The P_MOVOC is a SIL-3 safety-certified voltage crowbar protector for high-speed permanent magnet (PM) motors used in machine tools, packaging, printing, and food machinery. Installed between the drive and the motor, it continuously monitors the DC-link voltage. When an overvoltage condition is detected — typically during uncontrolled deceleration where the motor regenerates energy back to the drive — the P_MOVOC crowbar-short-circuits the motor terminals within milliseconds, dissipating the excess energy and preventing permanent magnet demagnetization or drive damage.

How does the crowbar protection circuit work?

The device uses thyristor-based crowbar circuitry rated for the model's peak current (60 A / 120 A / 250 A). When the DC-link voltage exceeds the configured firing threshold, the crowbar fires and latches. The READY relay opens to signal the drive to stop, and the FIRING relay latches closed as a status output. After a thermal recovery period (3–15 minutes depending on model and crowbar duration), the device automatically resets. The crowbar can also be triggered externally via the 24 Vdc firing input for functional testing.

Which threshold variant is appropriate for the application?

Low-threshold models (suffix ..0000/..2000) fire at 860–900 Vdc phase-to-phase, suitable for standard PM motor drives. High-threshold variants (suffix ..1000/..3000) fire at 950–990 Vdc for drives with higher DC-link voltages. Models with ground fault protection (..2000/..3000) additionally monitor phase-to-ground voltage, with the ground fault threshold set below 1200 Vdc, providing comprehensive protection in poorly earthed or floating-neutral systems.