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Regenerative braking explained
Regenerative braking: it’s a bit like money for nothing.
Regenerative braking uses the car’s forward momentum when you lift off the accelerator to feed energy back into the car’s battery. It does this via the electric motor. When you accelerate, the electric motor drives the wheels; when you lift off the accelerator, it diverts the energy back into the battery.
In a non-EV, the car slows by applying friction via brake pads to the brake discs. While this slows down the car, the energy required to do so is dissipated as heat. In other words it’s wasted.
Not so electric cars.
However, regenerative braking takes some acclimatisation when you first step into an EV. And not all drivers feel comfortable with the braking effects.
So in most EVs you can adjust the severity of the regenerative braking to suit a driver’s preference or the roads and terrain being driven. This can vary from a light setting which minimises any rolling friction and maximises the car’s free-wheeling ability. This is generally preferable when cruising on motorways and on dual-carriageways when you want a lighter touch on the brake pedal
More aggressive levels of regenerative braking feature on cars such as the Nissan Leaf and its e-pedal, which can bring the car to a halt with a strength equivalent to pressing the brake pedal firmly. Simply by modulating the pressure on the accelerator, rather similar to dodgem cars at fairgrounds, the car can be driven smoothly. This is often referred to as ‘one-pedal driving’ and barely makes use of the conventional brake pedal.
When does regenerative braking work best?
Regenerative braking is at its best when you are in urban traffic with constant stop-start. You effectively use the one-pedal driving tehnique. To warn following drivers that you are slowing down, the brake lights engage when regenerative braking is being used.
It’s surprising how quickly you become used to the effects of regenerative braking and how you suddenly miss it if you step back into a traditional petrol or diesel car.
While many EVs feature a simple on or off mode for regenerative braking, others have different levels. The BMW i3 has five to choose from, for example. Latest EVs add ‘automatic’ mode for use with predictive cruise control to decide how strong the braking force should be.
What you should be aware of, however, is that should the car’s battery be full, regenerative braking will be disabled. The charge simply has nowhere to go. So the car’s normal brakes will be required in such instances.
Some trip computers can even show you how much energy or ‘free’ miles you’ve gained through regenerative braking over a period of time. While this amount isn’t huge, it’s rather pleasing to know how much you are gaining for nothing.
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