OVMS Home Assistant Integration

Overview

The Open Vehicle Monitoring System (OVMS) integration for Home Assistant connects your electric vehicle to your smart home via MQTT, creating a seamless monitoring and control experience. This integration automatically discovers all vehicle metrics published by your OVMS module and creates appropriate entities in Home Assistant.

Features

Real-time monitoring of vehicle metrics (battery, climate, location, etc.)
Remote control of climate systems, charging, and other vehicle functions
Automation integration with Home Assistant’s automation engine
Location tracking with GPS accuracy estimation
Advanced battery analytics including cell-level data with statistical analysis
Secure communication with TLS/SSL support for MQTT connections

How It Works

The integration operates through these components:

Your OVMS module publishes vehicle data to an MQTT broker
Home Assistant subscribes to these MQTT topics
The integration automatically:
- Transforms MQTT messages into appropriate Home Assistant entities
- Creates sensors, binary sensors, device trackers, and switches
- Categorizes entities by function (battery, climate, etc.)
- Maintains real-time state based on MQTT updates
- Provides services for sending commands back to your vehicle

MQTT Overhead and Performance

Data Usage and Bandwidth

The OVMS integration uses MQTT for communication, which is designed to be lightweight and efficient for IoT devices. Typical data usage depends on:

Number of metrics being published
Update frequency of metrics
Message payload size

For most vehicles, the total MQTT traffic ranges from 0.04 MB - 1 MB per day with default settings, depending on how actively the vehicle is used and how many metrics are enabled. This averages to approximately 10 MB per month when your car is connected to WiFi while at home, and driven to work around 1 hour per day.

Memory and CPU Usage

The integration’s resource footprint on Home Assistant server is minimal:

Memory: Typically 10-30MB RAM depending on the number of entities
CPU: Negligible impact during normal operation (1-3% on average systems)
Storage: Minimal state data, primarily in Home Assistant’s database

Comparison with OVMS V2 Server

Aspect	MQTT/Home Assistant Integration	OVMS V2 Server
Data Transfer	0.04-1MB/day (~10MB/month)	60KB/day baseline (~2MB/month)
Protocol Efficiency	Moderate (MQTT is IoT optimized but requires more bandwidth)	Higher (uses lighter MP protocol)
Server Resource Usage	Lower (leverages existing MQTT)	Higher (dedicated server needed)
Scalability	Excellent (thousands of clients)	Good (limited by server)
Historical Data	Home Assistant’s native history	Built-in data retention

The V2 server generally provides better efficiency and lower data usage than the MQTT integration, while the MQTT integration offers deeper integration with home automation systems.

Optimization Tips

To reduce data usage:

Don’t use the V3 (MQTT) protocol if data usage is a concern. MQTT needs significantly more bandwidth than the MP protocol used by V2.
Don’t activate the App’s background service mode (currently only applies to Android).
Don’t activate GPS Streaming Mode (feature #8).
Reduce the general update intervals (web UI: Config → Server V2/V3).

For MQTT-specific optimization:

Configure appropriate update intervals in your OVMS module
Use QoS level 0 for non-critical metrics
Use QoS level 1 for commands.
Consider disabling metrics you don’t need in your OVMS configuration
For large deployments, use a dedicated MQTT broker with optimized settings

Prerequisites for using the Home Assistant HACS integration

Home Assistant (2025.2.5 or newer)
MQTT integration configured in Home Assistant, or any external MQTT Broker that supports MQTTv3.1 (or newer). EMQX are confirmed to be working well.
OVMS module with firmware 3.3.001 or newer recommended
OVMS Server V3 enabled

Installation

Integration Installation

1. Configure OVMS Module

In your OVMS web UI:

Navigate to Config → Server V3 (MQTT)

Configure the following settings:

Server: Your MQTT broker address
Port: 1883 (mqtt://), 8083 (ws://), 8883 (mqtts://), or 8084 (wss://)
Username/Password: If required by your broker
Topic Prefix: ovms (default, can be customized)
Enable Auto-Start: YES

Save your configuration

2. Configure MQTT Broker Permissions

Ensure your MQTT broker permits these operations:

Subscribe Permissions:
- ovms/# (For all OVMS topics)
- homeassistant/# (For testing connection)

Publish Permissions:
- ovms/+/+/client/rr/command/# (For sending commands)
- ovms/+/+/status (For publishing status)

3. Install the HACS Integration

HACS Installation (Recommended)

In Home Assistant, go to HACS → Integrations
Click on + Explore & Download Repositories
Search for OVMS Home Assistant
Install the integration
Restart Home Assistant

Adding the HACS integration as a Custom Repository

If the integration is not available in the HACS store:

In Home Assistant, go to HACS → Integrations
Click the three dots in the upper right corner
Select Custom repositories
Enter the following information:
- Repository URL: https://github.com/enoch85/ovms-home-assistant
- Category: Integration
Click Add
The OVMS integration will now appear in your HACS Integrations list
Click on it and select Download
Restart Home Assistant after installation

Manual Installation of the HACS integration

Download the repository as a ZIP file
Extract it and copy the custom_components/ovms folder to your Home Assistant’s custom_components directory
Restart Home Assistant

4. Set Up the HACS Integration

In Home Assistant, go to Settings → Devices & Services → Integrations
Click on + Add integration and search for OVMS
Enter MQTT broker details and connection information
Configure topic structure to match your OVMS settings
Select your vehicle ID when prompted

Available Services

The integration provides several services to control your vehicle:

ovms.send_command: Send any command to the OVMS module
ovms.set_feature: Set an OVMS configuration feature
ovms.control_climate: Control the vehicle’s climate system
ovms.control_charging: Control the vehicle’s charging functions

MQTT Topic Structure

The integration supports these MQTT topic structures:

Default: ovms/username/vehicle_id/metric/...
Alternative: ovms/client/vehicle_id/...
Simple: ovms/vehicle_id/...
Custom: Define your own structure with placeholders

Secure MQTT with TLS

For secure MQTT connections, you can configure TLS/SSL. This is especially important for remote connections.

Certificate Authority Setup

Generate certificates on your MQTT broker
Import the CA certificate to OVMS through the web interface: * Go to ‘Tools’ > ‘Editor’ * Create a folder at ‘/store/trustedca/’ * Save your CA certificate as a .pem file in this folder * Run ‘tls trust reload’ from the OVMS shell

Configure OVMS for Secure MQTT

In the OVMS web UI:

Navigate to ‘Config’ > ‘Server V3 (MQTT)’
Enable TLS
Set the port to 8883 (or your secure port)
Configure authentication if required
Save and restart the MQTT service

Troubleshooting

If no entities are created:

Check if your OVMS module is publishing to the MQTT broker
Verify the topic structure matches your configuration
Enable debug logging by adding to your configuration.yaml:
```
logger:
  default: info
  logs:
    custom_components.ovms: debug
```
Warning! The debug output is substantial. It may fill your disk if you are not careful, don’t leave it turned on.
Verify ACL permissions in your MQTT broker

Additional Resources

For advanced usage, dashboard examples, and technical details, refer to the full documentation at: https://github.com/enoch85/ovms-home-assistant

Manual Configuration (non HACS)

As an alternative to using the integration, you can manually configure Home Assistant to work with OVMS using MQTT sensors defined in your configuration.yaml file. This approach gives you more control over which metrics are tracked and how they are displayed.

1. Setup MQTT Broker Connection

This can be either an external broker or the built-in MQTT broker in Home Assistant.

2. Configure OVMS

Follow the same MQTT configuration as above in your OVMS module.

3. Configure Home Assistant YAML

Add MQTT sensors to your configuration.yaml file. Example sensors:

mqtt:
  binary_sensor:
    - name: "OVMS 12V Battery Alert"
      state_topic: "ovms/CAR/UNIQUEID/metric/v/b/12v/voltage/alert"
      icon: mdi:car-battery
  sensor:
    - name: "OVMS GPS Latitude"
      state_topic: "ovms/CAR/UNIQUEID/metric/v/p/latitude"
      icon: mdi:latitude
    - name: "OVMS GPS Longitude"
      state_topic: "ovms/CAR/UNIQUEID/metric/v/p/longitude"
      icon: mdi:longitude
    - name: "OVMS GPS Signal Strength"
      state_topic: "ovms/CAR/UNIQUEID/metric/v/p/gpssq"
      device_class: signal_strength
      unit_of_measurement: '%'
    - name: "OVMS GPS Time Updated"
      state_topic: "ovms/CAR/UNIQUEID/metric/v/p/gpstime"
      value_template: '{{ value_json | timestamp_local }}'
      device_class: timestamp
    - name: "OVMS 12V Battery"
      state_topic: "ovms/CAR/UNIQUEID/metric/v/b/12v/voltage"
      value_template: '{{ value | round(1) }}'
      icon: mdi:car-battery
      unit_of_measurement: 'V'

Replace “CAR/UNIQUEID” with your actual vehicle identifier. Add additional sensors based on the metrics available from your vehicle.