1500V Relays for Pre-Charge Circuits in EV Charging

High-voltage DC architectures are becoming common in energy storage installations and electric-vehicle charging systems, where controlled pre-charge of DC-link capacitors protects power electronics from inrush currents. Compact switching devices that handle these functions while supporting board integration are increasingly required. In this context, OMRON Electronic Components has introduced the G9KJ relay, designed as a PCB-mount alternative to contactors for pre-charge circuits operating at up to 1500V DC.

Pre-Charge Switching in High-Voltage Power Systems
In power electronics systems used in energy storage systems (ESS) and EV fast-charging equipment, pre-charge circuits limit the initial current surge when capacitors in the DC link are energized. Without controlled charging, large inrush currents can stress components such as the main contactor, DC-link capacitor, and protection circuitry.

The G9KJ relay is designed to act as the pre-charge control switch in these circuits. When the system starts, the relay routes current through a high-resistance path, gradually charging the capacitors before the main current path is activated. This sequence reduces electrical stress on the primary switching components and helps prevent unwanted system resets or protection trips.

The relay supports a 25 A make current and 5 A carry current (0 A break) and is specified for DC-link voltages up to 1500 VDC.

Compact Relay Design for PCB Integration
Traditional high-voltage switching in pre-charge circuits often relies on mechanical contactors, which occupy more space and typically require additional wiring or mounting structures. The G9KJ relay provides a board-mount alternative that can be integrated directly into power-electronics assemblies.

The relay measures 37.2 mm × 25.5 mm × 17 mm and uses a Type 1A (SPST-NO) configuration. By allowing direct PCB mounting, the device can simplify system assembly and reduce wiring complexity compared with external contactors.

Electrical characteristics include a maximum contact resistance of 100 mΩ and a coil power consumption of 530 mW, parameters intended to support efficient operation within high-voltage switching stages.

Supporting Higher-Voltage Energy Infrastructure
Demand for high-voltage switching components is increasing as both grid infrastructure and electric mobility systems move toward higher operating voltages.

In grid-connected energy storage, voltages in the 600 V to 1000 V range are commonly used to support large-capacity battery systems that stabilize renewable energy generation. At the same time, electric vehicles are moving toward 800 V to 1500 V battery architectures to enable faster charging, reduce current levels, and improve overall drivetrain efficiency.

Pre-charge circuits are a necessary element in these high-voltage power stages because they protect capacitors and switching devices during system start-up.

Relay Option for High-Voltage Pre-Charge Design
By providing a relay specifically rated for pre-charge switching conditions, the G9KJ offers an alternative to general-purpose high-voltage components. The device is intended to help designers specify pre-charge circuits with appropriate electrical ratings while balancing system size, cost, and reliability.

Applications include battery energy storage systems, EV fast-charging infrastructure, and other high-voltage DC power electronics platforms, where controlled capacitor charging is required before the main power path is engaged.

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