SAE Publishes New Wireless Charging Standard

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Standards are important to commerce. For instance, on the Transmongolian Railway, the tracks in Russia and Mongolia are set 1,520 mm apart while in China they are 1,435 mm apart. That difference makes it impossible for trains to cross the border unless the railway cars are lifted by a crane so a different set of wheels can be slid in underneath them, a slow and laborious process. In Japan, half the country uses 50 hertz AC electricity while the other half relies on 60 hertz AC, which prevents the two systems from working together. A lack of standards leads to commercial battles like VHS vs Betamax, cassette vs 8 track, and so on.

In the world of electric vehicles, there are a welter of charging standards. CCS and CHAdeMO are not compatible with each other. China has its own charging plugs and protocols. It would help speed the EV revolution if every electric car driver could recharge using any charging device instead of carrying around an assortment of adapters in the frunk. Imagine if every manufacturer needed a specially shaped nozzle on the gas pump to fill the tank. That would be ridiculous, wouldn’t it? And yet it is the norm for electric cars.

Standards are what the Society of Automotive Engineers does. Its goal is to have a set of uniform standards so everyone can get on with the business of doing business and making money. SAE has been working on a standard for wireless charging of electric cars since 2007. Now it is finally ready and is known as SAE standard J2954 — “Wireless Power Transfer & Alignment for Light Duty Vehicles.” For those who want to get down into the weeds to understand the technical details of the new standard, SAE has also promulgated standard J2847/6 — “Communication for Wireless Power Transfer between Light Duty Plug-in Electric Vehicles and Wireless EV Charging Stations.”

“The publication of these two groundbreaking SAE Wireless Charging and Communications documents is the result of countless hours of work from SAE taskforces and industry to offer confidence in the safety and interoperability of these technologies as we approach commercialization,” says Jack Pokrzywa, director of Global Ground Vehicle Standards at SAE International. “We are grateful for all of the significant contributions from technology providers, automotive industry manufacturers, government agencies and regulatory bodies that enabled the successful establishment of the standard.”

According to Forbes, SAE has found that over a 10 inch air gap, wireless charging can operate at up to 94 percent efficiency. There are three wireless charging levels — WPT 1, (3.7 kW), WPT 2 (7 kW) and WPT 3 (11 kW). Higher power protocols will be the subject of further research and agreement. At present, there is no standard for DC fast charging or vehicle to grid bi-directional connections, although the latter is technically possible. Further research into wireless charging for heavy duty vehicles like trucks and buses is also ongoing.

The importance of standard J2954 is that now EV manufacturers have one standard to follow if they choose to offer wireless charging to their customers. Wireless is the pinnacle of convenience. Park your car over a wireless hub and walk away. Charging will take place automatically without the need to ever touch a charging cable.

Companies like WiTricity are leaders in wireless charging technology. It has recently concluded an agreement with Mahle, a Tier One supplier to automobile manufacturers, to make its products available to them. Honda in particular has shown an interest in offering wireless charging to its customers and is working with WiTricity to make that happen.

Convenience is a big part of getting new technologies accepted by the general public. Just imagine if people who are considering the purchase of an electric car knew they would never have to visit a gas station again and would seldom if ever have to plug in. Driving can’t get much more convenient than that. Which is why wireless charging will play a small but important part in moving the EV revolution forward.

The advantage of wireless charging was demonstrated recently by electric buses in the city of Wenatchee, Washington. Wireless charging stations provided by Momentum Dynamics were been installed along the routes the buses travel. As they stop to drop off or pick up passengers, the buses are recharged wirelessly by charging equipment installed in the pavement. The proof of the pudding is that during last winter, one electric bus operated for 14 continuous hours with its battery never getting below a 90% state of charge. That’s a remarkable achievement considering the heat was on the whole time. Wireless charging is not the future. It is here and ready to serve the needs of EV drivers today.

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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new."

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