A1000 Fault oL2 — Drive Overload

Overview

The oL2 (Drive Overload) fault on the Yaskawa A1000 variable frequency drive indicates that the inverter's output current has exceeded its rated threshold for an extended period, threatening the thermal integrity of the internal insulated-gate bipolar transistors (IGBTs). Unlike an oL1 fault—which uses a mathematical curve to protect the motor from overheating—an oL2 fault is triggered to protect the drive itself. When the drive protects itself with an oL2 fault, it has reached its maximum electronic thermal overload capacity, typically after operating at high output current for 60 seconds (usually 150% of rated current in Heavy Duty mode or 120% in Normal Duty mode).

Symptoms

When your system encounters an oL2 fault, you may observe several of the following operational symptoms:

• Sudden Inverter Shutdown: The VFD immediately interrupts the output path to the motor, triggering a coast-to-stop operation to protect internal components.
• Alarm Panel Code Panel Display: The digital operator (JVOP-180) displays a flashing or solid oL2 code.
• Excessive Heat Sink Temperature: The cooling fans on the rear of the drive run at maximum speed, and the internal heatsink temperature (readable in monitor parameter U4-08) is elevated.
• Repetitive Trips at Identical Operating Points: The fault frequently occurs at the exact same point in the run cycle, such as during rapid acceleration, peak mechanical load, or when descending profiles require dynamic braking.
• Motor Stall or Hesitation: Right before the fault registers, the motor may struggle to hit its target speed or display unstable running behavior.

Possible Causes

To systematically troubleshoot an oL2 fault, you must understand the underlying causes that force the drive's output current to rise above acceptable limits:

• Inadequate Drive Sizing: The application demands more continuous torque than the installed A1000 rating can deliver. This is common when converting a system from Normal Duty (ND) to Heavy Duty (HD) without upgrading the physical drive frame size.
• Excessive Load During Acceleration or Deceleration: The acceleration time (C1-01) or deceleration time (C1-02) is set too short for the inertia of the connected load, forcing the drive to dump excess current to meet the ramp demands.
• Incorrect V/f Pattern Settings: If the voltage-to-frequency ratio (parameters in the E1 group) does not match the motor nameplate or the application needs, the drive may suffer from excessive excitation current, producing heat without useful torque.
• High Carrier Frequency Setting: Running a high carrier frequency (C6-02) to quiet motor whistle increases thermal dissipation inside the drive's IGBT switches. This forces the drive to derate its output current capacity and trip on oL2 much faster.
• Mechanical Hindrance, Jam, or Reducer Binding: Bearing failure, locked rotors, misaligned shafts, or frozen conveyance systems downstream force the motor to work harder, drawing current that exceeds the drive's thermal capability.
• Faulty Drive Current Detection Circuit: In rare scenarios, damaged internal current sensors (Halls or CTs) send inaccurate, inflated analog feedback to the main control board, tripping an oL2 fault under normal load conditions.

Step-by-Step Troubleshooting

Follow these consecutive industrial safety and troubleshooting steps to isolate and resolve the root cause of an oL2 error:

Step 1: Secure and Lock Out the Unit

Before working on any connection, completely isolate the A1000 from the main AC input power. Verify that the DC bus charge indicator LED on the drive is completely extinguished. Lock out and tag out (LOTO) the main breaker to ensure a safe workspace.

Step 2: Uncouple the Motor and Run a No-Load Test

To determine whether the issue is mechanical or electrical:

1. Uncouple the mechanical load from the motor shaft.
2. Restore power and temporarily run the drive in the Local Mode using the digital operator.
3. Accelerate the motor to target speed. Monitor the output current in parameter U1-03.

• Result A: If the current remains extremely low (within normal magnetizing limits) and no oL2 occurs, the issue is mechanical binding or a severely overloaded machine.
• Result B: If the drive still draws high current or trips on oL2 even when uncoupled, proceed to inspect the motor windings and the drive's configuration parameter set.

Step 3: Audit Parameters and Load Profile

Check key drive parameters to ensure they align with the physical load limits:

1. Check Acceleration and Deceleration Times: Increase the values of C1-01 (Acc Time) and C1-02 (Dec Time). If the system possesses high inertia, longer transition curves prevent short-term current spikes.
2. Check Torque Limit Parameters: Verify that torque limiters (L7-01 through L7-04) are not clamped too tight. If these are low, the drive may limit speed but load current will remain at maximum limits until an oL2 trip occurs.
3. Review Torque Compensation: If operating in Open Loop Vector (A1-02 = 2), verify that torque compensation gain (C4-01) is not set too high. Excessive torque compensation over-saturates the motor and creates huge current demands.

Step 4: Analyze Carrier Frequency and Thermal Parameters

High carrier frequencies generate significant switching heat. Check parameter C6-02 (Carrier Frequency Selection):

1. If C6-02 is set to high switching frequencies (e.g., 8, 10, or 15 kHz) to minimize audible motor noise, reduce it to a lower setting (e.g., 2.0 kHz or 5.0 kHz) and re-test.
2. Under lower carrier frequencies, the IGBTs switch slower, reducing thermal dissipation within the drive frame and often permanently resolving an oL2 trip.

Step 5: Test the Motor and Associated Cabling

Isolate the motor from the drive terminals (U, V, W) and use a Megohmmeter to check:

1. Phase-to-ground insulation resistance (should be >100MΩ).
2. Phase-to-phase winding resistance using a milliohm meter to confirm perfectly balanced windings.
3. Any slight imbalances or micro-shorts in stator windings can cause the drive to output asymmetrical current levels, generating localized IGBT heating.

Recommended Actions

Once diagnosis is complete, choose the most appropriate path forward based on your findings:

• Optimize Your Ramp Profiles: If the load has a high start-up inertia, implement an "S-curve" ramp profile using parameter group C2 to cushion structural transitions.
• Lower the Carrier Frequency: Drop the value of parameter C6-02 to the minimum acceptable level for your application to relieve thermal stress on the VFD power module.
• Upsize the Variable Frequency Drive: If the motor repeatedly draws near-limit current under normal operating conditions, your A1000 may be undersized. Replace the current drive with one frame size larger or switch the system parameter C6-01 from Normal Duty (ND) to Heavy Duty (HD) (note that this requires a physical derating of the drive’s maximum output current capacity).
• Establish External Blower Systems: If the load operates at low speeds under high torque, low-speed motor cooling will decrease, resulting in higher current. Install a constant-velocity external motor blower.
• Clean or Swap Cooling Fans: Ensure all internal drive cooling fans are rotating freely. Clean debris from the heat sink fins at the rear of the cabinet.

Recommended Replacement Parts

If the troubleshooting steps point toward component aging or mechanical breakdown, consider replacing these parts:

Related Articles

• Yaskawa A1000 Replacement and Migration Guide
• Understanding Drive Overload vs Motor Overload Protection
• Preventative Maintenance Procedures for Industrial VFDs

FAQ

Q: What is the main difference between an oL1 and an oL2 fault on the Yaskawa A1000?

An oL1 fault indicates that the drive’s internal electronic thermal model projects that the motor is overheating. An oL2 fault indicates that the drive itself has exceeded its electronic thermal capacity. In short, oL1 protects the motor, while oL2 protects the IGBT switches inside the VFD.

Q: Can a bad cooling fan trigger an oL2 fault?

Yes. If the internal heat sink fans fail, the VFD cannot adequately reject heat from the IGBT modules. This dramatically lowers the drive’s overload thermal memory threshold, causing it to trip on oL2 under current levels that would normally be perfectly safe.

Q: Why does the drive trip on oL2 right as the load starts to move?

This is typically caused by a mechanical lock or binding, an incorrect torque boost profile, or incorrect V/f patterns. The drive is injecting high current to break static friction, but because the shaft cannot turn, it remains stalled in a high-current draw state until the drive thermal model trips to prevent module damage.

Q: How does changing from Heavy Duty (HD) to Normal Duty (ND) affect oL2?

Switching parameter C6-01 changes the overload rating of the drive. Heavy Duty (HD) setting allows for a continuous lower current capacity but tolerates 150% overload for 60 seconds. Normal Duty (ND) allows for a higher baseline current but only tolerates 120% overload for 60 seconds. Match this setting strictly to your motor's nameplate and load application.