Automakers including General Motors, Chrysler, Ford, Toyota, Honda, Nissan, and Tesla Motors this month agreed to a common standard for the all-essential plug for their plug-in hybrids. The standard, known as SAE (Society of Automotive Experts) J1772, can charge at either 120 V or 240 V and deliver up to 70 amps at the higher voltage.  The standard will also support communication over power lines, which will help with vehicle identification and load shifting of these vehicles.  It has 5 pins, 2 for power, 2 for communications, and 1 for ground.

It is also interesting to note that the plug standard is not all that new. For example, a PDF file from AC Propulsion, Inc., documents a similar plug from 1999.

While it is a great development for plug-in hybrids, there are some practical limitations.  For example, a 50 kW Tesla motors battery would take three hours to charge, even under the maximum power rating of this system.  Even smaller plug-in hybrids would take half an hour or more.

As an engineer, it has been my pipe dream to have batteries that could handle a higher voltage / amperage. But for that to happen, the plug standard would have to change.

The European standard, while omitting the 2 prongs for communications, has a 400 V rating, which may allow it to deliver more power.  Although this would be incompatible with most US residential electrical systems, it leaves the open question as to whether or not commercial charging stations in the US could be viable at a higher voltage.

I don’t know about you, but I’m not willing to spend three hours at a gas station waiting for my car to charge.