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Quick Chargers for Electric Vehicles

The biggest perceived disadvantage of electric vehicles is the fact that, except for a few experimental models, they go a lot shorter distance between recharges than a conventional vehicle can go between refuelings. A lot of people, myself included, do not regard this as a real disadvantage because even this relatively short distance is enough for the vast majority of daily drives. Since it is easy (and usually cheaper) to recharge an electric vehicle while it's parked in your garage while you sleep, there's no inconvenience involved in refueling every day (which would be quite a pain in the neck if you had to go to a public fueling station, as you do for petroleum-based or most alternative fuels), and therefore for most uses the vehicle's "fuel tank" (battery) only needs to hold enough for one day's driving.

However, eventually you're likely to have to drive farther than you can on a single charge; if you don't have a "backup" conventional vehicle, or don't want to use it (say, because you're driving your electric vehicle across several states as Kris Trexler did in his Charge Across America), you then have no choice but to stop in the middle of your journey, plug your vehicle into a charger, and let it sit there while it "refuels". Conventional chargers take hours to bring an empty battery pack up to full charge; again, this is no disadvantage when the car is sitting in your garage overnight, but it can severely slow you down in the middle of a long drive. In a number of cities, networks of public chargers are being installed at places where it would be natural to park a car for at least an hour or two, like movie theaters, grocery stores, shopping centers, and auditoriums, as well as at hotels, banks, car dealerships... Because of the "charging profile", an hour or two on a modern charger is enough time to bring a modern electric vehicle's battery pack most of the way (about 70%-80%) up to full charge (filling the last fraction of the capacity is significantly slower). For road trips where you need to keep moving, however, you would really like to be able to charge your vehicle's battery pack most of the way to full in minutes, not hours.

50 kW MagneCharge quick charger

Enter the quick-charger! On Thursday, 10 September 1998, GM and Southern California Edison (SCE) unveiled a prototype of a 50 kW (kilowatt) recharging station that will fill the battery pack of a Chevy S-10 electric pickup truck (or an EV1 electric car) from almost empty to almost full in about twelve minutes, several times faster than the normal 6.6 kW recharging unit supplied with GM electric vehicles (which is in turn several times faster than you can typically recharge a vehicle converted from conventional to electric power by an aftermarket company, by the way). Twelve minutes is a lot smaller bite out of a road trip than a couple of hours, and if these stations were installed, say, at some of the rest stops between Los Angeles and San Francisco, it would make a trip in an electric vehicle between those cities almost as easy as in a gasoline car, rather than the unusual and rather remarkable expedition that it is today (a few people have made the drive that I know of).

50 kW charging "paddle"

Of course, the vehicle has to be able to accept that much input power! The 6.6 kW charger that GM supplies with their electric vehicles draws up to 30 amperes from a 220 volt appliance circuit; that requires some heavy-duty wiring in the garage where the charger is installed, and the vehicle circuitry is equally beefy--and a 50 kW charging rate is over seven and a half times as much power! So the Chevy S-10 pickups in the SCE fleet that are being used in this test have been specially modified to handle it; no current production vehicle, and none planned for the immediate future, can use this quick-charger. However, the much greater energy transfer rate has been "shoehorned" into a paddle that is the same size as the ones already in use--compare the photo above with the one on the top page of this website--and it is thought that up to 80 kW might be transferred through the smaller inductive charging paddle that will supplant the current standard design. Thus there is certainly already room to fit fast-charging hardware into future versions of current electric vehicle models. (Since I attended the unveiling of the GM fast charger, I have learned that AeroVironment has outfitted their PosiCharge rapid charger with a conductive coupler for the Ford Ranger EV, and that Ford is planning to build vehicles capable of accepting a quick charge from it, but I haven't yet heard when. I have also learned that the Dodge EPIC electric minivan has been capable of quick-charging for several years, albeit with a different heavy-duty conductive coupler that nobody else seems to be using.)

Taking another approach, the propulsion power-control circuitry in any electric vehicle already has to handle a large amount of power, 75 kW for each 100 HP the electric motor produces. AC Propulsion has taken advantage of this in their Reductive charging system by making the drive electronics double as charging electronics, which they (and Volkswagen, with whom they built a recent prototype) say reduces the complexity of the recharging system (conductive, inductive, Reductive--get it?) and allows the vehicle to be plugged in to a 220-volt appliance circuit for quick recharging without the intermediation of an expensive off-board fast-charger unit.

EV row at Rosemead SCE facility

Speaking of "current electric vehicle models", I couldn't resist posting a photo of the row of electric vehicles parked at the SCE headquarters in Rosemead, CA, where the prototype fast charger is installed. Every vehicle you see in this photo is electric! There are a couple of GM EV1's, a Honda EV Plus, a Chevy S-10, some Toyota RAV-4's, and the first Nissan Altra that I've seen "in the wild" (as opposed to at a car show or ride-and-drive event). This row of parking spaces has a variety of recharging units, both conductive and inductive (including at least one type of connector I've not previously seen), so that SCE can test whatever the manufacturers come up with! After all, they're going to supply the fuel for these now-and-future cars, so they need to know what the different kinds of "dispensers" are going to act like when plugged into their grid.

I found out about the press briefing to unveil the fast charger and its test program from the CALSTART News Notes; thanks for keeping me up to speed, and thanks especially to Susan Sines of SCE for getting me permission to "crash the party"!

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new 17 September 1998, revised 25 October 1998