19 December, 2015

Residential Charging Stations for Electric Vehicles

Residential Charging Stations for Electric Vehicles

You may be considering buying an electric vehicle (EV), or plug-in hybrid vehicle. These vehicles will help lessen our reliance on imported fuels but will require yet another power source – electricity.  The EVs are powered by a large battery pack that will need a home-based charging system in order to “re-fuel”.  In the Chevrolet Volt for example, the charger is installed in the vehicle, but other brands may have the chargers in garages or a weatherproof unit will stand outdoors along the driveway.  Regardless the placement, most garages and some older houses will need to be rewired to accommodate the charging equipment.
The EV charger should be on a ‘dedicated’ circuit, meaning no other fixture or appliance is on that circuit.  You wouldn’t want the circuit breaker to trip because someone used the garage door opener or turned on the lights.  The National Electric Code® (NEC), states a number of safety requirements including over-current trip, leakage current to ground protection (GFCI), and an automatic shut-off feature for when, not if someone drives off with the cable still plugged in to the car.  
Because the charger is operating for hours at a time, the following rule is in Section 625.14 of the 2011 NEC®: “Electric vehicle supply equipment shall have sufficient rating to supply the load served. For the purposes of this article, electric vehicle charging loads shall be considered to be continuous loads.”  You should consult a licensed electrician to evaluate the capacity of your electric system to ensure that you are ready to install an EV charger.  Heavier wiring to the garage and possibly to the house may be required. Many electricians suggest that a 50 ampere (amps) - 240 volt service run to the garage for a Level 2 charger (see below).

 photo copyright: the Society of Automotive Engineers (SAE.org)
The charging methods have been standardized by the Society of Automotive Engineers (SAE).  Approved in 1996; SAE Standard J1772, specifies three levels of chargers: 1, 2, and 3. Recent updates describe the design of a standard connector (plug) for attaching power to the EV at Levels 1 and 2.
    Level 1—The Level 1 charger is rated at 120 VAC and 20 amperes (amps) and will plug in to grounded electrical receptacle outlets. Charging at this level could take 8 to 24 hours to fully charge an EV, depending upon the battery size and its discharge level. This is not meant as the primary charging technique.  SAE suggests that EVs carry a portable Level 1 unit so that they can plug into any available 120 VAC grounded receptacle for emergency or ‘top-off’ charging. 
    Level 2—The Level 2 charger is to be used for everyday EV charging and is rated to run from a single-phase branch circuit, similar to an electric dryer circuit, operating at 240 VAC, at 30amps. Charging time at this rate will be from about 4 to 10 hours to fully charge the EV depending on its battery size and discharge level.
    Level 3— Level 3 standard is for “Fast Charging” similar to refueling at a service station. The charger is supplied by 480-VAC, three-phase equipment, and would reach a 50% charge in 10 to 15 minutes. A separate connector would supply DC from the off-board charger directly to the battery.
After many fits and false starts, it appears the EV era is now with us. The Tesla, Chevrolet Volt, and Nissan Leaf are now being sold in the U.S., and other manufacturers have products that will soon come to market.  Also, as in the early days of gas engine vehicles, people are constructing homebuilt EVs from existing cars, motorcycles, and trucks. So for drivers, it’s electrifying times ahead (pun intended).

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