Regenerative Braking Capacity

SafeWill

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@ajdelange, @CappyJax

About regenerative braking limitation encountered on the 3, I am still surprised at how limited it is compared to the Chevy Volt. I understand the limited capacity of the cold battery, on the other hand, I have never been limited in my memory for the last 6 years on the Volt. And someone driving a Bolt indicated that even at 0F, after 1km he is able to have full deceleration. Now deceleration doesn’t mean regeneration, and I am wondering how it is possible for the GM product to decelerate as usual even at very low temperatures, and the 3 getting limited at a cool 55F?
I am digging some answers as I had to literally jump on the brakes lately on my new 3 after 40 minutes driving at 55F because I expected the regenerative braking to take action when exited the highway but got too close from the vehicle in front of me. And to put the story in context, I had just put the heated seat, not warmed the cabin that also warms the battery pack (I am still learning my new sci-fi toy).
There seems to be a different technology between Tesla and GM, and I am wondering what it is.
The Volt has a remarkable reliability and the battery seems to be really tough, I don’t think I ever lost some range after 160,000 kms. So this specificity to decelerate even in super cold weather does not affect the components durability.
Now, can you make an EV car decelerate through the motor without regenerating the battery? Because I think this is where the difference of technology is.
I love the fact that EVs decelerate by itself without touching the brakes, I am a full supporter of that, but nowadays, it is always a surprise if I am going to use the brakes or not, which in my opinion is not safety oriented.
You seem to have an engineer perspective that understand the system deeper than the average people, could you enlighten me on this feature please?

Thank you
 

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@ajdelange, @CappyJax

About regenerative braking limitation encountered on the 3, I am still surprised at how limited it is compared to the Chevy Volt. I understand the limited capacity of the cold battery, on the other hand, I have never been limited in my memory for the last 6 years on the Volt. And someone driving a Bolt indicated that even at 0F, after 1km he is able to have full deceleration. Now deceleration doesn’t mean regeneration, and I am wondering how it is possible for the GM product to decelerate as usual even at very low temperatures, and the 3 getting limited at a cool 55F?
I am digging some answers as I had to literally jump on the brakes lately on my new 3 after 40 minutes driving at 55F because I expected the regenerative braking to take action when exited the highway but got too close from the vehicle in front of me. And to put the story in context, I had just put the heated seat, not warmed the cabin that also warms the battery pack (I am still learning my new sci-fi toy).
There seems to be a different technology between Tesla and GM, and I am wondering what it is.
The Volt has a remarkable reliability and the battery seems to be really tough, I don’t think I ever lost some range after 160,000 kms. So this specificity to decelerate even in super cold weather does not affect the components durability.
Now, can you make an EV car decelerate through the motor without regenerating the battery? Because I think this is where the difference of technology is.
I love the fact that EVs decelerate by itself without touching the brakes, I am a full supporter of that, but nowadays, it is always a surprise if I am going to use the brakes or not, which in my opinion is not safety oriented.
You seem to have an engineer perspective that understand the system deeper than the average people, could you enlighten me on this feature please?

Thank you
I am interested in this as well because I was surprised to hear that Tesla's won't bring the car to a complete stop.
My Leaf brings me to a complete stop with the e-pedal activated similarly to the sounds of it as your Volt. All the while showing regen and recently at around 32 F no different than it was when it was 80 out.
There are no regenerative braking assist levels to choose from, it is on or off. This is one area where all EV's could benefit especially knowing everyone drives different and the strength of the e-pedal is quite surprising for first time drivers and it can actually detract from the experience because it is so different.
 

ajdelange

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The first thing one needs to understand is that the machines in these cars are 4 quadrant machines. That means that torque can be supplied to or drawn from them whether they are running forward or in reverse. Or put more simply you can either send power to them or take power from them. There are, IMO, three things that make modern BEVs possible
1)Efficient motor/generators
2)Batteries with reasonable storage capacity for their size/weight/cost
3)Sophisticated electronics/software to control the motor/generator and manage the batteries.

"Dynamic braking" has been around for well over a century. An electric motor is used as a generator and the power generated is dumped into a load which, in the early days and in diesel electric locomotives today is a big resistor bank (heater). But the kinetic or potential energy dumped into a resistor is lost as heat. If you can get that generated energy back into the battery clearly the system will overall be more efficient and that's what these cars do. They use the current from the generator to charge the battery. The sophisticated electronics (Item 3) know about the status of the battery and how rapidly it can be safely charged. They can send commands to the generator to produce just that amount of energy. The braking torque applied to the wheels is proportional to the current taken and thus the amount of braking depends on how much the BMS thinks the battery should have. If the battery is the only sink for current then the battery will limit the amount of braking. But if there is another place to absorb current it isn't. If one shifts all or some of the current to another sink then the battery isn't the limit. There are lots of ways to waste power in a system. For example the AC produced by the motor has to be converted to DC to charge the battery. This is done by sending it through semi conductor "switches". If these are properly operated (switched full on to full off very fast) they are efficient and produce little heat. If they are only switched partially on then they get hot. This is how the 3 heats the battery without a separate battery heater. I am not suggesting that the Leaf or Volt do this. I'm just trying to get across that the designers have, with these modern electronics, very great flexibiiity in what they can do. The reason the Teslas and GM products exhibit different regen braking behaviour is because they are designed differently.

It is my understanding that some of the earlier cars do not attempt to regulate the temperature of the battery. Perhaps the battery chemistries in those cars are less sensitive to temperature and to rapid charging at high SoC than Tesla's. Perhaps the designers of those cars, rightly or wrongly, determined that there was no need to limit charge rates when the battery was cold or full. Perhaps they have load banks. I don't know. The point is that a designer can do pretty much anything he wants (within limits, of course).
 
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Perhaps the volt uses the regen energy to warm up the batteries so they can then accept the regen charge?
 

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Do you know any forum where we could eventually ask a (former) Tesla engineer about this subject?
 

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Does anyone else on here read this threads with extreme interest, but leave them feeling like they aren't very smart?
 

SafeWill

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Does anyone else on here read this threads with extreme interest, but leave them feeling like they aren't very smart?
I am sorry if I hurt someone with my last question. I have way less knowledge than most writers like Ajdelange or CappyJax, although it is precious informations to understand how it works.
If I were 20 years old again, I would probably do a job linked to the electric vehicle into antique cars. Not than I am not happy with what I am doing, realizing myself into my passion, but when you reached the ultimate goal you fixed 20 years ago, you look behind and you feel nostalgia of the effervescence of the beginning I suppose ☺
I just read a thread about a Chevy Bolt into a VW Vanagon done here in Quebec, it is just a matter of time before those conversions happens widely and we’ll mix Tesla components with GM stuff on a current basis.
Anyway, this regenerative matter is of certain interest for a future conversion.

@ajdelange, I would probably ask this person what could be the reason why there is such a decelaration capacity in cold weather on the GM product and why Tesla did not go that way, thinking it could have been a reliability issue but it doesn’t seem to be when we look at the the Volt or Bolt results (although I just read few articles about it and you can prove the opposite with different statistics unknown from me)

But as you talked about it, future vehicles would have solved the limited regenerative capacity with ultra capacitors, it is just a matter of time.
 

ajdelange

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Does anyone else on here read this threads with extreme interest, but leave them feeling like they aren't very smart?
You have to be very, very smart (smarter than Elon Musk and he must be pretty smart because he's worth $23B) to understand all the details of how this works. But you don't need to be that smart to understand the general concept if you can grasp one idea. Regenerative braking is based on the fact that the things we call "motors" aren't just motors, they are motor/generators. They are symmetrical machines. Step down on the pedal and you send more power from the battery to the machine (and thence to the road) and go faster. Back off on the pedal and you draw power from the road (causing you to slow down) to the machine and from it to the battery. This is not the way we have thought of "motors" before and is particularly unintuitive in the case of ICE cars. Taking your foot off the gas pedal does not (unfortunately) return petrol to the tank.

The recent questions here relate to what's between the pedal* and the machine and the answer is "a bunch of computers". This should make it clear that there is infinite flexibility in how the car can interpret you pedal inputs and translate them to machine commands. That's why the different makes respond differently WRT regenerative braking.

*We recognize but choose to ignore here for simplicity that some implementations require or respond to controls (paddles, switches) other than the "gas" pedal in managing regen and some, I believe, do not bring it on when the gas pedal is released instead requiring the brake pedal to be depressed.
 

ajdelange

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@ajdelange, I would probably ask this person what could be the reason why there is such a decelaration capacity in cold weather on the GM product and why Tesla did not go that way, thinking it could have been a reliability issue but it doesn’t seem to be when we look at the the Volt or Bolt results (although I just read few articles about it and you can prove the opposite with different statistics unknown from me)
I think I can answer that question broadly and the answer is that in the opinion of the Tesla engineers the current developed by their motors during deceleration at reasonable rates under normal driving conditions would exceed the levels that they considered prudent for charging their battery chemistry. They would, of course, not know why GM doesn't worry about this (unless you found one who used to work for GM). Possible answers are
1)GM wasn't aware of the extent to which fast charging of cold batteries shortens their life
2)GM was aware and didn't care
3)GM dumps excess regen energy into a resistive load rather than the battery
4)Tesla was over conservative
5)GM's battery chemistry is such that high current charging in the cold does not appreciably shorten battery life
6)....

Anyway, this regenerative matter is of certain interest for a future conversion.
I see. Clearly you have some trades to make. You will have to determine how to manage regen based on which battery chemistry you choose, how you want the vehicle to respond in potential regen sitruations, whether you intend to manage battery temperature etc. I'm afraid I don't know where to send you for information. The manufacturers (at least Tesla) seem pretty reluctant to reveal trade secrets. There is a ton of literature on battery technology (a couple of journals, several books) but these are highly technical and probably not of much practical use to a guy trying to put nuts and bolts together.

But as you talked about it, future vehicles would have solved the limited regenerative capacity with ultra capacitors, it is just a matter of time.
Caps may turn out to be the solution or part of it but they have a way to go. I grew up when a 100 microfarad 200V capacitor was considered big. It held 2 j fully charged. Today you can buy (from Amazon) a 500f 2.8V capacitor. It holds 1960 j but even so that's only about half a watt hour. I just happened to notice that rolling down a hill on my descente for about 30 sec the car was generating 15 kW. That amounts to 125 Whr and would require 250 of these capacitors to hold.


Looked further and found a 1000 f 16 V array that would hold 36 kWh for $490 it would only take 4 of those to hold the charge I produced rolling down that little hill.
 
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CappyJax

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I am sorry if I hurt someone with my last question. I have way less knowledge than most writers like Ajdelange or CappyJax, although it is precious informations to understand how it works.
If I were 20 years old again, I would probably do a job linked to the electric vehicle into antique cars. Not than I am not happy with what I am doing, realizing myself into my passion, but when you reached the ultimate goal you fixed 20 years ago, you look behind and you feel nostalgia of the effervescence of the beginning I suppose ☺
I just read a thread about a Chevy Bolt into a VW Vanagon done here in Quebec, it is just a matter of time before those conversions happens widely and we’ll mix Tesla components with GM stuff on a current basis.
Anyway, this regenerative matter is of certain interest for a future conversion.

@ajdelange, I would probably ask this person what could be the reason why there is such a decelaration capacity in cold weather on the GM product and why Tesla did not go that way, thinking it could have been a reliability issue but it doesn’t seem to be when we look at the the Volt or Bolt results (although I just read few articles about it and you can prove the opposite with different statistics unknown from me)

But as you talked about it, future vehicles would have solved the limited regenerative capacity with ultra capacitors, it is just a matter of time.

Ask any questions you like. We are all here to learn.

One big issue with lithium ion batteries is that if you charge them below freezing, you will kill the battery in a very very very short amount of time. That doesn't mean you can't charge any EV in below freezing temps. Most all the EVs have safeguards, so if you plug it in when the batteries are below freezing, the charger first warms the batteries before charging them.

When you have regenerative braking on, the EV's motors will become generators by simply changing the flow of current through the motor. The turning of the wheels creates power and that power is sent back to the batteries, but by creating that power, it creates a drag on the motors which is what creates the braking force.

When below freezing, the most efficient thing to do would be to use the regen power to heat up a resistive circuit in the battery coolant so as to warm the coolant to warm the batteries so they could be used sooner for regenerative braking. If this is not done, the batteries will still get warmer simply from the fact that they are being discharged in the course of their normal use. So, my guess is that GM has a resistive circuit which is used to warm the coolant, whereas Tesla just waits for the batteries to warm themselves from being discharged.
 

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You have to be very, very smart (smarter than Elon Musk and he must be pretty smart because he's worth $23B) to understand all the details of how this works. But you don't need to be that smart to understand the general concept if you can grasp one idea. Regenerative braking is based on the fact that the things we call "motors" aren't just motors, they are motor/generators. They are symmetrical machines. Step down on the pedal and you send more power from the battery to the machine (and thence to the road) and go faster. Back off on the pedal and you draw power from the road (causing you to slow down) to the machine and from it to the battery. This is not the way we have thought of "motors" before and is particularly unintuitive in the case of ICE cars. Taking your foot off the gas pedal does not (unfortunately) return petrol to the tank.

The recent questions here relate to what's between the pedal* and the machine and the answer is "a bunch of computers". This should make it clear that there is infinite flexibility in how the car can interpret you pedal inputs and translate them to machine commands. That's why the different makes respond differently WRT regenerative braking.

*We recognize but choose to ignore here for simplicity that some implementations require or respond to controls (paddles, switches) other than the "gas" pedal in managing regen and some, I believe, do not bring it on when the gas pedal is released instead requiring the brake pedal to be depressed.
Being rich doesn't make you smart. I don't think Musk is that smart. When you have billions of dollars and shotgun ideas, some of them are going to hit.
 

ajdelange

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Being rich doesn't make you smart.
I have a friend that says "I'd rather be lucky than smart" and I agree with that but my lifelong observation has been that all the people I know that have been lucky were the smart ones. Funny thing about that.


I don't think Musk is that smart.
You are entitled to your opinion, of course, but it's pretty apparent to most of the rest of us that he is a genius; a mad genius perhaps but a genius nevertheless. Admission to Standford alone should be sufficient evidence of that. People who aren't that smart don't get admitted to Stanford.


When you have billions of dollars and shotgun ideas, some of them are going to hit
It's been my privilege to work with several geniuses so perhaps I understand better how they work than most. The shotgun ideas are the source of the billions provided that a component of the individual's genius is what many would call "business sense". I have known geniuses that have none of that and they have not prospered. IOW part of genius is knowing which of the "shotgun ideas" are likely to hit. I always thought PayPal was a pretty dumb idea. This is what distinguishes me from Elon Musk in both intelligence and net worth.

As a total aside, one of things I noticed about geniuses is that they don't sleep more than a couple of hours a night and can go for days without sleeping at all. Note that Elon Musk has exhibited this symptom.
 
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ajdelange

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When you have regenerative braking on, the EV's motors will become generators by simply changing the flow of current through the motor.
I've tried to make the concept as simple as possible so people without degrees in engineering can understand at the highest level at least how regen braking works. But if you have interpreted what I said as implying that the control is simple you have misunderstood. This is not a matter of adjusting the field rheostat on a DC motor. These are three phase motors and translating driver input and car speed into proper torque and field commands is a very complicated process which must be done at a rate so high that DSP techniques are often employed. Beyond that D and Q commands must be translated, again at high speed, into current commands to the windings. These cars do what they can do not only because we have efficient motors and decent battery energy density but because of incredibly sophisticated electronics which can efficiently switch hundreds of amps at hundred of volts at sub microsecond rates.
 
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