Regen - better to decelerate sharply for less time or gently for longer time (or no difference)

[Andy H]

Putting aside the debate about what behaviours may annoy other drivers (or even be dangerous)...


Does it make a difference to the effectiveness of regen if the car gradually slows over a longer period vs "foot off" and slow rapidly over a shorter period?


Bonus question.. does the brake light behaviour differ between these styles? (as I do try to be nice to cars around me)

 

[The_Cable_Guy]

i personally think longer and slower is better, i doubt the regen harvesting is that good that you can let off at 70mph and the regen will be better harvested than part throttle let off gradually.

 

[fenton]

This is a great question and I do wonder about the brake light also

 

[Fursty Ferret]

Lower regen. If you can coast to a stop without touching the brakes that will be most efficient overall (because the only energy losses are air and road resistance). Following that, low regen will be best because powertrain losses are proportional to the square of the current, so keeping that lower will allow more energy to be recouped.

Brake light is linked to deceleration value - if you don't reach this, the light doesn't come on. The synoptic display with the little car on it has working brake lights if you're curious.

 

[WannabeOwner]

Does it make a difference to the effectiveness of regen if the car gradually slows over a longer period vs "foot off" and slow rapidly over a shorter period?

Neutral-coasting would be better still I've read threads that calculate Regen is 70% efficient

 

[Andy H]

Cool, thanks everyone. I prefer lower regen (or at least I am better at it), I tend to overcook the 'foot off' and end up having to use a tiny bit of throttle to compensate.

And yeah, I had wondered how much the visualisation is matched to the actual brake light - good to know its in sync.

 

[JIBYC]

Less regen = less heat loss = more efficient?

That said, when it's cold, regen dumps energy into the cabin heater and front inverter to raise the cabin and battery pack temperature. As always there's probably a happy medium somewhere

(Or you can stick it in Track Mode for maximum regen that's borderline uncomfortable)

 

[herrlich98]

The brake light and the on screen visualization match. It amuses me that the little steering wheel on the screen rotates with the actual steering wheel. I think I have double checked at night when you can see the bleed threw of the light in the rear window. For fast vs slow I wouldn't overthink it just do what feels right although I would think for general safety slower is probably best.

 

[Adopado]

An issue that may make a small difference is that if you let the regen act too strongly you may then require to regain speed again by slightly accelerating. This would use some extra energy.

 

[thalpin]

As above - regen over longer time/distance would likely be most efficient (due to IR-squared for power loss during transmission), in addition to it likely resulting in coming off the throttle (and therefore not maintaining/building speed) sooner which also saves energy consumption prior to regen being triggered.

 

[CWT3LR]

i personally think longer and slower is better, i doubt the regen harvesting is that good that you can let off at 70mph and the regen will be better harvested than part throttle let off gradually.

I'm really sorry - but I had a vision of Swiss Toni when I read that!

 

[init6]

I try to keep the green regenerative braking bar as high as possible without maxing it out.

 

[Adopado]

I try to keep the green regenerative braking bar as high as possible without maxing it out.

Somewhat counterintuitively it is best to minimise the green regen unless (admittedly this is quite a big "unless") it means you then can't avoid using the brakes. Regen is only "good" when you need to slow the car and would otherwise require to use the brakes. If there were two identical cars following exactly the same route and both avoided using their brakes during their respective drives the car that had used the most regen over the course of the route would have used the most energy. Honestly ... !

 

[init6]

Somewhat counterintuitively it is best to minimise the green regen unless (admittedly this is quite a big "unless") it means you then can't avoid using the brakes. Regen is only "good" when you need to slow the car and would otherwise require to use the brakes. If there were two identical cars following exactly the same route and both avoided using their brakes during their respective drives the car that had used the most regen over the course of the route would have used the most energy. Honestly ... !

Perhaps I should have been clearer, I only do this when I'm deliberately slowing down - as per the OPs question. Normal driving I wouldn't want regen/braking at all if I could help it.

 

[Idk3]

The brake light and the on screen visualization match. It amuses me that the little steering wheel on the screen rotates with the actual steering wheel. I think I have double checked at night when you can see the bleed threw of the light in the rear window. For fast vs slow I wouldn't overthink it just do what feels right although I would think for general safety slower is probably best.

Did not know of any of this about the visualisation haha !

 

[Astrape]

The synoptic display with the little car on it has working brake lights if you're curious.

Thankyou for bringing the words Synoptic Display into my life. Genuinely made my day with the beauty of that precise label!

 

[Astrape]

When regen is limited due to 100% / cold battery the car applies the friction brakes on strong liftoff. So limiting decel is also beneficial in that case.

 

[JIBYC]

When regen is limited due to 100% / cold battery the car applies the friction brakes on strong liftoff. So limiting decel is also beneficial in that case.

Not unless you've got the correct S/W and turned it on.

I believe it's still not available outside North America.

 

[Roy B]

To first order, it makes no difference. Regardless of your deceleration curve, you are removing the same amount of kinetic energy from the car and converting it into chemical energy in the battery.

To second order, the efficiency of this process will inevitably be dependent on many factors, including how strongly you are decelerating. But to answer the question you would need to understand how the efficiency of each component varies with driving style: the motors, for converting mechanical work into electrical energy, the inverters and other circuits responsible for producing the correct charging voltage, and finally the batteries themselves converting the electrical energy into chemical energy. Tesla probably knows the answer to your question, but to the rest of us it's largely unknowable.

Largely I wouldn't worry about it.

EDIT: Another complexity: these inefficiencies result in a portion of the kinetic energy of the car being converted into heat in the motors, the electronics and the batteries, rather than being stored as chemical energy. However, when it's cold and the car requires heat energy to maintain battery and/or cabin temperature anyway, this heat energy produced as a byproduct of regen isn't entirely wasted - although it is still a comparatively wasteful process compared to extracting heat energy from the air using a heat pump.

 

[Olle]

If you are approaching a red light that will be red for a while so that you have time to optimize for energy:

Regen max until you have just barely enough energy to coast up to the light.

Here is why:
At higher velocity, the main portion of the car's resistance is aerodynamic. If you were to literally coast from high speed to a stop, most of your kinetic energy would be lost to aerodynamic drag, the rest to rolling resistance and 0 would end up in the battery. A Tesla max regen is somewhere around 70 kW, where your drivetrain is still in very low loss territory. Remember that it is designed to go as high as 200 kW to 750 kW i the other direction (depending on model). Aerodynamic losses win big over electrical losses at higher speeds.

This feels very counter intuitive since growing up with ICE cars we learn that the most efficient way is to coast to a stop while saving the brakes at the same time.