How an electric car works: the components explained simply

An electric car has far fewer moving parts than a petrol one, but that does not make it simple. Energy passes through a few components working together, and if one of them has a problem the car usually shows a fault and limits power. Here they are, one at a time.

The traction battery

This is the car’s “fuel tank”: a pack of lithium-ion cells grouped into modules, usually working at 350–400 volts. Some newer models, such as the Hyundai Ioniq 5, Kia EV6 or Porsche Taycan, use an 800-volt architecture that allows fast charging at higher power.

The battery has its own “brain”, the battery management system (BMS). It monitors the voltage of each cell group, the temperature and the current, balances the cells and stops charging or discharging if anything goes out of range. Battery condition is measured, not guessed: a battery test shows exactly how the cells are doing.

The inverter

The battery supplies direct current, but the traction motor runs on three-phase alternating current. The inverter converts it and, by the way it does so, controls the motor’s speed and torque. Under braking the process reverses: the inverter sends the energy produced by the motor back into the battery. It is a power component that gets very hot, which is why it is liquid-cooled. When problems show up here, inverter repair comes into play.

The electric motor and reduction gear

Most electric cars use permanent-magnet synchronous motors; some, like the early Tesla Model S, used induction motors. The motor delivers peak torque almost from zero, which is why the car pulls away so briskly.

Instead of a conventional gearbox, most EVs have a single-speed reduction gear. The motor spins fast enough to cover the whole speed range without changing gear.

The on-board charger and DC-DC converter

• The on-board charger (OBC) turns alternating current from a socket or wallbox into direct current for the battery. Its power, for example 7.4 or 11 kW, sets how fast you charge on AC.
• With DC fast charging, the station bypasses the on-board charger and feeds the battery directly.
• The DC-DC converter steps down the main battery’s voltage to charge the 12-volt battery and power the lights, screens and control units. It takes the place of the alternator.

If the car no longer charges at home but works at a fast charger, the on-board charger is often to blame. More on DC-DC converters and on-board chargers.

The cooling system

The battery works best in a narrow temperature range, roughly the one you find comfortable yourself. That is why most EVs have liquid cooling circuits for the battery, inverter and motor, and many also have a heat pump. A neglected cooling circuit shortens battery life; see hybrid battery cooling.

Regenerative braking

When you lift off the accelerator or brake gently, the motor becomes a generator and charges the battery. You recover some of the energy and use the brakes far less. We cover it in detail in the article on regenerative braking.

What about hybrids?

A hybrid has the same electric components, only smaller, plus a combustion engine. The differences between hybrid, plug-in and electric are in our guide to the types of hybrid and electric cars.