The electric and plug-in hybrid car industry is learning the lesson of the mobile phone makers. Instead of allowing a plethora of incompatible charging plugs to sprout up, the Society of Automotive Engineers (SAE) International hopes to forestall confusion by settling on one charging plug design for North America. SAE has selected the J1772 combo plug as the standard, which uses paired couplers to allow for both AC and DC charging using the same plug.
Published this week, the SAE International decision marks the first official charging standard for North American cars. According to SAE, it was the result of consultation with 190 “global experts” from the automotive, charging equipment, utilities industries and national laboratories.
The J1772 has two charging plugs incorporated into a single design and is said to reduce charging times from as long as eight hours to as little as 20 minutes. It’s based on the 2009 J1772, which had only an AC charging plug. The current version includes a DC plug underneath the AC plug, which means that not only are both options available, but cars with the older J1772 couplings, such as the 2012 Nissan Leaf and 2013 Chevrolet Volt, can still use the new plug.
The dual capability is because AC and DC each have their strengths and weaknesses. AC is easier to access, since it’s mains current and the car's on-board system can rectify it into DC to charge the battery. The problem is that beyond a certain point AC has heating problems for the car, so charging is inherently slow. DC is much faster – theoretically limitless, but it requires an external charging station. The choice of currents means that car makers don’t need to choose between plentiful but slow, and fast but scarce.
The new standard also sets charging levels and safety features for the plug – those features include its ability to be safely used in all weather conditions, and the fact that its connections are never live unless commanded by the car during charging.
J1772 beat out its main rival, the Japanese CHAdeMO plug (which is also available as an option for the Nissan Leaf and is used in over a thousand chargers installed in Japan), along with Tesla’s proprietary Supercharger system. Whether the SAE standard will see an end to these rival plugs or the beginning of an automotive version of VHS versus Betamax remains to be seen.
Source: SAE International
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