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Regenerative brakes: how do they work?

Regenerative brake system diagram
Regenerative braking system diagram

If you are looking for a hybrid or electric vehicle, you may have heard of regenerative braking. If you’re wondering what that is and how it works, you’ve come to the right place.

What are regenerative brakes?

Regenerative brakes use electric motors instead of a traditional friction braking system to slow and stop a car. Hybrid and electric vehicles typically use these types of brakes.

With a traditional hydraulic braking system – usually disc brakes or drum brakes – braking wastes energy. It takes the kinetic energy to move your car forward and turns it into heat instead of motion. While effective at slowing down a moving vehicle, friction braking wastes energy.

With regenerative braking, the braking system captures that kinetic energy and transfers it to the car’s batteries. The system wastes less energy than friction brakes. The use of regenerative brakes helps to maintain and supplement the range in an electric or plug-in hybrid vehicle.

In a conventional hybrid, the energy recovered from regenerative braking powers some of the auxiliary functions in the car, such as the audio and climate control systems. This relieves the load on the engine and electrical system and improves efficiency.

There is another type of regenerative braking called Hydraulic Power Assist. It usually only applies to commercial vehicles. Electric regenerative braking is the type of system relevant to the average driver learning about regenerative braking.

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What types of EVs have regenerative brakes?

All electric and plug-in hybrid vehicles currently on the market in the US have a regenerative braking system. Some conventional hybrids do, too, such as the Toyota Prius.

Here are some cars on the market with regenerative brakes. This list is not exhaustive:

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Pros

Energy Recovered: Hydraulic brakes waste energy by converting kinetic energy into heat. However, regenerative braking puts that energy into the car’s batteries and converts it into a little extra driving range.

Improved Range: Regenerative braking does not add significant mileage to your driving range. Still, those gains in recovered energy can add up quite a bit if used liberally and regularly. Hybrid and EV drivers know that every mile of battery range counts.

Reduced brake wear: The more you use regenerative brakes, the less you need to use traditional friction brakes. That means less trips to a service center for brake pads, brake discs and shoes. With regenerative braking, some hybrids and EVs can travel approximately 100,000 miles between braking services.

cons

Getting used to: Regenerative brakes take some getting used to, especially if you’re looking for a used example of an early EV or hybrid. This technology is advancing, but regenerative braking sometimes has a weird feeling that can be jarring to the driver.

Less reliable at high speeds: Friction braking is a very old technology that is very reliable. When you step on the brake in a car with hydraulic disc or drum brakes, the vehicle comes to a stop reliably and quickly. Regenerative brakes are not as good as emergency friction brakes that require the car to come to a complete stop quickly. Therefore, hybrids and EVs typically use both types of braking systems.

Low speed, low benefit: When you use regenerative braking when driving at low speeds in the city, it doesn’t generate enough energy to have a significant impact on your car’s range. For this reason, using regenerative brakes when driving at low speeds makes little sense.

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How regenerative brakes work

Regenerative brakes work by reversing electric motors that propel a car. It acts like a generator, feeding energy back to the hybrid or electrical system to supplement a little bit of range. These small increases in battery range can accumulate with regular use and improve efficiency over time.

Drivers can activate regenerative brakes in several ways. Some hybrid and electric cars have a paddle near the steering wheel that activates the regenerative brakes. However, activation is seamless in most cars with regenerative braking. By depressing the normal brake pedal with your foot, the regenerative and friction brakes work together to slow the vehicle. Cars with a particularly aggressive system can use regenerative brakes when the car is coasting. Sometimes called single-pedal driving, drivers can use the feature in a specific driving mode that emphasizes efficiency on longer journeys.

Although regenerative braking uses a different technique than friction braking, it achieves the same goal, which is to slow down and stop a moving car. Since it has the same effect as regular brakes, the brake lights will still come on when using regenerative brakes as a safety measure.

Let’s say you are driving a Nissan Leaf in e-Pedal mode. When you take your foot off the accelerator, the regenerative brakes are activated automatically. At the same time, the brake lights at the rear of the car illuminate as if you were pressing the brake pedal.

Brake and regenerate

Regenerative brakes are a great way to preserve the range of an EV and improve the efficiency of a hybrid. You can use them a lot to recover a lot of energy, or you can let them work in the background without changing your driving. Either way, you’ll be glad your next hybrid or EV has them.

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