ELECTRIC CAR



CONTENTS

1. Why are going for ?

2. Different types of electricity production .

3. Advantages and disadvantages of the different methods.

4. Conclusion

5. (

300 volts DC). things that used to get their power from the engine: the water pump, 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.

| [pic] |

|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. See How the Power Grid Works for a discussion of 3-phase power. 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.

The Charging System

Any electric car that uses batteries needs a charging system to recharge the batteries. The charging system has two goals:

• To pump electricity into the batteries as quickly as the batteries will allow

• To monitor the batteries and avoid damaging them during the charging process

The most sophisticated charging systems monitor battery voltage, current flow and battery temperature to minimize charging time. The charger sends as much current as it can without raising battery temperature too much. Less sophisticated chargers might monitor voltage or amperage only and make certain assumptions about average battery characteristics. A charger like this might apply maximum current to the batteries up through 80 percent of their capacity, and then cut the current back to some preset level for the final 20 percent to avoid overheating the batteries.

|Charging Current |

|When lead-acid batteries are at a low state of charge, nearly all the charging current is absorbed by the chemical |

|reaction. Once the state of charge reaches a certain point, at about 80 percent of capacity, more and more energy goes into|

|heat and electrolysis of the water. The resulting bubbling of electrolyte is informally called "boiling." For the charging |

|system to minimize the boiling, the charging current must cut back for the last 20 percent of the charging process. |

Jon Mauney's electric car actually has two different charging systems. One system accepts 120-volt or 240-volt power from a normal electrical outlet. The other is the Magna-Charge inductive charging system popularized by the GM/Saturn EV-1 vehicle. Let's look at each of these systems separately.

Normal Household Power

The normal household charging system has the advantage of convenience -- anywhere you can find an outlet, you can recharge. The disadvantage is charging time.

A normal household 120-volt outlet typically has a 15-amp circuit breaker, meaning that the maximum amount of energy that the car can consume is approximately 1,500 watts, or 1.5 kilowatt-hours per hour. Since the battery pack in Jon's car normally needs 12 to 15 kilowatt-hours for a full recharge, it can take 10 to 12 hours to fully charge the vehicle using this technique.

By using a 240-volt circuit (such as the outlet for an electric dryer), the car might be able to receive 240 volts at 30 amps, or 6.6 kilowatt-hours per hour. This arrangement allows significantly faster charging, and can fully recharge the battery pack in four to five hours.

In Jon's car, the gas filler spout has been removed and replaced by a charging plug. Simply plugging into the wall with a heavy-duty extension cord starts the charging process.

| |

|[pic] |

|Close-up of the plug |

|[pic] |

|Photo courtesy Jon Mauney |

|Plug the car in anywhere to recharge. |

In this car, the charger is built into the controller. In most home-brew cars, the charger is a separate box located under the hood, or could even be a free-standing unit that is separate from the car.

The Magna-Charge System

The Magna-Charge system consists of two parts:

• A charging station mounted to the wall of the house

|[pic] |

|Photo courtesy Jon Mauney |

• A charging system in the trunk of the car

|[pic] |

The charging station is hard-wired to a 240-volt 40-amp circuit through the house's circuit panel.

The charging system sends electricity to the car using this inductive paddle:

|[pic] |

|Photo courtesy Jon Mauney |

The paddle fits into a slot hidden behind the license plate of the car.

|[pic] |

|Photo courtesy Jon Mauney |

The paddle acts as one half of a transformer. The other half is inside the car, positioned around the slot behind the license plate. When you insert the paddle, it forms a complete transformer with the slot, and power transfers to the car.

One advantage of the inductive system is that there are no exposed electrical contacts. You can touch the paddle or drop the paddle into a puddle of water and there is no hazard. The other advantage is the ability to pump a significant amount of current into the car very quickly because the charging station is hard-wired to a dedicated 240-volt circuit.

The competing high-power charge connector is generally referred to as the "Avcon plug" and it is used by Ford and others. It features copper-to-copper contacts instead of the inductive paddle, and has an elaborate mechanical interconnect that keeps the contacts covered until the connector is mated with the receptacle on the vehicle. Pairing this connector with GFCI protection makes it safe in any kind of weather.

Equalization

Jon Mauney points out the following:

An important feature of the charging process is "equalization." An EV has a string of batteries (somewhere between 10 and 25 modules, each containing three to six cells). The batteries are closely matched, but they are not identical. Therefore they have slight differences in capacity and internal resistance. All batteries in a string necessarily put out the same current (laws of electricity), but the weaker batteries have to "work harder" to produce the current, so they're at a slightly lower state of charge at the end of the drive. Therefore, the weaker batteries need more recharge to get back to full charge.

Since the batteries are in series, they also get exactly the same amount of recharge, leaving the weak battery even weaker (relatively) than it was before. Over time, this results in one battery going bad long before the rest of the pack. The weakest-link effect means that this battery determines the range of the vehicle, and the usability of the car drops off.

The common solution to the problem is "equalization charge." You gently overcharge the batteries to make sure that the weakest cells are brought up to full charge. The trick is to keep the batteries equalized without damaging the strongest batteries with overcharging. There are more complex solutions that scan the batteries, measure individual voltages, and send extra charging current through the weakest module.

Doing a Conversion

A majority of the electric cars on the road today are "home brew" conversion vehicles. People with an interest in electric cars convert existing gasoline-powered cars to electric in their backyards and garages. There are many Web sites that talk about the phenomenon and show you how to do it, where to get parts, etc.

A typical conversion uses a DC controller and a DC motor. The person doing the conversion decides what voltage the system will run at -- typically anything between 96 volts and 192 volts. The voltage decision controls how many batteries the car will need, and what sort of motor and controller the car will use. The most common motors and controllers used in home conversions come from the electric forklift industry.

Usually, the person doing the conversion has a "donor vehicle" that will act as the platform for the conversion. Almost always, the donor vehicle is a normal gasoline-powered car that gets converted to electric. Most donor vehicles have a manual transmission.

The person doing the conversion has a lot of choices when it comes to battery technology. The vast majority of home conversions use lead-acid batteries, and there are several different options:

• Marine deep-cycle lead-acid batteries (These are available everywhere, including Wal-mart.)

• Golf-cart batteries

• High-performance sealed batteries

The batteries can have a flooded, gelled or AGM (absorbed glass mat) electrolyte. Flooded batteries tend to have the lowest cost but also the lowest peak power.

Once the decisions about the motor, controller and batteries are made, the conversion can start. Here are the steps:

➢ Remove the engine, gas tank, exhaust system, clutch and perhaps the radiator from the donor vehicle. Some controllers have water-cooled transistors, while some are air-cooled.

➢ Attach an adapter plate to the transmission and mount the motor. The motor normally requires custom mounting brackets.

➢ Usually, the electric motor needs a reduction gear for maximum efficiency. The easiest way to create the gear reduction is to pin the existing manual transmission in first or second gear. It would save weight to create a custom reduction gear, but normally it is too expensive.

➢ Mount the controller.

➢ Find space for, and build brackets to safely hold, all the batteries. Install the batteries. Sealed batteries have the advantage that they can be turned on their sides and fitted into all sorts of nooks and crannies.

➢ Wire the batteries and motor to the controller with #00 gauge welding cable.

➢ If the car has power steering, wire up and mount an electric motor for the power steering pump.

➢ If the car has air conditioning, wire up and mount an electric motor for the A/C compressor.

➢ Install a small electric water heater for heat and plumb it into the existing heater core, or use a small ceramic electric space heater.

➢ If the car has power brakes, install a vacuum pump to operate the brake booster.

➢ Install a charging system.

➢ Install a DC-to-DC converter to power the accessory battery.

➢ Install some sort of volt meter to be able to detect state of charge in the battery pack. This volt meter replaces the gas gauge.

➢ Install potentiometers, hook them to the accelerator pedal and connect to the controller.

➢ Most home-brew electric cars using DC motors use the reverse gear built into the manual transmission. AC motors with advanced controllers simply run the motor in reverse and need a simple switch that sends a reverse signal to the controller. Depending on the conversion, you may need to install some sort of reverse switch and wire to the controller.

➢ Install a large relay (also known as a contactor) that can connect and disconnect the car's battery pack to and from the controller. This relay is how you turn the car "on" when you want to drive it. You need a relay that can carry hundreds of amps and that can break 96 to 300 volts DC without holding an arc.

➢ Rewire the ignition switch so that it can turn on all the new equipment, including the contactor.

Once everything is installed and tested, the new electric car is ready to go!

A typical conversion, if it is using all new parts, costs between $5,000 and $10,000 (not counting the cost of the donor vehicle or labor). The costs break down like this:

• Batteries - $1,000 to $2,000

• Motor - $1,000 to $2,000

• Controller - $1,000 to $2,000

• Adapter plate - $500 to $1,000

• Other (motors, wiring, switches, etc.) - $500 to $1,000

Summery: -- Electric vehicles are probably the simplest form of self propelled mechanical transportation. People have the impression that electric cars are pollution free and will eventually replace fossil fuel powered engines. Electric vehicles offer a unique driving experience .With their low center of gravity, most electric cars, offer superb handling as well as rapid initial acceleration. Electric motors offer almost continuous torque even at lower speeds. This allows a vehicle to do things that conventional fossil fuels vehicles can not do. For example, if you were to drive up to a street curb with a conventional gasoline powered car, stop and then try to climb the curb, you would have to rev up the motor and only then would you be able to drive over the curb. With an electric vehicle, you would be able to climb the curb with out any real effort. Today, most railroads around the world use diesel electric locomotives with the diesel engine generating the electricity to power the electric motors which actually turns the wheels. American military tanks use the same technique. Electric vehicles are also ideal for use in areas that have very high gasoline costs or where conventional FUEL is simply not available.

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