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Electric vehicles are more prevalent now than ever before, as sales continue to increase. But how do they work? In this guide, we explain what goes on under the hood—and under the seats—of an all-electric car.
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The Electric Powertrain
EVs can’t go without certain parts—the giant battery pack and the motor, to start. The battery, referred to as the traction battery pack, isn’t like a gas-powered car’s 12-volt lead-acid starting, lighting, and ignition (SLI) battery. The traction battery is much larger, requiring EV manufacturers to hide it beneath the seats. SLI batteries deliver short-term electricity to a gas vehicle’s starter motor, igniting the spark plugs and thus the engine. In contrast, traction batteries provide steady electrical currents for several hours.
Most traction battery packs are made up of several modules, each of which contains hundreds of individual cells. Each cell contains an anode (a negative electrode), which passes ions through the cell’s liquid electrolyte to a cathode (a positive electrode). The electrons produced by this process travel through an external circuit, powering whatever device the pack is connected with. When the traction battery pack is plugged into an external charging source (like an EV charger), the reverse occurs, with the cathode sending electrons back to the anode.
Lithium-ion batteries—the most common battery in EVs—can only accept power from a direct current (DC). But the most reliable EV motors can only get power from an alternating current (AC). This means today’s EVs require an inverter, which turns the battery pack’s DC into an AC. The inverter does this by running the DC through the primary coils in its transformer. An electronic switch powered by a semiconductor transistor array flips the DC’s flow direction back and forth, creating an AC in the transformer’s secondary coils. The inverter then sends the AC toward the vehicle’s electric traction motor. (The inverter has another important job, too, but we’ll get to that momentarily.)
When the AC reaches the motor, its electrons create a magnetic field. Because the current is alternating, the magnetic field’s north and south poles swap back and forth, creating a rotation that stimulates a free-floating rotor in the motor’s stator. The rotor spins, moving an axle that causes the vehicle’s wheels to turn. The speed at which the wheels turn is controlled by the inverter, which is responsible for managing the electrical current’s frequency. The higher the frequency, the faster the rotor turns, resulting in a faster wheel rotation.
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Peripheral Components
So what about all the other stuff in an EV? Today’s electric cars mean little without their infotainment interfaces, climate control systems, and other creature comforts, which also need power. Rather than getting their electricity from a little SLI battery (as in a gas vehicle), these systems take power from the aforementioned electric powertrain. They don’t do much to reduce an EV’s range, although the heat and AC can have a slightly larger effect.
Range is typically referred to in terms of distance per charge. If an EV has a 300-mile range, a fully-charged traction battery pack can keep the vehicle running for up to 300 miles before running out of power. A few things can affect an EV’s range, from hauling heavy material to driving in cold weather. This doesn’t mean drivers living in cold climates can’t use an EV for work or leisure; it just means they might have to pay closer attention to their routes and nearest charger locations.
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Charging
Speaking of chargers, EVs can’t do much without them. Some are hardwired into the electrical grid, while others are plugged in via standard household outlet or 240-volt circuit. (Your electric stove or clothes dryer probably uses the latter.) We’ve already discussed the way electrons flow through the battery cells’ cathodes and into the anodes when an EV is charging, but even that process is variable, becoming slower or faster based on the type of charger being used. This is because different chargers are capable of different energy outputs.
Level 1 chargers, which plug into your typical 120-volt household outlet, offer an output of roughly 1-2 kilowatts (kW). This means the average EV battery pack will take 30 to 50 hours to reach 80% capacity for today’s vehicles—too slow for most purposes.
Level 2 chargers, which can be hardwired or plugged into a 240-volt circuit, offer a far more impressive output of 7 to 19 kW. This will bring the average EV battery up to 80% in 4 to 10 hours, making it the ideal charger for shopping centers and residential garages.
Level 3 chargers, known as DC fast chargers—like Tesla’s Supercharger—bring the average EV battery to 80% capacity in less than an hour, thanks to their 50 to 350 kW output.
Tesla Superchargers require a proprietary connector (NACS), but the company has pushed to make this the new standard. Starting in 2024, Ford, GM, Mercedes, Rivian, and Volvo vehicles will work with these chargers via an adapter for their existing CCS ports. These same brands pledge to build the connectors directly into their vehicles beginning in 2025.
Beyond gaining a deeper understanding of a rapidly expanding market, learning how an EV works can help you determine whether you might someday want one. If you’re still on the fence, we recommend looking at electric cars’ impact on the environment compared with gas-powered cars.