Eickhoff Inverter Pre-charge Unit | Model: C054255zb

Description

Eickhoff Pre-charge Unit C054255zb Product Overview

This product is an original Eickhoff pre-charge unit from Germany, model C054255zb. In the AC frequency converter drive system of coal mining machines or tunneling machines, the DC bus support capacitor is equivalent to a short circuit in the cold state. The function of the pre-charge unit is to pre-charge the capacitor through a current-limiting resistor at the moment of power-on of the main circuit, smoothly raising its voltage to close to the peak voltage of the power grid before closing the main contactor. This avoids the huge inrush current burning out the contacts, causing power grid fluctuations, or damaging the frequency converter module. It is a key safety threshold to ensure the safe and shock-free start-up of high-power frequency converter equipment.

Core Functions and Working Principle

Suppressing Inrush Current: Upon power-on, the current first charges the DC bus capacitor through the power resistor within the unit, limiting the inrush current to a safe range.

Sequential Control and Monitoring: The internal logic monitors the DC bus voltage. When the voltage reaches a set threshold (typically about 90% of the rated value), a signal is sent to drive the main contactor to engage, simultaneously bypassing the pre-charge resistor, and the system enters normal operation.

Fault Protection: If the pre-charge process times out or fails, the unit will issue a fault signal and lock the system to prevent forced startup when there is an abnormality in the main circuit, protecting the expensive downstream IGBT power modules.

System Role: It is an indispensable front-end protection module in main drive systems (such as traction and cutting frequency converters) or auxiliary multi-drive systems (such as EiMC control cabinets).

Fault Symptoms and Diagnosis

Typical Fault Manifestations:

After the equipment is powered on, the control system reports “Pre-charge fault,” “DC bus voltage low,” or “Main contactor not engaged.”

When the main power switch is closed, the sound of the contactor repeatedly engaging/disengaging (arcing) is heard.

The equipment cannot enter the “ready” state, and the drive system cannot start.

Possible causes: Burned-out pre-charge resistor, faulty internal monitoring relay, damaged control board, or interrupted signal communication with the main controller.

Quality and Service Commitment: Every pre-charge unit we provide is a genuine Eickhoff product, with its resistance value, operating threshold, and control logic fully matched to the original equipment. When replacing this unit, we strongly recommend simultaneously checking the status of the main DC contactor contacts and the health of the DC bus capacitors to rule out related faults. We can provide technical confirmation and basic commissioning guidance based on model matching.