Frequency inverter (drive)Illustrative example

Siemens SINAMICS G120

The drive trips on undervoltage (F30003) under load; noticeable ripple observed on the DC-link voltage.

Duration: 2-3 business daysUpdated: 2026-07-07

Before

Faulty — board out of service

After

Repaired — tested under load

Fault

The drive trips on undervoltage (F30003) under load; noticeable ripple observed on the DC-link voltage.

Analysis

Mains and input phases were healthy. DC-link ripple and bus collapse under load pointed to aged electrolytic capacitors. ESR measurement showed high internal resistance.

Repair Steps

1
Mains/input verification
Input phases and rectifier found healthy.
2
Capacitor measurement
DC-link capacitors measured with ESR meter; high ESR found.
3
Recap
Capacitors replaced with new ones of the original value/rating.
4
Test under load
DC-link ripple returned to normal; F30003 did not recur.

Changed Components

DC-link electrolytic capacitors
Balancing resistors

Test Result

DC link stable under load; ripple within manufacturer tolerance.

This is an illustrative repair flow that shows the process; no real customer/board information is shared.

Related Repair Cases

ABB ACS580Frequency inverter (drive)Delta MS300Frequency inverter (drive)

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