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High-Power Chargers, Thermal Designs, and Reliability

(Joseph Gottlieb, CTO, Tuesday, June 9, 2020)

What is the biggest threat to the reliability of high-power electric vehicle (EV) chargers? It’s not rain or wind lightning (though those things can be bad for high-power charging systems). The real threat to the reliability of high-power chargers is the effect that heightened temperatures have on high-power electronic components. To put it in perspective, every increase of ten degrees centigrade in the junction temperature of a high-power semiconductor component effectively cuts the life of that component in half. For instance, if a power transistor has a mean time between failure (MTBF) of 40,000 hours (about 4.6 years of continuous operation) at 40°C instead runs at a junction temperature of 50°C, it’s life will be cut down to 20,000 hours, or 2.3 years of continuous operation. Since most high-power systems don’t have redundant components designed into them, this cuts the total system MTBF to 20,000 hours.

Effective thermal design is as much an art as a science. Engineers have to balance getting adequate airflow for their charger against providing adequate environmental shielding. But just getting enough air into the charger cabinet is not enough – the air has to get to the most critical components before it gets too hot to effectively cool the components. This requires consideration of cabinet geometries, air ducting within the cabinet, and the layout of the components within the cabinet. Once all of this is done, the impact of changes in ambient temperature and humidity must also be determined. Finally, the final design needs to be verified through testing. Knowing where to look for the problems helps as well.

As a leader in the development and manufacturing of bi-directional, high-power energy systems for both vehicle charging and photovoltaic solar applications, Rhombus is an expert in designing high-power charging systems for EVs, and especially in the area of V2G charging. We have built hundreds of V2G-capable high-power, high-reliability chargers for a variety of different sizes and classes of EVs. Find out how we can help you by contacting us at, or by reading our Energy Storage Reference Architecture white paper.

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