Daly BMS Prometheus Exporter

A Python application that reads data from a Daly BMS (Battery Management System) via a USB-to-RS485 interface and exposes all metrics through a Prometheus-compatible HTTP endpoint.

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Features

• Reads all standard Daly BMS data frames (using dalybms python lib):
  • Pack voltage, acquisition voltage, current, and State of Charge (SOC)
  • Min/max individual cell voltages and their cell numbers
  • Min/max temperature sensor readings
  • Charge and discharge MOSFET states
  • BMS heartbeat counter and remaining capacity
  • Individual cell voltages (labelled cell="1" … cell="N")
  • Individual temperature sensor readings
  • Per-cell balance-active flags
  • Full alarm and fault flag decode (34 named bits)
• Serves all metrics at a configurable Prometheus /metrics endpoint
• Configurable via a .env file or environment variables (no code changes needed)
• Supports multiple BMS instances via BMS_INSTANCE label (untested)

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Requirements

• Python 3.8+
• A USB-to-RS485 adapter (e.g. CH340/CP2102 based)
• Daly BMS connected via RS-485

Python dependencies

pyserial>=3.5
prometheus-client>=0.17.0
python-dotenv>=1.0.0

Install them with:

pip install -r requirements.txt

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Quick start

1. Clone and install dependencies

   git clone https://github.com/pirus99/Daly-BMS-Python-Database-Export.git
   cd Daly-BMS-Python-Database-Export
   pip install -r requirements.txt

2. Configure the application

   Copy the example environment file and edit it for your setup:

   cp .env.example .env
   $EDITOR .env

   At minimum you need to set SERIAL_PORT to the device path of your USB-to-RS485 adapter (see Configuration below).

3. Run the exporter

   python exporter.py

   You should see output like:

   2024-01-15T12:00:00  INFO      daly_bms_exporter  === Daly BMS Prometheus Exporter ===
   2024-01-15T12:00:00  INFO      daly_bms_exporter  Model    : Daly BMS
   2024-01-15T12:00:00  INFO      daly_bms_exporter  Port     : /dev/ttyUSB0 @ 9600 baud
   2024-01-15T12:00:00  INFO      daly_bms_exporter  Metrics  : http://0.0.0.0:8000/metrics
   

4. Scrape with Prometheus

   Add the exporter to your prometheus.yml:

   scrape_configs:
     - job_name: daly_bms
       static_configs:
         - targets: ['localhost:8000']

5. Visualise in Grafana

   Use the exposed labels (model, instance, cell, sensor, alarm) to build dashboards. All metrics are prefixed with daly_bms_.

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Configuration

All configuration is done via environment variables. If a .env file exists in the same directory as exporter.py, it is loaded automatically. Environment variables set in the shell take precedence over .env.

Variable	Default	Description
SERIAL_PORT	/dev/ttyUSB0	Path to the USB-to-RS485 device (e.g. COM3 on Windows)
BAUD_RATE	9600	RS-485 baud rate (Daly default)
SERIAL_TIMEOUT	1.0	Serial read timeout in seconds
BMS_ADDRESS	0x40	RS-485 address of the BMS (hex or decimal)
BMS_MODEL	Daly BMS	Human-readable model name (used as a Prometheus label)
BMS_INSTANCE	bms0	Instance identifier for multi-BMS setups
WEB_SERVER_ADDRESS	0.0.0.0	Address the HTTP server binds to
WEB_SERVER_PORT	8000	TCP port for the metrics endpoint
METRICS_PATH	/metrics	URL path served to Prometheus
POLL_INTERVAL	10.0	How often the BMS is polled (seconds)
MAX_CONSECUTIVE_ERRORS	3	Errors before daly_bms_up is set to 0

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Exposed Prometheus metrics

Availability

Metric	Type	Description
daly_bms_up	Gauge	1 if BMS is reachable, 0 otherwise
daly_bms_scrape_duration_seconds	Gauge	Time to complete one full poll
daly_bms_scrape_errors_total	Counter	Total communication errors since start

Electrical

Metric	Type	Description
daly_bms_pack_voltage_volts	Gauge	Battery pack voltage (V)
daly_bms_acquisition_voltage_volts	Gauge	Acquisition / terminal voltage (V)
daly_bms_pack_current_amperes	Gauge	Pack current (A); positive = charging
daly_bms_soc_percent	Gauge	State of charge (%)
daly_bms_remaining_capacity_ampere_hours	Gauge	Remaining capacity (Ah)

Cell voltages

Metric	Labels	Description
daly_bms_cell_voltage_max_volts	model, instance	Highest cell voltage (V)
daly_bms_cell_voltage_min_volts	model, instance	Lowest cell voltage (V)
daly_bms_cell_voltage_delta_volts	model, instance	Max − min cell voltage (V)
daly_bms_cell_voltage_max_cell_number	model, instance	Cell number with highest voltage
daly_bms_cell_voltage_min_cell_number	model, instance	Cell number with lowest voltage
daly_bms_cell_voltage_volts	model, instance, cell	Per-cell voltage (V)

Temperatures

Metric	Labels	Description
daly_bms_temperature_max_celsius	model, instance	Highest temperature (°C)
daly_bms_temperature_min_celsius	model, instance	Lowest temperature (°C)
daly_bms_temperature_celsius	model, instance, sensor	Per-sensor temperature (°C)

Status

Metric	Type	Description
daly_bms_charge_mos_active	Gauge	1 if charge MOS is enabled
daly_bms_discharge_mos_active	Gauge	1 if discharge MOS is enabled
daly_bms_heartbeat_counter	Gauge	BMS internal heartbeat counter
daly_bms_cell_count	Gauge	Number of cells
daly_bms_temperature_sensor_count	Gauge	Number of temperature sensors
daly_bms_charger_connected	Gauge	1 if a charger is connected
daly_bms_load_connected	Gauge	1 if a load is connected
daly_bms_charge_discharge_cycles_total	Gauge	Total charge/discharge cycles
daly_bms_cell_balance_active	Gauge (per cell)	1 if cell balancing is active

Alarms and faults

The metric daly_bms_alarm_active{alarm="<name>"} is set to 1 when an alarm condition is active. The following alarm label values are available:

cell_overvoltage_l1, cell_overvoltage_l2, cell_undervoltage_l1, cell_undervoltage_l2, pack_overvoltage_l1, pack_overvoltage_l2, pack_undervoltage_l1, pack_undervoltage_l2, charge_overtemp_l1, charge_overtemp_l2, charge_undertemp_l1, charge_undertemp_l2, discharge_overtemp_l1, discharge_overtemp_l2, discharge_undertemp_l1, discharge_undertemp_l2, charge_overcurrent_l1, charge_overcurrent_l2, discharge_overcurrent_l1, discharge_overcurrent_l2, soc_low_l1, soc_low_l2, cell_voltage_diff_l1, cell_voltage_diff_l2, cell_temp_diff_l1, cell_temp_diff_l2, charge_mos_overtemp_l1, charge_mos_overtemp_l2, discharge_mos_overtemp_l1, discharge_mos_overtemp_l2, charge_mos_fault, discharge_mos_fault, temp_sensor_fault, cell_fault, sampling_circuit_fault, cell_balance_fault.

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File structure

.
├── config.py          # All configuration constants (env-var backed)
├── daly_bms.py        # Daly BMS RS-485 protocol implementation
├── exporter.py        # Prometheus HTTP server + polling loop (entry point)
├── requirements.txt   # Python dependencies
├── .env.example       # Example environment / config file
└── tests/
    └── test_daly_bms.py  # Unit tests (no hardware required)

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Running tests

pip install pytest
python -m pytest tests/ -v

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Wiring

Daly BMS  ──RS-485──  USB-to-RS485 adapter  ──USB──  PC / Raspberry Pi

Connect the A and B differential pair of the RS-485 adapter to the corresponding terminals on the Daly BMS communication port. No external power is required on the RS-485 bus; the BMS supplies it.

Note: Make sure your user account has permission to access the serial device (e.g. sudo usermod -aG dialout $USER on Debian/Ubuntu, then log out and back in).

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Disclaimer

This script is tested with a Raspberry Pi 2 B+ and a CH340 USB RS485 Converter connected to a DALY SMART BMS. I had to configure my .env to use verbose Workaround, because otherwise the --status fetch does not work properly.

There is absolutely NO WARRANTY for any damages made to any component of your Setup. This script is mainly built by using Copilot. It's reviewed to the best of my knowledge but could possibly may harm your battery, BMS or other components connected to the same RS485 bus, if misused or malfunctioning. Please use carefully and double check your configuration and setup. It's your responsibility!

Some things weren't tested yet:

UART: ❌ Not Tested

Sinowealth Chip: ❌ Not Tested

Multiple Instances on One Device/Bus: ❌ Not Tested

DALY non "SMART" BMS: ❌ Not Tested

Please feel free to contribute experiences from your setup.

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License

Free for personal and non-commercial use.

You may use, modify, and distribute the software.

Commercial use requires a license from the author.