Yaskawa A1000 AL-11 Fault — What It Means
The AL-11 (or Er-11) fault code on a Yaskawa A1000 VFD indicates a Motor Speed Error. The drive’s feedback system has detected that the actual motor speed is significantly lower than the commanded speed, even though the torque reference is too high for the load or acceleration profile. In other words, the VFD is demanding more torque than the motor and load can deliver, causing a speed mismatch between what the drive expects and what the encoder or feedback device reports.
This fault typically triggers during acceleration or under heavy load conditions when the motor cannot keep pace with the drive’s speed command. The VFD compares real-time feedback from an encoder or speed sensor against the target speed, and when the difference exceeds an internal threshold while torque demand is maxed out, it shuts down to protect the motor and system from damage.
Before You Replace Anything
Many technicians replace the encoder or option card first, but incorrect parameter settings (especially acceleration time C1-01) cause this fault more often. Check and adjust parameters before replacing hardware.
Common Causes
- Acceleration time too low (~35%) Parameter C1-01 set too aggressively forces the motor to ramp up faster than the load can handle, causing torque saturation and speed mismatch.
- Encoder cable or connection fault (~25%) Broken encoder cable, loose connector pins, or damaged terminations prevent feedback signals from reaching the VFD, triggering a speed error.
- Mechanical overload (~15%) Load is too heavy for the motor rating, motor cooling has failed, or cycle time is too short for the inertia, causing the motor to fall behind commanded speed.
- Faulty encoder or option card (~15%) Damaged encoder (misaligned, broken disk, or failed electronics) or faulty feedback option card (PGX2, PGL2) delivers incorrect speed data to the drive.
- Motor wiring or terminal issues (~7%) Loose motor terminals, short circuit in motor power cable, or relay contact problems create intermittent power delivery and speed instability.
- Control board or IGBT damage (~3%) Internal VFD control board failure or damaged IGBTs cause erratic torque control and feedback processing errors.
Quick Diagnosis
Answer these to narrow it down fast.
Does the fault clear after a power cycle and not return immediately?
No: The fault is persistent, likely due to a hardware issue (encoder, cable, option card) or incorrect motor parameters.
Is the encoder cable securely connected at both the drive and motor, with no visible damage?
No: Repair or replace the encoder cable and re-secure all connectors before testing again.
Does the motor run smoothly in open-loop mode (encoder feedback disabled)?
No: The motor or mechanical load has a problem (binding, overload, or cooling failure). Inspect the motor and load mechanically.
Step-by-Step Fix
- Cycle power to the VFD and clear the AL-11 fault. Observe whether it returns immediately or only under load.
- Inspect encoder wiring at both the option card and motor encoder connector. Re-seat connectors, check for bent pins, corrosion, or damaged cable insulation.
- Increase acceleration time by adjusting parameter C1-01 (Acceleration Time 1) to a higher value. Start with doubling the current setting and test operation.
- Verify motor parameters E1-04 (motor rated current), E1-06 (motor rated frequency), E1-07 (motor rated speed), E1-09 (motor poles), and E1-11 (motor no-load current) match the motor nameplate exactly.
- Check mechanical load by disconnecting the motor from the load and running it unloaded. If the fault clears, the load is too heavy or binding.
- Test in open-loop mode by disabling closed-loop feedback. If the motor runs without fault, the encoder or feedback path is defective.
- Replace components in order if the fault persists: encoder first, then encoder cable, then option card (PGX2 or PGL2), then control board. Test after each replacement.
Parts Often Needed
| Part | Notes |
|---|---|
| Yaskawa encoder (model-specific, e.g. UTOPH-81BWF) | Amazon | Match the encoder type to your motor and option card. Consult the A1000 manual for compatible part numbers. |
| Yaskawa encoder cable | Amazon | Replace if cable insulation is damaged, connectors are loose, or continuity test fails. |
| Yaskawa feedback option card (PGX2, PGL2, or equivalent) | Amazon | Required for closed-loop control. Verify the card is properly seated and not physically damaged before replacing. |
| Yaskawa A1000 control board | Amazon | Replace only after confirming encoder, cable, and option card are good. Control board failures are rare for this fault. |
When to Call a Pro
Call a qualified VFD technician or automation specialist if you are not trained to work with industrial drives and encoders. AL-11 troubleshooting requires understanding of VFD parameter programming, encoder wiring, and feedback loop diagnostics. High DC bus voltages (up to 800V on larger A1000 models) present serious shock hazards. If encoder replacement, option card work, or parameter tuning does not resolve the fault, the control board or IGBT module may be damaged, which requires factory-level diagnosis and parts that are not available through retail channels.
Rough cost: A pro service call runs about $200-600 depending on whether the fix is parameter adjustment, encoder replacement, or option card replacement.