storagefaults.comstoragefaults.com

Analysis by Marcus & Team

SolarEdge Hybrid Inverter Error 18x44: DC Bus Voltage Low

Troubleshoot SolarEdge Error 18x44 (DC Bus Voltage Low) in residential hybrid inverters. Diagnostics, repair, safety tips, and prevention for homeowners.

Frequently Asked Questions

•What are the typical signs of DC bus capacitor failure in SolarEdge inverters?

Bulging, leakage, discoloration, or elevated temperature are common indicators. Measuring capacitance and ESR can confirm the failure.

•How does a faulty BMS affect the DC bus voltage in a SolarEdge hybrid inverter?

A faulty BMS can prevent the battery from supporting the DC bus during standby, leading to a voltage drop. Incorrect SOC reporting or communication errors can also contribute.

•What NEC requirements are relevant to DC disconnects in SolarEdge hybrid inverter systems?

NEC 690.13 outlines requirements for DC disconnect switches, including location, rating, and marking. The disconnect must be readily accessible and capable of isolating the PV array from the inverter.

Related questions

Loading related questions...

Marcus leads the technical research department at Storage Faults. Together with a team of systems analysts, he specializes in translating complex solar storage error codes into actionable diagnostic steps for the US market.

← Back to list

Technical Background:

SolarEdge hybrid inverters utilize a DC bus to interface the PV array, battery, and grid. The DC bus voltage is regulated by the inverter's power electronics to ensure efficient energy transfer and stable operation. Error 18x44 signals that the inverter's control system has detected a DC bus voltage below the acceptable lower limit during standby. This can be caused by multiple factors including component failure or incorrect configuration. Standby mode typically entails keeping essential circuitry powered up for fast response, leading to a minimal DC bus voltage.

Symptoms:

SolarEdge hybrid inverter reports Error 18x44, indicating a low DC bus voltage condition specifically when the inverter is in standby mode (not actively charging/discharging battery or exporting power).

Possible Causes:

Degradation of DC bus capacitors, leading to increased ESR (Equivalent Series Resistance) and voltage droop under minimal load.
Firmware bug causing misreporting or incorrect voltage threshold settings during standby.
Faulty DC bus voltage sensor or related circuitry, providing inaccurate readings to the control system.
Issues with the pre-charge circuit for the DC bus capacitors. The circuit may not be properly charging the capacitors during startup or maintaining the voltage in standby.
DC leakage currents within the inverter, drawing down the DC bus voltage when idle.
Incorrect battery configuration or BMS (Battery Management System) communication failure, preventing proper battery support of the DC bus during standby.

Solution:

1

*Visual inspection**: Power down the inverter using the DC disconnect and AC breaker. Open the inverter enclosure (qualified electrician only). Visually inspect the DC bus capacitors for bulging, leakage, or other signs of damage.
2

*Capacitance Measurement**: Using a multimeter with capacitance measurement capability, carefully discharge the DC bus capacitors (after disconnecting from all power sources!) and measure their capacitance. Compare the measured values to the manufacturer's specifications. Replace any capacitors that are out of spec.
3

*Firmware Update**: Check for and install the latest firmware update for the inverter. Refer to the SolarEdge documentation for the correct procedure. A bug fix might address the false error reporting.
4

*Voltage Sensor Test**: Use a multimeter to measure the DC bus voltage at the test points specified in the service manual. Compare the measured voltage to the value reported by the inverter's monitoring system. If there is a significant discrepancy, the voltage sensor may be faulty and require replacement. Qualified personnel only.
5

*Leakage Current Test**: After ensuring all power sources are disconnected and DC bus capacitors are safely discharged, use a multimeter in DC current mode to check for leakage current from the DC bus to ground. High leakage current (above manufacturer specifications) can indicate insulation breakdown or component failure.
6

*Battery System Check**: Verify the battery system is properly configured and communicating with the inverter. Check the BMS status and ensure the battery voltage and SOC are within the specified operating range. Refer to the battery manufacturer's documentation for troubleshooting.
7

*DC Disconnect Verification**: Inspect the DC disconnect switch for proper operation and ensure it is fully isolating the PV array from the inverter when in the OFF position. Use a multimeter to verify that there is no voltage present on the inverter's DC input terminals when the disconnect is open. Complies with NEC 690.13.

Safety Warning:

High DC voltages are present within the inverter enclosure. Always disconnect all power sources (PV array and AC grid) before opening the enclosure. Follow proper lockout/tagout procedures to prevent accidental energization. Arc flash hazards exist. Only qualified electricians should perform maintenance or repairs. NEC 690 provides guidance on safe work practices for PV systems. Comply with NEC 706 (Battery Safety).

Prevention:

• Regularly monitor the inverter's performance using the SolarEdge monitoring portal. Look for any trends in DC bus voltage or other parameters that could indicate a developing problem.
• Schedule periodic maintenance inspections by a qualified electrician to check the condition of the inverter components, including the DC bus capacitors.
• Keep the inverter enclosure clean and free of dust and debris to prevent overheating.
• Ensure the inverter firmware is always up to date.
• Perform battery capacity testing annually.

Expert Tip:

Access the SolarEdge service menu (usually requires a specific key combination or software) to view detailed DC bus voltage logs and error history. This can provide valuable insight into the nature and frequency of the problem. Also use an IR thermometer to locate hot spots on the DC bus capacitors which indicates higher ESR and failing capacitors.