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Could an electric car have only regenerative brakes and no conventional friction brakes?


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My understanding is that combustion cars have brakes that turn the car's kinetic energy into heat energy, and electric cars have both these conventional brakes and can also do regenerative braking that turns some of the car's kinetic energy into electricity instead of heat. The reason they have both is that regenerative brakes can't apply nearly as much braking force as normal brakes. My question is, would it be possible for regenerative braking to be engineered to be capable of stopping a car just as quickly/effectively as conventional friction brakes can?

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Probably yes, technically it could be done but how the hell the driver could modulate the braking force as easily as conventional  brakes would be a bit of a challenge.

With our i3 it can be driven effectively without using the brake pedal in normal driving, but if an emergency or unforeseen stop or retardation is required the friction brakes are definitely needed.

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Electromagnetic or eddy current braking could easily stop a 2 ton car on a sixpence. The Bullet train uses such a system as do many other train. Even mine haulers rely solely on them

 

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I don't believe so.

Regenerative braking is used to pump charge back into the batteries. I understand you know how that process takes place. 

However as you pointed out because that energy is converted into electricity and not excess heat (through friction) there is a specific amount of power to be generated by the motor.

In order to achieve the equivalent braking power, with typical deceleration of 1g, you'd need to around 250kW on a 2 tonne car in 3s.

Where you start seeing it as an issue is that at 350V(Tesla Battery system) that equals to over 700Amps of charging current. Something no Battery or wiring could withstand.

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Certainly possible to produce non-friction brakes that perform just as well as conventional brakes but not really using a regenerative system with Lithium-Ion batteries because the current produced would exceed the acceptable charging rate of the batteries and therefore you would need to get rid of the excess energy via heat radiators - and if you put in all that extra expensive you might as well just stick with the set up you see today (and you need a split braking system to pass safety regulations which the mechanical friction brakes easily provide).

If we get you a new energy store (different Battery tech/super capacitors) then it could be a possibility.

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18 hours ago, Boxbrownie said:

 but how the hell the driver could modulate the braking force as easily as conventional  brakes would be a bit of a challenge.

It think it would be even easier to modulate than friction brakes... there are no hydraulic fluid to push, no surface dirt to worry about, no brake pads to clamp and the sensors could modulate braking pressure much more precisely. Not that much different from drive-by-wire throttle... drive-by-wire anything to be honest. The difference would be maybe that pressing the pedal much harder, may not result in more braking, because the car most likely going to keep consistently braking at the grip limit no matter what and would never lock-up brakes under any circumstances, but that is kind of desirable anyway.

I think the only confusing part here is "regenerative brakes" - you could not use regenerative braking on it's own, because it is designed as Battery charging method, rather than dedicated to stopping the car. So I think it would remain the case that first part would be regenerative via engine (slowing down) and then electromagnetic brake to fully stop. The difference is that regenerative braking charges the batteries, but electromagnetic brake would use the energy to stop the wheels (which is not desirable).

In short, yes it absolutely possible to use electromagnetic brakes to brake, but they would not be working on principle of regenerative braking. You don't even need EV for that - ICE or hybrid could do that as well in theory. I guess the reason why they are not used is that using electricity to brake is undesirable on EVs and simply having metal slab rubbing against friction pad to turn torque into heat is more preferable, than using electricity to do the same.

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