Sunsynk Battery Not Charging or Discharging: Causes and Fixes

Key Takeaways

• Settings are the most common cause: check battery type, capacity, and charge/discharge limits first.
• Cold temperatures can prevent charging, with the rate gradually diminishing below 10°C and stopping at 0°C.
• Incorrect cable sizing or fuse ratings can limit performance or cause faults, especially with larger inverters or multiple batteries.
• Any work inside a live battery enclosure, on incoming AC tails, or on grid-protection settings requires a registered, competent person.

Why Your Sunsynk Battery Isn't Charging or Discharging

If your Sunsynk battery is not charging or discharging, the issue often stems from incorrect settings, communication problems between the battery and inverter, or environmental factors like cold temperatures. Sunsynk identifies several common causes, ranging from software configuration to hardware limitations. Addressing these systematically can help restore normal operation.

Understanding Sunsynk Battery Fault Modes

Your Sunsynk inverter and battery system rely on continuous communication and correct configuration to manage energy flow. The inverter's Battery Management System (BMS) monitors the battery's State of Charge (SOC), voltage, and temperature, adjusting charging and discharging to protect the battery and ensure efficient operation. When this process is interrupted, or if parameters are outside safe limits, the system may prevent charging or discharging to avoid damage. This protective action often manifests as a fault code or a simple lack of activity.

Common Faults and Their Solutions

Sunsynk documents specific fault codes and general fault modes that can prevent your battery from charging or discharging.

Essential Settings for Battery Operation

Many charging and discharging issues can be resolved by correctly configuring your inverter's battery settings.

1. Battery Type: For Sunsynk batteries, set the battery type to “Lithium”.
2. Battery Capacity: Ensure the battery capacity corresponds to the number of Sunsynk batteries used x 100 Ah (for 5kW Batteries). Bigger batteries will have different capacities.
3. Max A Charge / Max A Discharge: For 5kW 0.5C Batteries, check the “Max A Charge” and “Max A Discharge” are set to the number of Sunsynk batteries used x 50 A. Other batteries may vary, so consult your battery's specifications.
4. Activate Battery: Ensure “Activate Battery” is checked in the inverter settings.
5. System Mode Timer: If you are using a timer to control battery charging/discharging, go to the System_1 tab and tick the Use Timer checkbox. Adjust the SOC values to align with the previously configured Low Batt setting on the battery settings page. Alternatively, you may increase the value to the desired level for battery charging from the grid/generator and select the corresponding checkbox.
6. Low Voltage Recovery Settings: If you are attempting to recover a low voltage battery, access the battery settings and switch to AGM V. In system settings, change to Zero Export + Limit to Load Only. This will bypass the Load and direct all PV energy to the battery. If doing a grid charge, make sure Grid Signal and Grid charge are both checked, and Grid Charge in Grid start is set to 10% (the lowest available setting). In battery settings, change the Shutdown and Low Battery to 38V and the Batt Empty V to 41V (the lowest you can set this).

Ensuring Correct Battery Cabling and Protection

Incorrect cabling and protection can lead to performance issues, faults, and even safety hazards.

• Cable Sizing: The standard battery cables for Sunsynk batteries are 25mm² in size, which can handle a maximum charge/discharge rate of 122.5 A. If you are using an inverter with a capacity of 8 kW or larger, you will need to consider upgrading to a larger power cable size to fully utilize the maximum charge/discharge rates.
• Multiple Batteries: If you are using two or more batteries, Sunsynk recommends utilizing a common busbar. In this case, use the 25mm² standard cable from each battery to the busbar. From the busbar, use the appropriate size power cable, along with the correct size fuse isolator, to connect to the inverter.
• Cable Length: Please ensure all interconnecting battery cable sizes are the same length as cables of differing lengths can cause battery unbalances.
• Voltage Drop: For a 51.2V nominal battery such as the W5.3, the voltage drop should be no more than 2%.
• Current Limits: The current passed through 25mm² copper cables should NEVER exceed 122.5A. Exceeding this can cause damage to the inverter and batteries and will void your manufacturer warranty.
• Fuse and Busbar Ratings: The fuse isolator/breaker between the inverter and batteries should also be appropriately rated for the passthrough of current. Similarly, when using a busbar, the busbar must be rated for the appropriate DC current being sent to/from the inverter.

What You Can Check Yourself, and What You Cannot

You can perform several checks yourself to diagnose and potentially resolve battery charging and discharging issues:

• Settings Verification: Carefully review all inverter and battery settings as outlined above. Incorrect settings are a frequent cause of problems.
• Visual Inspection: Check all battery cables for secure connections, signs of damage, or corrosion. Ensure all interconnecting battery cables are of the same length.
• Environmental Conditions: Monitor the ambient temperature around your batteries, especially in cold weather, as low temperatures can prevent charging.
• Basic Resets: For SUN-BATT models, you can attempt a manual BMS reset by pressing and holding the Silver Power Button on the Front Panel for 12-15 seconds.

However, certain tasks require a registered, competent person:

• Firmware Updates: While battery firmware updates can resolve issues, they often require specific tools or technical support from Sunsynk. Do not attempt these without guidance.
• DC Charging of Low Voltage Batteries: If your battery voltage is below 40V, Sunsynk advises contacting their technical support. Charging a battery with an external DC charger requires an electrically qualified/competent person to conduct the charging from a DC power supply. High Voltage (HV) batteries must NOT be left unattended overnight whilst charging, as over voltage can lead to damage of lithium cells and fires.
• Internal Battery Work: Any work that involves opening the battery enclosure, working on live battery terminals, or modifying internal battery components must be performed by a qualified professional. In South Africa, such electrical work requires a Certificate of Compliance (CoC).

What the Published Sources Do Not Tell You

While Sunsynk provides extensive support documentation, there are some gaps:

• Specific Fault Codes for SUN-BATT Batteries: Sunsynk's article titled "SUN-BATT - Fault Codes" is currently empty and does not list any specific fault codes for these models.
• Comprehensive Third-Party Battery Compatibility: The documentation focuses on Sunsynk's own batteries and their inter-compatibility, but does not provide a list of approved third-party batteries.
• Detailed Firmware Update Procedures: While firmware updates are mentioned as a solution for some issues, detailed, user-friendly steps for performing these updates are not publicly available; users are typically directed to contact support.
• Specific Modbus Protocol Details: The need for the correct Modbus protocol for BMS communication is stated, but the specific details for different battery models are not provided in the public articles, only mentioned as being in inverter manuals.
• Guidance on Identifying Older vs. Newer L/G/W Series Batteries: While identification features for newer SUN-BATT models are given, similar guidance for L/G/W series batteries, particularly for remote firmware updates, is not explicitly covered.