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Daly BMS Bluetooth Monitor

Tested Daly 100A BMS

Tested Daly 100A BMS used for the Raspberry Pi 4 deployment described in this repository.

If this project helps you monitor your Daly BMS, consider supporting its maintenance and future improvements.

Donate with PayPal style button

Node.js service that connects to a Daly BMS over Bluetooth and exposes battery metrics as JSON through a small REST API. This project was tested and deployed on a Raspberry Pi 4, making it a practical base for continuous local monitoring and Home Assistant integrations.

What This Project Is For

This service is useful when you want to:

  • read Daly BMS data from a Raspberry Pi 4 over Bluetooth,
  • expose the decoded values through HTTP for local dashboards or automations,
  • integrate battery data into Home Assistant using a simple REST endpoint,
  • keep a lightweight monitor running in Docker on a Linux host.

How It Works

The application does three things:

  1. Connects to a Daly BMS over Bluetooth using @abandonware/noble.
  2. Sends the Daly status command and decodes the binary response.
  3. Exposes the decoded values through:
    • GET /bms
    • GET /status

The API response is JSON, which makes it easy to consume from Home Assistant, scripts, dashboards, or another backend.

Tested Environment

This setup was tested on:

  • Raspberry Pi 4
  • Linux-based host with Bluetooth enabled
  • Docker and Docker Compose

It may work on other Linux systems, but Raspberry Pi 4 is the known tested target for this repository.

Requirements

Before deploying, make sure you have:

  • Raspberry Pi 4 or another Linux host with Bluetooth support
  • Docker installed
  • Docker Compose available as docker compose
  • Access to the host D-Bus socket at /run/dbus
  • The Bluetooth MAC address of your Daly BMS

Project Structure

.
├── app.js
├── domain/
│   └── Daly2Bt.js
└── docker/
    ├── Dockerfile
    └── docker-compose.yml

Configuration

The current Bluetooth target is hardcoded in domain/Daly2Bt.js:

const ADDRESS = 'd0:25:11:3b:42:1a';

Before deployment, update that value to match the MAC address of your own Daly BMS.

Deploy With Docker Compose

From the repository root:

docker compose -f docker/docker-compose.yml build
docker compose -f docker/docker-compose.yml up -d

Useful follow-up commands:

docker compose -f docker/docker-compose.yml logs -f
docker compose -f docker/docker-compose.yml down

Why This Compose File Uses Host Networking

Bluetooth access from containers is easier on Raspberry Pi and Linux when the container uses:

  • /run/dbus:/run/dbus
  • network_mode: host

Those settings are already included in docker/docker-compose.yml.

API Endpoints

GET /status

Returns the current Bluetooth connection state.

Example response:

{
  "status": "Connected"
}

GET /bms

Requests data from the Daly BMS and returns decoded values as JSON.

Example request:

curl http://localhost:3000/bms

Example JSON response:

{
  "voltages": [3.448, 3.5, 3.455, 3.533, 3.493, 3.484, 3.487, 3.479],
  "temperatures": [-40, -40, -40, -40, -40, -40, -40, -40],
  "num_temperature_sensors": 2,
  "temp_one": 26,
  "temp_two": 31,
  "total_voltage_v": 27.8,
  "current_amp": -0.1,
  "remaining_capacity": 84.7,
  "max_cell_voltage": 3.533,
  "minimum_cell_voltage": 3.448,
  "average_cell_voltage": 3.483,
  "voltage_difference": 0.085,
  "soc_ah": 84.7,
  "num_cells": 8,
  "cycles": 272,
  "balancing_state": true,
  "cd_load_status": true,
  "fd_status_discharge": true,
  "power_w": 5
}

What The Data Is Useful For

With this service you can monitor:

  • per-cell voltages,
  • total pack voltage,
  • charge or discharge current,
  • remaining capacity,
  • cell imbalance,
  • charge and discharge status,
  • temperature probe readings,
  • cycle count,
  • estimated battery power.

This is especially useful for:

  • solar battery systems,
  • off-grid monitoring,
  • RV or mobile power systems,
  • local dashboards,
  • Home Assistant energy and battery views.

Home Assistant Integration

Once the container is running, Home Assistant can pull data from the /bms endpoint with REST sensors.

Example configuration:

rest:
  - resource: http://RASPBERRY_PI_IP:3000/bms
    scan_interval: 30
    sensor:
      - name: BMS Daly Total Voltage
        value_template: "{{ value_json.total_voltage_v }}"
        unit_of_measurement: "V"
        device_class: voltage

      - name: BMS Daly Current
        value_template: "{{ value_json.current_amp }}"
        unit_of_measurement: "A"
        device_class: current

      - name: BMS Daly Remaining Capacity
        value_template: "{{ value_json.remaining_capacity }}"
        unit_of_measurement: "Ah"

      - name: BMS Daly Cycle Count
        value_template: "{{ value_json.cycles }}"
        unit_of_measurement: "cycles"

Notes For Home Assistant

  • Replace RASPBERRY_PI_IP with the IP address of the Raspberry Pi running this service.
  • If Home Assistant runs on the same host, you can use http://localhost:3000/bms.
  • The backend returns JSON data only. Friendly names, units, and device classes are defined in Home Assistant.
  • The temperatures array may contain -40 placeholders when those indexed values are not used by your BMS. The direct probe values are exposed separately as temp_one and temp_two.

Maintenance Notes

For long-term use, keep these points in mind:

  • confirm the BMS Bluetooth MAC address whenever hardware changes,
  • review container logs after reboots or Bluetooth failures,
  • keep Docker and the Raspberry Pi OS updated,
  • avoid changing the host networking and D-Bus mounts unless you test Bluetooth access again.

Troubleshooting

If the service does not return BMS data:

  1. Confirm Bluetooth is enabled on the Raspberry Pi 4.
  2. Check that the BMS MAC address in domain/Daly2Bt.js is correct.
  3. Verify the container is running:
docker compose -f docker/docker-compose.yml ps
  1. Inspect logs:
docker compose -f docker/docker-compose.yml logs -f
  1. Test the endpoints manually:
curl http://localhost:3000/status
curl http://localhost:3000/bms

Spanish Documentation

If you prefer the same guide in Spanish, see README-ES.md.