AUTOMOTIVE DESIGN TAKING THE HEAT OUT
In recent years the design of electric vehicle charging wallboxes has been transformed, with devices packing more power and faster charging speeds than ever into increasingly compact housing. This makes managing and mitigating temperatures inside the wallbox a major challenge for design engineers, as Steve Drumm explains
The G9KC’s lower operating temperature reduces the likelihood of reaching current throttling thresholds E
lectric vehicle (EV) charging wallboxes are an increasingly common sight at homes, businesses, public parking
areas and petrol stations. With the EV market set to continue its rapid growth in the coming years, wallbox manufacturers are eager to make their devices the most appealing, namely by making them as compact as possible, while providing safety, eff iciency, and the fastest possible charging speeds. The problem here is that packing
high power electronics into increasingly small spaces creates more heat. Heat is one of the top enemies of wallbox design. If temperatures are too high then this will have an eff ect on charging speed and eff iciency, and will cause components to wear prematurely. On a particularly hot day, or if a fault is causing the wallbox to overheat, then it may not be able to function at all. Chargers are often in continuous use, or may be used by a series of vehicles in rapid succession, giving the wallbox no opportunity
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to cool down between charges. In direct sunlight, a wallbox’s internal temperature can easily reach 70-80˚C, and cycle through 50-60˚C variances within the space of a couple of hours. Many chargers will have temperature sensors which will activate a reduction in charging current in overtemperature conditions. While this is good for safety, it means slower charging rates and more inconvenience for the end user.
CHARGER TYPES EXPLAINED Wallboxes are Mode 3 type chargers. Electric vehicle supply equipment (EVSE) is classifi ed into four diff erent modes: Mode 1, Mode 2, Mode 3 and Mode 4. Mode 1 is the least widely adopted because it does not have safety communication with the EV, and as such is not permitted in some countries, nor is it supported by the majority of EV manufacturers. Mode 2 involves using a charging cable equipped with an in-cable control and protection device, connected
to a household socket. While this is considered safer than Mode 1, charging speeds are still poor compared to Modes 3 and 4. Mode 3 AC chargers are by far
the most common in homes and businesses. While these do not achieve the same charging speeds as the Mode 4 DC fast chargers found at public charging points, they provide safe and secure slow charging – ideal for charging overnight or during the working day. However, since these devices are installed in homes and businesses, space and aesthetics are highly important, and become a key diff erentiator between manufacturers.
BALANCING PERFORMANCE AGAINST HEAT DISSIPATION With manufacturers therefore eager to make their devices as compact as possible, while also delivering as much power as possible, this creates a fundamental confl ict. The electronics
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