SP9012 (Alarm 12) Spindle Overcurrent (DC Link) fault in Fanuc drive

SP9012 (Alarm 12) Spindle Overcurrent (DC Link) fault in Fanuc drive

Description

SP9012 is the Spindle Amplifier's version of a short circuit or massive current draw. It is displayed as "Alarm 12" on the drive seven-segment display. This alarm indicates that the current flowing through the DC link into the inverter section has exceeded the absolute hardware limit of the transistors. Unlike a thermal overload which takes time to build up, this is an instantaneous trip designed to save the IGBTs from explosion. It usually happens during aggressive acceleration or heavy cutting.

Cause

• Motor Insulation Failure: The most common cause is the spindle motor winding shorting to the case ground due to coolant ingress.
• Output Short: The power cable connecting the drive to the motor has rubbed through its insulation and is arcing to the machine frame.
• Parameter Mismatch: The drive model code does not match the motor model, causing the current regulation loop to become unstable.
• IGBT Failure: The power transistor module inside the spindle drive has physically failed.

Solution

1. Megger Test: Disconnect the power cable from the drive. Use a megohmmeter (500V or 1000V setting) to test the motor windings to ground. A healthy motor should read >100 Megohms. Anything under 1 Megohm is a dead motor.
2. Cable Inspection: Check the military-style connector at the motor. Is it filled with oil? This is a common short point.
3. Isolation Test: Power up the machine with the motor cable disconnected. If Alarm 12 appears immediately, the Spindle Amplifier is damaged.