Omron’s 4-pole relay fits on a PCB to reduce the heat generated in three-phase power electric vehicle wallboxes during high-power charging. More people are transitioning from internal combustion engine to electric vehicles to reduce carbon emissions. As EV numbers increase, more reliable and high-speed EV supply equipment and chargers are needed.
Charging speeds have improved, but higher charging currents require higher-rated electronic components that generate more heat in the EV wallbox charger. This heat generation limits many home chargers’ useful lives, but Omron has developed a high-power PCB relay—the G9KC—to promote faster charging without the extra heat.
High Temperatures Challenge EV Wallboxes
An EV wallbox is installed in people’s driveways and garages to allow charging at any time. Wallboxes vary in charging speeds, depending on access to single or three-phase power. Three-phase power is an AC circuit with three wires, with each wire’s voltage phase-shifted by 120 degrees relative to the other wires. Three-phase power can accommodate higher loads, allowing higher-powered charging points.
The usual charging speeds for home wallboxes range from 3 kW to 7.4 kW for single-phase power. Wallboxes with much higher charging speeds can be installed for homes with three-phase power, but the specific values range by geographical location. For example, in Europe, three-phase power wallboxes range from 11 kW up to 22 kW, whereas in the U.S., they range from 9.6 kW to 19 kW.
Naturally, higher-powered circuits give off more heat as an operational byproduct of the components. High heat is typically generated from the relays within the wallbox because these components have a high contact resistance, which helps generate a larger current and more heat. The result increases the wallbox’s internal temperature.
Wallbox heat generation. Image used courtesy of Omron
However, high temperatures significantly impact the wallbox’s charging performance and efficiency and can cause temporary power limitations. The heat suppresses the charging current, leading to longer charging times. Increasing the number of elevated heat cycles the wallbox experiences often causes the internal components to degrade and fail prematurely.
Because higher power systems produce more heat, it’s difficult for EV infrastructure designers to balance the heat generated with the need to provide a high charging power. Current wallbox designs have reduced size and are often enclosed in completely sealed units to prevent water from entering. Smaller units are even more susceptible to internal heat spikes.
Taking Away the Heat
Omron has developed and released its G9KC relay with a mechanically coupled, double-break contact design for three-phase high-charging wallboxes. The relay can reduce the operating temperature in wallboxes up to 22 kW while improving the charging process’ efficiency and speed.
Diagram of 3-phase EV charger. Image used courtesy of Omron
The relay uses a 4-pole structure to replace the traditional, larger multipole contractors in wallboxes. The relay has an initial contact resistance of less than 6 mΩ, which reduces the chance of localized hotspots forming within the wallbox to prevent component deterioration and wallbox failure. The G9KC also has a low operation temperature, which decreases the number of charge cycles that reach the charging current throttling thresholds.
The G9KC is also small. Contractors are bulky units, but the G9KC relay can be used on a printed circuit board (PCB) to create smaller, lighter designs. The G9KC has received approval from various certification bodies, including UL/C-UL, TUV, and CQC. It has been designed to meet the specifications of IEC 62955—Residual direct current detecting device (short circuit capability) and IEC 61851-1—Electric vehicle conductive charging systems.
Benefits Beyond Thermal Dissipation
While thermal dissipation is a key challenge with EV wallboxes, the G9KC also has several other advantages for wallboxes. It can reduce charging time because heat suppresses the charging current, decreasing the chance of overheating. The G9KC also enables smaller and slimmer wallboxes.
While the relay has been designed for EV wallboxes, it is a versatile component that can be used to perform input/output switching operations in many other devices, including photovoltaic inverters, industrial inverters, energy storage systems, DC quick chargers, and uninterruptible power supplies.
