What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

ABB ACS880 Fault 7121 Motor Stall on Servo Press: Causes and Parameter Fix

admin

Fault 7121 (Motor stall) on ABB ACS880 drives in servo press applications is often misdiagnosed.

Understanding the Fault Logic:
The ACS880 triggers 7121 when motor speed is below the stall speed threshold (31.24) while torque is above the stall torque threshold (31.25) for longer than the stall time (31.26). Default settings are too sensitive for press applications.

Common Causes:
1. Parameters too tight: At BDC, a servo press motor legitimately produces high torque at near-zero speed. Adjust 31.24 to 5% of rated speed and 31.25 to 120% of rated torque.
2. Mechanical binding: Check if the fault occurs at a consistent slide position.
3. Encoder feedback loss: If the drive loses encoder feedback, it sees zero speed with high torque demand - identical to a stall.
4. Undersized motor: If the press was recently retooled with heavier material, the motor may be genuinely overloaded.

Parameter Adjustments for Press Applications:
- 31.24 (Stall speed): reduce to 2% of rated speed
- 31.25 (Stall torque): increase to 150% of rated torque
- 31.26 (Stall time): increase to 60s

anna_controls

Fault 7121 on ACS880 in press applications: check parameter 30.01 (stall speed limit). The default is often too high for press forming where the slide moves very slowly under load. Reduce it to 2-3% of rated speed. Also verify that the motor model parameters in group 99 match the actual motor nameplate. Wrong motor data causes the stall detection to trigger falsely.

dave_toolmaker

The stall speed threshold in the ACS880 is parameter 30.01. Default is usually 10% of rated speed. For press applications where the slide legitimately moves very slowly during forming (especially with dwell), you may need to reduce this to 2-3%. Otherwise the drive thinks the motor is stalled when it's actually just moving slowly under high load.