The Schneider Electric VW3A68180 is an additional charging unit designed for Altivar variable-speed drive systems. Its job is to provide supplementary charging current to the DC bus capacitors, speeding up the pre-charge cycle on larger drives or multi-drive configurations where the standard internal charging circuit would take too long.
What It Does in the Drive System
In an Altivar drive cabinet, the DC bus capacitors need a controlled pre-charge to limit inrush when the mains contactor closes. The VW3A68180 adds extra charging capacity, typically used when the drive's internal charging resistor is undersized for the total bus capacitance — common in multi-motor line-ups or single drives with extended DC-bus capacitance banks. It connects in parallel with the drive's own charging circuit and is controlled by the drive's logic. If you are maintaining an older Altivar installation and the pre-charge cycle takes too long or the internal resistor runs hot, this is the factory add-on that addresses it.