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It's not really "exact" how it works because it depends on the system - electric, hybrid, it's not the same. But the general idea is that when you brake, you normally waste kinetic energy as heat in the brake pads. With regeneration, instead of that, you use the electric motor (or a generator) in reverse mode: it becomes a resistance that slows the car down while producing electrical current. That current recharges the battery. It's basically a motor running backwards.
The thing is, it's not all or nothing. Modern systems handle it intelligently: when you brake gently, the electric motor does almost all the work and recharges. When you brake hard (like an emergency stop), the traditional brakes also kick in because otherwise it would be too slow. The electric motor on its own is pretty gradual. And obviously you can't recover more energy than you used to accelerate - there are always losses. But on the road or in the city with lots of braking, it can add decent range, maybe 10-20% depending on how you drive.
Do you have an electric or hybrid car at home, or are you just asking out of curiosity?
The other answer explains the concept pretty well, but I can go into a bit more detail on how it actually works. When you brake in an electric car, instead of wasting all the energy from your movement as heat in the brake pads (like in a normal car), the electric motor works in reverse - it becomes a generator. The wheels turning drive the motor, which produces electrical current that recharges the battery. It's not magic, of course: you don't recover 100% of the energy, there's always some loss, but you recover a pretty good chunk of it depending on the system and how you brake.
With my old rental electric car, I really noticed the difference. When you brake gradually, the recovery works well and you feel the motor slow you down. But if you slam on the brakes, the physical pads take over because the motor can't dissipate energy fast enough. On city drives with lots of stops, it really added to the range - maybe 15, 20% depending on how you drive. On the highway or open road, it's barely anything since you brake less often.
So yeah, it works like a reversible system: the same motor that pushes you forward becomes a generator when the wheels force it to spin. Hybrids do the same thing, just with more variations depending on whether they're using the electric motor, the gas engine, or both.
Are you driving an electric vehicle or just checking out how it works? The cool thing to understand is that the electric motor becomes a generator when you decelerate - it basically runs backwards, and that rotation creates current that gets sent back to the battery instead of being wasted as heat like with regular brakes. So you don't need to use the actual brake pads as much, which makes them last longer and you get extra range at the same time!
lea65 asker
Are you driving an electric vehicle or just curious how it works?
I'm driving an electric vehicle, and I want to understand how it's actually used in practice.
I've seen it up close with hybrid cars you come across regularly, and it's really straightforward when you get down to it: the electric motor works normally when you accelerate, but as soon as you ease off or brake, it turns into a generator. Instead of just wasting the energy as heat in the brake pads like a regular car, the motor pushes electricity back to the battery to recharge it - kind of like a bike dynamo that generates current when you pedal.
The real difference between electric and hybrid is just that on a hybrid, the gas engine kicks back in afterward and you lose some of it, whereas in a pure electric you recover almost all the braking energy. That's why city driving with lots of stops gives you way more range compared to highway driving - the more you brake, the more you recharge your battery, it's a win-win cycle.
The electric motor acts as a generator the moment you lift off the accelerator, not just when you hit the brakes. That's where a lot of people get it wrong - you're constantly recovering energy during deceleration, even without touching the brake pedal. The system converts kinetic energy (the motion) into electricity that charges the battery back up, and it reduces wear on your traditional brakes as a result. The more gradually you decelerate, the more you recover; if you brake hard, the mechanical brakes take over and you lose some of that potential.
The electric motor can work as a generator when the car slows down - it captures the kinetic energy and converts it back into current to recharge the battery. This is possible because unlike a combustion engine, an electric motor can spin both ways and convert mechanical energy into electrical energy. The catch that others haven't really brought up is that it works way better when you decelerate gradually (like in city driving) than when you do hard emergency braking - then the regular brakes take over and you still lose a lot of energy.
The common pitfall is thinking it works the same way in every situation - in reality, the efficiency varies hugely depending on speed, the type of braking, and the battery. On a pure electric vehicle, the motor turns into a generator and sends the kinetic energy back to the battery, but it only works really well if the battery isn't already fully charged (otherwise it refuses the energy). On a hybrid, it's even more nuanced because the system chooses whether to use mechanical brakes or regeneration based on what's optimal at that particular moment.
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