Regenerative braking: how the motor brakes and recharges (slightly) the battery

On an electric scooter, the motor doesn't just serve to accelerate; it can also brake by sending a portion of the energy back to the battery. This is called regenerative braking. It's practical and saves brake pads, but it also has limitations that you need to be aware of, especially on a powerful machine.

The motor becomes a generator

A motor with permanent magnets generates a voltage at its terminals, similar to a bicycle dynamo. When braking electrically, the controller stops sending current to the motor and reverses its function: it allows the motor to generate current in the opposite direction. This current creates a torque that opposes the rotation, causing the wheel to slow down.

In vector control (FOC), it's very straightforward: the torque command becomes negative. The controller regulates the braking current as precisely as the acceleration current, resulting in smooth and controllable braking.

Where does the energy go?

The kinetic energy of the scooter is converted into electricity. A portion is lost as heat in the motor and the controller; the remainder passes through the controller and returns to the battery. In this process, the controller's power bridge operates in reverse: it boosts the motor's voltage so that it exceeds the battery's voltage, allowing the battery to be recharged.

At low speeds, the motor produces little voltage, and the electric braking becomes weak. It cannot bring the scooter to a complete stop, nor can it hold it stationary on an incline.

How much energy is actually recovered?

Less than one might think in normal use. On a flat surface, most of the energy is consumed by air resistance and friction, not braking. The benefit is more noticeable in the city, with frequent stops, and especially on long descents. The main advantage of electric braking lies elsewhere: it provides smooth and consistent braking, and it reduces wear on brake pads and rotors.

Here are the limitations you should be aware of

Battery fully charged

A fully charged battery can no longer accept a charge. The braking current would cause its voltage to exceed the cell limits. The BMS (Battery Management System) or the controller then reduces or even cuts off the electric braking. The practical consequence is that, when starting with a fully charged battery at the top of a hill, the electric brake may be significantly weaker than usual.

The maximum charging current of the battery

A battery accepts less current during charging than during discharge. The braking current returned to the battery must remain below this limit; otherwise, the Battery Management System (BMS) may shut down, and with it, the entire system. On an adjustable controller, the motor braking current and the current returned to the battery are set separately.

The controller voltage

During braking, the voltage rises above the battery voltage. A controller without sufficient voltage headroom can be damaged by strong regenerative braking when the battery is fully charged. This is one of the reasons why a controller should be chosen with some margin, as explained in our controller guide.

Adhesion

On a single-motor scooter, the electric braking only affects one wheel. This can cause the wheel to slip, especially on wet surfaces. The braking force is applied gradually, similar to a mechanical brake.