Yaskawa A1000 oL7 Fault — What It Means
The oL7 fault on a Yaskawa A1000 drive means High Slip Braking overload. Specifically, the output frequency stayed constant for longer than the time set in parameter n3-04 during High Slip Braking. In practical terms, the drive is reporting that the motor and load could not complete the braking event within the allowed time window.
This fault occurs when the drive tries to stop the motor using High Slip Braking but the load has too much inertia, the deceleration ramp is too aggressive, or the braking capacity (resistor or drive capability) is not enough to hold the commanded slip condition long enough. The drive aborts the stop and throws oL7 to protect itself.
Before You Replace Anything
Technicians sometimes replace the entire drive when oL7 appears, but Yaskawa’s documented corrective action is to lengthen deceleration parameters and verify braking resistor installation first. Check parameter n3-04 and the decel ramps before swapping the drive.
Common Causes
- Deceleration time too aggressive (~50%) The ramp parameters ask the motor to stop faster than the load inertia allows, so the drive cannot maintain the slip condition long enough and faults.
- Excessive load inertia (~25%) High-inertia loads (heavy flywheels, fans, or conveyors) store more kinetic energy than the drive’s braking capacity can dissipate in the allowed window.
- Missing or undersized braking resistor (~15%) Without a braking resistor to absorb regenerated energy, the drive cannot maintain High Slip Braking long enough to stop the motor within the n3-04 time limit.
- Mechanical binding or process load spike (~7%) If the load suddenly binds or the process demands more braking torque than expected, the drive cannot hold the frequency constant and faults.
- Parameter n3-04 set too short (~3%) The time limit in n3-04 does not allow enough margin for normal High Slip Braking completion, even under normal load conditions.
Quick Diagnosis
Answer these to narrow it down fast.
Is a braking resistor installed and wired to the drive's B1/B2 terminals?
No: No braking resistor means regenerated energy has nowhere to go. Install a braking resistor rated for your drive model and retrain the stop sequence.
Does the motor stop smoothly when you manually lengthen all deceleration times by 50 percent?
No: The fault persists even with gentle deceleration. Inspect the load for mechanical binding or excessive inertia and verify n3-04 is set appropriately.
Does the fault history (monitor menu) show oL7 occurring at the same point in every stop cycle?
No: Random oL7 faults suggest intermittent binding, unstable process conditions, or a marginal braking resistor connection.
Step-by-Step Fix
- Confirm the fault on the operator keypad and note the frequency and load condition when oL7 appeared. Check the drive’s fault history in the monitor menu to see if the fault is repeatable or random.
- Verify the braking setup by inspecting whether a braking resistor is installed and correctly wired to terminals B1 and B2. If no resistor is present and your application requires High Slip Braking, you must add one.
- Check parameter n3-04 (High Slip Braking time limit) using the keypad. If this value is very short, increase it to allow more time for the braking event to complete.
- Review and lengthen deceleration parameters for all active ramps (typically A1-02, A1-03, and multi-step decel settings). Yaskawa’s documented remedy is to reduce deceleration severity to match the load inertia.
- Inspect the mechanical load for binding, unusual friction, or process events that spike torque during stops. Rotate the motor shaft by hand (power off and locked out) to feel for tight spots or drag.
- Test-run the drive after making parameter changes. Command a normal stop under load and watch the operator display to confirm the motor decelerates smoothly without triggering oL7.
- If the fault persists, consult the A1000 technical manual for your specific frame size and verify the braking resistor ohmic value and power rating match the drive’s requirements. Replace the resistor if it is damaged or undersized.
Parts Often Needed
| Part | Notes |
|---|---|
| Yaskawa braking resistor (frame-specific) | Amazon | Consult your A1000 model’s accessory table for the correct ohmic value and wattage. Common frame sizes use resistors in the 20–100 Ω range. |
| Braking resistor wire harness | Amazon | If the original resistor cable is damaged or corroded, replace it with wire rated for the resistor’s peak current. |
When to Call a Pro
Call a qualified drives technician or systems integrator if you are not familiar with VFD parameter programming, if you do not have the A1000 technical manual with the braking resistor selection table for your frame size, or if the fault persists after lengthening deceleration times and verifying the braking resistor. High Slip Braking interacts with motor control algorithms and DC bus voltage limits, so incorrect parameter changes can damage the drive or create unsafe stopping behavior. A pro will use the drive’s event recorder and real-time monitors to capture exactly when oL7 occurs, measure DC bus ripple during braking, and size the braking resistor or adjust n3-04 based on actual load inertia calculations.
Rough cost: A pro service call runs about $200–500 for parameter tuning and braking resistor installation if needed.