How to Fix Yaskawa A1000 oC Fault Overcurrent Troubleshooting?

Staring at an oC fault on your Yaskawa A1000? Learn why overcurrent occurs, how to perform an isolation test, and which parameters to adjust.

 

How to Fix Yaskawa A1000 oC Fault: The Overcurrent Guide

If you are standing in front of your Yaskawa A1000 and the digital operator is flashing oC (Overcurrent), your drive is in "Self-Preservation" mode. This is one of the most common, yet serious, faults you'll encounter.

In simple terms, the electricity flowing out of the drive reached a level that could melt the internal components. To prevent a total hardware failure, the A1000 cuts power to the motor instantly. Let’s walk through the steps to find the "surge" and get your machine running again.

Common Causes of the oC Fault

When an A1000 trips on oC, it usually falls into one of these four categories:

• Mechanical Blockage: The motor is trying to turn, but the machine is jammed, a bearing is seized, or the load is physically too heavy.
• Electrical Short: A short circuit in the motor windings or the cables (Phase-to-Phase or Phase-to-Ground).
• Acceleration/Deceleration is Too Fast: You are asking a heavy load to change speed too quickly, causing an inductive current spike.
• Internal Drive Failure: The drive's internal power module (IGBT) has failed.

Step-by-Step Troubleshooting for oC

1. The "Isolation" Test (The #1 Pro Tip)

We need to know if the problem is inside the drive or out in the field.

• Power down the drive and wait for the "Charge" LED to turn off.
• Disconnect the motor wires from terminals U, V, and W.
• Power the drive back up and try to "Start" it in Hand mode.
• If oC still appears: The drive's internal hardware is damaged. You likely need a new VFD or a professional repair.
• If the drive runs fine without the motor: The drive is healthy! The problem is 100% in your cables, motor, or the machine.

2. Check the Mechanics (The Hand-Spin Test)

If the drive passed the isolation test, it’s time to look at the machine:

• With the power Off and Locked Out, try to rotate the motor shaft or the machine by hand.
• If it feels stiff, "crunchy," or won't move at all, your oC fault is actually a mechanical jam or a bad bearing.

3. Review the "Ramp" Parameters (Group C1)

If the fault only happens during the first few seconds of starting:

• Check Parameter C1-01 (Acceleration Time 1).
• If you are starting a heavy fan or a loaded conveyor, try increasing this time (e.g., from 10 seconds to 30 seconds). A slower ramp-up reduces the starting current draw.

4. Verify Motor Data (Group E2)

If the drive doesn't know the motor's true capacity, it can't manage the current correctly.

• Check Parameter E2-01 (Motor Rated Current).
• Ensure this matches the FLA (Full Load Amps) on your motor nameplate. If this is set too low, the drive may be overly sensitive.

Checking the IGBTs (The Diode Test)

If the drive trips on oC even with the motor disconnected, you likely have a blown power transistor.
With power OFF and capacitors discharged:

• Use a multimeter in Diode Mode.
• Check the resistance between the DC+ / DC- terminals and the U, V, and W terminals.
• If any reading shows "0.000" (a dead short) in both directions, that phase of the drive is blown.

How to Reset the oC Fault

1. Identify and fix the mechanical jam or electrical short.
2. Press the RESET key on the digital operator.
3. If the fault happened during a long run, let the drive sit for 2 minutes to allow internal components to cool before restarting.
4. Warning: If you reset oC and it trips again immediately, do not keep trying. Repeatedly starting into a short circuit will eventually destroy the drive's output stage.

Summary

The Yaskawa A1000 oC fault is a protector. Usually, it’s a mechanical jam or an accel time (C1-01) that is too aggressive. Perform the Isolation Test first—it will tell you within 5 minutes if you need a mechanic to fix a machine or an electrician to replace the drive.