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SolarEdge Inverter DC Injection Fault in Off-Grid Systems

Troubleshooting DC injection faults in off-grid SolarEdge hybrid inverters. Diagnose and resolve DC current leakage affecting AC output & system safety.

Frequently Asked Questions

•What is the acceptable DC injection limit for a SolarEdge inverter?

Refer to the SolarEdge inverter's datasheet or installation manual for the specified DC injection limit. Typically, it's in the range of a few milliamps.

•How can I check the grounding of the inverter and the PV system?

Use a multimeter to measure the resistance between the grounding electrode conductor (GEC) and all exposed metal parts of the inverter and PV array. The resistance should be less than 1 ohm, according to NEC 250.

•What are the potential consequences of DC injection on the AC load?

DC injection can cause overheating and saturation of transformers in connected appliances, leading to reduced efficiency, premature failure, and potentially hazardous conditions.

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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.

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Technical Background:

DC injection refers to the presence of DC current on the AC output of the inverter. In a properly functioning inverter, the DC power from the PV array or battery is converted to pure AC power. DC injection can occur due to component failures within the inverter's DC-AC conversion stage or issues with the isolation transformer (if present). Off-grid operation increases sensitivity because the inverter must create its own AC sine wave without grid support.

Symptoms:

The SolarEdge inverter reports a "DC Injection" fault during off-grid operation. The inverter may shut down, limit AC power output, or display an error message related to excessive DC current on the AC output.

Possible Causes:

Failure of an IGBT or MOSFET within the inverter's H-bridge.
Degradation or failure of DC link capacitors, leading to DC ripple on the AC output.
Grounding issues creating a DC current path through the AC wiring.
Transformer saturation (if the inverter utilizes a transformer).
Firmware or software bugs causing incorrect PWM modulation.
Isolation faults in the battery management system (BMS) impacting DC-AC conversion.

Solution:

1

Disconnect AC and DC power to the inverter and wait for the capacitors to discharge. Verify zero voltage using a calibrated multimeter.
2

Inspect the inverter's internal components for signs of physical damage (e.g., bulging capacitors, burnt components) using visual inspection and an IR thermometer.
3

Use a multimeter to measure the DC voltage on the AC output terminals. Values exceeding manufacturer specifications (typically a few milliamps) indicate a DC injection fault.
4

Check the grounding connections for proper bonding and continuity to NEC 250 standards. Confirm that there are no unintended ground loops.
5

If possible, update the inverter firmware to the latest version. Consult the SolarEdge documentation for the correct procedure.
6

Perform an isolation test on the DC input and battery connections to rule out leakage currents using a megohmmeter. Refer to manufacturer's specifications for test voltages and acceptance criteria.
7

Replace the inverter if the fault persists after completing the above steps. Contact SolarEdge technical support for RMA procedures.

Safety Warning:

High voltages are present within the inverter. Only qualified electricians with experience in power electronics should perform diagnostic and repair procedures. Always disconnect all power sources before working on the inverter. Wear appropriate personal protective equipment (PPE), including safety glasses, insulated gloves, and arc-rated clothing. Refer to NEC Article 690 for solar photovoltaic systems safety requirements and NEC Article 706 for energy storage systems. Follow all manufacturer safety guidelines.

Prevention:

• Regularly inspect the inverter's cooling system to ensure proper ventilation. Overheating can accelerate component degradation.
• Perform routine insulation resistance tests on the DC input and battery cables.
• Monitor inverter performance data (e.g., DC voltage, AC voltage, current) to identify potential issues early.
• Keep the inverter firmware updated to the latest version.
• Implement a robust surge protection strategy on both AC and DC sides to mitigate transient voltage events.

Expert Tip:

Access the inverter's service menu (refer to the SolarEdge system manual for the key combination) to view detailed diagnostic data, including DC injection levels. This data can help pinpoint the source of the fault.