Why doesn’t regen work below 5mph?

[dgaultiere]

Been wondering this forever and haven’t seen this answered anywhere. Is there a technical (battery-related, or other) reason that it is not possible to stop the car via regen under 5mph?

If not then why does tesla do this? It would be super convenient if I never had to touch the brake when coming to a full stop...

 

[uwym]

It's technical. The ELI5 is that one type of motor design can regen to 0, but it has lower performance. A different motor design provides higher performance, but it can't regen to 0. Tesla (mostly) uses the higher performance one, and the Leaf uses the lower performance one. It's partially explained here

 

[suwaneedad]

If you keep cruise on, I believe the car will stop for you rather than hitting the car in front of you. That will reduce your need for foot braking to stop signs and traffic lights which the car doesn't 'see' yet in terms of its EAP logic.

 

[Dana1]

Been wondering this forever and haven’t seen this answered anywhere. Is there a technical (battery-related, or other) reason that it is not possible to stop the car via regen under 5mph?

If not then why does tesla do this? It would be super convenient if I never had to touch the brake when coming to a full stop...

Regenerative braking systems

 

[Webeevdrivers]

The new Nissan Leaf comes to a full stop without ever touching the brake. It is part of the Epedal feature. But I believe I read that the final stop is achieved by the epedal feature actually applying the friction brakes. Don’t know for sure. Not an expert. I very much like the epedal feature of the leaf though. Wish the 3 had it.

 

[BryanJ.Greene]

Below 5 mph there's not enough energy to capture to do much more slowing. Brakes are better at the lowest speeds.

And there are 2 settings, max and low. The max dumps 60kW into the batteries. Don't know the low spec.

The rest is physics.

 

[SigNC]

I like the fact that is stops regen below 5 as this way you can make small movements easily.

 

[Swampgator]

If you keep cruise on, I believe the car will stop for you rather than hitting the car in front of you. That will reduce your need for foot braking to stop signs and traffic lights which the car doesn't 'see' yet in terms of its EAP logic.

Be careful with your wording. TACC will do that. Regular (non-EAP) cruise control will ram you right into another care no problem.

 

[aesculus]

Be careful with your wording. TACC will do that. Regular (non-EAP) cruise control will ram you right into another care no problem.

I sort of discovered this in a soft way a few days ago when I got a MS75D loaner from the SC without AP.

 

[Uncle Paul]

It is good for the physical brakes to be pushed from time to time. Keeps everthing moving and not locking up.

Tesla has a good system, where the regeneration takes about 95% (or more) of the braking, but the driver still has control over the final fine control.

 

[Needsdecaf]

The Nissan Leaf E Pedal is pretty damn useful. Not super smooth though.

 

[coleAK]

Been wondering this forever and haven’t seen this answered anywhere. Is there a technical (battery-related, or other) reason that it is not possible to stop the car via regen under 5mph?

If not then why does tesla do this? It would be super convenient if I never had to touch the brake when coming to a full stop...

First off I can come to a complete stop in our 3 without touching the break. Second, why does it matter? The car has breaks and if you rarely use them they won’t function at capacity when you need them in an emergency situation.

 

[SomeJoe7777]

Both the induction motors (used in S, X, and front motor of AWD 3's) and the PMSR motors (used in rear motor of 3's) need a magnetic field set up inside the motor in order to convert current to torque (acceleration) or counter-torque to current (regen). You must use a small amount of current from the battery and send it through the windings of the motor in order to set up this magnetic field.

Below 5 MPH, the amount of power required to set up the magnetic field exceeds the amount of power you can create from regen, so there is no point in attempting to recover that power. Theoretically you could do it and allow the motor to slow the car to 0 MPH, but that would actually result in a net power loss, so it's more efficient to just use the friction brakes.

The Leaf and other EVs that use straight permanent magnet motors can regen all the way to 0 without this efficiency loss because the permanent magnets are responsible for setting up the magnetic field. No power from the battery is necessary.

The small permanent magnets in the Model 3's PMSR motor are not powerful enough to set up the magnetic field, they are only there to smooth out low-speed torque ripple which is inherent to the reluctance motor design.

 

[dgaultiere]

Both the induction motors (used in S, X, and front motor of AWD 3's) and the PMSR motors (used in rear motor of 3's) need a magnetic field set up inside the motor in order to convert current to torque (acceleration) or counter-torque to current (regen). You must use a small amount of current from the battery and send it through the windings of the motor in order to set up this magnetic field.

Below 5 MPH, the amount of power required to set up the magnetic field exceeds the amount of power you can create from regen, so there is no point in attempting to recover that power. Theoretically you could do it and allow the motor to slow the car to 0 MPH, but that would actually result in a net power loss, so it's more efficient to just use the friction brakes.

The Leaf and other EVs that use straight permanent magnet motors can regen all the way to 0 without this efficiency loss because the permanent magnets are responsible for setting up the magnetic field. No power from the battery is necessary.

The small permanent magnets in the Model 3's PMSR motor are not powerful enough to set up the magnetic field, they are only there to smooth out low-speed torque ripple which is inherent to the reluctance motor design.

THANK YOU! This is the explanation I was looking for. I knew there had to be a technical reason for this.

 

[David99]

Everyone that has driven an EV that comes to a complete stop (as if there was such a thing as an 'incomplete stop') prefers that. It makes perfect sense to have one pedal driving. Yes regen isn't effective below a certain speed and it would take a small amount of energy to make the motor bring the car to a stop. But that's a minuscule amount for a desirable and comfort feature. When using auto pilot, the car uses the friction brakes to do the last little bit to completely stop the car. So the functionality is already there. I wish Tesla would finally make it an option so users can turn it on or off as they like. Same as creep when you let got of the brake.

 

[Needsdecaf]

Both the induction motors (used in S, X, and front motor of AWD 3's) and the PMSR motors (used in rear motor of 3's) need a magnetic field set up inside the motor in order to convert current to torque (acceleration) or counter-torque to current (regen). You must use a small amount of current from the battery and send it through the windings of the motor in order to set up this magnetic field.

Below 5 MPH, the amount of power required to set up the magnetic field exceeds the amount of power you can create from regen, so there is no point in attempting to recover that power. Theoretically you could do it and allow the motor to slow the car to 0 MPH, but that would actually result in a net power loss, so it's more efficient to just use the friction brakes.

The Leaf and other EVs that use straight permanent magnet motors can regen all the way to 0 without this efficiency loss because the permanent magnets are responsible for setting up the magnetic field. No power from the battery is necessary.

The small permanent magnets in the Model 3's PMSR motor are not powerful enough to set up the magnetic field, they are only there to smooth out low-speed torque ripple which is inherent to the reluctance motor design.

Actually, the Leaf will apply the friction brakes when the epedal is active. It’s not just regen. It will even automatically apply brake hold on a hill.

How does the 2018 Nissan Leaf e-Pedal work?

 

[Amp3dFlux]

Both the induction motors (used in S, X, and front motor of AWD 3's) and the PMSR motors (used in rear motor of 3's) need a magnetic field set up inside the motor in order to convert current to torque (acceleration) or counter-torque to current (regen). You must use a small amount of current from the battery and send it through the windings of the motor in order to set up this magnetic field.

Below 5 MPH, the amount of power required to set up the magnetic field exceeds the amount of power you can create from regen, so there is no point in attempting to recover that power. Theoretically you could do it and allow the motor to slow the car to 0 MPH, but that would actually result in a net power loss, so it's more efficient to just use the friction brakes.

The Leaf and other EVs that use straight permanent magnet motors can regen all the way to 0 without this efficiency loss because the permanent magnets are responsible for setting up the magnetic field. No power from the battery is necessary.


Soooo..here we are at the end of 2019, and this has happened. Is the case now as you describe with the updated, one-pedal driving? The minimal power loss is less than the miniscule wear and tear on brakes < ~5mph?