Electric-car Motors and Batteries
Electric cars can use AC or DC motors:
•If the motor is a DC motor, then it may run on anything from 96 to 192 volts. Many of the DC motors used in electric cars come from the electric forklift industry.
•If it is an AC motor, then it probably is a three-phase AC motor running at 240 volts AC with a 300 volt battery pack.
DC installations tend to be simpler and less expensive. A typical motor will be in the 20,000-watt to 30,000-watt range. A typical controller will be in the 40,000-watt to 60,000-watt range (for example, a 96-volt controller will deliver a maximum of 400 or 600 amps). DC motors have the nice feature that you can overdrive them (up to a factor of 10-to-1) for short periods of time. That is, a 20,000-watt motor will accept 100,000 watts for a short period of time and deliver 5 times its rated horsepower. This is great for short bursts of acceleration. The only limitation is heat build-up in the motor. Too much overdriving and the motor heats up to the point where it self-destructs.
AC installations allow the use of almost any industrial three-phase AC motor, and that can make finding a motor with a specific size, shape or power rating easier. AC motors and controllers often have a regen feature. During braking, the motor turns into a generator and delivers power back to the batteries.
Right now, the weak link in any electric car is the batteries. There are at least six significant problems with current lead-acid battery technology:
•They are heavy (a typical lead-acid battery pack weighs 1,000 pounds or more).
•They are bulky (the car we are examining here has 50 lead-acid batteries, each measuring roughly 6" x 8" by 6").
•They have a limited capacity (a typical lead-acid battery pack might hold 12 to 15 kilowatt-hours of electricity, giving a car a range of only 50 miles or so).
•They are slow to charge (typical recharge times for a lead-acid pack range between four to 10 hours for full charge, depending on the battery technology and the charger).
•They have a short life (three to four years, perhaps 200 full charge/discharge cycles).
•They are expensive (perhaps $2,000 for the battery pack shown in the sample car).
In the next section we'll look at more problems with battery technology.
The EV Challenge
The EV Challenge (www.evchallenge.org) is an innovative educational program for middle and high school students that centers around building electric-powered cars:
•Middle school students build and compete model solar-powered cars.
•High school students convert full-sized gasoline-powered vehicles into electric vehicles. It's a complete conversion project, as described in the previous section of this article.
Students learn about electric technology throughout the year and then come together for a two-day finale. In addition to building the electric vehicle, high school students compete in autocross (speed and agility) and range events, vehicle design, oral presentations, troubleshooting, Web site design, and community involvement.
The EV Challenge gets a majority of its funding from corporate sponsors and government organizations, including Advanced Energy Corporation, CP&L/Progress Energy, Duke Power, Dominion Virginia Power, the NC Energy Office, the NC Department of Environment and Natural Resources, and the EPA.
Jon Mauney (whose car is featured at the beginning of this article) is on the steering committee for EV Challenge. According to Jon, CP&L started the EV Challenge program in North Carolina. The program then spread to South Carolina, Florida, Virginia, West Virginia, and Georgia, and is now spreading nationwide. Thousands of students have participated in the EV Challenge.
If you or your school would like more information on the EV Challenge program, please see www.evchallenge.org.