Chapter 19: DC Circuits
Applications

Electric Vehicles

We have recently been studying dc circuits, and many of these circuits have included an element that creates a difference in electronic potential between two points. In an actual circuit, this element may be an electronic device (called either a voltage source or a power supply) or it could be a battery.

In physics and engineering texts, a battery looks like this: . An "ideal" battery always provides the same voltage, regardless of the current it provides; a more accurate picture of a battery is an ideal battery in series with an internal resistor. Such a battery provides a lower voltage when it provides more current. In physics, we are interested in the most basic features of the world and the devices in it. Thus, we study the features which are common to all batteries, such as internal resistance. We also learn how to account for batteries in basic electrical circuits. To learn some battery basics, check out the technical information provided by AER Energy Resources, Inc.

The world of batteries is extraordinarily complex. People love the convenience of portable devices of all kinds. These devices all use energy, and so a portable energy source must be provided. Ideally, this energy source must be small, rugged, light, reusable, inexpensive, able to provide adequate voltage and current, and it must be able to store as much energy as possible. Of course, no one battery is ideal for all applications. Which of these features is most important depends on what type of device the battery is powering, and where it is used. For instance, NASA needs batteries which can operate at extremely low temperatures, whereas the army wants batteries to operate at high temperatures. In current technology, there are extreme pressures to design longer running batteries for laptop computers and cellular telephones.

This speed demon is the formula lightning electric racer developed by the Purdue School of Engineering and Technology at IUPUI.

The greatest challenge for battery technology is probably the electric car. Over the last 30 years (at least) there has been much concern over the health and environmental effects of air pollution. Also, since the oil crises of the 1970's, there has been concern about US dependence on imported oil. Private cars are a big contributer to both. Thus, there have been numerous attempts to address these problems by requiring cars to burn cleaner fuels, to burn less fuel per mile, or to produce fewer pollutants per gallon of fuel burned. The most extreme step is to require that cars stop burning fuels entirely--to run exclusively on electricity. Unfortunately, this has not proved to be a simple task, and some people doubt that the problems can be solved.

The most promising solution thus far seems to be hybrid electric vehicles. These vehicles contain both a gasoline burning engine and an electric motor. The two systems are used together to produce a car that produces less pollution and gets better mileage than a traditional gas powered car, but provides better performance and range than an all electric car. Lets look at two examples: the General Motors EV1 (an all electric car) and the Toyota Prius (a hybrid).

GM introduced the EV1 last year, the car is available through Saturn dealers, but is currently being sold only in Arizona and California. In addition to GM, there is plenty of other information about the EV1 on the web. The car costs about $35,000, and is a two seat subcompact. The top speed is only about 80 mph, but, the acceleration is pretty brisk, 0-60 in 9.0 seconds. The primary difficulty that most people have with the EV1 is its steep price and limited driving range (only about 80 miles).

Toyota started selling the Prius in Japan last December, and plans to introduce it (or something similar) in the US in the year 2000. The Prius sells for only $17,000 (although they are taking a loss until production increases) and produces 1/2 to 1/10th the pollutants of a similar sized all-gas car (depending on which pollutant you are asking about). In contrast to the EV1, it is a five seat sedan, about the size of a Corolla; furthermore, its estimated range on a single 13 gallon tank is an astounding 800 miles. The fuel efficiency of this vehicle is an interesting point in its own right. It is better in the city (about 66 MPG) than it is on the highway (as little as 50 MPG!).

How do these vehicles work? There are two basic possibilities: parallel and series. In parallel hybrids, the electric motor and the gasoline engine are both connected to the drive train, and a control system decides how much power to draw from each one. The electric motor is more efficient at low speeds, so it is in charge of acceleration. As the speed increases, the load is shifted to the gas engine which is more efficient at high speed. In a series configuration, the engine is used exclusively to charge the batteries, and the motor is used exclusively to prpel the car. In either case, the kinetic energy of the car is also used to charge the batteries during deceleration. This technique is called "regenerative braking."

More information: 1. 2. 3. 4.

Electric Vehicles

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