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In an EV’s regenerative braking system, the motor works in conjunction with the hydraulic system to slow and stop the vehicle, recharging the battery as you slow down or stop.
EV motors actually work in two directions, forward to propel the vehicle and backward as a generator to charge the battery. When the vehicle slows down, the generator converts the kinetic energy - the energy of motion - into electrical energy to charge the vehicle's battery. The vehicle is actually slowed by the motor working in reverse, recapturing energy and sending it back to the battery.
In case you want a quick refresher on the physics of this, think of pulling back an archer’s bow. When the bow is pulled back, the arrow hasn’t moved yet, but it has the potential to shoot out and move really fast. The energy stored in the pulled back arrow is referred to as potential energy, and is like the energy stored in the battery. When the bow is released, then the potential energy translates into kinetic energy, which is also known as motion. When the car slows, its kinetic energy (motion) is turned back into potential energy stored in the battery.
This is in comparison to how a traditional break system works in a gas car: with hydraulic brakes, brake pads engage with the rotors or drums to slow and stop the vehicle. The heat caused by braking is actually energy which is released from the car and lost.
How Much Energy Can Regenerative Braking Capture?
In general, it has been found that regenerative braking can recapture around half of the energy that is lost when a car brakes, which translates to a 10-25% efficiency gain.
Can You Adjust the Regenerative Braking Levels?
Most EVs come with different settings allowing you to adjust how much regenerated energy you want. The maximum setting, often used for city driving and referred to as “one pedal driving,” will stop the car entirely when you release the accelerator. In this setting, you don’t need to apply the brakes, but can simply decrease pressure on the accelerator pedal until you want to stop the car. When the regenerative brake system hits its limit, the hydraulic braking system will engage and stop the vehicle. This setting takes a little getting used to.
If maximum regenerative braking is too much of an adjustment for you, the lightest brake settings will allow you to drive the vehicle in a relatively normal fashion, applying the hydraulic braking system to stop the car. In this setting you’ll feel a light sensation of the motor reversing when you let off the accelerator. Touching the brakes will increase the regeneration and slow the car. You will feel the regeneration disengage (like the car is in neutral) as the vehicle is near a complete stop and then you depress the brake to completely stop the vehicle as normal. This setting is recommended for highway driving so that when you let off the accelerator the effect is not as pronounced as with high-reg settings.
Other benefits of regenerative braking
The regenerative braking systems have another great advantage over traditional hydraulic braking systems: cost. According to the U.S. Department of Energy, “An EV typically requires minimal scheduled maintenance, and brake systems generally last longer than those on conventional vehicles because of regenerative braking”. For a comparison, Toyota suggests that you service the brakes in one of their ICE cars every 30,000 to 35,000 miles. I recently serviced my EV (air conditioning issue) and the brake and rotor wear were both over 50% all around at 53,000 miles. This means I can potentially get 3-3.5x longer use out of my brakes than in an ICE car.
