Knox Inverter Battery Settings: Pairing Guide for Lead-Acid and Lithium

Key Takeaways

• Always match battery settings by name on your Knox inverter's LCD, as program numbers can vary by firmware. This caveat must reach every article.
• For lithium batteries, the inverter relies on the battery's Battery Management System (BMS) for critical voltage parameters.
• Incorrect battery settings can lead to reduced battery lifespan, poor system performance, or inverter damage.
• If you are unsure about any wiring or advanced configuration, stop and consult a qualified solar technician.

How do I correctly configure my Knox inverter for my battery type?

Correctly configuring your Knox hybrid inverter for your specific battery type is essential for optimal performance and battery longevity. The most common cause of battery issues with these inverters is incorrect settings for charge voltages, currents, and State of Charge (SOC) cutoffs. The first step is to identify your battery chemistry (lead-acid or lithium-ion) and then access the inverter's LCD settings menu to make the necessary adjustments.

Diagnosis and Initial Checks

Before adjusting any settings, perform these checks to ensure your system is ready for configuration.

1. Identify Battery Type: Determine if you have lead-acid (e.g., AGM, Gel, Wet) or lithium-ion batteries. This dictates the specific settings you will use.
2. Locate Inverter LCD: Access the LCD display and control buttons on your Knox inverter.
3. Navigate to Battery Settings: Use the inverter's navigation buttons to find the "Battery Type" setting. Note that menu or program numbering can differ by model and firmware on rebadged units, so always match settings by name. This caveat must reach every article.
4. Check BMS Communication (Lithium): If you have lithium batteries, ensure the Battery Management System (BMS) is communicating with the inverter. A "BMS communication fault" (F58) indicates a problem. The inverter relies on the BMS for voltage parameters in "Lithium Mode."
5. Verify Battery Voltage Range: Ensure your battery bank's nominal voltage falls within the inverter's supported "Battery Voltage Range" of 40-60V.

Knox Inverter Battery Settings Table

This table outlines the key battery settings for Knox (Deye rebadge) inverters. Remember to match settings by name on your inverter's LCD, not by a specific program number, as these can vary. This caveat must reach every article.

Configuring Battery Parameters

1. Select Battery Type: On the LCD, navigate to the "Battery Type" setting and select either "Lead-acid" or "Li-ion" based on your installed battery bank.
2. Set Max Charge/Discharge Current: Adjust the "Max. A charge/discharge" setting according to your specific inverter model and battery manufacturer's recommendations. For the SUN-3.6K-SG03LP1-EU model, the maximum is 90A. For the SUN-5K-SG03LP1-EU model, it is 120A. For the SUN-6K-SG03LP1-EU model, the maximum is 135A. Ensure this value does not exceed your battery's maximum continuous charge/discharge rate. This is configurable by LCD setting.
3. Configure Battery Capacity: Input the total amp-hour (Ah) capacity of your battery bank into the "Battery capacity" setting. This helps the inverter accurately estimate the State of Charge (SOC).
4. Lead-Acid Specific Settings:

• • Absorption Voltage (Absorption V): Set this to 57.6V for AGM batteries, 56.4V for Gel batteries, and 59.0V for Wet cell batteries. This is the voltage at which the battery is held during the absorption phase of charging. These settings are typically referenced to 25°C (77°F) ambient temperature. Higher temperatures may require slightly lower voltages, and lower temperatures slightly higher voltages, to prevent over or undercharging.
  • Float Voltage (Float V): Set this to 53.6V for AGM batteries, 54.0V for Gel batteries, and 55.0V for Wet cell batteries. This is the voltage at which the battery is maintained after being fully charged. These settings are typically referenced to 25°C (77°F) ambient temperature. Higher temperatures may require slightly lower voltages, and lower temperatures slightly higher voltages, to prevent over or undercharging.
  • Equalization Voltage (Equalization V): For AGM batteries, set this to 57.6V, and for Wet cell batteries, set it to 59.0V. The manual suggests equalization every 30 days for 3 hours for AGM batteries. Equalization drives the cell into the hydrogen gassing region; ensure this is done in a well-ventilated space with no sparks or flames. Gel batteries typically do not require equalization. These settings are typically referenced to 25°C (77°F) ambient temperature. Higher temperatures may require slightly lower voltages, and lower temperatures slightly higher voltages, to prevent over or undercharging.
  • SOC Thresholds: For lead-acid batteries, the inverter will shut down if SOC drops below 20%, alarm below 35%, and AC output will restart at 50% SOC.

5. Lithium-Ion Specific Settings:

• • Lithium Mode: Select "Lithium Mode." The inverter will then "Follow its BMS voltage parameters" for charging and discharging, relying on the battery's internal Battery Management System (BMS) for precise voltage control.
  • SOC Thresholds: For lithium batteries, the inverter will shut down if SOC drops below 10%, alarm below 20%, and AC output will restart at 40% SOC.
  • BMS Communication: Ensure the "BMS_Err_Stop" setting is active. If communication between the inverter and the battery BMS is disconnected when BMS_Err_Stop is active, the inverter will stop. If you disable this, the inverter will continue to operate without BMS data, which is not recommended for lithium batteries.

6. Charging Source Priority: Configure "Grid Charge" and "Gen Charge" settings to enable or disable charging from the grid or a generator, respectively. You can also set "Gen Start (SOC)" (e.g., 30%) for automatic generator start and "Gen Start (Charge Rate)" (e.g., 40A) for the charging current from the generator. Similarly, "Grid Charge (Current)" (e.g., 40A) sets the current from the grid.
7. Activate Battery Feature: If your battery is over-discharged, use the "Activate Battery" feature to initiate slow charging from solar or the grid to recover it.

Safety: Working with Batteries and Inverters

Working with solar inverters and batteries involves significant electrical hazards. Always prioritize safety.

• Qualified Personnel: Only qualified personnel can install this device with battery.
• Disconnect All Power: To reduce risk of electric shock, disconnect all wires before attempting any maintenance or cleaning. Turning off the unit will not reduce this risk.
• Insulated Tools: Be very cautious when working with metal tools on or around batteries. Dropping a tool may cause a spark or short circuit, even an explosion. Use insulated tools.
• Correct Polarity: Before final DC connection, ensure positive(+) connects to positive(+) and negative(-) to negative(-). Reverse polarity connection will damage the inverter.
• Over-Current Protection: A separate DC over-current protector or disconnect device is required between the battery and the inverter. Be very cautious when working with metal tools on or around batteries. Dropping a tool may cause a spark or short circuit, even an explosion.
• Ventilation for Lead-Acid: When performing equalization on lead-acid batteries, ensure the area is well-ventilated to disperse hydrogen gas, and keep all sparks and flames away.
• Never Charge Frozen Batteries: Never charge a frozen battery.

When to call a technician instead

While many settings can be adjusted through the LCD, some situations require professional assistance to ensure safety and system integrity.

• Persistent Faults: If your inverter displays a "BMS communication fault" (F58) or any other critical error that you cannot resolve after following the manual's instructions, contact a technician.
• Uncertainty with Wiring: If you are unsure about the correct wiring of your battery bank to the inverter, especially regarding polarity or cable sizing, do not proceed. Incorrect wiring can cause severe damage and fire.
• Warranty Concerns: Any attempts to modify, alter, or repair the inverter can void its 5-year warranty. If you suspect an internal issue, contact your installer or a service center.
• Complex System Integration: For systems involving parallel inverters or advanced grid-tie configurations, a professional can ensure all parameters are correctly synchronized and compliant with local regulations.
• Battery Damage: If your battery appears physically damaged, is leaking, or shows signs of overheating, do not attempt to troubleshoot it yourself. This poses a significant safety risk.