19 Common Inverter Fault Codes and How to Fix Them

Inverters are essential components in electrical automation systems, commonly used to control motors with increased energy efficiency, safety, and operational performance. However, like all machinery, inverters can encounter faults over time, especially with continuous operation. Understanding common inverter fault codes and how to address them is critical for maintaining system reliability and minimizing downtime. Below are 19 common inverter fault codes, their causes, and practical solutions.

Inverter Overcurrent Fault (OCF)

An inverter may experience an overcurrent fault when the motor's load exceeds its capacity, or when the machine is physically blocked. This can occur due to incorrect motor data input or a malfunction in the motor itself. To resolve this, check whether the motor nameplate data entered in the inverter settings is accurate. Verify that the overcurrent protection thresholds are correctly configured. Additionally, ensure that the motor is not blocked and that the load being driven by the motor is appropriate for the inverter’s specifications. If the motor is too heavy or the machine is stuck, the inverter may also trigger an overcurrent fault.

Motor Short Circuit Fault (SCF)

A motor short circuit fault can manifest in several forms, including phase-to-phase short circuits (SCF1), impedance short circuits (SCF2), or ground leakage currents (SCF3). These faults are typically caused by problems such as faulty motor insulation, long motor cables, or lack of protection like motor reactors or sine wave filters. To address the issue, check the insulation of the motor cables and confirm the motor itself is in good condition. If the cable length exceeds 80 meters, consider using a motor reactor or a sine wave filter to reduce leakage currents. Additionally, reduce the inverter's switching frequency if required and inspect the inverter’s power components for failure.

Braking Overspeed Fault (OBF)

This fault occurs when excessive braking or load inertia causes a sudden increase in the inverter’s DC bus voltage. It is often seen when braking is too forceful or when the load's inertia is too large. To fix this, increase the deceleration time in the inverter settings to manage the braking process more gradually. If no braking resistor is in use, consider enabling the deceleration time adaptation (brA) function. In more severe cases, adding a braking resistor may be necessary to handle the energy created by the braking process more efficiently.

Overheating is a common issue for inverters, often caused by excessive motor load or inadequate cooling. When the inverter’s power components heat up beyond safe limits, an overheating fault is triggered. To address this, first, ensure that the inverter’s ventilation is unobstructed and clean. If the ambient temperature around the inverter is too high, take steps to lower it. Additionally, make sure that the cooling fan and other heat-dissipation components are functioning properly. In the event of overheating, allow the inverter to cool down before restarting it.

Motor Overload Fault (OLF)

When a motor exceeds its thermal protection limits due to excessive current, a motor overload fault will occur. This is typically a result of overloading the motor beyond its rated capacity. To resolve the issue, verify that the motor load is within specifications. Check the motor thermal protection settings in the inverter and ensure they are correctly configured. If the motor has overheated, wait for it to cool down before attempting to restart it.

Motor Phase Loss Fault (OPF)

A motor phase loss fault can happen when there is a poor connection between the inverter and motor, or if the motor is undersized for the inverter. This issue often causes unstable and intermittent motor operation, which prevents the inverter from detecting the motor’s current properly. To resolve this fault, check the connections between the inverter and motor, ensuring that the motor size and inverter match. If performing tests with a small motor, disable the motor phase loss protection function. Also, verify that all motor parameters, including rated voltage and current, are correctly set in the inverter.

Input Overvoltage Fault (OSF)

The input overvoltage fault occurs when the voltage supplied to the inverter exceeds its rated limits or fluctuates too much. This can damage the inverter and cause operational issues. To fix this, check the main power supply voltage and ensure it remains within the acceptable range for the inverter. Make sure the voltage fluctuations do not exceed the inverter’s tolerances.

Communication faults in inverters are caused by interruptions in the inverter’s communication bus. This can happen due to wiring issues, incorrect communication program settings, or external interference. To resolve the issue, check the communication connections and ensure they are secure. Review the communication program and verify that the timeout settings are correct.

An undervoltage fault occurs when the inverter’s input power supply voltage is too low or fluctuates beyond the permissible range. To fix this, check the main power supply voltage to ensure it stays within the inverter’s allowable limits. Additionally, verify that the undervoltage management parameters in the inverter settings are configured properly.

Input Phase Loss Fault (PHF)

This fault happens when one of the phases of the inverter’s input power supply is lost or incorrect. It can also occur if the inverter is powered by a DC bus and the phase loss protection is not properly disabled. To resolve this, check the inverter’s power supply and phase sequence. If the inverter is powered by DC, disable the input phase loss protection function (IPL).

Braking Unit Short Circuit Fault (BUF)

A short circuit in the braking unit is often caused by a burnt brake resistor or faulty wiring. This can prevent the inverter’s braking system from operating correctly. To fix this fault, check the brake resistor and ensure it is functioning properly. If the brake unit is not connected correctly or the inverter is of a larger power rating, the fault management settings may need to be adjusted to bypass the fault monitoring.

Pre-Charging Circuit Fault (CrF)

The pre-charging circuit fault occurs when the relay or pre-charging resistor fails. This is a critical fault, as it affects the inverter’s ability to safely start. To resolve this issue, power off the inverter and allow it to reset. If the fault persists after restarting, repair the inverter or ｒｅｐｌａｃｅ the damaged components in the pre-charging circuit.

Motor Overspeed Fault (SOF)

Motor overspeed faults occur when the motor exceeds its rated speed, typically due to unstable motor operation or excessive load inertia. To resolve this fault, check the motor’s parameters in the inverter settings, including the motor nameplate data and the inverter's gain settings. In some cases, adding a braking resistor can help stabilize the motor and prevent overspeed faults.

Motor Self-Tuning Fault (tnF)

This fault happens when the motor fails to undergo proper self-tuning due to incompatibility with the inverter, incorrect wiring, or other issues. To resolve this, ensure that the motor and inverter are compatible. Double-check the motor's wiring and verify that the inverter’s settings are correct for the specific motor being used.

Speed Feedback Loss Fault (SPF)

The speed feedback loss fault occurs when the inverter loses the encoder’s feedback signal, which is essential for monitoring motor speed. To fix this, check the encoder’s connections to ensure they are secure. Inspect both the mechanical and electrical connections to confirm that the encoder is functioning correctly.

Encoder Fault (EnF)

An encoder fault occurs when the encoder fails to transmit the proper feedback signal to the inverter. This can happen due to faulty wiring or incorrect settings in the inverter. To resolve this, check the inverter’s encoder-related settings, including pulse count (PG|) and encoder type (EnS). Inspect the encoder and its connections for any issues.

If the inverter’s Chinese panel fails to display or operate, it may be due to a faulty panel or an internal power issue. Check the connection between the panel and the inverter, and verify that the inverter’s 24V power supply is functioning correctly. If the problem persists, replacing the panel may be necessary.

No Main Power Supply (nLP)

This fault occurs when the inverter only has control power but no main power supply. This can happen if the incoming fuse is blown or the power supply is disconnected. To resolve this, check the power supply to the inverter and inspect the fuse. Ensure that all connections are tight and that the DC reactor is properly connected if used.

Power-Off Lock (PrA)

A power-off lock fault occurs when certain safety functions in the inverter prevent operation due to an unpowered PWR control terminal. To resolve this, ensure the PWR control terminal is powered and check the related control connections.

Inverter Fault Codes: Causes and Solutions

Understanding common inverter fault codes and knowing how to address them is crucial for maintaining the operational efficiency of electrical systems. Inverters, like any complex machinery, are susceptible to a range of issues, but with proper maintenance and troubleshooting, most faults can be resolved quickly. By addressing inverter faults promptly, you can minimize downtime and extend the lifespan of your equipment.

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