How to Fix Fuji Drive OC1 Fault Overcurrent During Acceleration?

Staring at an OC1 fault on your Fuji Frenic inverter? Learn why overcurrent occurs during acceleration and follow our guide to adjust parameters and check your motor.

 

Solving the Fuji Drive OC1 Fault: Why Your Inverter Trips on Start

If you are looking at your Fuji Electric Frenic inverter and the screen is flashing OC1, your drive is in protective mode. In the Fuji ecosystem, "OC" stands for Overcurrent, and the "1" specifically means the trip happened during Acceleration (the ramp-up phase).

This is a "Hard Fault." The drive's internal sensors detected a massive surge of electricity that exceeded its safe limit and shut down in microseconds to prevent the internal transistors (IGBTs) from frying. Let’s look at how to find the "clog" in the system.

Common Causes of the OC1 Fault

When a Fuji drive trips on OC1, it usually falls into one of these three real-world categories:

• Acceleration Time is Too Short: You are asking a heavy load to go from 0 to 60 too fast, causing a huge current spike.
• Mechanical Jam: The motor is trying to turn, but the machine is stuck, rusted, or blocked.
• Torque Boost is Too High: The drive is shoving too much "starting juice" into the motor, causing it to saturate and trip.
• Electrical Short: A short circuit in the motor windings or the output cables.

Step-by-Step Troubleshooting for OC1

1. Increase the Acceleration Time (Function F07)

This is the most common fix. If your load has high inertia (like a large fan or a heavy conveyor), it needs more time to speed up.

• Navigate to Function Code F07 (Acceleration Time 1).
• Increase the value. For example, if it is set to 5.0 seconds, try increasing it to 10.0 or 15.0 seconds.
• A longer ramp-up time reduces the starting current draw.

2. The "Uncoupled" Test (The Isolation Fix)

To find out if the problem is the drive or the motor, we need to separate them:

• Power down and disconnect the motor wires from the U, V, and W terminals.
• Try to run the drive without the motor connected.
• If OC1 still appears: The drive's internal hardware (IGBT) is likely damaged.
• If the drive runs fine: The drive is healthy! The problem is 100% in your cables, motor, or the mechanical load.

3. Check the Torque Boost (Function F09)

Fuji drives have a feature called "Torque Boost" to help motors start under heavy load. If this is set too high, it creates an overcurrent.

• Check Function Code F09 (Torque Boost).
• Try lowering this value slightly. If the drive is pushing 10% boost at start-up, try lowering it to 5% or 2%.

4. Verify the V/f Pattern (Function F04 & F05)

If the drive doesn't know the motor's true rated voltage and frequency, it will miscalculate the current.

• Check F04 (Base Frequency) and F05 (Rated Voltage).
• Ensure these match the nameplate on your motor exactly.

How to Reset the OC1 Fault

1. Identify and fix the mechanical jam or adjust the ramp settings.
2. Press the RESET key on the Fuji keypad.
3. If the fault happened due to high heat, let the drive sit for 2 minutes before resetting.
4. Warning: If you reset OC1 and it trips again immediately, stop! Repeatedly trying to start into a short circuit will eventually destroy the drive.

Summary

The Fuji OC1 fault is a signal that your "speed-up" settings are clashing with your physical load. Start by lengthening your Accel Time (F07) and lowering your Torque Boost (F09). In 90% of cases, these two parameter tweaks will solve the problem!