KUKA KSS01305 DC Bus Undervoltage Error – Causes, Symptoms & How to Fix

• Error Code: KSS01305
• Category: Power Supply / Drive System
• Severity: High
• System: KRC4 / KSP Drives
• Impact: axis disabled, robot stops, possible drive protection triggered

Quick Fix for KUKA KSS01305

If the robot suddenly stops with th is error:

• Reset the controller and observe if the error returns
• Check incoming power supply (voltage drop or instability)
• Inspect KSP drive LEDs for faults
• Verify all power and motor cables are firmly connected
• Run the robot at lower speed and acceleration

⚠️ Always power down before checking cabinet power or drive wiring.

👉 If the robot runs fine at low speed but trips during acceleration, the issue is usually power-related or load-related.

What Is KUKA KSS01305?

KSS01305 is triggered when the DC bus voltage falls below the minimum threshold required by the KSP drives.

The DC bus is critical because it:

• Supplies energy to all servo drives
• Maintains stable torque output
• Supports multi-axis coordinated motion

When voltage drops:

• Drives cannot maintain torque
• Axes lose stability or stop
• The system shuts down to prevent damage

Typical Symptomson Site

• Robot stops during acceleration or heavy motion
• Axes fail to enable after startup
• SmartHMI shows KSS01305 repeatedly
• KSP drives indicate fault (often after motion start)
• Motion becomes unstable before stopping

👉 A key pattern: works at idle → fails under load

Common Causes for KUKA KSS01305

1. Incoming Power Instability

Most frequent root cause.

• Voltage dips from plant power
• Weak or overloaded power line
• Loose cabinet input wiring

👉 Especially common in factories with large equipment switchingon/off

2. DC Bus Capacitor Aging

Over time, capacitors lose capacity.

• Reduced energy buffering
• Voltage drops under load
• Intermittent undervoltage alarms

👉 Very commonon older KRC4 cabinets

3. KSP Drive Internal Issues

• Drive not handling bus voltage correctly
• Internal protection triggered
• Overheating affecting performance

4. High Load / Aggressive Motion

• Heavy payload
• High acceleration settings
• Multiple axes moving simultaneously

👉 Causes sudden current demand → voltage dip

5. Power Cable or Connection Problems

• Loose terminals
• Worn motor power cables
• High resistance connections

6. Parameter or Firmware Issues

• Incorrect DC bus thresholds
• Firmware mismatch between KRC4 and KSP
• Corrupted drive parameters

How to Troubleshoot KUKA KSS01305

Step 1 – Check Incoming Power

• Measure input voltage at cabinet
• Look for voltage drop during motion
• Inspect main contactor and fuses

Step 2 – Monitor DC Bus Voltage

Use:
SmartHMI → Drive Diagnostics → DC Bus

• Observe voltage in real time
• Check if it drops during acceleration

Step 3 – Inspect KSP Drives

• Check LED status
• Identify which drive is affected
• Swap modules if necessary

Step 4 – Check Cables & Connections

• Tighten all power connections
• Inspect motor cables for wear
• Check grounding and shielding

Step 5 – Reduce Load and Test

• Remove payload if possible
• Lower speed and acceleration
• Run test cycle

👉 If stable at low load → problem is power or capacity

Step 6 – Replace Faulty Components

If issue persists:

• Replace DC bus capacitors or power modules
• Replace KSP drive
• Replace damaged cables

Recommended Replacement Parts

• KUKA KSP 600-3x20 Servo Drive (00-198-265): For internal bus or electronics faults.
• Main Contactor or DC Bus Capacitors (KUKA OEM spec): To restore bus stability.
• Motor Power Cables and Connectors (High-flex, Shielded): To prevent voltage drop or disconnection.
• Power Supply Monitoring Modules: For early detection of undervoltage events.

⚠️ Compatibility Tip: Confirm robot serial number, axis number, and KSS version before replacing drives or power components.

Pro Diagnostic Tip for KUKA KSS01305

• Navigate to SmartHMI → Drive Diagnostics → DC Bus Monitoring.
• Monitor bus voltage and current in real-time.
• Log undervoltage events to identify intermittent power drops.
• Check for correlation with high-torque operations or multiple axis movements.
• Repeated KSS01305 often indicates aging capacitors or unstable cabinet power.

How to Fix KSS01305

• Stabilize incoming power supply
• Replace aging DC bus components
• Repair or replace power cables
• Reduce load or optimize motion profile
• Replace faulty KSP drive if needed

Prevention & Maintenance

• Regularly inspect cabinet power supply and DC bus components.
• Maintain stable incoming voltage.
• Ensure proper ventilation and cooling of drives.
• Avoid overloading axes or sudden acceleration spikes.
• Replace aging KSP drives proactively.

Related KUKA Errors

⚠️ Technical Note: DC bus undervoltage often triggers or correlates with:

• KSS01306DC Bus Overvoltage Error – Bus voltage excursions beyond safe limits.
• KSS00401Motor Error– Drive/motor current interruptions caused by undervoltage.
• KSS01404Servo Drive Error– KSP drive internal faults linked to DC bus issues.
• KSS00406Position Deviation Error– Undervoltage causing torque loss and axis deviation.

FAQ About KUKA KSS01305

What does KUKA KSS01305 mean?

It indicates the DC bus voltage supplying the servo drives dropped below safe levels, stopping axis motion.

Can the robot operate with DC Bus Undervoltage?

No. Drives may be disabled and motion blocked until voltage stabilizes or components are repaired.

How do I fix KUKA DC bus undervoltage errors?

Check cabinet power, inspect drives and motor connections, monitor DC bus voltage, and replace faulty components if needed.

Can heavy payload or acceleration cause KSS01305?

Yes. Excessive load or sudden motion can temporarily lower bus voltage, triggering the error.