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Yaskawa A.820 Regenerative Error: Causes, Troubleshooting & Repair Guide
Error Overview
- Alarm Code: A.820
- Type: Regenerative / Overvoltage Error
- Category: Servo / Electrical Protection
- Severity: High (can stop robot during deceleration)
- Related System: Servo drive, regenerative resistor, power supply, motor
Field insight:
In real-world applications, the Yaskawa A.820 regenerative error is usually caused by excessive regenerative energy generated during braking or deceleration — not random servo drive failure.
In most cases, the problem occurs because the system cannot dissipate braking energy fast enough, causing DC bus voltage to rise beyond safe limits.
What Does Yaskawa A.820 Regenerative Error Mean?
The Yaskawa A.820 alarm occurs when excess voltage builds up inside the DC bus during motor deceleration.
In simple terms:
When the motor slows down, it temporarily acts like a generator and sends energy back into the servo drive.
If th is energy cannot be absorbed or dissipated properly, voltage rises and the system triggers protection.
This is what differentiates A.820 from other Yaskawa alarms:
- A.710 overcurrent alarm→ current spike or electrical overload
- A.720 overload alarm→ excessive mechanical load
- A.810 encoder error→ feedback signal instability
- A.820 regenerative error→ voltage buildup during braking or deceleration
Quick Fix (5-Minute Check First)
Before deep troubleshooting, try th is:
- Reduce deceleration rate
- Lower speed temporarily
- Restart system after alarm
- Check for recent parameter changes
If the alarm disappears after reducing deceleration → the issue is likely excessive regenerative energy.
Common Symptoms of A.820 Regenerative Error
- Alarm appears during deceleration or stopping
- Robot stops abruptly after high-speed movement
- Alarm occurs more frequently under heavy load
- System runs normally at lower speed
- Repeated faults during rapid stop-start cycles
Main Causes of Yaskawa A.820 Regenerative Error
A.820 faults typically originate from one of four system layers:
Brake Resistor Failure (Most Common)
The braking resistor is responsible for dissipating regenerative energy as heat.
1. Brake Resistor Failure (Most Common)
The regenerative resistor dissipates braking energy as heat.
Common failure conditions include:
- Open circuit resistor
- Burnt or thermally damaged resistor
- Incorrect resistance or power rating
- Loose or unstable wiring connection
If the resistor cannot absorb braking energy, DC bus voltage rises rapidly during deceleration.
2. Servo Drive Regeneration Circuit Failure
Inside the servo drive, the regeneration circuit controls excess energy flow.
Common causes include:
- IGBT degradation
- Faulty regenerative control circuitry
- Aging DC bus capacitors
- Long-term thermal stress
In aging systems, internal servo drive degradation is a common cause of persistent A.820 alarms.
3. Wiring and Connection Problems
- Loose brake resistor terminals
- Damaged resistor cable insulation
- High-resistance electrical connections
Even minor connection instability can reduce energy dissipation efficiency.
4. Motion Parameter or Load Conditions
- Excessively short deceleration time
- High-inertia load systems
- Frequent stop-start operation
- Aggressive braking profiles
These conditions generate more regenerative energy than the system can safely absorb.
In some situations, unstable deceleration may also trigger speed-related faults.
If abnormal motion occurs during braking, reviewing Yaskawa A.840 overspeed error troubleshooting may help identify related motion control instability.
3. How to Troubleshoot Yaskawa A.820 Regenerative Error
Unlike overload alarms, A.820 troubleshooting should focuson braking energy dissipation and deceleration behavior.
Step 1 – Identify When the Alarm Appears
- During stopping→ deceleration issue
- At high speed cycles→ excess regenerative energy
- Random occurrence→ resistor or power issue
Step 2 – Reduce Deceleration First
- Increase deceleration time
- Smooth stop profile
- Reduce sudden braking
If the alarm disappears after adjusting deceleration parameters, the issue is configuration-related rather than hardware failure.
Step 3 – Check Regenerative Resistor
Inspect:
- Connection status
- Signs of overheating
- Resistance value
A failed resistor cannot absorb braking energy.
Step 4 – Evaluate Load Inertia
Check:
- Payload changes
- Tooling weight
- System inertia
High inertia directly increases regenerative energy during braking.
If excessive load is suspected, reviewing Yaskawa A.720 overload alarm troubleshooting may help identify additional mechanical stress issues.
Step 5 – Verify Power Supply
- Measure input voltage
- Check for instability
- Ensure proper grounding
In some cases, unstable incoming power may worsen DC bus overvoltage conditions.
Reviewing Yaskawa A.750 power supply alarm troubleshooting may help identify related electrical instability.
Step 6 – Evaluate Servo Drive
- Check regenerative circuit
- Review alarm logs
- Test with another unit if possible
If voltage regulation remains unstable after resistor and parameter checks, the servo drive may be degraded internally.
Key Diagnostic Signs of Yaskawa A.820 Regenerative Fault
|
Symptom |
Likely Cause |
|
Alarm during deceleration |
Excess regenerative energy |
|
Frequent at high speed |
Parameter issue |
|
Occurs under normal operation |
Resistor failure |
|
Random voltage-related alarms |
Power supply issue |
Recommended Parts for A.820 Repair
Regenerative Resistor
If the resistor is damaged or undersized, it cannot absorb braking energy effectively.
Replacing or upgrading the resistor is often the fastest solution.
Servo Drive
If regenerative voltage control becomes unstable, the Yaskawa servo drive may require repair or replacement.
Servo Motors
In high-inertia systems, properly matched Yaskawa servo motors help maintain stable braking and motion control performance.
Motor & Power Cables (Secondary Check)
Although less common, unstable electrical transmission can contribute to abnormal regenerative conditions.
Inspect Yaskawa motor cables and power cables if electrical instability is suspected.
Yaskawa A.820 Alarm: Repair or Replace Decision Guide
Repair (Most Cases)
- Adjust deceleration parameters
- Replace or reconnect brake resistor
- Optimize motion profiles
- Improve grounding and wiring
Most A.820 alarms are resolved through resistor replacement or parameter optimization.
Replace
- Resistor repeatedly fails
- Drive cannot regulate voltage
- System operates beyond design limits
Replacement is recommended when voltage stability cannot be restored after tuning and resistor verification.
Prevention Tips
- Avoid aggressive deceleration
- Match resistor capacity with system load
- Monitor braking cycles
- Maintain stable power supply
- Optimize motion profiles
Related Yaskawa Alarm Codes
Understanding Yaskawa Alarm Codes helps isolate root causes more efficiently:
- Yaskawa A.710 overcurrent alarm troubleshooting(electrical overload conditions)
- Yaskawa A.720 overload alarm troubleshooting(mechanical load and inertia issues)
- Yaskawa A.810 encoder error troubleshooting(feedback instability affecting motion control)
- Yaskawa A.840 overspeed error troubleshooting(speed instability during motion or braking)
These alarms are frequently interconnected in high-speed robotic applications.
FAQ
What causes Yaskawa A.820 regenerative error most often?
Brake resistor failure and servo drive regeneration circuit degradation are the most common causes.
Can deceleration settings trigger A.820?
Yes. Excessively short deceleration time can generate excessive regenerative energy.
How do I confirm resistor failure?
Check resistance value and inspect for physical burn damage or open circuit.
Can the system run without a brake resistor?
Not recommended. It will likely cause repeated A.820 alarms and potential DC bus damage.
When should the servo drive be replaced?
When A.820 alarms persist after resistor, wiring, and parameter issues have been ruled out.
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