How to Reform WEG VFD Capacitors

This technical note from WEG Electric Corp outlines the purpose, background, and step-by-step procedure for reforming electrolytic capacitors in variable frequency drives (VFDs) that have been stored without power for extended periods. Proper reforming is essential to prevent capacitor failure, protect the drive, and ensure reliable motor operation.

Key Points

  • VFD capacitors must be reformed if the drive has been stored without power for 9–12 months.
  • Proper voltage levels depend on the drive model (220V, 380V, 500V, 660V ranges).
  • A 24-hour resting period after reforming is required before the drive can be placed into service.
  • Electrolytic capacitors degrade over time without applied voltage, risking rupture or short circuit.
  • Reforming involves applying reduced input voltage for 1 hour without a motor connected.
  • Failure to reform capacitors can result in catastrophic damage to the drive and other components.