SP9001 (Alarm 01) Spindle Motor Overheat (Thermostat) fault in Fanuc drive

SP9001 (Alarm 01) Spindle Motor Overheat (Thermostat) fault in Fanuc drive

Description

SP9001 (Alarm 01) is the "Hard" thermal alarm for the spindle motor. Unlike Alarm 09 (which is calculated or soft-thermal), Alarm 01 indicates that the physical thermostat switch embedded in the motor windings has opened. These switches are usually normally closed (NC) and open at a specific temperature (e.g., 140°C). When the circuit opens, the drive shuts down immediately to prevent the varnish on the motor windings from burning off.

Cause

• Fan Failure: The external blower fan on the motor is not running or is spinning backwards.
• Extreme Duty Cycle: The machine is being run at low RPM with high torque (heavy milling) for hours, which generates more heat than the fan can dissipate.
• Thermostat Failure: The bimetallic switch inside the motor has failed open due to vibration.
• Cable Break: The two small signal wires in the feedback cable connecting to the thermostat are broken.

Solution

1. Cool Down: Allow the motor to sit for 1 hour. If the alarm clears, it was a genuine overheat.
2. Continuity Test: Unplug the connector at the motor. Identify the thermal pins (consult manual). Check for continuity. Infinite resistance means the switch is open (Hot or Broken).
3. Jumper Test (Diagnostic Only): To verify if the cable/drive is good, you can temporarily jumper the thermal pins at the drive connector. If the alarm clears, the issue is the motor or cable. Do not run the machine this way.