltage_set/state — Voltage Set
can-bus01/number/can_amp_set/state — Current Set
etc.

Buttons (send the string PRESS to command topic)

can-bus01/button/001_can_on_button/command — Wake-up
can-bus01/button/002_can_off_button/command — Hibernate
can-bus01/button/fan_full_speed_button/command — Fan 100 %

Number Commands

can-bus01/number/10_set_voltage_limit/command — 49 – 58 V
can-bus01/number/14_set_ac_current_limit/command — 0 – 21 A
etc.

Additional Resources

Huawei R4875G1 CAN protocol spreadsheet
Beyond Logic review of Huawei rectifiers
DIY Solar Forum discussion
Full user-manual PDFs for R4875G1/G5, R4850G2, R4830G2 are linked in the repository.

CAN-BUS-control-R4875G1-with-ESPHome-and-MQTT

Project Overview