How Does Regenerative Brakes Work In a Car? Myth Explained


How does regenerative brakes work in a car? When you let off the accelerator in EV your car is still moving forward so the rotor in the electric motor continues to turn, this pushes current in the other direction of the motor so the motor becomes a generator and charges up the battery.

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The world’s largest electric vehicle is a dump truck, very creatively named the E-Dumper. weighing in at 45 tons it is a beast.

with six-foot tires, 55 tons of capacity in a 600-kilowatt-hour battery pack, that’s equivalent to around 6 Tesla Model-S. Besides being a giant this thing is also incredibly efficient, and never needs to be charged, all thanks to regenerative braking.

This truck climbs up the hill with a full charge, it loads up its entire bed full and then goes back down the hill and recovers a ton of energy from regenerative braking, but how exactly does this work?

If you’ve ever driven an EV before you know that regen braking is that sensation you get when you let off the accelerator, the car instantly starts to slow down instead of coasting like a normal gas car.

Before we can understand braking in an EV let’s talk about how it works in a gas car. Let’s imagine you’re traveling down the road and you see a stop sign up ahead, you let go of the gas so you’re no longer putting energy into the car to make it move, but the car is still rolling because it has kinetic energy.

You press on the brake and that causes the braking system to close a set of pads around a disc that is next to your wheel, and that causes your car to slow down using friction applied directly to that disc.

This works great, we’ve been using it for over a hundred years to stop cars moving at high speeds. Regen braking is built directly into the electric motor, without getting into a bunch of physics terms and explaining a bunch of equations. There are a couple of things you should know about an electric motor if you want to understand regen braking.

There are two major parts in an electric motor and that is the stator and the rotor. The stator is the stationary part and the rotor is the part that moves or turns in the electric motor.

How an electric motor works on a very basic level is that you push current through the stator, this creates a magnetic field that then turns the rotor. So when you press on the accelerator in an Eevee you’re just pushing current to that stator.

But when you let off the accelerator in EV your car is still moving so that the rotor continues to turn, this pushes current in the other direction of the motor so the motor becomes a generator and charges up the battery.

Normally this energy would just be wasted to friction using brake pads, but an EV you can capture that wasted energy and use it to charge up the very efficient battery.

This is a big reason why EV brakes don’t wear out as often, you don’t have to replace them hardly at all. But this has a lot of advantages beyond brake wear, this extends your range a little bit.

Most of the EV estimated range you’ll see for electric vehicles includes regen braking while you’re driving.

This is why EV’s are awesome in stop and go traffic because you’re constantly speeding up and slowing down. You’re speeding up and using your battery but then when you slow down you’re recouping that energy again.

But you’ll also see that if you’re driving on a hilly highway or you’re driving uphill a lot you’re going to waste much more energy. Beyond that, you also get one-pedal driving, which simplifies the driving process.

You press down to go and you let go to stop, some people don’t like that and it takes a little bit of getting used to but once you’ve been driving with it for a while you’ll realize it has a lot of advantages and makes driving a lot more enjoyable.

We get a lot of questions around the brakes because we’re adding performance to the car, and more power and more torque, along with that comes the requirement to make it stop better as well.

Part of that question comes from the fact that people when they think of electric vehicles, think about regenerative braking, which is amazing tech when you first experience it but it is really simple.

When you put your foot on the accelerator you’re putting electricity into the motor and spinning it up, when you stop doing that the wheels are then spinning the motor and turning it into a generator. That’s creating electricity and putting it back into the battery.

That energy slows the car down and so regenerative braking has nothing to do with the brakes it’s kind of the opposite, it saves the brakes.

When you’re using regen braking you’re not using the brakes at all, one of the downsides with drum brakes is the way they wear and they need adjustment.

If you’re not using the brakes and with regen braking, you can almost drive just by just not accelerating.

We can drastically reduce the wear on these drum brakes and we think this is going to be fine. This combination of original drum brakes that can lock up the wheels and stop the car, brings that feel, we bring that feel and that control back through the regenerative braking system and reduces the wear and reduces the need to adjust the brakes all the time.

As we have already said previously braking creates friction which in turn creates heat and energy and that can be used to charge up your battery and extend the car’s range. This is what’s known as regenerative braking, or some manufacturers also call it recuperation.

You’re simply using the car’s brakes as tiny supplementary generators, of course, it makes sense to capitalize on this free energy by increasing the friction to create as much energy as possible to top-up the battery.

The only problem is that this can make the car feel a bit unnatural to drive as it breaks quite aggressively as soon as you lift off the gas pedal.

What is Regenerative Braking And The E-Pedal?

What a lot of manufacturers have done is to install phased regenerative braking, so that you can choose how aggressive you want the braking force to be. Nissan has even gone so far as to introduce something called the e-pedal.

This is regenerative braking that is so aggressive you don’t need to use the brake at all around town, you can drive the car entirely on the throttle. Of course, that takes some getting used to but it does become second nature after a while.

Alternatively, you can turn the pedal off altogether and then the car will pretty much freewheel quite cleanly, however you like your regenerative braking, whether you like it very strong, moderate, or off altogether the option is there.

The thing to remember is when you first get into an electric car the regenerative braking could well be the thing that takes the most time to get used to.

Break regeneration, or regenerative charging, as it’s also known, is one of those things that feels a bit odd at first but it doesn’t take very long to get used to.

And if you were wandering in an electric or hybrid car with heavy brake regeneration activated, the brake lights do come on when you lift off the throttle even if you don’t touch the brake pedal itself.

When I first test drove the Kohner electric one of the things that I noticed about it was the sense of inertia when you were using regen, this isn’t regen while you’re braking, this is regen modes in use while you’re driving forward.

For example, if you’re driving on a flat straight road at 50 miles an hour and you’re in coasting mode, there’s only a sense of freewheeling or acceleration. If you’re in regen 2 or 3 you can feel a sense of inertia but deceleration at the same time, as feeling the sense of acceleration.

You can feel yourself going forward but you can feel something is dragging you back as well, and for me, that was an unusual feeling. Because I keep thinking how can that be, how can regen be working and doing something while I’m accelerating?

It’s like a self-charging electric car, you are using the battery power to propel yourself forward but somehow at the same time as propelling yourself forward, it regenerates as well.

That doesn’t make sense because we expect regen to occur when we’re breaking, not when we are on the throttle. So what is it and how does it work?

I have no idea, I’m not an engineer I wish I knew how these motors work with regen so that I could understand what it’s doing because it does appear to have some sort of regen going on whilst you’re accelerating

Talking about it is one thing, describing it is another, and that’s what I’m going to attempt to do today.

To describe it as best I can it is like walking forwards and having someone walking in front of you walking backward, they’re walking slower than you and they’re pushing on your chest. You can feel the resistance of them pushing you versus your attempt to accelerate.

One of the things that doesn’t make sense is when you do all the tests to try and work out what’s the most efficient coasting mode, regen 1, regen 2, region 3 or is one more efficient than another in different circumstances.

I’ve done some of those tests over seven months with the Kona, to be honest, there’s not a lot of difference between any of them. I think it’s more to do with your driving style and how it suits each regen mode.

It seems to be as economical in each mode, so how can that be if in one mode it’s not using any power at all and then the other mode you’re consuming power but gaining it back at the same time?

It sort of doesn’t make sense, unless that regen process is so efficient that whatever your output you can gain straight back into the battery. It would make more sense to say that regen zero coasting must be more efficient because zero energy use must be better than inputting some energy use, there must be some loss somewhere.

When you are driving it’s not noticeable anywhere so it’s more about your driver comfort than anything else.

It works when you’re using energy from the battery to propel yourself forward downhill, pushing through a resistance that’s there but that resistance, in theory, is giving you regen that puts us the same energy back into the battery or maybe more.

Related Questions

Do All-Electric Vehicles Have Regenerative Braking?

To get the most from electric cars and to get the highest mileage available in an electric car the manufacturers have fitted regenerative braking into all new cars. Even though it doesn’t give you hundreds of extra miles it does give you some that you wouldn’t normally have.

Does Regenerative Braking Use Brake Pads?

Even though regenerative braking does help to slow your car down you still need brake pads even though you wouldn’t use them as much as a conventional ICE car so they last much longer.

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