Yaskawa Sigma-7 A.720 after running for a while, what to check?
I'm getting an A.720 alarm on my Yaskawa Sigma-7 SERVOPACK. It usually happens after the machine has been running for a while, not immediately. What should I check first?
An A.720 alarm on a Yaskawa Sigma-7 SERVOPACK indicates a continuous overload, meaning the servomotor has been operating under a torque exceeding its rating for an extended period. This is a Gr.1 alarm and can be reset once the underlying cause is addressed and the motor has cooled. It typically occurs at constant speed with high friction, under a heavy process load, or when holding a vertical or out-of-balance load at standstill.
Likely causes and checks
1Duty cycle exceeds motor overload characteristics
- Points to it
- The motor is operating continuously under a torque that exceeds its rated capacity for the given duty cycle. This often manifests after the machine has been running for some time, as heat builds up.
- Check
- Compare the effective (RMS) torque over the operating cycle with the motor's rating and overload characteristics. Reconsider the operating conditions or evaluate if a motor with higher capacity is needed.
2Mechanical friction or binding
- Points to it
- Increased friction or binding in the mechanical system can cause the motor to draw more torque than usual. This can develop gradually over time, leading to the alarm after a period of operation.
- Check
- Compare the operation reference with the motor speed. Then, inspect lubrication points, check alignment of mechanical components, and verify the shaft load against its allowable value. Look for signs of dry ways or failing bearings.
3Holding load at standstill (vertical axis, counterbalance problem)
- Points to it
- If the alarm occurs while the axis is stationary in servo-lock, it suggests the motor is continuously exerting excessive torque to hold a load, often due to gravity on a vertical or unbalanced axis.
- Check
- Check the holding torque required at standstill. Evaluate the counterbalance system and the brake arrangement to ensure they are functioning correctly and adequately supporting the load.
4Wiring or parameter fault
- Points to it
- Incorrect motor or encoder wiring, or misconfigured parameters (such as Pn282 or Pn080), can lead to the SERVOPACK misinterpreting the motor's load or operating conditions, causing an overload alarm.
- Check
- Verify the motor and encoder wiring connections. Check the settings of parameters Pn282 and Pn080, specifically looking at the 'n.□□X□' value for Pn080.
Next check: Given that the alarm appears after running for a while, the first step should be to compare the effective (RMS) torque over the cycle with the motor's rating and overload characteristics, as this points to the duty cycle exceeding the motor's capabilities. Also, check for any A.910 warnings that might have preceded the A.720 alarm.
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