Zevotron via flickr creative commons.)

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Plugging In Your Volt: Not With Just Any Old Cord

By · October 28, 2008

When you imagine plugging an electric or plug-in hybrid car into the wall to recharge, what do you envision in your hand? A standard orange extension cord? Time to change that picture; production electric-drive vehicles will all use a special cord, with a plug and socket on the car end that’s unlike any you’ve seen before.

GM’s much-touted Chevrolet Volt plug-in hybrid will plug into a wall socket to recharge its 16-kilowatt-hour battery pack for up to 40 miles of travel solely on electricity. It may be many Americans’ first exposure in a century to cars that plug into the wall.

GM plug-in wand

A still-shot from a GM promotional video shows the shape of the plug-in cord.

Next up in the growing lineup of hybrid Saturn Vue models will be the Vue Two-Mode Plug-In Hybrid, which will run up to 10 miles on electricity alone at 35 mph or less. That vehicle is expected to launch late in 2010, at roughly the same time as the Volt. It replaces the nickel-metal-hydride battery pack from the Vue Two-Mode with a lithium ion pack, and it will use the same plug and socket as the Volt.

Both of these cars, and many others, will come with an onboard charger that converts standard 110V (or 220V) household alternating current into direct current of the correct voltage to recharge the battery pack. Every car will come with its own cord, with the special plug on one end to connect to the car, and a standard three-prong plug on the other end to plug into the wall socket in your garage—or perhaps your carport.


A Special Cord, For Good Reasons

Why is a special cable needed? There are several reasons, including predictable charging, better connections, future “smart charging”, and a desire for global standards for auto technology. All of these factors feed into a committee that has been working since August 2006 to agree on the Society of Automotive Engineers (SAE) J1772 standard, which defines the mechanical and electric specifications for the plug and socket to be used in plug-in hybrid and electric-drive cars. It includes shock protections and an interlock to prevent driving away with the cord in place, and specifies that the equipment must last for at least 10,000 charge cycles. General Motors is one of several “very active” parties in developing this standard.

Trivia

Gasoline hoses last changed in 1975, when cars requiring unleaded fuel were launched with narrower filler necks, so that the wider nozzles that carried leaded fuel wouldn’t fit, preventing the leaded fuel from poisoning the catalytic converters.

An industry-standard plug and socket allows charging not only at home, but at charging stations elsewhere. If all chargeable vehicles have the same socket, then charging stations only need to offer one type of cord—in the same way that all cars have the same pipe for fuel filling, so all gas pumps can use identical nozzles.

Better electrical connections come from the power cord’s positive locking, which keeps the connection between the plug and socket nice and tight, and requires the user to actively disengage the cord to remove it. This eliminates any chance the cord might simply fall out of the car socket, averting a safety hazard.

Among the unknowns, thus far, are the length of the cable (and whether there will be options there), the cost of a replacement cable, and whether it can be extended on its grid-plug end with a standard heavy-duty extension cord. A broader question is whether plug-in cars can practically be used by drivers without garages or carports of any kind—those who park at the curb, for instance.

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Demonstration of plug-in capabilities of Saturn Vue Plug-in Hybrid. If all chargeable vehicles have the same socket, then charging stations only need to offer one type of cord—in the same way that all cars have the same pipe for fuel filling, so all gas pumps can use identical nozzles.


Let's Get Smart, About Charging Our Plug-in Hybrids

A standard power cord carries only power, nothing more. But one day, your local utility will want to encourage you to charge your car in their “off-peak” hours, when they have plenty of spare power. The lowest demand for any utility comes from 11 pm to 5 am, and utilities will likely give hefty discounts to owners who agree to let the utility decide when their car should start charging during those hours.

Here’s the vision: You come home, plug in your car, and go about your evening. Through “smart meters” now being installed in many California homes (and in other locations), the utility will know that you’ve connected a car to that particular electric plug. If you’ve signed up for off-peak car charging, the utility will assess its overall load, and then decide when to start sending power to your car. It might start charging the cars in a neighborhood in sequence, to prevent them all switching on simultaneously.

In return for letting your power company control the charging time, you’ll get much cheaper rates on that power. For purposes of reference, by the way, charging an electric car is roughly the same as operating four plasma TV sets.

That’s the vision, anyway. The first Volts and electric cars that roll out in 2010 aren’t likely to take advantage of smart charging, but those cars will last 10 years or more—and by 2020, such schemes will surely be available in more advanced parts of the country.

To make all this possible, the power grid has to be able to communicate with the vehicle. So extra wires, just for communications traffic, are built into the charging cable. The signals that come from the smart meter will enter the car via these channels, and the meter will in turn receive data from the car—on how large the battery pack is, how much energy it will need, and so forth.

And that’s something your regular old extension cord just can’t handle.

New to EVs? Start here

  1. Seven Things To Know About Buying a Plug-In Car
    A few simple tips before you visit the dealership.
  2. Incentives for Plug-in Hybrids and Electric Cars
    Take advantage of credits and rebates to reduce EV costs.
  3. Buying Your First Home EV Charger
    You'll want a home charger. Here's how to buy the right one.