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Engineers designing next-generation electric vehicle (EV) chargers and energy storage systems face relentless pressure to increase efficiency and capacity. Meeting this demand requires shifting to higher operating voltages, often up to 1500V_DC. While elevated voltages improve energy conversion and integration with renewable sources, they introduce significant challenges in component sizing. This week’s New Tech Tuesdays explores the engineering challenges of managing high-voltage inrush currents and examines how modern printed circuit board (PCB) power relays shrink footprints while protecting critical circuitry.

Managing High-Voltage Scaling

Power architectures in EV charging infrastructure, energy storage systems, and solar-plus-storage installations continue to push DC bus voltages higher. At a given power level, a higher DC bus voltage can reduce current, which helps lower conduction losses, heat generation, and conductor sizing. In EV fast-charging and energy storage system (ESS) architectures, this can enable higher-power charging and more practical integration with local energy storage and renewable generation. However, scaling up the voltage often inflates the equipment size. Historically, controlling such large DC voltages requires bulky, heavy contactors, creating a footprint dilemma for designers who must keep systems compact.

Protecting Systems with a Pre-Charge Relay

High-voltage systems rely on large capacitors that draw a large inrush current when powered on. Unchecked, this sudden surge can easily damage sensitive electronic components. A pre-charge circuit safely manages this initial load by pairing a pre-charge relay with a current-limiting resistor. When the system powers up, the pre-charge relay closes first, routing current through the resistor to safely charge the capacitor. Once the DC-link capacitor reaches a predefined voltage threshold near the source voltage, the main contactor closes, and the pre-charge circuit disengages.

The Newest Products for Your Newest Designs^®

The G9KJ PCB high-power relays (Figure 1) from Omron Electronics provide a compact PCB-mounted option for high-voltage pre-charge circuits. OMRON optimized the G9KJ for inrush-current prevention in high-voltage DC systems up to 1500V_DC. Capable of handling a 25A making current and a 5A carry current, this relay is designed for controlled pre-charge operation in EV charging, energy storage, and power conversion systems.

Figure 1: The G9KJ drastically reduces mounting area and volume compared to traditional screw-type relays. (Source: Mouser Electronics)

Transitioning to a PCB-mounted design yields significant space savings. Compared to general-purpose screw-terminal relays rated for 1500V_DC, the G9KJ delivers an 80 percent reduction in mounting area and a 90 percent reduction in weight.^[1] Tipping the scales at a mere 16g, the relay eliminates the need for manual screw fastening, which streamlines board assembly and reduces wiring space.

In addition to form factor, safety and efficiency remain paramount in high-voltage design. The G9KJ features a minimum 14mm clearance and 25mm creepage distance between the coil and contacts, ensuring robust isolation. Additionally, the relay operates with high sensitivity, requiring only 530mW of coil power.

Tuesday’s Takeaway

As EV chargers and solar-tied battery banks move toward 1500V_DC architectures, safely mitigating inrush current is no longer just a design goal—it is a strict necessity for performance and safety. By transitioning away from bulky, traditional screw-mounted contactors, engineers can leverage modern PCB power relays to maintain rigorous safety standards without sacrificing valuable board real estate.

Sources

[1] https://www.mouser.com/pdfDocs/c249ef2d-221a-48e5-a9f4-2254f41125d1_G9KJ-White-Paper.pdf