Electric car technologies
Electric Car technologies will rapidly improve over the next decade because manufacturers are desperately researching and trying to improve current technology in order to get ahead in this emerging market. It will be exciting to see where electric car technology goes from here.Electric cars and how they work – Electric car technology An electric car utilizes electric motors (instead of an internal combustion engine) to drive the wheels and motor controllers which supply electrical power to the motors. Current electric car technology uses rechargeable battery packs carried on board the vehicle as a source of electrical power for the motors. Additional small electric motors are used to power accessories in the car such as the water pump, power steering pump and air conditioner (in a traditional car the engine powers these). An onboard charger allows the battery pack to be charged when depleted, usually from a standard household outlet. Most other parts of an electric car are similar to a traditional internal combustion engine car.
Motor Controllers An important part of electric car technology is the motor controller which takes power from the batteries and delivers it to the electric motor. The accelerator pedal is connected to 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 takes DC from the battery pack and converts it into AC to send to the motor. It does this using very large transistors that rapidly turn the batteries voltage on and off to create a sine wave.
Electric motors and drivetrain Electric cars utilize a direct motor-to-wheel configuration which is a very energy efficient system involving few moving parts. Various electric car technologies exist for motor and drivetrain set up. Sometimes one electric motor will drive either the front wheels or rear wheels, sometimes more than one electric motor is used to drive front wheels or rear. Having four motors connected directly one to each wheel allows for each of the wheels to be used for both propulsions and as braking systems, thereby increasing traction in both cases. In some electric car technologies, the motor can be housed directly in the wheel, which lowers the vehicle’s center of gravity and reduces the number of moving parts even further. When not fitted with an axle, differential, or transmission, an electric car has less drivetrain rotational inertia. Gearless electric car technology eliminates the need for gear shifting, resulting in very smooth acceleration and braking. Electric motors provide relatively constant torque even at very low motor speeds. This is because the torque of an electric motor is a function of current, not its rotational speed. The result is that an electric car usually has very good acceleration performance.
Batteries Rechargeable batteries used in electric cars include lead-acid (“flooded” and VRLA), NiCd, nickel metal hydride, lithium ion, Li-ion polymer, and, less commonly, zinc-air and molten salt batteries. Individual batteries are usually arranged into large battery packs to give the required energy capacity. The amount of electricity stored in battery packs is measured in ampere hours or in coulombs, with the total energy often measured in watt hours. Historically, electric cars have had issues with high battery costs, limited travel distance between battery recharging, charging time, and battery lifespan. Recent electric car technology advancements have addressed many of these battery problems resulting in many electric vehicles recently being prototyped. Since the late 1990s, advances in battery technologies have been driven by the demand for more powerful laptop computers and mobile phones. The electric car marketplace is now reaping the benefits of these advances. Batteries are usually the most expensive component in electric car technology but increasing returns of scale may serve to lower their cost when electric cars are manufactured on the scale of modern internal combustion vehicles. Electric car batteries eventually wear out and must be replaced. The rate at which they expire depends on a number of factors, but primarily on the number of cycles (discharges and recharges) performed. The depth of discharge (DOD) can also affect battery life. This is the recommended energy level that a battery should not fall below. For example, deep cycle lead-acid batteries generally should not be discharged to below 20% of their total capacity. More modern battery chemistries can survive deeper cycles however. In real world use, some fleet Toyota RAV4 electric cars, using NiMH batteries, have exceeded 100,000 miles (160,000 km) with little degradation in their daily range. Battery replacement costs of electric cars may be partially or fully offset by the lack of regular maintenance such as oil and filter changes, clutch replacement etc, which are required for traditional cars.
The future of battery electric cars depends primarily upon improvements to the cost and availability of batteries with high energy densities, power density, and long life. All other aspects of electric car technology such as motors, motor controllers, and chargers are fairly mature. The range of an electric car depends on the number and type of batteries used, and the performance demands of the driver. The weight and type of vehicle are also obviously important. Lead-acid batteries are the most available and inexpensive batteries but have an energy density of only 30-40 Wh/kg and generally only have a range of 30 to 80 km (20 to 50 miles). NiMH batteries have a higher energy density, up to 80 Wh/kg, and may deliver up to 200 km (120 mi) of range. Lithium-ion batteries can store 160 Wh/kg and can provide electric cars with around 160–320 km (100-200 miles) of range per charge. Lithium ion polymer batteries have the highest energy density, up to 200 Wh/kg. Finding the economic balance of range against performance, battery capacity versus weight, and battery technology versus cost challenges every electric car manufacturer.The latest electric car technology can employ supercapacitors in combination with batteries, to store rapidly available energy for the motors, in order to keep batteries within safe resistive heating limits and extend battery life. The “Ultrabattery” combines a supercapacitor and a battery in a single unit, creating an electric car battery that lasts longer, costs less and is more powerful than current technologies used in electric cars.Electric cars and how they work – Charging Batteries in electric cars must be periodically recharged. They are most commonly charged from standard electrical outlets at home or using a street or shop recharging point. Charging time is limited primarily by the capacity of the grid connection. A normal household outlet is between 1.5 kW (in the US, Canada, Japan, and other countries with 110 volt supply) to 3 kW (in countries with 240 V supply). The main connection to a house might be able to sustain 10 kW, and special wiring can be installed to use this. At this higher power level charging may only require a couple of hours. The power delivery rate at a petrol station may be as high as 5,000 kW so recharging points at such places could provide rapid recharge times. Its important to note that most batteries do not accept charge at greater than their charge rate (“1C”), because high charge rates have an adverse effect on the discharge capacities of batteries. The development of fast charging systems is one area that electric car technology is currently focusing on. Altairnano’s NanoSafe batteries can be recharged in several minutes, versus hours required for other rechargeable batteries. A NanoSafe cell can be charged to around 95% charge capacity in approximately 10 minutes.Most people, however, do not always require fast recharging because they have enough time during the work day or overnight to recharge. As the charging does not require attention it takes only a few seconds for an owner to plug in and unplug their vehicle much like a cell phone. Many electric car drivers prefer recharging at home, accessing cheaper electricity and avoiding the inconvenience of visiting a fuel station. Some workplaces provide special parking bays for electric cars with chargers provided – sometimes powered by solar panels.Two electric car technologies exist for connecting the charging power to the car (electric coupling).
- conductive coupling is known as a direct electrical connection. This might be as simple as a mains lead into a weatherproof socket through special high capacity cables with connectors to protect the user from high voltages.
- inductive charging A special ‘paddle’ is inserted into a slot on the electric car. The paddle is one winding of a transformer, while the other is built into the electric car. When the paddle is inserted it completes a magnetic circuit which provides power to the battery pack. In one inductive charging system, one winding is attached to the underside of the car, and the other stays on the floor of the garage. The major advantage of the inductive electric car technology is that there is no possibility of electric shock as there are no exposed conductors, although interlocks, special connectors and ground fault detectors can make conductive coupling nearly as safe. The inductive charging technology can also reduce vehicle weight, by moving more charging components off board.However, there is no reason that conductive coupling equipment cannot take advantage of the same concept. Conductive coupling equipment is lower in cost and much more efficient due to a vastly lower component count.
Regenerative braking Using regenerative braking, an electric car technology present on many electric cars, a significant portion of the energy expended during acceleration may be recovered during braking and stored in the batteries to be reused, thereby increasing the efficiency of the electric car. Regenerative braking utilizes the fact that an electric motor can also act as a generator during braking and its electrical output supplied to an electrical load. It is the transfer of energy to the load which provides the braking effect. All electric car technologies use traditional friction-based braking in addition to mechanical regenerative braking for a number of reasons. Regenerative braking alone is not as effective at lower speeds, a back-up is required in the event of failure of the regenerative brake, regenerative braking only acts on driven wheels so if the electric car is two wheel drive traditional brakes are necessary on the other two wheels, no regenerative braking occurs if the battery is fully charged, and finally regenerative braking alone is not enough for emergency braking.
Cabin heating and cooling Electric car technologies vary for cabin heating and cooling. While heating can be simply provided with an electric resistance heater, higher efficiency and integral cooling can be obtained with a reversible heat pump (currently implemented in the hybrid Toyota Prius). Positive Temperature Constant junction cooling is also attractive for its simplicity – this kind of system is used for example in the Tesla Roadster. Some electric cars, for example, the Citroën Berlingo Electrique, use an auxiliary heating system such as petrol-fueled units.