In school I learned that braking is a waste of fuel as the kinetic energy transfers to sound and heat (which is effectively a loss, right?). So how does regenerative braking recoup some of that energy into the car’s battery?
In: Engineering
Electric motors and generators are basically the same thing. They have a series of permanent magnets and a coil of wire inside. When you apply an electric current to the coil, it generates a magnetic field, which pushes against the magnets (opposites attract, likes repel) causing the motor to rotate, turning the wheels and making it propel your electric car.
However, this can also work in reverse. If you apply an external mechanical force to the motor, without applying power to it, the rotating magnets will generate a current within the coil. Causing the motor to become a generator. This current can then be collected and used to recharge your car’s battery. Of course there’s no such thing as free energy and no generator is 100% efficient. So some energy is lost along the way through forces like friction and heat. Which slows down rotation of the wheels, causing the entire vehicle to slow down in the process.
Regenerative breaking in EVs is used similarly to engine breaking in internal combustion vehicles. It’s no replacement for the mechanical breaks, but it does assist them. It’s a proven system that has been used on trains for a long, long time. That’s why diesel-electric locomotives have all those big fans on the roof. Since they don’t have batteries, the electric current is passed through huge resisters and converted into heat. It helps slow the train down while saving wear and tear on the mechanical breaking system.
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