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Mitsubishi FR-A800 VFD Troubleshooting: Common Faults, Parameter Fixes & Field Tips

by Bryan Hellman



A comprehensive technical guide to diagnosing FR-A800 drive issues — including motor tuning, load-related trips, braking resistor sizing, and electrical noise mitigation.

Table of Contents

  1. Introduction
  2. How the FR-A800 Detects Faults
  3. Quick Reference: FR-A800 Fault Codes
  4. Common FR-A800 Faults and Their Solutions
  5. Motor Tuning on the FR-A800
  6. Braking Resistor Sizing for the FR-A800
  7. Noise Mitigation, Grounding & Wiring Best Practices
  8. Load-Related Trips & Torque Issues (E.OLT)
  9. FR-A800 Series Inventory at Industrial Automation Co.
  10. Featured Mitsubishi FR-A820 Drives
  11. Practical Engineering Caveats & Real-World Considerations
  12. Summary
  13. Need Mitsubishi Drives or Support?

Introduction

The Mitsubishi FR-A800 is a high-performance variable frequency drive used across manufacturing, material handling, and process industries. Its diagnostics are powerful, but interpreting fault behavior requires an understanding of how the drive models motor torque, DC bus energy, and thermal conditions.

Many faults—especially intermittent ones—are triggered by load characteristics, environmental conditions, and wiring practices rather than drive failure. This guide explains how the FR-A800 interprets real-world conditions so troubleshooting can be targeted and effective.

How the FR-A800 Detects Faults

The FR-A800 uses predictive monitoring rather than simple threshold trips. It continuously evaluates:

  • Motor current and the rate of change
  • DC bus voltage during both motoring and regenerative operation
  • Heatsink temperature and cooling fan status
  • Slip, torque estimation, and effective motor/load inertia
  • Noise level on input command and feedback terminals

From this, it decides when to trip on:

  1. Load and torque disturbances
  2. DC bus imbalance or regen behavior
  3. Parameter misconfiguration or tuning issues
  4. Thermal and airflow problems
  5. Electrical noise, grounding, or control wiring faults

Quick Reference: FR-A800 Fault Codes

Fault Code Meaning Typical Cause Category First Checks
E.OC1 Overcurrent during accel Load spike / accel ramp Pr.7, mechanics, motor data
E.OC2 Overcurrent at constant speed Load variation / binding Process load, mechanics
E.OC3 Overcurrent during decel Inertia / decel ramp Pr.8, load inertia, tuning
E.OV1 Regen OV during accel Inertia / regen Brake resistor, accel profile
E.OV2 Regen OV at steady speed Regen load Load characteristics
E.OV3 Regen OV during decel High inertia / fast decel Pr.8, resistor sizing
E.UVT Undervoltage Weak or unstable supply Tighten lugs, measure voltage
E.FIN Heatsink overtemperature Airflow/ambient Fan, cabinet ventilation
FN/FN2 Cooling fan alarm Fan wear/failure Replace fan
E.OLT Stall prevention stop Torque overload Pr.22, alignment

Common FR-A800 Faults and Their Solutions

 

 

Overcurrent Trips (E.OC1 / E.OC2 / E.OC3)

Overcurrent trips occur when actual motor current exceeds the drive’s internal protection threshold. This typically indicates sudden torque demands, mechanical resistance, incorrect acceleration/deceleration profiles, or tuning-related modeling errors.

  • E.OC1 — Overcurrent during acceleration
  • E.OC2 — Overcurrent at constant speed
  • E.OC3 — Overcurrent during deceleration

Likely Causes

  • Sudden load spikes during acceleration
  • Mechanical binding in couplings, bearings, conveyors, gearboxes
  • Incorrect motor parameters entered into the drive
  • Acceleration/deceleration times too short for actual inertia
  • Incomplete or inaccurate motor tuning
  • Output cable degradation or insulation breakdown

Engineering Fixes

  1. Verify correct motor data parameters:
    Pr.80, Pr.81, Pr.83, Pr.84, Pr.9, Pr.71
  2. Lengthen acceleration time (Pr.7)
  3. Perform rotational auto-tuning (Pr.96 = 2)
  4. Inspect mechanical load for binding or torque spikes
  5. Test insulation resistance & inspect output cabling

⚠️ Common Misdiagnosis:
Most E.OC1/E.OC3 faults are caused by mechanical load issues or aggressive accel/decel ramps — not a failing drive.

 

 

Overvoltage Trips (E.OV1 / E.OV2 / E.OV3)

Overvoltage occurs when regenerative energy pushes DC bus voltage beyond safe operating limits. This happens when load inertia or overhauling characteristics return energy faster than the drive can dissipate.

  • E.OV1 — Regen overvoltage during acceleration
  • E.OV2 — Regen overvoltage at constant speed
  • E.OV3 — Regen overvoltage during deceleration (most common)

Likely Causes

  • High-inertia loads regenerating during decel
  • Overhauling loads generating sustained regen
  • Deceleration time too short (Pr.8)
  • Missing or undersized braking resistor
  • High incoming mains voltage

Engineering Fixes

  1. Increase deceleration time (Pr.8)
  2. Add or resize braking resistor
  3. Enable regen suppression (Pr.30)
  4. Measure mains voltage under load

💡 Field Tip:
Repeated E.OV3 trips almost always indicate decel too fast for real inertia — or the braking resistor is improperly sized.

 

 

Undervoltage (E.UVT)

E.UVT trips when the DC bus drops below the minimum operating level, commonly during acceleration or high torque demand.

Likely Causes

  • Weak or overloaded supply
  • Loose connections or oxidized line lugs
  • Phase imbalance or loss
  • Upstream contactor chatter or drop-out

Fixes

  • Measure supply voltage during acceleration
  • Tighten/retorque all line terminals
  • Replace unstable contactors or breakers
  • Add a DC choke to stabilize supply

⚠️ Common Misdiagnosis:
Undervoltage is frequently blamed on the drive, but most E.UVT faults trace back to loose terminals or weak supply infrastructure.

 

 

Overheat & Fan Alarms (E.FIN / FN / FN2)

These alarms protect the inverter from thermal overload caused by insufficient cooling, poor enclosure ventilation, or fan failure.

  • E.FIN — Heatsink overtemperature
  • FN/FN2 — Fan alarm

Causes

  • Blocked or insufficient airflow
  • Elevated enclosure ambient temperature
  • Fan wear, bearing failure, or contamination

Fixes

  • Verify enclosure ventilation & airflow paths
  • Check ambient temperature against derating limits
  • Replace fan assembly as preventive maintenance

🔧 Technician Insight:
Fans often degrade gradually — rising temperature trends or intermittent E.FIN alarms are early indicators of fan end-of-life.

 

 

Motor Tuning on the FR-A800

Motor tuning allows the FR-A800 to accurately model electrical and mechanical characteristics. Incorrect tuning often causes nuisance trips, torque instability, or noisy low-speed operation.

Pre-Tuning Checklist

  • Motor safely unloaded
  • Correct U–V–W phase order
  • Motor nameplate data entered (Pr.80–84, Pr.9, Pr.71)
  • Encoder shield terminations verified

Tuning Options

  • Pr.96 = 1 — Stationary auto-tune
  • Pr.96 = 2 — Rotational auto-tune
  • Advanced vector tuning modes for high-torque applications

Post-Tuning Checks

  • Stable low-speed rotation
  • Predictable torque response under load
  • Reasonable inertia values
  • No new faults introduced

 

 

Braking Resistor Sizing for the FR-A800

High-inertia or overhauling loads return energy to the inverter during decel. A properly sized resistor prevents overvoltage faults and ensures controlled stops.

When a Braking Resistor Is Needed

  • High-inertia loads
  • Short decel time requirements
  • Vertical/overhauling loads
  • Frequent cycling

Field-Sizing Method

  1. Identify drive kW rating
  2. Estimate braking power at ~10% of motor kW
  3. Select resistor within Mitsubishi’s Ω range

Browse braking units and resistors:
https://industrialautomationco.com/collections/mitsubishi

⚠️ Common Misdiagnosis:
Operators often blame OV faults on a failed resistor, but overly fast decel (Pr.8) is the more frequent cause.

 

 

Noise Mitigation, Grounding & Wiring Best Practices

Electrical noise can cause false trips, encoder instability, or parameter misreads. Proper wiring discipline is essential for reliable FR-A800 operation.

Grounding

  • Use single-point (star) grounding
  • Avoid daisy-chained ground loops

Shielding

  • Use VFD-rated shielded motor cable
  • Terminate shields in a 360° clamp at the drive end

Cable Separation

  • Maintain 8"+ separation between control and power wiring
  • Cross unavoidable intersections at 90°

Additional Mitigation

  • Ferrite cores for encoder/signal wiring
  • AC reactors
  • DC chokes

⚠️ Common Misdiagnosis:
Many nuisance faults stem from poor cable routing or grounding — not firmware or drive hardware.

 

 

E.OLT (stall prevention) occurs when the drive detects that torque demand exceeds available torque even before stall occurs.

Typical Situations

  • Mechanical jams
  • Load surges in conveyors/processing
  • Misalignment or failing mechanical components
  • Torque limits set too low

Fixes

  • Increase torque limit (Pr.22)
  • Increase acceleration time
  • Inspect bearings, couplings, alignment
  • Improve tuning/slip compensation

 

 

FR-A800 Series Inventory at Industrial Automation Co.

Industrial Automation Co. stocks a wide range of Mitsubishi FR-A800 products:

  • FR-A820 — 200V class
  • FR-A840 — 400V class
  • FR-A860 — High-capacity series
  • Fans, resistors, option cards, and accessories

Browse inventory:
https://industrialautomationco.com/collections/mitsubishi

 

 

These FR-A820 models are commonly used in conveyors, pumps, OEM equipment, and modernization projects.

Mitsubishi FR-A820-00490-1-N6
Compact 200V-class drive for mid-size motors.
https://industrialautomationco.com/products/mitsubishi-fr-a820-00490-1-n6

Mitsubishi FR-A820-3.7K-1
Popular 3.7 kW drive for conveyors and pumps.
https://industrialautomationco.com/products/mitsubishi-fr-a820-3-7k-1

Mitsubishi FR-A820-00490-E1N6
North America-optimized E1N6 version.
https://industrialautomationco.com/products/mitsubishi-fr-a820-00490-e1n6

Mitsubishi FR-A820-04K-1
Versatile 4 kW model for OEM machines.
https://industrialautomationco.com/products/mitsubishi-fr-a820-04k-1

Mitsubishi FR-A820-00046-E1N6
Compact FR-A820 for small automation tasks.
https://industrialautomationco.com/products/mitsubishi-fr-a820-00046-e1n6

Mitsubishi FR-A820-7.5K-1
Robust 7.5 kW option for pumps, blowers, packaging lines.
https://industrialautomationco.com/products/mitsubishi-fr-a820-7-5k-1

 

 

Practical Engineering Caveats & Real-World Considerations

⚠️ Load Inertia & Braking:
Always calculate actual inertia. The 10% braking rule is a starting point — real stopping energy depends on duty cycle, stop frequency, and thermal limits.

⚠️ Thermal & Cabinet Design:
Proper ventilation is essential. Even with good fans, poor enclosure airflow frequently causes E.FIN trips.

⚠️ EMC & Wiring:
Noisy or retrofit installations may require reactors, filters, and improved shield terminations beyond standard practices.

⚠️ Motor Condition:
Worn bearings or misalignment can distort tuning results. Always verify real current and vibration.

⚠️ Transient Faults:
Not every fault indicates hardware failure. Investigate process events before replacing components.

 

 

Summary

Most FR-A800 faults trace back to:

  • Inertia and torque mismatches
  • Regenerative energy during stopping
  • Incorrect motor configuration or tuning
  • Noise, grounding, and wiring issues
  • Thermal limits or fan degradation

By methodically checking motor data, accel/decel settings, braking hardware, wiring practices, and mechanical conditions, you can eliminate nuisance trips and improve uptime.

 

 

Need Mitsubishi Drives or Support?

Industrial Automation Co. provides:

  • FR-A820, FR-A840, and FR-A860 drives in stock
  • Fans, braking resistors, option cards
  • Technical support to match or replace existing drives

Browse Mitsubishi drives:
https://industrialautomationco.com/collections/mitsubishi

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