ELECTRIC CAR

INTRODUCTION:
Ironically, one of the hottest fields of research for alternative-fuel automobiles is not a new development. Electric automobiles, believed by many to offer the best hope for an emission-free automobile in the near future, have been around as long as their gasoline-powered counterparts.
The first automobiles were powered by steam engines, similar to those seen on steam locomotives. They relied on coals or a fire to heat water and create compressed steam, which was then used to push a cylinder and move the car. Steam was a cumbersome technology for automobiles, however. There was a widespread fear of boiler explosions (although these fears were, quite likely, unfounded). In addition, a lightweight steam engine ... required constant maintenance beyond the skill of most casual owners. The water necessary to run a steam engine also presented a problem; in remote locations where there was a small or nonexistent supply of soft water, water would have to be pumped in to service the cars. Perhaps the most basic factor working against the steam engine was that the gasoline was much more thermally efficient; that is, more of its energy was converted to useful work, rather than waste heat. Because these early vehicles were cumbersome and inconvenient, inventors quickly began to search for other methods of propulsion that would be more flexible.
It soon became evident that the future of the automobile lay in one of two directions: electric, or gasoline-powered. Both of these technologies offered a convenient, portable fuel source which could easily be converted to motion through the use of a simple motor or engine. Thus the race was on between the two technologies. However the electric powered vehicles have an upper hand over the gasoline powered automobiles as far as maintenance, efficiency and life span is concerned.

ELECTRIC VEHICLE (cars)
Electric Car, automobile propelled by one or more electric motors, drawing power from an onboard source of electricity. Electric cars are mechanically simpler and more durable than gasoline-powered cars. They produce less pollution than do gasoline-powered cars. Electric vehicles (EVs) are cars that run on electricity stored in batteries. EVs are often confuse;d with hybrid electric vehicles which combine an internal combustion engine with a battery. EVs are the only truly zero emission car available today because they have no tailpipe exhaust and no evaporative emissions from fuel systems. Manufacturers have developed a broad spectrum of EVs - from neighborhood electric cars which can be used for short trips around town to full function electric cars which can be used for longer trips and have the body of conventional cars. The availability and styles of these vehicles vary from year to year, but with battery technology getting more sophisticated, manufacturers will have the ability to design electric vehicles with extended range, faster charging and more power.
From the outside, it is very difficult to guess that a car is electric. In most cases, electric cars are created by converting a gasoline-powered car, and in that case it is impossible to tell. When you drive an electric car, often the only thing that clues you in to its true nature is the fact that it is nearly silent.


A typical electric car, this one has some particularly snazzy decals. This vehicle is owned by Jon Mauney.

HISTORY
Electric motive power started with a small railway operated by a miniature electric motor, built by Thomas Davenport in 1835. In 1838, a Scotsman named Robert Davidson built an electric locomotive that attained a speed of four miles an hour. In England a patent was granted in 1840 for the use of rails as conductors of electric current, and similar American patents were issued to Lilley and Colten in 1847.
Between 1832 and 1839 (the exact year is uncertain), Robert Anderson of Scotland invented the first crude electric carriage, powered by non-rechargable Primary cells.
By the 20th century, electric cars and rail transport were commonplace, with commercial electric automobiles having the majority of the market. Electrified trains were used for coal transport as the motors did not use precious oxygen in the mines. Switzerland's lack of natural fossil resources forced the rapid electrification of their rail network.
Electric vehicles were among the earliest automobiles, and before the preeminence of light, powerful internal combustion engines, electric automobiles held many vehicle land speed and distance records in the early 1900s. They were produced by Anthony Electric, Baker Electric, Detroit Electric, and others and at one point in history out-sold gasoline-powered vehicles.



Edison and an electric car, 1913 (courtesy of the National Museum of American History)
ELECTRIC CARS
An electric car is a car powered by an electric motor which is controlled by several components which make it function much like a standard gasoline powered car. The only difference is when you step on the accelerator the electronic "brain" tells the motor how fast to revolve. Instead of ann explosion making pistons turn and electric car uses clean electromagnetic forces created by electrical current. In most cases, electric cars are created by converting a gasoline-powered car. When you drive an electric car, often the only thing that clues you in to its true nature is the fact that it is nearly silent.
Everything else about the car is stock. When you get in to drive the car, you put the key in the ignition and turn it to the "on" position to turn the car on. You shift into "Drive" with the shifter, push on the accelerator pedal and go. It performs like a normal gasoline car. Here are some interesting statistics:
• The range of this car is about 50 miles (80 km).
• The 0-to-60 mph time is about 15 seconds.
• It takes about 12 kilowatt-hours of electricity to charge the car
after a 50-mile trip
• The batteries weigh about 1,100 pounds (500 kg).
• The batteries last three to four years.

MECHANISM
Mainly its motion is provided by electric motors. The motion may be provided either by wheels or propellors driven by rotary motors, or in the case of tracked vehicles, by linear motors. The electrical energy used to power the motors may be obtained from a direct connection to land-based generation plants, as is common in electric trains; from chemical energy stored on the vehicle in batteries or diesel fuel; from nuclear energy, on nuclear submarines and aircraft carriers; or more esoteric sources such as flywheels, wind and solar.

Under the hood, there are a lot of differences between gasoline and electric cars:
• The gasoline engine is replaced by an electric motor.
• The electric motor gets its power from a controller.
• The controller gets its power from rechargeable batteries.

The Controller
The heart of an electric car is the combination of:
• The electric motor
• The motor's controller
• The batteries
The controller takes power from the batteries and delivers it to the motor. The accelerator pedal hooks to a pair of potentiometers (variable resistors), and these potentiometers provide the signal that tells the controller how much power it is supposed to deliver. The controller can deliver zero power (when the car is stopped), full power (when the driver floors the accelerator pedal), or any power level in between.
The controller normally dominates the scene when you open the hood, as you can see here:

The 300-volt, 50-kilowatt controller for this electric car is the box marked "U.S. Electricar."
When you push on the gas pedal, a cable from the pedal connects to these two potentiometers:

The potentiometers hook to the gas pedal and send a signal to the controller.
The signal from the potentiometers tells the controller how much power to deliver to the electric car's motor. There are two potentiometers for safety's sake. The controller reads both potentiometers and makes sure that their signals are equal. If they are not, then the controller does not operate. This arrangement guards against a situation where a potentiometer fails in the full-on position.
DC CONTROLING



A simple DC controller connected to the batteries and the DC motor. If the driver floors the accelerator pedal, the controller delivers the full 96 volts from the batteries to the motor. If the driver take his/her foot off the accelerator, the controller delivers zero volts to the motor.

The very simplest DC controller would be a big on/off switch wired to the accelerator pedal. When you push the pedal, it would turn the switch on, and when you take your foot off the pedal, it would turn it off. As the driver, you would have to push and release the accelerator to pulse the motor on and off to maintain a given speed.
Obviously, that sort of on/off approach would work but it would be a pain to drive, so the controller does the pulsing for you. The controller reads the setting of the accelerator pedal from the potentiometers and regulates the power accordingly. Let's say that you have the accelerator pushed halfway down. The controller reads that setting from the potentiometer and rapidly switches the power to the motor on and off so that it is on half the time and off half the time. If you have the accelerator pedal 25 percent of the way down, the controller pulses the power so it is on 25 percent of the time and off 75 percent of the time.
Most controllers pulse the power more than 15,000 times per second, in order to keep the pulsation outside the range of human hearing. The pulsed current causes the motor housing to vibrate at that frequency, so by pulsing at more than 15,000 cycles per second, the controller and motor are silent to human ears.

AC CONTROLING



An AC controller hooks to an AC motor. Using six sets of power transistors, the controller takes in 300 volts DC and produces 240 volts AC, 3-phase. The controller additionally provides a charging system for the batteries, and a DC-to-DC converter to recharge the 12-volt accessory battery.

In an AC controller, the job is a little more complicated, but it is the same idea. The controller creates three pseudo-sine waves. It does this by taking the DC voltage from the batteries and pulsing it on and off. In an AC controller, there is the additional need to reverse the polarity of the voltage 60 times a second. Therefore, you actually need six sets of transistors in an AC controller, while you need only one set in a DC controller. In the AC controller, for each phase you need one set of transistors to pulse the voltage and another set to reverse the polarity. You replicate that three times for the three phases -- six total sets of transistors.
Most DC controllers used in electric cars come from the electric forklift industry. The Hughes AC controller seen in the photo above is the same sort of AC controller used in the GM/Saturn EV-1 electric vehicle. It can deliver a maximum of 50,000 watts to the motor.
The Motor
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.
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).
You can replace lead-acid batteries with NiMH batteries. The range of the car will double and the batteries will last 10 years (thousands of charge/discharge cycles), but the cost of the batteries today is 10 to 15 times greater than lead-acid. In other words, an NiMH battery pack will cost $20,000 to $30,000 (today) instead of $2,000. Prices for advanced batteries fall as they become mainstream, so over the next several years it is likely that NiMH and lithium-ion battery packs will become competitive with lead-acid battery prices. Electric cars will have significantly better range at that point.
When you look at the problems associated with batteries, you gain a different perspective on gasoline. Two gallons of gasoline, which weighs 15 pounds, costs $3.00 and takes 30 seconds to pour into the tank, is equivalent to 1,000 pounds of lead-acid batteries that cost $2,000 and take four hours to recharge.
The problems with battery technology explain why there is so much excitement around fuel cells today. Compared to batteries, fuel cells will be smaller, much lighter and instantly rechargeable. When powered by pure hydrogen, fuel cells have none of the environmental problems associated with gasoline. It is very likely that the car of the future will be an electric car that gets its electricity from a fuel cell. There is still a lot of research and development that will have to occur, however, before inexpensive, reliable fuel cells can power automobiles.
Accessory Battery
Just about any electric car has one other battery on board. This is the normal 12-volt lead-acid battery that every car has. The 12-volt battery provides power for accessories -- things like headlights, radios, fans, computers, air bags, wipers, power windows and instruments inside the car. Since all of these devices are readily available and standardized at 12 volts, it makes sense from an economic standpoint for an electric car to use them.
Therefore, an electric car has a normal 12-volt lead-acid battery to power all of the accessories. To keep the battery charged, an electric car needs a DC-to-DC converter. This converter takes in the DC power from the main battery array (at, for example, 300 volts DC) and converts it down to 12 volts to recharge the accessory battery. When the car is on, the accessories get their power from the DC-to-DC converter. When the car is off, they get their power from the 12-volt battery as in any gasoline-powered vehicle.
The DC-to-DC converter is normally a separate box under the hood, but sometimes this box is built into the controller.
Regenerative Braking
The electric motor applies resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.
Regenerative braking converts otherwise wasted energy from braking into electricity and stores it in the battery.
In regenerative braking, the electric motor is reversed so that, instead of using electricity to turn the wheels, the rotating wheels turn the motor and create electricity. Using energy from the wheels to turn the motor slows the vehicle down.
If additional stopping power is needed, conventional friction brakes (e.g., disc brakes) are also applied automatically.
ADVANTAGES
1. no engine.
2. no gas/petrol tank.
3. no emission.
4. no noise.
5. no apparent pollution.
DISADVANTAGE
1. high price.
2. efficiency of battery is less.

CONCLUSION
The future was unclear because of the low range and small lifespan of the batteries. But there are several developments which could bring back electric vehicles outside of their current field of application -- namely operational yards and indoor operation. The first improvement[1] was to decouple the electric motor from the battery through electronic control while employing ultra-capacitors to buffer large but short power demands and recuperable braking energy. The development of new cell types compared with intelligent cell management improved both weak points mentioned above. The cell management is not only able to monitor the health of the cells but by having a redundant cell configuration (one cell more than needed) and a sophisticated switched wiring it is possible to condition one cell after the other while the rest are on duty. Perhaps the most important point is that a monovalent operation (electric only) is no longer considered dogma. The use of fuel cells instead of internal combustion engines can create propulsion systems that are nearly emissions-free (regarding local emissions).


REFERENCES

1. http://www.wickipedia.com/
2. http://www.howstuffworks.com/
3. http://www.google.com/
4. http://www.answers.com/
5. http://www.electriccars.com/