Electric vehicles have their own terminology – some familiar, others technical – that can seem mysterious and confusing to the uninitiated. Knowing what these terms mean is essential to deciding not only if an EV is right for you, but also which EV is best for you. For example, do you care how quickly your car accepts gasoline from the pump? No, but you will need to know how fast your car and your home can replenish a battery to take advantage of home charging, and there is no standard answer. But we can get you closer through an understanding of charging-related terms, and more.
Alternating Current (AC)
The form electricity takes in the grid and in homes and other structures
With alternating current, electrons regularly change direction. The relevance of AC in the EV world is that all batteries require direct current (DC), in which electrons always flow in the same direction. So, whenever a vehicle is charged, AC must be converted, or rectified, into DC.
In Level 1 and Level 2 charging, a hidden component in every EV called the onboard charger module handles this task, as well as controlling the charging rate. In the case of public DC fast charging, the charger is external and supplies DC directly to the car’s battery, bypassing its onboard charger module, which is a bottleneck for current flow. The DC fast charger starts with nearly twice the household voltage and rectifies AC externally using components too large for a car to accommodate. These are the two reasons why DC charging can be much faster than Level 2.
Alternating current gets its name because the current changes direction, which happens 60 times per second in the U.S. It’s hard to grasp what that means, and it’s even more confusing when you dig deeper and learn that when the current reverses, technically, it goes from positive to negative in the same conductor. But AC has advantages over DC, such as minimal losses when transmitted over long distances, and the fact that transformers can be used to increase or decrease its voltage. Ironically, most electric cars use AC drive motors, so yes, the DC from the battery must be converted back into AC, a process called inversion, to propel the vehicle. In fact, hybrids typically use AC motors, meaning the current is literally constantly being converted from AC to DC or vice versa. Whenever these conversions occur, whether inside the car or outside, energy losses are associated.
Conventional gasoline and diesel vehicles use belt-driven alternators, which are AC generators, even though all electrical demands are DC.
Alternator
A type of generator that produces alternating current
In all modern conventional cars, the gasoline or diesel engine drives an alternator via a belt to generate the electricity that keeps the starting battery charged and powers the lights, electronics, and other electrical components on board. Nowadays, literally all these devices require DC, which makes a type of generator that produces only alternating current seem like an odd choice, but alternators are the generator of choice because they are smaller, lighter, and more durable, mechanically, than DC generators – three of the criteria that most interest automakers. This has been the case since the 1960s, when solid-state rectification (converting AC to DC) became viable. Alternators incorporate such rectifiers and voltage regulators to ensure the proper DC voltage.
Amps
Abbreviation for amperes, a measure of electrical current that EV owners are most likely to encounter when setting up Level 2 home charging.
Level 2 means 240 volts, but the amount of energy delivered to the car also depends on current flow, which varies significantly among Level 2 chargers. To use the classic plumbing analogy for electricity flowing in a wire, voltage represents the pressure forcing water through a pipe, and current is the water flow determined mainly by the pipe’s diameter. To get more water out of the end of the pipe, you can either increase the pressure or the pipe diameter. It’s the same with electricity: increase the voltage or the current (amperage) to get more power (measured in watts) at the other end of the wire. Just like the pipe, a larger diameter wire has less resistance and allows for greater current flow.
Amperes are the unit for the electrical service a home can distribute from the utility – like 50, 100, or 200 amps – and the current a given circuit or a Level 2 charger can pass.
Battery Pack
The complete energy storage component in an electric or hybrid vehicle, including the individual battery cells as well as supporting electronics and, typically, thermal management provisions.
The cells in a pack, regardless of type, are usually grouped into modules, which add structure and simplify replacing faulty cells. Packs include a battery management system that tracks the pack’s state of charge and monitors cell voltages and temperatures. Packs contain their own fuse and a means of manual disconnection from the rest of the vehicle for maintenance. Contactors (heavy-duty relay switches) are typically present, especially in pure battery-electric systems, to isolate the battery from the vehicle if it fails an onboard safety test or if a collision is detected.
Nissan Leaf 2011 Battery Pack | Manufacturer Image
Battery electric vehicles use circulating liquid to manage battery temperature, except for the Nissan Leaf (pack shown), which has no active thermal management. In most of these packs, there are channels through which coolant (usually a mix of water and conventional antifreeze) flows and then exits the battery to be conditioned either in a simple radiator or in a heat exchanger connected to an air conditioning or heat pump circuit.
Battery Cell
The smallest component of a battery, hundreds of which may be needed to achieve the voltages necessary to power a hybrid or electric car.
Like all other individual battery cells, these operate at only a few volts each. (What we call a battery with a higher voltage, like a 12-volt car battery, is itself a collection of separate cells in a case – in this example, six cells.) Lithium-ion battery cells come in three basic types, namely three shapes: cylindrical, prismatic, and pouch. The cylindrical batteries that power some EVs look so much like something you might put in a flashlight that one might think they are unsophisticated. Detractors have said as much about their packaging efficiency because their shape leaves space between them, but Tesla seems to have done very well for most of its history, even though the brand is now interested in prismatic cells, which are shaped like a deck of cards or a candy bar. The style of choice among most other EV manufacturers has been the pouch, which resembles a nearly empty Ziploc mylar sandwich bag. Unlike the other two styles, the floppy pouch relies on a battery module for its structure.
Chevrolet Volt Battery Pouch Cell | Manufacturer Image
Battery Module
A structural subset of an electric vehicle’s battery pack in which the battery cells are divided and contained for monitoring and, if necessary, replacement
Since a battery cell’s voltage is on the order of a few volts, dozens or even hundreds of them are used in EVs, grouped into enclosures that provide structure (particularly important for pouch cells) and simplify wiring. Each module typically has its own voltage and temperature sensor and has only two terminals, regardless of the number of cells wired together, which depends on the manufacturer’s design. Typically, modules include insulated channels through which coolant flows to manage the thermal state of the battery pack.
Combined Charging System (CCS)
A nearly universal (except for Tesla) EV charging connector on the U.S. market that combines the J1772 AC connector with two conductors for DC fast charging into a single composite port.
While early Japanese-origin electric cars relied on a separate connector called CHAdeMO for DC fast charging, most new EVs with this capability (except for Tesla, which has its own connector) provide this composite CCS port. When searching for public charging options online or via an app, owners of these cars must select J1772 for Level 2 charging and CCS for DC fast charging.
Combined Charging System Gun (left) and Car Port |
Direct Current (DC)
The form electricity takes in batteries and in most electronic circuits
With direct current, electrons flow in a single direction. The main relevance in the EV world is that electricity is transmitted in the power grid as alternating current (AC). So, whenever the car’s battery is charged, AC must be converted or rectified into DC. With Level 1 and Level 2 charging, the car itself accomplishes this via an invisible component called the onboard charger module. DC fast chargers start with nearly twice the household voltage and rectify AC externally using bulky components often hidden away from the charging area before supplying DC directly to the car’s battery, bypassing its integrated charger module, which is a bottleneck for current flow.
Although some EVs use DC drive motors, most use AC motors, meaning the vehicle must convert the battery’s DC into AC to accelerate – and vice versa during regenerative braking. Rectification and inversion, which is the name for DC-to-AC conversion, result in inefficiencies, but automakers choosing AC motors are thinking about the vehicle’s overall performance and efficiency, not a single component or process. For what it’s worth, even a conventional vehicle relies on AC through the use of an alternator, which is a generator that produces AC, even though DC reigns throughout the vehicle.
DC Fast Charging
A type of public charging that can charge compatible vehicles several times faster than the fastest Level 2 AC charger by supplying higher DC voltage directly to the battery. Tesla Superchargers are DC fast chargers.
Current EVs are better suited for DC fast charging when time is of the essence (e.g., on a long trip or when range is low). The term “fast” is in the name, but EV beginners won’t find DC fast charging comparable to a gasoline fill-up, which can provide hundreds of miles of range in minutes. Automakers generally claim DC fast charging involves 30-minute sessions, but that rarely represents a full charge. While more and more automakers include free DC fast charging with the purchase of a new EV, almost all acknowledge that frequent fast charging will compromise the vehicle’s battery life. When there is a cost, fast charging is more expensive than public Level 2 charging, usually enough to negate the financial benefits of electric driving with home charging.
Electrify America Charging Station | Manufacturer Image
DC fast chargers and the three-phase AC they require make them extremely expensive for home installation. The power they provide ranges from 24 to 350 kW, but there is no guarantee the EV, regardless of its own acceptance specification, will charge at that rate.
Destination Charging
A new name for public Level 2 charging where EVs can be parked long enough to add appreciable miles
Popularized by Tesla, the term destination charging aims to distinguish slower away-from-home charging from DC fast charging (or Supercharging, in Tesla parlance).
Drag Coefficient (Cd)
A measure of a vehicle’s resistance to the air it passes through
The sleeker shape of current vehicles reflects an aerodynamic movement that started several decades ago, partly to improve fuel efficiency. Drag, like a stuck parking brake or any other form of resistance, opposes the effort of the engine or drive motor. The higher a vehicle’s drag coefficient, the harder its engine works and the more fuel it consumes, whether gasoline, diesel, or electricity.
A vehicle’s drag coefficient is influenced not only by its size and shape but also by the surface area of its underside and how high it sits off the ground. Vehicles that hug the ground tend to be more aerodynamic, which is why modern vehicles with active suspensions are often designed to automatically lower at highway speeds. There’s no doubt that the most efficient vehicles on the market – typically hybrids and electrics – are hatchbacks, because the high rear end is inherently more aerodynamic than a traditional sedan or coupe with a trunk that drops abruptly from the roofline. Vehicle designers work in wind tunnels to try to gain hundredths of a point on future models. After going as far as possible with general shapes, engineers have turned their attention to airflow around the wheels, in and above engine compartments with active grille shutters and flush exterior door handles, which increasingly retract flush with the body sides. Side mirrors are a long-standing target that would be replaced by cameras if not for federal and state regulations requiring named mirrors.
EVSE
Electric Vehicle Service Equipment (or Supply Equipment)
An EVSE is what we commonly call an electric car charger, whether it’s the provided maintenance charging cord or a more robust Level 2 unit you can install at home or find at a “destination” public charging station. The reason for this different name is that, in electronics, the name charger is technically reserved for the component that handles battery charging and, if necessary, converts AC to DC. The EVSE does neither. Every car is equipped with an onboard charger, which you can’t see, that fulfills these roles. The EVSE is primarily a safety device that protects you and your vehicle from damage, incorporating a bit more than a ground-fault circuit interrupter, switches, and circuits that communicate how much power it can supply to an EV.
Whether it’s a J1772 or Tesla connector, 240 volts is a lot to hold in your hand, especially if you’re outside in the rain. The EVSE will not provide high voltage to the cable until the connector is plugged into the EV. Once inserted, the car can detect the EVSE’s pilot signal, which indicates how much power it can supply. Charging can then begin, and the EVSE triggers a heavy-duty switch, called a contactor, that powers the cable. You can usually hear this contactor click. Similarly, if you remove a connector from an EV, as soon as you press the unlock button, the car and EVSE stop charging, so there is no danger.
Frunk
A contraction of “front” and “trunk” representing the front trunk that the elimination of a front-mounted internal combustion engine often makes possible in electric vehicles.
Like the name itself, frunks tend to amuse and satisfy people, and they can add versatility to a vehicle, but they aren’t always an advantage. We remind buyers not to lose sight of the vehicle’s overall cargo capacity. For example, the Volkswagen ID.4, which has no frunk, offers more cubic feet of storage volume behind the rear seat than its competitor, the Ford Mustang Mach-E, when its frunk and rear cargo volumes are combined.
Inverter
An electronic component that converts direct current to alternating current
Inverters are crucial components in electric cars, as well as most hybrids, because the vast majority of electric motors used in both types of vehicles are AC while batteries are always DC, making conversion necessary via a traction inverter, so named because its sole task is to create AC to power an AC traction motor. The term inverter has also proliferated due to Ford’s use of this technology in its Pro Power Onboard option that powers 120- and 240-volt outlets in the beds of 2021 F-150 hybrids (and, subsequently, F-150 Lightning EVs). This system can supply AC power from the hybrid battery alone, even if a low state of charge will cause the hybrid truck’s engine to start. Pro Power Onboard recalls so-called inverter generators, backup generators that similarly generate AC, rectify it to DC, and then convert it back to AC. That seems ridiculous, but it’s this redundant conversion that allows inverter generators to run their engines at variable speeds depending on load – a more efficient and quieter approach – leaving AC production to the electronics. Conversely, conventional generators are actually alternators that must run at a constant speed (full speed and maximum power, essentially) just to maintain a constant 60-hertz AC cycle.
J1772
The international SAE standard governing EV charging, but also the name of the type of charging connector on most non-Tesla EVs and chargers in the U.S.
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