Good day to you all!

So, I have 2 x Luxpower 5KW inverters, linked to 2 CFE 5.12KW 48V Lithium batteries.

A few months ago, the following issue started: The batteries would discharge as per normal use, once the batteries reach 69% they would then rapidly discharge down to 0%, the grid would then kick in and automatically recharge the batteries to 100%.

It's always in the early morning and then early evening when there is no sun. These are the times the battery drops to 70% with normal no sun usage and then they crash to 0%. So always uses GRID to recharge the batteries at these times.

Anyone with a similar issue or suggestion what is going on?

Many thanks!!

Solution: Resetting the Battery Management System (BMS) to Address Rapid Discharge

The rapid drop from 69% to 0% state of charge (SOC) on your CFE 5.12kWh lithium batteries suggests a potential issue with the Battery Management System (BMS) misreporting the SOC. This can happen if the BMS has drifted or lost calibration, causing the inverter to misinterpret the battery’s true capacity. Resetting the BMS by recalibrating the full and empty states in voltage mode (or lead-acid mode) may resolve this issue. Below is a step-by-step guide to safely reset the BMS for your Luxpower inverters and CFE batteries.

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Preliminary Checks

1. Confirm BMS Communication:

   • Verify if your Luxpower inverters are set to communicate with the CFE batteries via BMS (using CAN or RS485) or if they are in voltage mode.

   • Check the inverter’s LCD or app for the battery type (setting 3). It should be set to “Lithium” with battery code 6 (for CFE). If it’s in voltage mode, the BMS is bypassed, and the issue may be related to incorrect voltage settings.

2. Gather Battery Specifications:

   • Refer to the CFE 5.12kWh battery manual for the following:

     • Full Charge Voltage: Typically 56.4V–57.6V for a 51.2V nominal lithium battery.

     • Empty Voltage (Cutoff): Typically 48V–49V to prevent over-discharge.

   • If you don’t have the manual, contact your CFE supplier or assume conservative values (e.g., full charge at 56.5V, cutoff at 48V).

3. Safety Warning:

   • Do not discharge the battery below its specified minimum voltage (e.g., 48V) to avoid triggering the BMS’s over-discharge protection, which could damage the battery or require professional intervention.

   • Work with a qualified technician if you’re unsure about any step, as incorrect settings can harm the battery or inverter.

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Step-by-Step BMS Reset Procedure

This process involves switching the inverter to voltage mode (or lead-acid mode), disconnecting BMS communication, and cycling each battery individually to recalibrate the BMS. Perform the steps carefully to avoid over-discharging or overcharging.

Preparation

1. Switch to Voltage/Lead-Acid Mode:

   • On the Luxpower inverter’s LCD or app, go to setting 3 (Battery Type).

   • Change from “Lithium” to “Lead Acid” or “Voltage Mode” (depending on your firmware’s terminology).

   • Set the following voltages based on CFE battery specifications:

     • Charge Voltage: Set to 0.1–0.2V above the full charge voltage (e.g., 56.6–56.7V if the spec is 56.5V). This ensures the BMS recognizes a full charge without overcharging.

     • Discharge Cutoff Voltage: Set to the minimum safe voltage (e.g., 48V). Do not set it lower to avoid over-discharge.

   • Save the settings.

2. Disable BMS Communication:

   • Unplug the CAN or RS485 communication cable between the inverter and the battery. This forces the inverter to rely on voltage readings instead of BMS data.

   • If you’re unsure which cable is the communication line, consult the Luxpower or CFE manual or contact your installer.

3. Isolate Batteries:

   • Since you have two CFE batteries, work on one battery at a time to ensure proper recalibration.

   • Turn off or disconnect the slave battery (check the CFE manual for master/slave configuration). Ensure only the master battery is connected to the inverter.

Resetting the First Battery

4. Discharge the Battery:

   • Operate the system normally to discharge the master battery until it reaches the cutoff voltage (e.g., 48V) or the inverter alarms for low battery.

   • Critical: Monitor the battery voltage closely via the inverter’s LCD or a multimeter. Stop discharging immediately if the voltage approaches the minimum specified value to prevent over-discharge.

   • If the inverter cuts off early (e.g., at 69% SOC), the BMS may still be intervening. Double-check that the communication cable is disconnected and the inverter is in voltage/lead-acid mode.

5. Recharge the Battery:

   • Allow the inverter to charge the battery from the grid (or solar, if available) until it reaches the set charge voltage (e.g., 56.6–56.7V).

   • The slight overvoltage (0.1–0.2V above spec) should trigger the BMS to recognize the battery as fully charged, recalibrating the 100% SOC point.

   • Caution: Do not exceed 0.3V above the specified full charge voltage to avoid overcharging, which could stress the battery or trigger BMS protection.

6. Verify Calibration:

   • Once fully charged, check the inverter’s SOC reading (if available) or measure the voltage to confirm it aligns with the battery’s full charge specification.

   • Reconnect the BMS communication cable and switch the inverter back to “Lithium” mode (battery code 6 for CFE).

Resetting the Second Battery

7. Switch Batteries:

   • Turn off or disconnect the first (master) battery.

   • Connect the second (slave) battery to the inverter, ensuring it’s the only battery active.

   • Repeat steps 4–6 for the second battery, discharging to the cutoff voltage and recharging to the full voltage.

Final Setup

8. Reconnect Both Batteries:

   • Reconnect both batteries (master and slave) as per the CFE manual’s configuration.

   • Ensure the BMS communication cable is reconnected.

   • Set the inverter back to “Lithium” mode with battery code 6.

9. Test the System:

   • Monitor the system over a few days to confirm the rapid discharge from 69% to 0% no longer occurs.

   • Check that the SOC readings align with expected battery behavior during discharge and charge cycles.

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If the Issue Persists

• Possible Battery Fault: If recalibration doesn’t resolve the issue, one or both batteries may have cell imbalances or degradation. Contact your CFE supplier to check warranty status (typically 10 years) and request a professional inspection of cell voltages and BMS logs.

• Cell Imbalance Cause: If the batteries are kept at 100% SOC for extended periods without cycling, cell imbalances can develop. To prevent this, cycle the batteries (discharge to 20–30% SOC) once or twice a month, especially during high solar production periods.

• Inverter Settings: Double-check other inverter settings, such as maximum discharge SOC (setting 11, set to 20–30%) and time-based charge/discharge schedules (settings 13 and 14). Ensure they allow grid charging during early morning and evening to avoid unnecessary battery cycling.

• Firmware Update: Contact Luxpower support ([email protected]) to verify your inverter’s firmware version. Older firmware may cause BMS communication issues.

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Additional Recommendations

• Use Monitoring Tools: If possible, install a monitoring tool like Solar Assistant to track real-time SOC, voltage, and current for better diagnostics.

• Join Community Groups: Connect with other Luxpower users via the LuxpowerSA Facebook group or WhatsApp community for shared experiences and solutions.

• Professional Assistance: If you’re uncomfortable performing these steps or lack access to the inverter’s app, consult your installer or a qualified solar technician.

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Safety Notes

• Always follow the CFE battery and Luxpower inverter manuals for specific voltage settings and procedures.

• Avoid discharging below the minimum specified voltage or charging above the recommended voltage to prevent damage.

• If you notice unusual battery behavior (e.g., overheating, swelling, or BMS errors), stop the process and contact the supplier immediately.