178B3775 by Danfoss

The 178B3775 is an AC variable frequency drive produced by Danfoss as part of the VLT 6000 HVAC Drives series. Designed for fan, pump, and compressor duty cycles, the unit modulates motor speed to maintain stable airflow and temperature in commercial building automation. By converting fixed mains frequency into a pulse-width-modulated output, the drive helps reduce energy use, limit mechanical stress on connected equipment, and improve process control across multiple HVAC zones.

Rated to accept a three-phase supply of 380-460 VAC, the drive fits common electrical services found in chilled-water plants and rooftop air handlers. The motor output rating is 22 kW / 30 HP, allowing direct connection to medium-sized induction motors. The housing uses a Compact NEMA 1 enclosure, so the electronics are protected against accidental contact and are intended for installation inside clean electrical rooms. Operators adjust and monitor parameters through the integrated LCP (Local Control Panel), a detachable keypad that provides text feedback and quick access to setpoints. For environments where airborne chemicals are unlikely, the circuit boards are supplied with no coating, which helps preserve thermal dissipation.

In Danfoss nomenclature, the application code Graham identifies parameter groups tuned for pressure-independent air-handling sequences, so the drive can integrate with differential pressure transmitters. Because the model is ordered without fieldbus options, speed references are introduced through analog inputs or the locally mounted keypad. The unit is classified as an HVAC Drives model, so it emphasizes variable-torque motor control and automatic sleep functions that match the load profile of building systems. The drive is supplied without an input filter, so any required RFI mitigation must be handled with external line filters selected for the installation's EMC class.