The advice for ice cream flavors is just as relevant for vehicle powertrains: You don’t have to hate chocolate to love vanilla. At least for the foreseeable future, there’s no point at which internal combustion engines will completely go away. Despite having been around just as long as gasoline cars, battery electric vehicles (BEVs) are still in their infancy, and there’s a lot to know about what makes them work.
The Key Components
Every electric vehicle has three essential components that make it work: The electric motor, the battery, and the battery controller.
1. The Motor
You might think that an EV's motor is just a larger version of a slot car's, but electric motors have come a long way. Early EV motors were brushed direct current (DC) motors, meaning they had a commutator—a metal cylinder with multiple metal contact segments mounted on the motor’s armature. As the commutator spun, it made contact with “brushes” made of soft carbon material that supplied current to a rotor.
Most manufacturers these days have started building EVs that use brushless direct current (DC) motors. These motors use an electronic servo system that eliminates the mechanical contact required in brushed DC motors. Brushless motors offer significant advantages, especially for EV builders: Most notably, they have a higher power-to-weight ratio than brushed motors. Brushed motors also sustain wear thanks to friction, and they create dust when they do. Eventually, the brushes need to be replaced.
The third type of electric motor in use by EV manufacturers is the induction motor. Three-phase alternating current (AC) induction motors are used more and more in EV production today, because they’re highly efficient, they offer good speed regulation, and they do away with the troublesome commutators. In an AC induction motor, a three-phase AC power supply is connected to the stator winding, creating a revolving magnetic field. Because the magnetic field spins, the rotor can stay fixed. The disadvantage of an AC induction motor is that the magnetic field itself consumes power. In a permanent magnet motor like a brushless DC motor, the rare earth magnets inside always generate an electric field, regardless of whether or not the car is on.
For small cars designed primarily for efficiency, the brushless DC motor has been the way to go. For high-performance cars that require a ton of power, the induction motor is king.
2. The Batteries
These power storage units are completely different from your typical lead-acid car battery. All electric vehicles today use lithium-ion batteries as storage tanks for electrical energy. It’s amazing to realize that Li-ion batteries have only been around since about 1985. In that time, they’ve revolutionized everything. EV batteries use a lithium compound as the positive electrode, and they typically use graphite as the negative electrode. Lithium ions move from the negative electrode through an electrolyte over to the positive electrode during discharge, and then travel back again when charging.
These rechargeable batteries have massive advantages as energy sources. They have a high energy density, they are resistant to self-discharging if left for a period of time, and they have no “memory effect.” Early rechargeable nickel-cadmium batteries would hold less charge if they weren’t completely discharged before charging again. If, for example, one of these batteries was connected to a charger when it still had 50% of a full charge left, the battery would eventually only be able to charge to 50% capacity. With LI-ion batteries, this is no longer an issue, a critical convenience for EV charging. Though visiting a charging point may not be as easy everywhere as topping up the fuel tank at a gas station, EV owners don't have to set aside hours and hours of charging time or leave their cars overnight at public charging stations to preserve the lives of their batteries.
EVs use multiple batteries arranged in battery packs to power the motors.
Two things make an electric vehicle go faster or have longer range: Bigger battery packs and larger motors.
3. The Battery Controller
The battery controller acts as the traffic cop between the battery and the motor. Hook a battery straight up to a motor, and it will turn at something like 20,000 RPM with full torque until the battery is depleted. That’s fine if you’re attempting some kind of land-speed record, but it's no good if you’re stuck in traffic.
The battery controller is what you see if you can see anything at all under the hood of an EV. Without getting too far into the weeds, the battery controller is the brain that manages all the batteries' power, sending it to the motor in a way that allows you to use it to stop and start in traffic.
4. The Drivetrain
You could essentially remove the gas engine from your car, replace it with an electric motor, connect it to your transmission, and have it work exactly the same way your vehicle drives today. But the drivetrain in a conventional vehicle is massively inefficient. By the time power reaches your wheels, the drivetrain—the transmission, center differential (if it’s an all-wheel drive vehicle) and front or rear differential—have sapped 15 percent of the power generated by the engine. Nobody really cared much when gas was cheap and plentiful, but losing 15 percent of your power just to turn all the gears in the transmission and differential is unsustainable in the long run.
Electric motors are small, and easily controllable, though, and you can do pretty amazing things with them. Some of the earlier EVs used a single motor with driveshafts that powered the front wheels. Then, as things advanced, EV developers began powering the front wheels using two motors, each connected to a wheel by a short driveshaft. Today, manufacturers are increasingly using two, three or even four hub motors. Some also use in-wheel motors with no shaft at all—these simply connect to the wheel to provide direct power, with virtually no drivetrain loss.
Other Components
There are a ton of other advancements that are helping EVs to be as efficient as possible or to provide more power than ever.
All of these advancements attempt to either recapture lost power or avoid losing it in the first place. A good example is regenerative braking, which is in use on hybrid and plug-in hybrid electric vehicles (PHEVs), too. When you apply the brakes in a conventional car, all of that energy from friction is wasted. In an EV or a hybrid car, regenerative braking essentially turns the electric motor into a generator, sending that scavenged electricity generated from friction right back to the batteries.
One of the many variables in getting the most range out of an EV is temperature. If you run an EV at an optimal, constant temperature—say 75 degrees—you’ll get the full range out of it. Drop that temperature down into the single digits, though, and an EV can lose half of its maximum range between the Li-ion battery's reduced cold-weather efficiency and the heat running to keep you from freezing to death in the passenger cabin.
To combat this, manufacturers like Tesla, Volkswagen, Kia, and Nissan have introduced heat pumps to replace the electric heating elements that manage the car’s interior temperature. A heat pump essentially works like an air conditioner in reverse, absorbing heat from the atmosphere, compressing it, and turning it into hot air.
The Bottom Line
The automotive industry isn't ready to leave fossil fuels behind just yet. We expect that at least another generation will grow up knowing the term "gas tank"—but they'll probably be just as comfortable with the words "fuel cell." As automakers work to address emissions and convert to renewable energy, electric vehicles are becoming more and more commonplace, and they're getting better and better. A savvy consumer would do well to learn a bit about EVs now. Consider how fuel economy and charging speeds might factor into your life, and be prepared when the time comes to weigh your options.
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