The basics of the electric car are very simple indeed: a few magnets, a battery, and some wheels, and you have electric propulsion. But the devil is in the details, ain’t he? You’d have a hard time getting to work or going to Costco in a contraption made with crude 19th-century technology, so the last 20 decades have seen immense strides in making technological marvels (like Flux’s fleet of electric vehicles) possible.
A Tesla Model 3, for instance, has dozens of systems controlled by thousands of microprocessors working together to make your everyday trip as unremarkable as possible—quiet, clean, fun and comfortable. But how do they do it? We want to tell you about some of these systems that are unique and/or essential to EVs. So Flux blog reader, let’s learn about regenerative braking.
What is regenerative braking?
The cool kids call it “regen,” and the concept is a simple one: use the energy absorbed during braking to charge your car’s battery. It’s a system that’s used on all modern hybrid and electric vehicles, a system that’s key to maximizing efficiency and minimizing maintenance.
How do I use it?
You don’t need any special knowledge or training to use regenerative braking; just press the brake pedal as you normally do and the car’s systems do the rest. Some hybrids and almost all EVs allow the owner to fine-tune the amount of regen; in fact, some cars let you ramp it up even more and allow “one-pedal driving.” This feature automatically brings the car to a gentle and full stop when the driver takes their foot off the accelerator pedal (and yes, the brake lights illuminate to warn the driver behind you).
How does it work?
When you take your foot off the accelerator pedal or step on the brake while driving your EV, the electrical system changes the polarity of the motor so it becomes a generator, recharging your battery. As power demand from the battery to the motor drops below zero (EVs and hybrids have a little graphic representation somewhere on the instrument display), the motor’s polarity reverses, so that instead of the battery sending power to turn the wheels, the wheels turn and send energy to be stored back in the battery as the vehicle slows or comes to a stop.
What’s polarity, you say? Take two magnets of opposite polarity and they’ll repel each other; if they’re the same they’ll stick together as firmly. Put them on opposite ends of a rotor and they’ll chase/repel each other like a cat chasing its tail, and if there’s wire nearby a current will flow. Which direction it flows is dictated by…you guessed it! Polarity. (Here’s a nice little YouTube video if you’re still looking for more on polarity.)
And pardon us while we geek out a little further: Einstein’s theories tell us energy is mass and vice versa, and energy can be converted to another form of energy (or matter), but can’t be destroyed or lost. So instead of turning that energy into heat and friction as in a gas-burning car, much of it (as much as 70 percent) goes into an inverter (a device that turns DC to AC power or vice versa—you may have used one camping. It lets you plug a household AC appliance into your car’s DC electrical system) and charges the battery. This explains why our EVs can be over five times more efficient than similar gas cars. Don’t worry if you don’t understand it; you don’t need to and there’s no quiz.
Besides the motor/generator, inverter and battery, the regenerative braking system needs…brakes! Yes, even if you’re doing one-pedal driving, your car has regular old-timey friction brakes (most likely discs and hydraulically-applied pads) for when you need more braking force than the resistance from the regenerative braking can provide.
So why is regenerative braking so great?
- Little brake wear: Not only do you avoid having to do expensive brake jobs every 10,000-30,000 miles, you’ll be making less brake dust, which has some pretty nasty stuff in it—bad for public health and the environment.
- Extends range: Since regen recaptures 50-70 percent of the kinetic energy that’s stored as a car accelerates, it allows batteries to be smaller, further increasing range and efficiency. For hybrids and plug-in hybrids, it greatly increases fuel economy; a Toyota Prius returns 50 mpg around town while a four-cylinder Camry, which weighs about the same, gets half that.
- Tunable driving characteristics: For many EV models, including the Chevrolet Bolt EV, Tesla Model 3, Kia Niro EV and Hyundai Kona EV, you can select different levels of regenerative braking. While the different levels don’t affect how much energy is recaptured, they do change how the brakes feel; in other words, how much the car “creeps” after you release the brakes or how slowly it coasts to a stop after you lift off the accelerator. Still, we find it ironic that you can tuna car but you can’t tuna fish… Thanks folks, we’ll be here all night.
- Makes traffic jams fun: Well, maybe “fun” isn’t the right word, but it does make extended stop-and-go driving easier. You just lift and press with your right foot like you’re driving a golf cart, which noticeably helps fight fatigue in your legs.
Is there a catch with regen? Sort of…
- Emergency stopping: Our cars are stuffed with devices and systems to warn us from and help us avoid collisions, but the most effective system is you and your years of driving experience. Practice emergency braking and use your brake pedal occasionally so that when you need to stop quickly, you’ll do it without thinking. At 70 mph your car is crossing a football-field length of road every three seconds; you don’t have time to think it through.
- Your brakes still need service: Just because you don’t use them doesn’t mean you won’t need them. One-pedal driving can mean your brakes don’t get the occasional workout they need to stay at 100 percent. Don’t summon the failure fairy; follow your owner manual’s service recommendations, especially in snowy climates where the roads are salted in winter..
- Put brake shops out of business: Owning or working at a brake shop is an honored and lucrative profession, but since brake pads and rotors on hybrids and EVs will likely last the life of the car this once-hallowed institution will shrink to a tiny fraction of its peak size. This could have a cascading effect that will spread to other industries like pleasure boats and vacation cabins.
Regen braking is yet another great reason to drive an EV. We hope this helps you understand it.