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How does regenerative braking work in an electric vehicle?

03 March 2021
This article first appeared in the March edition of the Australian Automotive Aftermarket Magazine.

How to improve the range of an EV by stopping

Regenerative braking is a system found in both electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) that recharges your battery by braking. It’s a simple but effective technology is widely used in electric vehicles and is an efficient way to mitigate the loss of energy while braking. 

 

What is regenerative braking?

A moving vehicle creates kinetic energy and when the brakes are applied, this energy must go somewhere. In a conventional braking system, friction-based disk brakes are used to slow vehicles. The kinetic energy from the movement of the vehicle is being converted into heat via friction and dissipating into the atmosphere, resulting in a loss. 

Regenerative braking is when an electric vehicle’s kinetic energy is harvested through the action of slowing down and is sent back into the battery as usable power. Put simply, braking in an EV regenerates your power and gives you more range. 




However, not a lot of power is retrieved in this process and it is often depleted as the vehicle accelerates. While it does not fully reimburse the power expended to accelerate, regenerative braking is efficient enough to increase an EVs overall range when compared to a similar car with conventional braking systems. Overall, regenerative braking is not designed to make a car more efficient; it is designed to make it less inefficient.

The most efficient way to drive is at one constant speed never accelerating or decelerating, but as that isn’t feasible in real world driving, the next best option is to mitigate energy lost with regenerative braking.

Note: EVs and PHEVs DO often have disk brakes as well that serve to substitute the limitations of regen braking and act as emergency brakes for if the powered systems fail.

 

How does regen braking work?

As you slow the speed of an electric vehicle, regenerative braking engages the motion of the wheels to act as a sort of crankshaft, sending energy to the motor via rotation of the motor shaft. 

This transfer of energy from the wheels to motor slows the vehicle down, often rapidly, and is why EV owners refer to ‘one pedal driving’; ie. they rarely use the brake pedal.

The rotation that is applied from wheels to motor opposes the movement of the motor shaft and creates a counter electromotive force, or back EMF. In short, the reverse force on your motor’s magnets, converts rotational energy into electrical energy. 

Simply put, in this scenario, the EV motor essentially serves the role of a generator powered by a crankshaft while regenerative braking, harvesting power that is stored in the battery for later use. 

Is your workshop getting enquiries about electric vehicles? Ask me about Australian-made three phase charging for your workshop by calling 1300 EVUP 00 or email emma@evup.com.au 

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