8 EV CHARGING http://components.omron.com/eu-en Issue 4 2025 Power Electronics Europe www.power-mag.com Bringing the Cool to EV Charging Steve Drumm, Strategic Marketing Manager – Solutions in Energy, OMRON Electronic Components Europe B.V., explains how consumer, commercial and industrial AC EV chargers can get cooler, smaller, and longer lasting. EV-Charger Design Challenges The ongoing shift toward electrification holds the promise of cleaner and more energy-efficient living. On the other hand, end-user expectations continue to drive demand for more compact equipment that fits neatly and stylishly into lives and living spaces while also delivering higher performance. These demands for smaller, slimmer, and faster apply to everything, from accessories and small appliances to power adapters and chargers including electric vehicle service equipment (EVSE). High-power EVSE wallboxes are an increasingly common sight in today’s homes and businesses. These support Mode 3 charging, which stipulates built-in control and protection functions for safety, and can charge an EV at up to 22kW from a three-phase AC supply. By providing convenient access to safe and secure charging, ideal for use overnight or during the working day, these wallboxes can certainly help dispel the speed of charge and range anxiety often cited as the main reasons for motorists’ reluctance to adopt EVs as daily transport. On the other hand, size and aesthetics are highly important and become a key differentiator between manufacturers. However, cramming the circuitry into the smallest and thinnest possible enclosure brings thermal management challenges that must be addressed to ensure the long-term reliability of the EVSE as well as user safety. Wallboxes like these could be in continuous use or may be connected to several vehicles in rapid succession, especially when installed in a workplace scenario, giving little or no opportunity to cool down between charges. In direct sunlight, the internal temperature can easily reach 70-80˚C, and cycle through 50-60˚C variances within the space of a couple of hours. While units equipped with temperature sensors can throttle the charging current in overtemperature conditions, which is good for safety, this means slower charging rates and less convenience for the end user. On a particularly hot day, or if a fault is causing the wallbox to overheat, the charger may not be able to function at all. Addressing these thermal challenges can enhance reliability, safety, and the user experience. Self-Heating Effects Within the wallbox circuitry, resistive components, power transistors, inductors, transformer windings, cables, and connectors exhibit self-heating due to power dissipation that increases with the square of the current flowing (I2R). A surprising amount of I2R-related heat in the wallbox is associated with the contact resistance of the main switching device, which is usually an electromagnetic relay or contactor. Unlike power transistors, which can be connected in parallel to distribute load current, paralleling electromagnetic switches is impractical. As the full load current must pass through the relay, the contact resistance when closed has a considerable heating effect. Even a one milliohm increase in the relay contact resistance can equate to as much as *18˚C in increased load terminal temperature rise. Excessive heat dissipation within the enclosure is undesirable, of course, and also mitigates against achieving slimmer and more compact wallbox designs. For a given heat load, a small-sized enclosure has less surface area from which to dissipate heat and so will experience a higher temperature rise. In addition, packing components more tightly in the
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