The FANUC SV0440 alarm indicates that the deceleration power is too large. This alarm occurs when the regenerative discharge amount of the common power supply or servo amplifier becomes excessive, or when the regenerative discharge circuit is abnormal.
During servo motor deceleration, the motor returns energy back into the drive system. This regenerated energy must be properly discharged through the regenerative discharge circuit or regenerative resistor. If the deceleration energy is too high, the regenerative resistor is not connected correctly, the regenerative discharge circuit is abnormal, or the resistor capacity is not sufficient, the CNC system may generate the SV0440 alarm.
This alarm is often seen on the fourth axis, especially when using FANUC β series or βi series servo drives. Troubleshooting should focus on whether a regenerative resistor is installed, whether the correct short-circuit wiring is used when no separate regenerative resistor is installed, whether the regenerative resistor wiring is correct, and whether the resistor capacity is suitable for the actual deceleration load.
Quick Summary of FANUC SV0440 Alarm
| Alarm Code | SV0440 |
|---|---|
| Alarm Meaning | Excessive Deceleration Power |
| Main Cause | The regenerative discharge amount is too large, or the regenerative discharge circuit is abnormal. |
| Common Condition | Often occurs during motor deceleration, especially on the fourth axis using β series servo drives. |
| Key Connectors | CXA20, CZ6, CZ7 |
| Key Terminals | CXA20 pins 1 and 2, CZ6 RC and RI |
| Key Check Items | Regenerative resistor installation, short-circuit wiring, discharge resistor wiring, resistor resistance, resistor temperature, drive type, common power supply module |
What Does FANUC SV0440 Alarm Mean?
SV0440: Excessive Deceleration Power
The FANUC SV0440 alarm means that the regenerative discharge amount is too large or that the regenerative discharge circuit has an abnormal condition.
When a servo motor decelerates, the motor can generate regenerative energy. This energy must be absorbed or discharged properly. If the regenerative energy exceeds the capacity of the discharge circuit or resistor, the resistor may heat abnormally and the system may issue SV0440 to protect the drive and power circuit.
If the regenerative resistor is not installed, not wired correctly, has the wrong resistance value, overheats, or is not large enough for the actual machine load, SV0440 may occur. If multiple axes show this alarm at the same time, the problem may be related to the common power supply or a multi-axis integrated drive.
Common Causes of FANUC SV0440 Alarm
The most common causes of FANUC SV0440 excessive deceleration power alarm include:
1. Regenerative Discharge Amount Is Too Large
The direct cause of SV0440 is excessive regenerative discharge energy during deceleration.
If the motor decelerates too quickly, the axis load is heavy, or the machine generates too much regenerative energy, the regenerative discharge circuit may not be able to handle the energy properly.
2. Regenerative Discharge Circuit Abnormality
If the regenerative discharge circuit is abnormal, the drive may fail to discharge regenerative energy correctly.
This may be caused by incorrect wiring, missing short-circuit wiring, loose connector contact, incorrect regenerative resistor connection, damaged resistor, or internal drive circuit failure.
3. No Regenerative Resistor Installed
If the drive requires a regenerative resistor but none is installed, SV0440 may occur during deceleration.
In this case, a suitable regenerative resistor should be configured according to the drive model and machine load condition.
4. Incorrect Short-Circuit Wiring When No Separate Regenerative Resistor Is Used
Some drives require specific short-circuit wiring when a separate regenerative discharge unit is not used.
For example, depending on the drive type, CXA20 pins 1 and 2 may need to be short-circuited, while related terminals such as CZ6 RC and RI should be handled according to the drive wiring requirement. Different drives may use different short-circuit positions, so the correct wiring should be confirmed according to the drive model.
5. Regenerative Resistor Wiring Error
If a regenerative discharge resistor is installed, the wiring should be checked carefully.
Important connection points may include CXA20 and CZ6. Incorrect wiring, loose contact, wrong connector position, or wrong terminal connection may cause SV0440.
6. Regenerative Resistor Capacity Is Not Enough
Even if the resistor is connected correctly, SV0440 may still occur if the regenerative resistor capacity is not sufficient.
If the deceleration energy exceeds the resistor capacity, the resistor may overheat. In this case, the resistor selection should be confirmed and a suitable regenerative resistor should be used.
7. Regenerative Resistor Overheating
If the regenerative resistor becomes too hot, the system may generate SV0440.
Check whether the resistor temperature is too high, whether the resistor is installed in a well-ventilated area, and whether the surrounding temperature allows normal heat dissipation.
8. Fourth Axis βi Servo Drive Application
SV0440 often appears on the fourth axis when using a FANUC β series or βi series servo drive.
If the alarm occurs on the fourth axis, confirm the drive type first. If it is a βi series drive, check whether the regenerative resistor is connected correctly according to the wiring diagram for that specific drive.
9. Servo Drive Failure
If the regenerative resistor, wiring, short-circuit connection, resistance value, and heat dissipation condition are all normal, the servo drive may be faulty.
In this case, the servo drive should be replaced for testing.
10. Common Power Supply Internal Regenerative Resistor Failure
If multiple axes show SV0440 at the same time, the issue may be related to the internal regenerative resistor of the common power supply.
In this situation, the common power supply module may need to be replaced. If a multi-axis integrated drive reports SV0440 on multiple axes, replace the integrated drive for testing.
How to Troubleshoot FANUC SV0440 Alarm
When troubleshooting FANUC SV0440, the key point is to determine whether the problem is caused by missing regenerative resistor, incorrect short-circuit wiring, wrong resistor wiring, insufficient resistor capacity, excessive deceleration power, or a faulty drive/power supply module.
You may need to check:
- Whether the alarm occurs during servo motor deceleration
- Whether the alarm appears on the fourth axis
- Whether the fourth-axis drive is a β series or βi series servo drive
- Whether a regenerative resistor is installed
- Whether the drive requires short-circuit wiring when no separate regenerative resistor is used
- Whether CXA20 pins 1 and 2 are short-circuited when required
- Whether the CZ6 RC and RI wiring is correct according to the drive model
- Whether the regenerative resistor wiring at CXA20 and CZ6 is correct
- Whether the regenerative resistor resistance value is correct
- Whether replacing the regenerative resistor clears the alarm
- Whether the regenerative resistor overheats during operation
- Whether the resistor capacity is suitable for the machine deceleration load
- Whether the resistor has enough space and airflow for heat dissipation
- Whether reducing the movement speed temporarily prevents the alarm
- Whether multiple axes show the alarm at the same time
- Whether the common power supply module or multi-axis integrated drive needs to be replaced
Recommended Solution
The correct solution for FANUC SV0440 depends on whether the machine uses a separate regenerative resistor, built-in regenerative resistor, or common power supply regenerative discharge circuit.
1. Confirm Whether a Regenerative Resistor Is Installed
First, confirm whether the servo drive is configured with a regenerative resistor.
If the drive requires a regenerative resistor but none is installed, a suitable regenerative resistor should be configured. Operating without the required regenerative resistor may cause SV0440 during deceleration.
2. If No Regenerative Resistor Is Installed, Check the Required Short-Circuit Wiring
If no separate regenerative resistor is used, some drives require specific short-circuit wiring.
For example, CXA20 pins 1 and 2 may need to be short-circuited depending on the drive configuration. For certain β series drives, terminals such as CZ6 RC and RI should also be checked according to the applicable wiring diagram.
Because different drives may use different short-circuit positions, confirm the correct wiring before operation.
3. If the Short-Circuit Wiring Is Correct but SV0440 Remains, Reduce Movement Speed Temporarily
If no regenerative resistor is installed, and the required short-circuit wiring has already been confirmed correct, reducing the movement speed may be used only as a temporary measure.
This can reduce deceleration energy and help avoid the alarm temporarily. However, for normal operation, a suitable discharge resistor should be configured according to the machine requirement.
4. If a Regenerative Resistor Is Installed, Check the Wiring
If the machine is already equipped with a regenerative discharge resistor, check the wiring carefully.
Important connection points include CXA20 and CZ6. Confirm whether the resistor wiring is connected to the correct terminals and whether there is any loose connector, wrong pin, poor contact, or wiring damage.
5. Check the Resistance Value or Replace the Regenerative Resistor
If the regenerative resistor wiring is correct, measure the resistor value and confirm whether it matches the required specification.
If the resistance value is abnormal, or if the resistor is suspected to be faulty, replace the regenerative resistor and test again.
6. Check Whether the Regenerative Resistor Is Overheating
Confirm whether the regenerative resistor becomes abnormally hot during operation.
If the resistor temperature is too high, check whether the resistor capacity is suitable, whether the surrounding environment temperature is too high, and whether the resistor has enough space and airflow for heat dissipation.
7. Confirm Whether the Resistor Capacity Is Sufficient
If the resistor is connected correctly but still overheats or SV0440 continues to occur, the regenerative resistor may not have enough capacity for the actual deceleration load.
In this case, confirm the resistor selection according to the drive model and machine load condition. A larger or more suitable regenerative resistor may be required.
8. Check the Servo Drive If Wiring and Resistor Are Normal
If the regenerative resistor wiring, resistance value, capacity, and heat dissipation condition are all normal, the servo drive may be faulty.
Replace the servo drive and test whether the SV0440 alarm is cleared.
9. If Multiple Axes Alarm at the Same Time, Check the Common Power Supply
If SV0440 appears on multiple axes at the same time, the problem may be related to the internal regenerative resistor of the common power supply.
In this case, replace the common power supply module. If the machine uses a multi-axis integrated drive and multiple axes report the alarm together, replace the integrated drive for testing.
If your machine shows FANUC SV0440 excessive deceleration power alarm, please contact REACO CNC directly. Our team can help check the regenerative resistor wiring, CXA20 and CZ6 connections, βi servo drive configuration, resistor capacity, resistor overheating condition, common power supply module, and servo drive replacement options.
REACO CNC Support for FANUC SV0440 Alarm
REACO CNC provides support for FANUC CNC systems, servo drives, common power supply modules, regenerative discharge resistors, β series servo amplifiers, and related CNC hardware issues.
We can help with:
- FANUC CNC alarm analysis
- FANUC SV0440 alarm troubleshooting
- Excessive deceleration power issue analysis
- Regenerative discharge resistor wiring checking
- CXA20 and CZ6 connection checking
- βi servo drive regenerative resistor configuration support
- Fourth axis deceleration power troubleshooting
- Regenerative resistor resistance checking guidance
- Regenerative resistor overheating analysis
- Common power supply module replacement support
- Servo drive repair or replacement support
- Replacement FANUC CNC parts supply
If you are not sure whether the SV0440 alarm is caused by missing regenerative resistor, incorrect short-circuit wiring, wrong CXA20/CZ6 connection, insufficient resistor capacity, excessive deceleration load, common power supply fault, or servo drive failure, you can send us the CNC system model, alarm screen, servo drive model, axis information, regenerative resistor wiring photos, and machine operating condition. Our team will help check the possible cause.
FAQ About FANUC SV0440 Alarm
What is FANUC SV0440 alarm?
FANUC SV0440 alarm means excessive deceleration power. It occurs when the regenerative discharge amount of the common power supply or servo amplifier is too large, or when the regenerative discharge circuit is abnormal.
What causes FANUC SV0440 excessive deceleration power alarm?
The alarm may be caused by missing regenerative resistor, incorrect short-circuit wiring, wrong regenerative resistor connection, insufficient resistor capacity, resistor overheating, excessive motor deceleration energy, common power supply regenerative circuit fault, or servo drive failure.
Why does SV0440 often occur on the fourth axis?
SV0440 often occurs on the fourth axis when using FANUC β series or βi series servo drives because the deceleration energy and regenerative discharge condition may be more sensitive on that axis configuration.
What should I check if no regenerative resistor is installed?
If no regenerative resistor is installed, confirm whether the drive requires short-circuit wiring. Depending on the drive, CXA20 pins 1 and 2 may need to be short-circuited, and related terminals such as CZ6 RC and RI should be checked according to the correct wiring diagram.
What should I check if a regenerative resistor is installed?
If a regenerative resistor is installed, check whether the wiring at CXA20 and CZ6 is correct, whether the resistor value is normal, and whether the resistor overheats during operation.
Can reducing movement speed help with SV0440?
Reducing movement speed may temporarily reduce deceleration energy and help avoid SV0440, but it should not replace proper regenerative resistor configuration. For normal operation, the correct discharge resistor should be installed and wired properly.
Can a wrong regenerative resistor value cause SV0440?
Yes. If the regenerative resistor value is incorrect or the resistor is damaged, the drive may not discharge regenerated energy properly, causing SV0440.
Can resistor overheating cause SV0440?
Yes. Excessive deceleration power can cause the regenerative resistor to heat abnormally. If the resistor temperature is too high, check resistor capacity, surrounding temperature, and heat dissipation condition.
What if multiple axes show SV0440 at the same time?
If multiple axes show SV0440 at the same time, the common power supply internal regenerative resistor may be abnormal. Replace the common power supply module. If it is a multi-axis integrated drive, replace the drive for testing.
How can I fix FANUC SV0440 alarm?
Check whether a regenerative resistor is installed, confirm required short-circuit wiring such as CXA20 pins 1 and 2 when applicable, check CZ6 RC and RI wiring, inspect regenerative resistor wiring at CXA20 and CZ6, measure resistor resistance, confirm resistor temperature and capacity, reduce speed temporarily if needed, and replace the servo drive or common power supply module if all external checks are normal.
Need Help with FANUC SV0440 Alarm?
If your CNC machine has a FANUC SV0440 excessive deceleration power alarm, please contact REACO CNC. We can help analyze the alarm cause and provide suitable FANUC CNC repair, regenerative resistor wiring checking, βi servo drive support, CXA20/CZ6 connection guidance, common power supply troubleshooting, or servo drive replacement support.
Reference Source: Beijing FANUC. This article is based on technical documentation provided by Beijing FANUC. For More Fanuc CNC repair Cases and technical articles, please back to Fanuc Technical Support Center.
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