Sunsynk Battery Cut-Off Settings: Shutdown, Low Batt, and Restart Explained

Key Takeaways

• Your Sunsynk inverter uses State of Charge (SOC) thresholds to protect your battery from over-discharge and manage power supply.
• Always consult your battery's manufacturer specifications for its recommended Depth of Discharge (DoD) before setting the Shutdown value.
• If using Low Power Mode, your system timer settings must be lower than the Low Batt threshold, which inverts the usual rule.
• While these are owner-adjustable settings, understanding your battery's limits and the inverter's behaviour is crucial for system longevity.

Understanding Sunsynk Battery Cut-Off Settings for Classic, Acure, and Elite Inverters

Sunsynk Classic, Acure, and Elite inverters use several key battery settings to manage discharge, protect your battery, and ensure system stability. These settings define critical State of Charge (SOC) thresholds that dictate when the inverter stops drawing power, issues warnings, or resumes operation. The primary settings are Shutdown, Low Batt, and Restart, which form a ladder of protection and operational points for your battery. Grid Start and Battery Empty V also play roles in battery management.

How Your Sunsynk Inverter Manages Battery Discharge

Your inverter constantly monitors the battery's SOC. As the battery discharges, its SOC percentage drops. When the SOC reaches the 'Low Batt' threshold, the inverter will begin to alarm, indicating that the battery is getting low. If the SOC continues to fall and reaches the 'Shutdown' value, the inverter will stop drawing power from the batteries to prevent over-discharge, protecting the battery's lifespan. Once the battery is recharged (typically by solar or grid), and its SOC rises above the 'Restart' value, the inverter's AC output will resume, and the battery can once again supply the load. This sequence ensures your battery operates within safe limits.

Configuring Battery Cut-Off and Restart Thresholds

The following table details the key battery settings for Sunsynk Classic, Acure, and Elite inverters, along with Sunsynk's guidance on their configuration.

SOC Ladder Ordering Rules

Sunsynk provides specific rules for ordering these settings to ensure proper system operation:

• Timer Target SOC vs Low Batt: To avoid clashes, the target SOC in the system timers should not be set below the Low Batt%.
• Grid Start vs Low Batt/Shutdown: The Grid Start% should be set lower than both Low Batt% and Shutdown%.
• Low Power Mode Exception: These ordering rules are not correct if you intend to use Low Power Mode. Special considerations apply (see below).

Special Considerations for Low Power Mode

Low Power Mode is a feature on Classic, Acure, and Elite inverters designed to reduce the inverter's self-consumption when battery SOC is low and there is no PV generation. When this mode is enabled, the usual rules for timer settings are inverted:

• Timer Setting Requirement: System timer settings must be at least 1% lower than the Low Batt setting. If timer settings are not lower, it will prevent the system from entering low power mode.
• Recommended Buffer: To prevent the system from frequently switching in and out of Low Power Mode, it is best practice to keep a larger buffer, around 5-10% difference, between the timer settings and the Low Batt value.
• Grid Charge: The Grid Charge setting in the Battery Settings menu must be disabled for Low Power Mode to activate, otherwise it will force a grid charge.

What you can change yourself, and what you cannot

The battery cut-off settings discussed here (Shutdown, Low Batt, Restart, Grid Start, and timer settings) are generally considered owner-facing settings. You can adjust these through your inverter's display or via Sunsynk Connect to suit your battery's specifications and your energy usage patterns. Changing these settings does not typically require a registered person or affect your Certificate of Compliance (CoC), as they relate to battery management rather than grid protection or export limits. Always refer to your battery manufacturer's datasheet for recommended discharge limits.

What the published sources do not tell you

Sunsynk's documentation provides clear relationships and ordering rules for battery cut-off settings, but it does not offer specific numeric values for Shutdown, Low Batt, or Restart for different battery types or use cases. For instance, while it states "a battery with 90% DOD should have its shutdown value set to 10% minimum," it does not provide a comprehensive table of recommended values for various battery chemistries or capacities.

Additionally, the documentation does not provide a settable float voltage for lithium batteries; instead, it offers a "Disable Float Charge" toggle for systems with BMS communication. There is also no specific guidance on reserving a certain percentage of battery capacity for load-shedding events, nor is a 10% floor specified for the Grid Start setting, beyond the instruction that it should be lower than Low Batt and Shutdown.