How was increased regenerative braking achieved with 8.0?

[Trunk Gap]

On a car w 250mi range let's say, utilizing regen n an average, typical way....how many miles are you "earning back"? Realize lots of variables, what's a ballpark?

Love the new regen btw, noticeably stronger and much easier to time, IMO.

 

[No2DinosaurFuel]

Tesla should have 3 slot slider for the regen. Low, normal, and high for those who want to drive with 1 foot.

On my old spark EV I would always drive in L which is like for normal ICE car as hill driving. It slows the car down quite a bit and most of the time I rarely use the brakes until the last moment at a full stop.

I don't understand why tesla can just up the regen for those who wants it.

 

[cynix]

WITH THAT SAID, nothing prevents Tesla from just hitting the mechanical brakes to simulate regenning down to zero and just have the brakes apply below 10mph and smoothly slow you to a stop.

At the very least, they should apply brakes to simulate regen when regen is limited (battery too cold or too full), so the driver can expect the same behaviour all the time.

 

[brianman]

Tesla should have 3 slot slider for the regen. Low, normal, and high for those who want to drive with 1 foot.

On my old spark EV I would always drive in L which is like for normal ICE car as hill driving. It slows the car down quite a bit and most of the time I rarely use the brakes until the last moment at a full stop.

I don't understand why tesla can just up the regen for those who wants it.

I'll add another for you: Off.

I use Standard for day to day, but I'd love to have Off as an option for (some) road trips and high performance driving.

 

[David99]

On a car w 250mi range let's say, utilizing regen n an average, typical way....how many miles are you "earning back"? Realize lots of variables, what's a ballpark?

Depends entirely on the driving. Regen will not do anything going steady on a more or less flat freeway. Going in the city with lots of sop and go, regen will make a significant difference. Going through mountains with lots of up and down and regen will make a lot of difference as well.
So whatever your typical driving is, the effect will differ.
I think in a best case scenario it would be 20-30%. Normal every day driving, maybe 10-15%. Now some people will jump in and quote Tesla's blog where they say regen is about 80% efficient. That's only the motor/inverter efficiency, not the real world gain-back. As you drive all other losses still apply which have to be added in. For example KIA mentioned a 17% gain in range through regen as a real world number from average driving. A developer of electric motors/inverters once told me best case would be 20% real world gain.

 

[AWDtsla]

Tesla had an ability to nearly double regen with dual motors. There should be plenty of regen capability left, should they choose to turn it on.

Seems like 8.0 makes less regen under 10mph, which frankly sucks around the city. At least this aspect of the car can be datalogged by almost anyone.

https://teslamotorsclub.com/tmc/posts/1751721/

 

[Jawae]

Could someone with 8.0 take a photo of the green "regen" energy bar? One way to possibly objectively measure is to look at the number of Wh that are put back into the battery during max regen. I don't have a photo, but on my 7.1 (I haven't received update yet), it appears to be around the mid 50's. This is highway speed. Of course, at lower speeds, max Wh will be less.

 

[Cosmacelf]

At the very least, they should apply brakes to simulate regen when regen is limited (battery too cold or too full), so the driver can expect the same behaviour all the time.

What an awesome idea! It is actually dangerous when regen is limited like that since you are totally not expecting it. The car really should behave the same way regardless of battery state. IMHO it's a safety issue.

 

[MartinAustin]

I use Standard for day to day, but I'd love to have Off as an option for (some) road trips and high performance driving.

It's always good to be able to have it off once in a while.

Especially for snow.

All this talk about regen being changed on the RWD models... did no-one think to examine the "What's New" text? The description of improved regen that is included in dual-motor cars is not present on the RWD cars. I personally have noticed no difference in the regen of my P85 since changing to 8.0. I don't think there is any.

My theory is they have improved regen on the dual-motor models by improving what's going on with the front motor. When the car is in "torque sleep" on the highway, you only get regen on the rear motor if you have totally disabled the front motor. Perhaps they have found a way to enable regen on both motors during torque sleep - for more than 60kW of regen, the max amount I ever see at high speeds.

You're never going to get a useful increase in regen at low speeds, even with a dual-motor car. However, at 70mph+ when you take your foot off the accelerator, there is a LOT of energy that can be captured.

Interesting thought - since the battery has to be charged with DC, it's reasonable to assume that the power coming out of the motors during regen is 3-phase AC and is converted to DC using the same power electronics that are used when charging at home on AC power. Right? As we all know, 80A x 240V is 19.2kW. However the 60kW displayed on my dashboard during regen is obviously as lot higher than that. Supercharging often applies 90kW + to the battery, but that bypasses the AC charging electronics. I wonder, what's the max amount of charging power that can be continuously fed through the AC charging electronics. Perhaps the relatively instantaneous nature of regen actually allows very high wattages to be applied through the charging electronics - whereas when you're charging for a few hours at home, applying 19.2kW can be quite taxing on the charging electronics from a heat standpoint. So perhaps they have increased the wattage of full regen power in dual motor models, by improvinging the use of the front motor. Since I don't have a dual motor car, someone will have to go out and test this. Look at the dashboard... does the regen wattage meter show more than 60kW in a dual-motor car with 8.0 ?

 

[chillaban]

During regen, it's just driving the motors' inverters in reverse. It is not using the rectifiers for AC wall charging.

The primary limitations are related to the cooling of the motors and the battery pack, as well as not compromising motive power by having the system soak up too much heat during regen.

 

[Ibrido]

I noticed it immediately. But I am also curious, how did they do it with software update alone?

It is software setting. Example - if 20% brake pedal press OR accelerator pedal release, generate 150 amps of current (there is actually a map corresponding to complete pedal position). This AMOUNT of current generation is actually hindrance to vehicle's kinetic energy i.e. regenerative braking. This 150 can be adjusted against say 20% (change the map) which you will see as more or less aggressive regenerative braking.

The map is dynamic, because regeneration (motors acting as generators) causes motors to heat as well so according to temperature of motors & battery, map OR cooling flow is adjusted.

Any regeneration above hardware's capability will require new hardware so Tesla can play with software as far as it is under motor's capability.

Wish I can explain it better if you have any further doubts

 

[Chopr147]

It is software setting. Example - if 20% brake pedal press OR accelerator pedal release, generate 150 amps of current (there is actually a map corresponding to complete pedal position). This AMOUNT of current generation is actually hindrance to vehicle's kinetic energy i.e. regenerative braking. This 150 can be adjusted against say 20% (change the map) which you will see as more or less aggressive regenerative braking.

The map is dynamic, because regeneration (motors acting as generators) causes motors to heat as well so according to temperature of motors & battery, map OR cooling flow is adjusted.

Any regeneration above hardware's capability will require new hardware so Tesla can play with software as far as it is under motor's capability.

Wish I can explain it better if you have any further doubts

Thank you.
My confusion is due to looking at it in a mechanical sense. ie....The re-gen is set to a certain resistance at the factory. You know turn a screw to lessen or strengthen the resistance.
I will need to look at this car less like a standard car and more like a computer on wheels.
There is NOTHING to tinker with, i'll just have to be happy cleaning it all the time

 

[RogerHScott]

I will need to look at this car less like a standard car...

I.e., "not at all like..."

There is NOTHING to tinker with...

Nothing for you to tinker with -- everything for Tesla to tinker with

 

[SD Diver]

Actually (having done a few years of high power AC servomotor control for a defense contractor), it isn't just software. AC induction motors, even with resolvers for rotor position, are a pain to control as a servomotor and at extremely low speeds (e.g. commanding a fixed position, slowing down to a stop). Once the speed gets down to a certain level, you have a lot more torque pulsing effects that might lead to low speed shudder especially if something else happens (e.g. hitting a small bump in the pavement, wind blowing, etc). And the net effect would be a loss in energy as opposed to regen.


WITH THAT SAID, nothing prevents Tesla from just hitting the mechanical brakes to simulate regenning down to zero and just have the brakes apply below 10mph and smoothly slow you to a stop. That aspect is just software. But inherently, a PMSM makes sense for true regen down to zero. An ACIM does not.

Hmmm... id iq...

 

[chillaban]

Hmmm... id iq...

Don't forget choosing a slip angle for ACIMs too

 

[AmpedRealtor]

I don't notice any change to regen in my P85, but I have noticed that sport steering mode seems generally less sensitive and twitchy at freeway speeds. Probably just in my head.

 

[David99]

I don't understand why people assume regen produces so much heat. The losses in the motor and inverter and battery are about the same as when discharging the battery = normal driving. The cooling system can handle higher rates easily. Regen are always relatively short moments followed by normal driving. If overheating was the reason regen power was limited to 60 kW then there would be even more reason to limit acceleration also to the same amount as it happens much more often and longer.

 

[AWDtsla]

I don't understand why people assume regen produces so much heat. The losses in the motor and inverter and battery are about the same as when discharging the battery = normal driving. The cooling system can handle higher rates easily. Regen are always relatively short moments followed by normal driving. If overheating was the reason regen power was limited to 60 kW then there would be even more reason to limit acceleration also to the same amount as it happens much more often and longer.

First law of thermodynamics? Who said regen is just as efficient as normal driving?

 

[chillaban]

I don't understand why people assume regen produces so much heat. The losses in the motor and inverter and battery are about the same as when discharging the battery = normal driving. The cooling system can handle higher rates easily. Regen are always relatively short moments followed by normal driving. If overheating was the reason regen power was limited to 60 kW then there would be even more reason to limit acceleration also to the same amount as it happens much more often and longer.

In my professional experience controlling AC motors, even on a PM motor, generation was considerably less efficient than motoring. In my particular case I was working on permanent magnet 3 phase motors, and we were achieving something like 90% efficiency motoring but only around 75% to 80% efficiency generating. You could definitely hear a difference in the inductor whine too between generating and motoring.

 

[David99]

First law of thermodynamics? Who said regen is just as efficient as normal driving?

Tesla
The Magic of Tesla Roadster Regenerative Braking
In this article they mention the wheel to battery efficiency is 80%. That was the first version of the Roadster. Efficiency in the Model S has been improved since then. In normal driving the Model S motor/inverter is 90% efficient, the battery also just over 90%. So combined we are slightly above 80% so regen is in the same ballpark.