SP9009 (Alarm 09) Spindle Motor Overheat (Soft) fault in Fanuc drive

SP9009 (Alarm 09) Spindle Motor Overheat (Soft) fault in Fanuc drive

Description

SP9009 is the thermal protection alarm for the main spindle motor. Unlike servo motors, spindle motors are often induction motors designed for high-speed continuous rotation. They generate significant heat. The motor winding contains a thermistor or thermostat. When the winding temperature exceeds the rated limit (often 140°C), the contact opens or resistance changes, signalling the drive to stop. This prevents the insulation varnish on the copper windings from melting.

Cause

• Cooling Fan Failure: Most spindle motors have a separate electric fan (blower) on top. If this fan fails or is clogged with chips, the motor cannot shed heat.
• Clogged Ducting: The air channels around the motor fins are packed with oily dust.
• Overload: Running the machine at low RPM with high torque (heavy face milling) for extended periods. Induction motors cool poorly at low speeds.
• Sensor Failure: The thermal switch inside the motor is broken and reporting a false overheat.

Solution

1. Check the Blower: Put your hand over the motor fan exhaust. Is there strong airflow? If not, check the 200V/24V power supply to the external cooling fan.
2. Duty Cycle: If the motor is hot to the touch, let it cool for 45 minutes. If the alarm clears, you are running the cycle too aggressively.
3. Check Resistance: Measure the resistance across the thermal sensor pins on the feedback connector. It should be a short (0 ohms) for a thermostat or a specific k-Ohm value for a thermistor. Open circuit usually means overheat (or broken wire).