SV5

Access Servo Parameters

Using the Fanuc control panel, navigate to the servo parameters for the affected axis (typically PRM 2000-2100 range). Identify the deceleration time constant setting for the axis.

Document the original parameter value before making changes in case a rollback is needed.

Ensure the machine is powered down or in a safe mode before accessing parameters to avoid unintended motion.

Increase Deceleration Time

Incrementally increase the deceleration time constant by 10-20% (e.g., from 100ms to 120ms) to reduce regenerative energy spikes. Test the axis motion after each adjustment.

Small incremental changes prevent overcompensation, which could affect cycle time or accuracy.

Avoid excessive increases that may impact production timing—consult machine builder if unsure.

Monitor Alarm Recurrence

Run the machine through several cycles at normal operating conditions. Observe if the SV5 alarm reappears. If it persists, further increase the time constant or proceed to other causes.

Use a trend monitor on the control to log regenerative energy if available for precise tuning.

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Locate External Resistor

Identify the external regenerative resistor connected to the servo amplifier (refer to machine wiring diagrams). It is typically near the amplifier or in a designated enclosure.

Check the machine manual for the exact location and resistor specifications.

Ensure power is completely off and locked out before inspecting hardware to prevent electrical shock.

Inspect for Damage and Thermal Trip

Visually inspect the resistor for burn marks, cracks, or discoloration. Check if it has a thermal overload switch and verify if it has tripped (often indicated by a reset button or status light).

A tripped thermal switch often resets after cooling—wait 10-15 minutes before attempting a reset.

Do not bypass a thermal switch; it indicates an overheating issue that must be resolved.

Test Resistor Continuity

Using a multimeter set to resistance mode, test the resistor for continuity. A reading of infinite resistance indicates an open circuit, meaning the resistor has failed and needs replacement.

Compare the measured resistance to the rated value in the machine manual to confirm spec compliance.

Disconnect all wiring to the resistor before testing to avoid false readings or injury.

Analyze Cycle Time

Review the machine program or PLC logic to determine the cycle time and frequency of deceleration events for the affected axis. Note if cycles are under 10-15 seconds apart.

Use the control’s diagnostic screen to log cycle times if manual calculation is impractical.

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Add Dwell Time

Modify the program to insert a short dwell (e.g., 5-10 seconds) at the end of each cycle to allow resistor cooling. Test the modified program for alarm recurrence.

Start with minimal dwell to avoid significant production delays, increasing only as needed.

Ensure dwell addition does not interfere with other machine operations or safety interlocks.

Monitor Temperature

If possible, use an infrared thermometer to measure the regenerative resistor temperature after several cycles. If it exceeds 80-100°C, cooling time or ventilation improvements are needed.

Consider adding forced air cooling if dwell time adjustments are insufficient.

Avoid direct contact with hot components during measurement to prevent burns.

Check Resistor Specifications

Locate the part number or rating label on the external resistor and compare its power rating (watts) and resistance (ohms) to the machine builder’s recommendations in the manual.

If specs are unclear, contact the machine OEM or Fanuc support with the amplifier model for guidance.

Power off and lock out the machine before handling hardware to avoid electrical hazards.

Calculate Load Requirements

Estimate the regenerative energy based on load inertia and deceleration rate (consult Fanuc servo tuning guides or OEM data). Compare this to the resistor’s capacity to confirm if it’s undersized.

Fanuc’s Servo Guide software can assist in calculating energy if manual computation is complex.

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Upgrade Resistor if Needed

If the resistor is undersized, replace it with a higher-capacity unit as per OEM or Fanuc recommendations. Ensure proper mounting and ventilation for the new resistor.

Consider a resistor with at least 20-30% higher capacity than calculated to account for future load increases.

Incorrect resistor values can damage the amplifier—verify compatibility before installation.

Confirm External Resistor Absence

Verify whether an external regenerative resistor is installed by checking wiring diagrams and physical connections. If absent, the internal circuit is handling all regenerative energy.

Some amplifiers have jumper settings for internal vs. external resistors—check the manual.

Power off and lock out the system before inspecting wiring to prevent shock.

Test Amplifier Behavior

Run the axis at reduced speed and deceleration rates to see if the alarm persists. If it occurs even at low energy levels, the internal circuit is likely damaged.

Use diagnostic LEDs on the amplifier (if available) to check for internal fault codes beyond SV5.

Do not operate the machine at full capacity during testing to avoid further damage.

Arrange Amplifier Repair

If the internal circuit is suspected to be faulty, contact Fanuc or a certified repair center for amplifier testing and repair. Provide the alarm history and amplifier model number.

Have a spare amplifier on hand if downtime is critical, as repairs can take days to weeks.

Do not attempt internal amplifier repairs without proper training—high voltage risks are present.