Contact sourcing considerations

In this article, PEI-Genesis unpicks the growing problem of EV connector standardization and compatibility.

For most electrical devices, users don’t have to worry about compatibility, because standardized connectors and a nationwide standard mains voltage keep everything simple. For EVs, a reliable grid solves the issues with frequency and voltage, but the connector conundrum remains.

Furthermore, the problem is complicated by EV manufacturers taking advantage of several charging options: Mode 1 for slow charging from typical home outlets, Mode 2 for faster charging from specially designed home outlets, Mode 3 for commercial street-side charging points and Mode 4 for rapid, direct current charging.

Currently there are four common EV connectors around: Type 1, Type 2, CHAdeMO and CCS.

Type 1 connectors, officially SAE J1772, were among the first used on EVs. These five-pin connectors supply single-phase AC power at between three and seven kilowatts and are mostly found in Asian markets. These have been largely supplanted by Type 2 connectors in the west.

The Type 2 connector, known as SAE J3068 and colloquially as mennekes after the original manufacturer, features an additional two pins and can carry either three-phase AC or high current DC depending on the configuration. In Europe, Tesla uses a modified version of the Type 2 connector that only fits Tesla EVs.

CHAdeMO connectors provide purely DC power at high currents and voltages. Finally, CCS, or Combined Charging System connector, is simply a Type 1 or 2 connector with an additional two DC pins for rapid DC charging.

CCS seems to have emerged victorious as the de facto standard, because it allows for flexible AC charging from home grids or any commercial charging station, excluding Tesla superchargers, but it also provides high current, high voltage DC to EVs with that charging capability.

It’s clear the ideal EV connector must be ergonomic, space efficient, safe and able to provide both AC and DC power. CCS connectors already combine all these design features, so problem solved? Not quite.

They fulfil the customer requirements but from an electrical engineering perspective there’s more to be done. For instance, high voltages and currents form the perfect environment for arcing between the contacts. The pilot signal helps mitigate this as any loss of continuity stops the charging but this doesn’t fully prevent resistive heating or contact damage.

A second of high voltage arc between contacts could score and scorch them. This damage exacerbates the problem, eventually leading to sudden connector failure. If this damage occurs on a charging station it means replacing the connector. However, if the damage occurs onboard the EV people could be stranded.

Regarding the contact design, extra effort can pay dividends. An example is Amphenol’s Radsok connector range which uses hyperbolic geometry to provide robust, high-density contacts mating. Instead of passively mating, these connectors push against the respective contact to ensure a complete and reliable connection.

While it seems like CCS might have solved the EV charging conundrum, more consideration of the subtleties means an ideal, future-proof design could be just around the corner.