Inverter Relay Clicking Sound: Meaning and Fixes

Key Takeaways

• The most likely cause of repeated inverter clicking is a disconnected or critically low battery.
• Your first check should always be the battery connections and the battery's voltage.
• Always disconnect all power sources (PV, grid, battery) before inspecting electrical connections.
• Stop DIY troubleshooting and contact a qualified technician if internal components are suspected or the issue persists after basic checks.

Why is my solar inverter's relay clicking repeatedly?

A clicking sound from your solar inverter often indicates that the internal transfer relay is attempting to switch between power sources but is unable to establish a stable connection. This can happen when the inverter tries to move between grid power, battery power, or solar power, but a problem prevents it from settling into a stable operating mode. For Growatt SPF 3500 ES / SPF 5000 ES and Axpert VM III inverters, this symptom, accompanied by flashing LCD/LEDs, is explicitly linked to a disconnected battery.

Diagnosis

Follow these steps to diagnose the cause of your inverter's clicking sound. Always prioritize safety by disconnecting power before touching any wiring.

1. Check Inverter Display for Error Codes

Observe your inverter's LCD display and any indicator LEDs. Many inverters will show a specific error code or message that points to the problem.

• Growatt SPF 3500 ES / SPF 5000 ES: Look for error code 56, which indicates "Battery is not connected well or fuse is burnt."
• Deye SUN-SG03LP1-EU: Error F24, "Working mode change," can occur when grid type, frequency, or battery mode changes. While not always a fault, frequent F24 errors with clicking might indicate instability.
• Axpert VM III: The manual notes that "When the unit is turned on, internal relay is switched on and off repeatedly. LCD display and LEDs are flashing" if the "Battery is disconnected."

2. Verify Battery Connections

A loose or corroded battery connection is a very common cause of intermittent power and relay clicking.

• Safety First: Before touching any connections, ensure all power sources to the inverter are disconnected: turn off the PV array, grid input, and battery breakers. For safety, always use insulated tools and wear appropriate personal protective equipment.
• Inspect Terminals: Visually check the positive (+) and negative (-) terminals on your battery bank and where they connect to the inverter. Look for any looseness, corrosion, or signs of overheating.
• Tighten Connections: If connections are loose, carefully tighten them. WARNING: Be very cautious when working with metal tools on or around batteries. A potential risk exists to drop a tool to spark or short circuit batteries or other electrical parts and could cause an explosion. Ensure there is nothing placed between the inverter terminal and the ring terminal, as this can cause overheating, as noted in the Growatt SPF 3500 ES / SPF 5000 ES manual.

3. Measure Battery Voltage

An insufficient battery voltage can prevent the inverter from starting or maintaining operation, leading to repeated attempts and clicking.

• Measure DC Voltage: Use a multimeter to measure the voltage across your battery terminals.
• Compare to Cold Start Voltage:
• • For Axpert VM III 1.5KW/3KW models, the cold start voltage is 23.0Vdc. For the 5KW model, it is 46.0Vdc.
  • For Growatt SPF 3500 ES / SPF 5000 ES inverters, the cold start voltage for Lead-Acid Mode is 46.0Vdc. For Lithium Mode, it's a cold start SOC of 30%, which is Low DC Cut-off SOC +10%.
• Low Voltage Indication: If the voltage is below these thresholds, the battery is too low to power the inverter. For Growatt SPF 3500 ES / SPF 5000 ES, a battery voltage "far too low (<1.4V/Cell)" can result in no response after power on.

4. Check AC Input (Grid/Generator) Stability

If your inverter is connected to the grid or a generator, instability in the AC input can cause the relay to cycle as it tries to decide whether to draw power from the grid or switch to battery/PV.

• Monitor Grid Status: Check if the grid power is stable. Frequent fluctuations in voltage or frequency can trigger the inverter's transfer relay.
• Growatt SPF 3500 ES / SPF 5000 ES: If "Mains exist but the unit works in battery mode" and the "Green LED is flashing," it could be due to "Insufficient quality of AC power (Shore or Generator)."

5. Check for Overload Conditions

An excessive load connected to the inverter can cause it to attempt to switch modes or shut down, leading to relay clicking.

• Reduce Load: Disconnect non-essential loads from the inverter's output.
• Solis S5-EH1P-L Series: An "Over-Load" fault indicates "Backup load power is too large, or some inductive load startup power is too large." This can cause the inverter to attempt to disconnect the load, potentially involving relay action.

6. Review Inverter Settings

Incorrect settings, particularly those related to battery type or output source priority, can lead to unexpected relay behavior.

• Battery Type Setting: Ensure the inverter's battery type setting matches your installed battery (e.g., AGM, Flooded, Lithium, User-Defined for Growatt SPF 3500 ES / SPF 5000 ES and Axpert VM III).
• Output Source Priority: Check the output source priority setting. For Axpert VM III, if "SUB" (solar first) is selected, the inverter will prioritize solar power, then utility, and finally battery. Frequent switching between these sources due to insufficient solar or grid power can cause clicking.

Cause/fix table

Inverter-Side Checks vs. Battery-Side Checks

When troubleshooting a clicking inverter, it's crucial to distinguish between issues originating from the inverter itself and those from the battery bank.

Battery-Side Checks: The most common cause of relay clicking, as commonly reported by installers and indicated in manuals, is a problem with the battery connection or charge level.

• Connection Integrity: Ensure all battery cables are securely fastened to both the battery terminals and the inverter's DC input. Loose connections create resistance, leading to voltage drops and intermittent power, which can cause the inverter's relay to cycle.
• Battery Voltage: Measure the battery voltage. If it falls below the inverter's minimum operating voltage or cold start voltage, the inverter will attempt to power on, fail, and then try again, causing the relay to click. For example, a Growatt SPF 3500 ES / SPF 5000 ES in Lead-Acid Mode requires 46.0Vdc for cold start. An Axpert VM III 5KW model also requires 46.0Vdc for cold start. If the battery voltage is "far too low (<1.4V/Cell)" for Growatt SPF 3500 ES / SPF 5000 ES, the unit may show no response at all.
• Battery Fuses/Breakers: Check any inline fuses or DC breakers between the battery and the inverter. WARNING: Be very cautious when working with metal tools on or around batteries. A potential risk exists to drop a tool to spark or short circuit batteries or other electrical parts and could cause an explosion. A blown fuse or tripped breaker will effectively disconnect the battery, leading to the clicking symptom. The Axpert VM III, for instance, includes "One piece of 150A fuse is provided as over-current protection for the battery supply."

Inverter-Side Checks: While less common for simple clicking, certain inverter settings or internal issues can contribute.

• Output Source Priority: Inverters like the Axpert VM III allow you to set an "Output source priority" (e.g., "SUB" for solar first). If solar input is intermittent or insufficient, and the grid is also unstable, the inverter might repeatedly switch between sources, causing the relay to click.
• Internal Faults: If the battery and external connections are confirmed to be sound, the clicking might point to an internal inverter fault. This could involve the transfer relay itself or the control circuitry that manages power flow. Error codes like Growatt's "09/53/57 Internal components failed" or Axpert's "53 Inverter soft start failed" would indicate such issues, requiring professional service.

Safety: Electrical Hazards and Battery Care

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

• Disconnect All Power: Before performing any inspection or maintenance, disconnect all power sources to the inverter: turn off the PV array, the AC grid input breaker, and the battery breaker. For models like the Solis S5-EH1P-L Series, you must "Wait 5 minutes after disconnection from the utility grid and the PV input" before touching any inner live parts due to stored energy in capacitors.
• Qualified Personnel: "All operations including transport, installation, start-up and maintenance, must be carried out by qualified, trained personnel," as stated in the Fox ESS H1(G2)/AC1(G2) manual. The Growatt SPF 3500 ES / SPF 5000 ES manual also states, "All the operation and connection please professional electrical or mechanical engineer."
• Insulated Tools and PPE: Always use insulated tools and wear appropriate personal protective equipment, including gloves and eye protection, when working with electrical systems. The Solis S5-EH1P-L Series manual advises, "Operator must put on the technicians’ gloves during the whole process in case of any electrical hazards."
• Battery Safety:
• • "Be very cautious when working with metal tools on or around batteries. A potential risk exists to drop a tool to spark or short circuit batteries or other electrical parts and could cause an explosion," warns the Growatt SPF 3500 ES / SPF 5000 ES manual.
  • "NEVER charge a frozen battery," is a critical warning found in manuals for Growatt SPF 3500 ES / SPF 5000 ES, Axpert VM III, and Deye SUN-SG03LP1-EU.
• No User Serviceable Parts: Many inverters, such as the Solis S5-EH1P-L Series, state, "There is no user serviceable parts inside, refer servicing to qualified and accredited service technicians." Opening the unit without authorization may void the warranty.

When to call a technician instead

While basic troubleshooting can resolve many issues, there are clear limits to DIY repairs.

• Persistent Issues: If the inverter continues to click after you have checked and secured all battery connections, verified battery voltage, and confirmed stable AC input, it's time to call a professional.
• Internal Faults: If your inverter displays error codes indicating internal component failure (e.g., Growatt SPF 3500 ES / SPF 5000 ES error 09/53/57 "Internal components failed" or Axpert VM III error 53 "Inverter soft start failed"), do not attempt internal repairs.
• Warranty Concerns: Many manufacturers, including Solis, explicitly state that "Improper access and operation may result in abnormal results and damage to the inverter. Un-authorised access may void the warranty." The Deye SUN-SG03LP1-EU manual advises to "Seek help from us if can not go back to normal state" for various faults.
• Complex Wiring: If you are unsure about any wiring connections, especially AC input or parallel system wiring, contact a licensed electrician. For parallel operations, Growatt SPF 3500 ES / SPF 5000 ES warns, "Be sure that all inverters will share the same battery bank. Otherwise, the inverters will transfer to fault mode."

If you encounter persistent problems or suspect an internal issue, contact your installer or the manufacturer's customer service for assistance. This ensures your safety and maintains your warranty.

--- Cross-Brand Caveat for Menu Numbering: It is important to note that while the provided manuals list settings by program number (e.g., "Program 01", "Program 05"), rebadged or differently-firmwared units of the same platform may renumber these menus. Therefore, users should always refer to the setting name (e.g., "Output source priority", "Battery type") rather than relying solely on the program number when configuring their inverter. ---