Victron ESS Mode 2 and 3: Advanced Control Guide

Key Takeaways

• Victron ESS Mode 2 and 3 enable advanced, external control over Multi/Quattro inverter/chargers.
• Mode 2 primarily uses ModbusTCP for fine-grained grid interaction and battery charging/inverting.
• Mode 3 allows direct external setting of the inverter's switch state and power setpoint, requiring a GX device.
• Victron Energy does not offer direct support for custom implementations of these advanced control modes.

What are Victron ESS Mode 2 and 3?

Victron Energy Storage Systems (ESS) offer advanced control capabilities through Mode 2 and Mode 3, allowing external systems to manage Multi/Quattro inverter/chargers. These modes extend the standard ESS functionality, providing programmatic access for sophisticated grid interaction and battery management. This guide details how these modes operate and their primary control points.

Understanding ESS Mode Functionality

ESS Mode 2 and Mode 3 are designed for scenarios where an external system, such as a home automation controller or a custom energy management system, needs to dictate the behavior of a Victron ESS installation. They build on the normal standalone operation of the Multi/Quattro inverter/charger.

ESS Mode 2: ModbusTCP Control

Mode 2 provides a set of ModbusTCP registers that allow an external system to control various aspects of the Multi/Quattro inverter/charger's operation. This includes managing grid power flow, enabling or disabling charging and inverting, and setting maximum power limits. It is suitable for applications requiring precise, real-time adjustments to the system's interaction with the grid and battery. For example, you can set a specific grid power setpoint to either draw power from the grid (positive value) or send power to the grid (negative value). The default grid power setpoint is 50 W.

ESS Mode 3: External Switch and Power Setpoint

Mode 3 offers a more direct form of control, allowing an external command to set the inverter's switch state and power setpoint. This mode requires a Multi or Quattro inverter/charger and a GX device to function. It is particularly useful when an external system needs to override the ESS's internal logic to force specific operational states, such as switching the inverter on or off, or setting a precise power level for grid interaction. For instance, you can command the system to take 2000W from AC input or feed back 100W through AC input.

Implementing Control Points

To implement control using ESS Mode 2 or 3, you interact with the Victron system through specific communication protocols and data paths.

Control Access Methods

The primary methods for accessing these control points are:

• ModbusTCP: This protocol allows direct communication with the GX device (unitid 100) to read and write register values. This is the main interface for ESS Mode 2.
• MQTT: A local broker on the GX device or a remote connection through a secure cloud allows for MQTT-based control.
• Custom Scripts on the GX device: Advanced users can run custom scripts directly on the GX device to implement complex control logic.

D-Bus Paths for Control

Many control points are also accessible via D-Bus paths, which are internal communication channels within the Victron system. These paths are often used by custom scripts running on the GX device.

• Grid power setpoint: com.victronenergy.settings /Settings/CGwacs/AcPowerSetPoint
• Enable/Disable charger: com.victronenergy.settings /Settings/CGwacs/MaxChargePercentage
• Enable/Disable inverter: com.victronenergy.settings /Settings/CGwacs/MaxDischargePercentage
• Maximum inverter power: com.victronenergy.settings /Settings/CGwacs/MaxDischargePower
• DVCC maximum system charge current: com.victronenergy.settings /Settings/SystemSetup/MaxChargeCurrent
• Maximum system grid feed-in: com.victronenergy.settings /Settings/CGwacs/MaxFeedInPower

Control Point Reference

The following table details the key control points available for ESS Mode 2 and 3, including their ModbusTCP registers and expected values. Note that some ModbusTCP registers have changed with Venus OS versions, such as register 2716 for Venus 3.50+ for the grid power setpoint.

Safety

When implementing custom control logic for Victron ESS Mode 2 or 3, it is crucial to understand the implications for system safety and support. Victron Energy explicitly states that they do not offer support to professional customers or end-users who implement features using this documented functionality, except in specific situations. This means that users are responsible for the safe and correct operation of their custom control systems.

For ESS Mode 3, there are specific considerations regarding managed batteries:

• The maximum charge current sent by a managed battery is always heeded and cannot be overruled by the setpoint. This protects the battery from overcharging.
• However, the maximum discharge current sent by the battery will be ignored. The implemented control loop should take care of discharge limits communicated by the battery. Failure to properly manage discharge limits in your external control logic could lead to battery damage or unsafe conditions.

Always ensure your custom control logic respects battery specifications and system limits.

When to call a technician instead

Implementing custom control solutions with Victron ESS Mode 2 and 3 can be complex. You should consider calling a qualified Victron installer or technician if:

• You are unsure about the correct implementation of ModbusTCP or MQTT protocols.
• Your custom scripts are not performing as expected, and you cannot diagnose the issue.
• You require official support or warranty validation for your system, as Victron Energy does not provide direct support for custom implementations.
• You are dealing with critical grid-tied applications where incorrect programming could lead to safety hazards or regulatory non-compliance.
• The system's behavior with managed batteries is not as expected, especially concerning discharge limits in Mode 3.

It is important to recognize the limits of DIY when dealing with advanced energy system controls.