YamBMS ( Yet another multi-BMS Merging Solution )

Tip

Not sure which YAML to choose ? ... YamBMS_Remote_Packages_example.yaml is a good basis for creating your custom YAML. Examples of BMS, Shunt and Balancer packages can be found in the examples folder. You don't have to import a shunt or balancer but you must import at least one BMS. You can mix different BMS models, the only condition is that the bms_id are numbered in order starting from 1 !

Important

The most important thing for proper functioning of YamBMS is that the voltage of your BMS is well calibrated. YamBMS logic is based on the min_cell_voltage and max_cell_voltage voltages of your BMS. If you use YamBMS, the internal charging logic of the JK-PB BMS will not be used. Please read the documentation and the setup instructions.

ESPHome application to combine information coming from your BMS / Balancer / Shunt and adds a smart layer before transmitting instructions to your inverter on RS485 or CAN bus using the protocols PYLON, SMA, Victron or LuxPower (EG4).

Note: Pylontech uses 15S/48V and many others uses 16S/51.2V ! Other battery profiles that utilise the PYLON protocol with different cell counts may also work, e.g. Alpha Ess Smile, BYD Battery-Box LV Flex Lite. Select the correct battery profile in the inverter to match your battery pack ! DISCLAIMER: Working with battery systems involves electrical hazards. Please read the complete documentation before installation and use this project at your own risk.

Sends over CAN / RS485 bus to your inverter :

• Battery Voltage
• Battery Current (+charge, -discharge)
• State of Charge (SoC) SoC 100% will be sent to your inverter only when the battery is fully charged
• State of Health (SoH)
• Requested Charge Voltage
• Requested Charge Current
• Requested Discharge Voltage
• Requested Discharge Current
• Min Cell V. and Cell ID
• Max Cell V. and Cell ID
• Min temperature and sensor ID
• Max temperature and sensor ID
• Battery name
• Alarms & Warnings

Come and discuss it on the DIY Solar Forum dedicated topic.

Contents

1. Supported devices
2. Hardware and schematic instructions
3. YamBMS behavior
4. YamBMS functions
5. YamBMS charging logic
6. Installation procedure
7. Troubleshooting
8. Changelog

YamBMS ( Yet another multi-BMS Merging Solution )

Home Assistant

Hardware highlighted

This project works with various ESP32 variants and also with the Raspberry Pi Pico (RP2040). Note that merging data from multiple BMS, balancers and shunts is resource-intensive, so I highly recommend a board based on the ESP32-S3 with PSRAM.

LilyGo T-Connect	Waveshare RS485-CAN	M5Stack AtomS3R
- ESP32-S3 - 8MB PSRAM - 3x RS485 port - 1x CAN port - 15x GPIOs	- ESP32-S3 - 8MB PSRAM - 1x RS485 port - 1x CAN port - 1x SH1.0 connector - 16x GPIOs	- ESP32-S3 - 8MB PSRAM - 1x BASE port (for adding RS485/CAN base) - 1x UNIT HY2.0 port (for adding RS485/CAN unit) - 6x GPIOs

Single-node

You install YamBMS on a single ESP32 connected to your BMS and your inverter.

• Max 3x BMS BLE
• Max 3x BMS UART
• several RS485 BMS on the same bus

Multi-node

Each BMS/Shunt/Balancer turns into a modbus server with its own address.

Important

The max number of UART BMS/Shunt per ESP32 is 2 (unless you use a UART expander) because you need to keep the last UART for the RS485 network. The max number of BLE BMS/Shunt/Balancer per ESP32 is 2, ESP32-S3 / AtomS3 can supervise 3 BLE devices.

YamBMS installs on node1 as a modbus client to collect information from all your BMS. The node1 is also connected to your inverter via the CAN bus.

The BMS/Shunt are connected to other ESP32 nodes connected on a dedicated RS485 bus for YamBMS. Each BMS/Shunt/Balancer becomes a modbus server.

The theoretical limit is 256 modbus server (BMS/Shunt) per RS485 bus but in reality this will depend on the capabilities of node1 (YamBMS) which will have to combine all the BMS/Shunt/Balancer together.

You can find more information about creating your YAML in this How To.

Tip

If you have a lot of BMS/Shunt/Balancer to combine, using an ESP32-S3 or AtomS3 for node1 is recommended.

@GHswitt multi-node example :

Note

Some boards with integrated RS485 transceiver have already a 120 Ohm resistor installed, for example the LilyGo T-CAN485, LilyGo T-Connect and LilyGo T-Connect Pro. If these devices are used in the middle, this resistor must be removed! Otherwise transmission errors can occur.

Try YamBMS with the DEMO firmware

You can simply test the application with a generic ESP32 without compiling and connecting anything on your ESP32. The DEMO firmware is composed of 3x BMS and 1x Shunt (fake) for a 48V LFP system.

Important

YamBMS_DEMO_ESP32.factory.bin is intended for a generic ESP32, does not work with ESP32-S3. If you want to test YamBMS DEMO with another board you need to compile the firmware with the YamBMS_RP_DEMO.yaml.

1. Download YamBMS_DEMO_ESP32.factory.bin
2. Follow the procedure explained in this document.

If you want to add a CAN transceiver on this DEMO board here are the GPIOs to connect it to :

tx_pin: 23 # to CAN board CTX
rx_pin: 22 # to CAN board CRX (with 4.7K resistor except for SN65HVD230)

Requirements

• ESPHome 2025.11.0 or higher
• ESP32 MCU (buying a board with ≥8MB flash is advised if you intend to monitor multiple BMS)
• CAN transceiver (only with TJA1050/TJA1051 => 4.7K resistor for 5V to 3V3 level shifing)
• BMS JK, JBD, Seplos (other BMS brands already integrated with ESPhome can be added easily)
• Inverters supporting CAN PYLON/GoodWe/SMA/Victron Low Voltage protocol
• Optional: 48V to 5V DC-DC converter to power the ESP32 from the JK-BMS VBAT pin (URB4805YMD-10WR3 or VRB4805S-6WR3)
• Optional: JK RS485 adaptor and RS485 to TTL 3V3 adaptor (see schematic section)

Data collection

Note

For your information, in January 2026 there were 160 YamBMS users.

If the ESP32 has an internet connection, the following data is sent to this script for statistics collection. Only @Sleeper85 have access to this information for the production of statistics, the support and the update service.

• ESP32 MAC address
• YamBMS version
• Board chip
• Board name
• BMS model
• BMS count
• CAN bus name
• CAN bus protocol
• Uptime
• Current date and time

References

• Thanks to @syssi for help and making many BMS components (JK, JBD, Seplos, Pace, etc.)
• Thanks to @txubelaxu for help and making the JK_RS485 component.
• Thanks to @shvm, @MrPabloUK and @GHswitt for their multiple contributions.
• Thanks to @uksa007 for making the first CANBUS code.
• Thanks to all the contributors.