Nuisance Blown Fuses on Ultra 3000

The story you are about to read is true. Only the names have been changed to protect the innocent…

Nuisance Blown Fuses on Ultra 3000

Case File: 2016_10_24_001

Problem: Nuisance Blown Fuses when Powering Ultra 3000 Drive

In this week’s Tech Files case review, we look at the strange case of an Ultra 3000 multi-axis servo drive blowing fuses when reapplying AC power after a removal of power.

Our case begins with a phone call from an end user that was frustrated with blowing fuses every time they powered up their Ultra 3000 drive.  The Bulletin 2098 Ultra 3000 Digital Servo Drives support simple standalone indexing as well as multi-axis integrated motion.  We gathered as much info as possible about the sequence of events that leads to the blown fuses. It was mentioned that they would remove power to the drive, and then reapply AC power after a short period of time.  When AC power was reapplied, the fuses would blow.

Like most cases, our first stop was Rockwell’s Knowledge Base.  A quick search pulled up this knowledge base article:

AID# 32551 – Ultra 3000: Nuisance fuse/breaker trips upon E-Stop recovery
https://rockwellautomation.custhelp.com/app/answers/detail/a_id/32551

The cause was listed as being linked to the soft start or precharge resistor still being bypassed via the drive’s internal relay due to the DC bus not dissipated below 80 – 90 vdc.

Solution, monitor the DC Bus voltage, a time delay could be employed that would restrict re-application of main AC power for 30 to 60 seconds. This will allow the bus to bleed down below 80 vdc to insure the soft start resistor is back in circuit. The application of an external active shunt (2090-UCSR-A300) would reduce the dissipation time of the DC bus so that this delay can be reduced.

What appeared to be a strange anomaly had been solved.

To learn more about the Ultra 3000 Multi-axis Servo Drive, visit:
http://ab.rockwellautomation.com/Motion-Control/Servo-Drives/Ultra3000-Multi-Axis-Digital

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