The main parts
A gasoline car burns fuel in an engine, which turns a shaft that is connected through a multi-speed transmission to the wheels. An electric car replaces most of that with a short chain of parts:
- a battery pack that stores energy
- a power inverter and control electronics
- one or more electric motors
- a charging system that takes in power from outside
Because there is no combustion, there is no fuel tank, exhaust pipe, spark plugs or oil changes for the engine. There are still tires, suspension, brakes, steering and a cooling system, so electric vehicles are not maintenance-free, only different.
The battery pack
Most current electric cars store energy in a large pack made of many individual lithium-ion cells, grouped into modules and typically placed low in the floor of the car. Keeping the heavy pack low generally helps lower the center of gravity. The chemistry inside the cells is described in the article on lithium-ion batteries, so here the pack is treated as a box that holds electrical energy.
The pack is managed by a battery management system, a set of electronics that monitors the voltage and temperature of cells, balances them, and limits charging and discharging to protect the battery. Packs usually have heating or cooling, using liquid or air, because cells work best within a moderate temperature range. This is one reason cold weather often reduces driving range: the battery is less efficient when cold, and energy is also spent heating the cabin.
From stored energy to a spinning wheel
A battery supplies direct current (DC), meaning the voltage flows one way. Many electric motors in cars run on alternating current (AC). The inverter converts DC from the battery into AC with a controlled frequency and strength. Changing the frequency and strength changes the motor’s speed and torque, so the inverter works like an electronic throttle when you press the accelerator.
Inside the motor, electric current flowing through coils of wire creates magnetic fields. These push and pull on a rotating part, the rotor, so that it keeps turning. The effect is the same as in a small fan motor, only larger and more carefully controlled. Common designs include induction motors and permanent-magnet motors. They differ in construction, cost and efficiency, and manufacturers choose between them for different reasons.
Electric motors deliver strong turning force from a standstill and work across a wide range of speeds. For that reason, many electric cars use a single fixed gear ratio instead of a multi-speed gearbox. Some have one motor driving the front or rear wheels, and others have a motor on each axle.
Electric cars also run a conventional low-voltage system for lights, screens, and other accessories, with the main pack’s voltage reduced by a converter.
Regenerative braking
A motor can also work in reverse. When you lift off the accelerator or press the brake, the control electronics can let the wheels turn the motor, which then acts as a generator. This produces electricity that flows back into the battery and, at the same time, creates resistance that slows the car.
This is regenerative braking. It recovers part of the energy that would otherwise be lost as heat in the brake pads. It does not recover everything, since there are losses at each stage, and it does not mean the battery can be recharged indefinitely by driving. It mainly helps in stop-and-go driving and when going downhill. Cars also keep friction brakes, which handle hard stops and low speeds, and because the motor does much of the everyday slowing, friction brakes often wear slowly. Some models offer a “one-pedal” mode, in which lifting off the accelerator produces strong regeneration.
Charging
Charging means sending electricity into the pack. The charger must supply the right voltage and current, and the car’s electronics control the process.
- Slower charging from a household or similar outlet uses AC supply, and an onboard charger in the car converts it to DC for the battery. Power is limited, so charging takes many hours for a large battery.
- Higher-power AC charging at a dedicated home or public unit is still handled by the onboard charger, but can be faster, within the car’s limits.
- DC fast charging uses a charger outside the car that supplies DC directly to the battery, which can be much quicker. Charging speed typically drops as the battery fills, and heat and the battery’s condition also limit it.
Connector types and charging standards differ by region and manufacturer, so it is worth checking which your car uses. Frequent fast charging and keeping a battery at very high or very low charge for long periods are often said to wear batteries faster, though advice varies by model, and the owner’s manual is the best guide.
Range and efficiency
Range depends on battery capacity and on how efficiently the car uses energy. Speed has a large effect, since air resistance grows quickly as a car goes faster. Temperature, tire pressure, hills, load and heating or cooling use also matter. Motors and drivetrains are generally efficient at turning electricity into motion compared with combustion engines, which lose a large share of fuel energy as heat. Total figures differ across models, so manufacturers’ stated ranges should be treated as estimates rather than guarantees.
What the car runs on
An electric car produces no exhaust at the tailpipe, but the overall environmental picture depends on how the electricity is produced, how the battery is made, and how it is eventually reused or recycled. A cleaner electricity supply improves the picture, which links the car to the wider energy transition. Comparisons between electric and gasoline vehicles depend on assumptions, so it is best to look for sources that explain theirs. Electric cars are also a common platform for self-driving cars research, since their drive systems are easily controlled by software, though the two technologies are separate.
Plug-in and hybrid cars
Not every car with a plug is fully electric. Hybrids pair a small battery and motor with a gasoline engine, and plug-in hybrids have a larger battery that can be charged from outside and used for shorter trips before the engine takes over. A fully battery-electric car, the subject of this article, has no combustion engine at all.
Key points
An electric car stores energy in a battery pack, converts it with an inverter and uses a motor to turn the wheels, often through a single gear. The motor can run backward during braking to return some energy to the battery. Charging, range and battery life all depend on how the pack is built, managed and used.