Tackling connector compatibility in electric vehicles

There are plenty of downsides when it comes to petrol, but its convenience is undeniable. It can be pumped into almost any vehicle with no difficulty. This is the opposite of electric vehicle (EV) charging, where every EV might have its own, uniquely designed connector. Dawn Robinson unpicks the growing problem of EV connector standardisation and compatibility 

For most electrical devices, we don’t have to worry about compatibility, because we use standardised connectors and a nationwide standard mains voltage, which keep everything simple. For electric vehicles (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.

A variety of connectors

Currently there are four common EV connectors around: type 1, type 2 including the Tesla supercharger, CHAdeMO and CCS.

Type 1 connectors, officially SAE J1772, were among the first to be used on EVs. These five-pin connectors supply single-phase AC power at between three and seven kilowatts (kW) 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. Designed in 2010 by a Japanese consortium, the CHAdeMO name is derived from the Japanese O cha demo ikaga desuka, translating to, “how about a cup of tea?”, a pun on the short time it takes to charge an EV through this connector.

Finally, CCS, or Combined Charging System connector, is simply a type 1 or 2 connector with an additional two DC pins that permit rapid DC charging. 

The CCS seems 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.

A perfect plug

It’s clear the ideal EV connector must combine several design features. It must be ergonomic and easy to use, it must be space efficient, it must include built-in safety features and, as we’ve seen, it must be able to provide both AC and DC power. CCS connectors already combine all these design features, so the problem is solved, right? Not quite.

They fulfil the customer requirements of an EV connector, but from an electrical engineering perspective there’s more to be done. For instance, the high voltages and currents present when an EV is charging forms the perfect environment for arcing between the contacts.

The pilot signal goes a long way to mitigating this as any loss of continuity stops the charging immediately, but this doesn’t fully prevent excessive resistive heating or damage to contacts.

Only a second of high voltage arc between contacts would be enough to score and scorch them. This damage further exacerbates the problem, eventually leading to an inevitable and sudden failure of the connector. If this damage occurs on a charging station it would mean replacing the connector, but if the damage occurs onboard the EV it could mean that people are left stranded with a dead car.

A little extra effort in the design of the contacts can pay dividends in mitigating against this. An ideal example is the RADSOK range of connectors from Amphenol, which use specialised hyperbolic geometry to provide robust, high-density mating between contacts. Instead of passively mating, these connectors are designed to push against the respective contact to ensure a complete and reliable connection.

So, while it seems like the EV charging conundrum might have found an answer in the CCS, a little bit more effort and consideration of the subtleties means an ideal, future-proof design could be just around the corner. 

Dawn Robinson is European Product Manager at cables and connectors specialist PEI-Genesis.