Question about regen

[Dan203]

So I've read that when the battery is full regen is disabled. When this happens is the resistance from regen taken away? Like if you're accustomed to single pedal driving and you reach a point where regen is disabled will this reduce/remove the resistance from the regen motor and force you to use the brake instead?

 

[phigment]

So I've read that when the battery is full regen is disabled. When this happens is the resistance from regen taken away? Like if you're accustomed to single pedal driving and you reach a point where regen is disabled will this reduce/remove the resistance from the regen motor and force you to use the brake instead?

Yes, the braking behaves just like a car without regen at that point.

 

[AlanSubie4Life]

the regen motor and force you to use the brake instead

I guess I was the one who said that recently to you, but...yes, that's what happens. It's not the "regen" motor, BTW - it's the same motor/motors that are used for everything else, it's just used as a generator instead (it cannot be used as such, of course, if there is nowhere left to store the energy).

There's no real downside to charging your car to 100% one time (or multiple times) and trying it out for yourself just to see what it is like. You'll see a lot of dots on the left hand side of the green/black bar below the speedometer.

 

[ZOMGVTEK]

The regen is the car using the regular drive motor to slow the car down. This energy normally would go into heating up the brakes, but instead it uses the motor as a generator and charges the battery. The issue here, is the battery can't take charge at an unlimited rate. The colder it is, the more reluctant it is to charge. The fuller it is, the slower it wants to charge as well. So as the battery nears full regen power starts to fade away. It's not quite so much that its suddenly disabled, it just has no more space left to put the power. There's no set level at which this becomes noticeable, it depends on the battery age, current state of charge, temperature, and possibly other factors.

But yeah, basically, if your battery is near full you won't have any braking effect as you lift off the throttle. It may be there, but its going to be very little.

 

[Dan203]

I guess I was the one who said that recently to you, but...yes, that's what happens. It's not the "regen" motor, BTW - it's the same motor/motors that are used for everything else, it's just used as a generator instead (it cannot be used as such, of course, if there is nowhere left to store the energy).

There's no real downside to charging your car to 100% one time (or multiple times) and trying it out for yourself just to see what it is like. You'll see a lot of dots on the left hand side of the green/black bar below the speedometer.

I haven't got the car yet. I was just curious if this could be a potential explanation for the people that claim to have "unintended acceleration". If you become dependant on regen as a method for stopping and it suddenly shut off then it could feel like acceleration. I just wasn't sure if that's how it worked or not. I thought that maybe when regen "shut off" it automatically switched to applying brake so that the force would be consistent. Apparently not.

This actually seems to be a bit dangerous. I know it's unlikely but what if there was some sort of regen failure? Or a glitch that caused it to turn of via software randomly. This could catch a driver completely off guard.

 

[AlanSubie4Life]

This actually seems to be a bit dangerous. I know it's unlikely but what if there was some sort of regen failure? Or a glitch that caused it to turn of via software randomly. This could catch a driver completely off guard.

I suppose it's possible. Generally speaking I don't find limited regen to be an issue, even if it changes with time (which it does - in long downhills you can get progressively less regen, but relatively small steps within the total range of available regen). In the end it is just like driving a regular car when you don't have regen, and the reflex to hit the brake if you need to slow down is quite ingrained. Some people do not like the changing behavior, though. I imagine the mixed reviews are due to personal preference and personal adaptability.

I don't think it's really related to the unintended acceleration, though regen in general might be a cause for "confusion" with some people. Obviously there are a lot of threads on that where people speculate about why people hit the accelerator rather than the brake. If anything, based on some people's theories, reduced regen would actually reduce instances of unintended acceleration.

 

[ZOMGVTEK]

For plenty of people I could see how this could be considered to be dangerous. I find it to be remarkably easy to depress the brake if I want to slow down. However the number of documented cases of real unintended acceleration in the past is quite substantial. Presumably in all of these cases all the driver needed to do was press the brake pedal, but since it didn't respond the way they expected, they ended up not pressing it hard enough to slow the vehicle while the throttle was held open.

Still, I don't see this as a Tesla problem. Its an industry wide limitation, and is worse on some cars than other. I had a Leaf that would have near zero regen at 80% when the battery is cold. And in that car, the brake pedal had a dead zone before it would use the friction brakes that was intended to be regen only. But with an old and cold battery, the car was apparently tuned very poorly and it didn't know there was no regen until you hit the brakes. So the first 1/4 of the pedal did absolutely nothing, until you pressed past it and then it suddenly slammed on the brakes. I knew it was coming every time, but there is nothing that could be done about it. The first stop every time the car was powered up with a cold battery just resulted in a harsh stop. It had some sort of electronic brake booster that literally 'moved' the brake pedal position internally, and it was somewhat unpredictable. I consider this to be dangerous and a severe design fault. But with a Model 3, something of this nature is unlikely and most things can be resolved over the air. If you just charge well below 100% you should basically always get good regen unless you park the car in very cold weather for days.

 

[Rocky_H]

I was just curious if this could be a potential explanation for the people that claim to have "unintended acceleration". If you become dependant on regen as a method for stopping and it suddenly shut off then it could feel like acceleration.

No, it's not related to lack of regen, but more from electric cars by default not having that constant pulling forward that automatic transmissions in gas cars do. You can tell this by when those events are always reported as ocurring. It is when someone is pulling into a parking spot, and when they are about to stop, the car lurches forward.

In a gas car with automatic, as people are slowing down to make that turn into the spot and slowly pulling up to the end of the spot, they were already slowing down with their foot on the brake to hold back the automatic creeping forward. And then they ride the brake, ride the brake, ride the brake, and then STOP. So they are used to that final stopping point being to just step all the way down on the pedal that their foot is on.

Sometimes people who are new to electric cars still have that old habit. Except the car doesn't creep forward to pull itself into the parking space with your foot riding the brake. So they have to be barely pressing the accelerator a little bit, and then a little bit more, and then a little bit more, and then..... if they revert to habit, they just step down on that accelerator pedal instead of remembering they have to switch over to the brake for that final stop.

Teslas do have a software switch called "creep mode" that you can enable that imitates that automatic transmission feel. Most Tesla drivers kind of don't like it and keep it turned off, but it can take a bit of getting used to for a couple days.

 

[ewoodrick]

Limited regen, in my mind is way overrated. If I don't slow when I let off the accelerator, I use the brake. If someone thinks that it is a big issue, then we need to revoke your driver license for non-regen vehicles.

And you can't call the Tesla a single pedal driving car.

 

[Runt8]

I haven't got the car yet. I was just curious if this could be a potential explanation for the people that claim to have "unintended acceleration". If you become dependant on regen as a method for stopping and it suddenly shut off then it could feel like acceleration. I just wasn't sure if that's how it worked or not. I thought that maybe when regen "shut off" it automatically switched to applying brake so that the force would be consistent. Apparently not.

This actually seems to be a bit dangerous. I know it's unlikely but what if there was some sort of regen failure? Or a glitch that caused it to turn of via software randomly. This could catch a driver completely off guard.

It’s not very dangerous - regen braking is pretty light, so in order to use it well you need to start braking pretty far in advance. For any sort of emergency braking situation you would end up using the brake pedal, regardless of how much regen you’re actually getting. After driving with it for awhile you find yourself subconsciously adjusting to the amount of regen you’re getting (which varies not only with state of charge but also with temperature and speed) and always ready to switch over to the brake pedal if necessary.

 

[Dan203]

Limited regen, in my mind is way overrated. If I don't slow when I let off the accelerator, I use the brake. If someone thinks that it is a big issue, then we need to revoke your driver license for non-regen vehicles.

And you can't call the Tesla a single pedal driving car.

I was thinking more about a scenario where it was working and then it hit a limit where it just shut off mid stop

 

[Dan203]

It’s not very dangerous - regen braking is pretty light, so in order to use it well you need to start braking pretty far in advance. For any sort of emergency braking situation you would end up using the brake pedal, regardless of how much regen you’re actually getting. After driving with it for awhile you find yourself subconsciously adjusting to the amount of regen you’re getting (which varies not only with state of charge but also with temperature and speed) and always ready to switch over to the brake pedal if necessary.

I tried both settings when I test drove. The Standard mode is pretty heavy. More than enough to bring me to a stop without touching the brake in most cases.

 

[Runt8]

I tried both settings when I test drove. The Standard mode is pretty heavy. More than enough to bring me to a stop without touching the brake in most cases.

On a Tesla regen braking alone will never bring you to a complete stop.

 

[JasonR67]

I was thinking more about a scenario where it was working and then it hit a limit where it just shut off mid stop

It never feels like it just turns off.. it goes from strong .... less strong .. less.. weak... none..

It doesn't take long for it to become predictable.

 

[jjrandorin]

I tried both settings when I test drove. The Standard mode is pretty heavy. More than enough to bring me to a stop without touching the brake in most cases.

You will find (when you have the car) that it is in fact NOT enough to "bring you to a stop without touching the brake in most cases" unless you are driving uphill.

it is enough to "bring you to 3-5 mph" in general usage, with a "tap" on the brake to stop, but tesla does not have "one pedal driving".

Also on the other topic of unintended acceleration, I posted what I feel that is in another thread, which is basically the same thing as @Rocky_H said.

My post in another thread on the topic of unintended acceleration:

=======================================
Friend crashed model 3 and they think due to foot obstruction (maybe)

Right, I think that too. What I believe happens in these "accidently stepped on the go pedal but thought it was the brake" situations is something along these lines:

1. Driver new to EVs and regen braking
2. Driver partially distracted (meaning any type of distraction, like looking at phone, talking to someone, fiddling with touchscreen, or even thinking heavily about whatever activity happens when they get wherever their destination is)
3. Driver starts to release the accelerator, car starts regen braking, all feels normal to the driver.
4. Driver realizes that they are not slowing down "enough" as their partial distraction snaps back into razor focus on whatever it is their car is approaching and going to hit due to "not slowing down enough"
5. Muscle and brain memory translates to them that the car is already slowing down. Since they are already slowing down, muscle / drive memory will communicate to them that their foot must already be on the brake... because they are slowing down.
6. They press harder on the "brake" to slow down more to avoid hitting whatever they were about to hit.

I believe all of that happens in a split second of semi conscious thought. When I first brought my model 3 home, it was my first EV. I turned ON creep mode, and turned regen braking down to low. This made the car drive much closer to what my ICE cars did. I only drove that way for a day or two, then turned off creep mode, and regen braking. I made SURE to be FULLY focused on the car during my commutes. No touching touch screen for anything, no bluetooth calls, no focus on what tasks I had to do at work or home when I was going to either place.. just focus on the car and what I was feeling.

I only drove like this (with this amount of focus on what the car was doing) for an additional couple of days, until I was comfortable that my muscle memory was aware of what THIS car was doing. Total of 3-4 days of "getting used" to the car. Everyone is different, but regen braking is foreign to people who are not EV drivers and can fairly easily cause the above confusion I think.

No statistics or anything, just my opinion.

 

[darth_vad3r]

So they are used to that final stopping point being to just step all the way down on the pedal that their foot is on.
[...]
and then..... if they revert to habit, they just step down on that accelerator pedal instead of remembering they have to switch over to the brake for that final stop.

You have to admit, that if we were in a parallel universe where creep did not (and never did) exist, this type of unintended acceleration wouldn't happen. Nobody would press down more on the same pedal they are using to move to stop.

I find the one-pedal regenerative driving experience without creep to be awesome for parking.
Let go of the accelerator to slow down a bit, let go of the accelerator a bit more to slow down a bit more, slow down to a crawl ... press the brake when I want to stop. Easy.

 

[darth_vad3r]

Limited regen, in my mind is way overrated. If I don't slow when I let off the accelerator, I use the brake. If someone thinks that it is a big issue, then we need to revoke your driver license for non-regen vehicles.

And you can't call the Tesla a single pedal driving car.

Ever heard of this non-regen vehicle called a manual or standard transmission aka "stick shift" ... and "engine-braking" and gearing down?

I used this all the time, and love regen because it simulates it ... I'd prefer to charge lower and keep regen (even if there weren't other reason to avoid 100%, like degradation).

 

[darth_vad3r]

It’s not very dangerous - regen braking is pretty light, so in order to use it well you need to start braking pretty far in advance. For any sort of emergency braking situation you would end up using the brake pedal, regardless of how much regen you’re actually getting. After driving with it for awhile you find yourself subconsciously adjusting to the amount of regen you’re getting (which varies not only with state of charge but also with temperature and speed) and always ready to switch over to the brake pedal if necessary.

I mainly agree with this, depending on the definition of "pretty far in advance". I also find standard regen stronger than "pretty light" for normal slowing down scenarios (not for stopping quick in an emergency).

Limited regen isn't dangerous. More annoying.

I typically slowed down in advance in my manual transmission car just for better fuel efficiency and to avoid gearing down and back up ... with full standard regen I seem to slow down later than before because letting off the pedal all the way is fairly strong and would slow me down to a trickle way too early for trailing traffic to not get annoyed with me. Yes, you can control the regen by slowly releasing the accelerator, but I usually give it a quick 'let go' first to cut off a bunch of speed. If regen is limited I don't find it dangerous, I just find it annoying ... "huh, crap, I guess I gotta put some wear and tear on the friction brakes this stop ... wish I had noticed that and slowed down earlier".

 

[darth_vad3r]

On a Tesla regen braking alone will never bring you to a complete stop.

If you are on an ever so slight incline, or slow down early enough on a flat, you can trickle to a stop and engage the friction brakes at 0 km/h. It's rare but I've done it. Usually I can get down to 5 km/hr or lower before using the friction brakes.

 

[M3BlueGeorgia]

On a Tesla regen braking alone will never bring you to a complete stop.

It'll bring you down to about 5mph and you are responsible for the rest.

You get used to it. In addition, you'll spend most of the time in traffic with TACC activated, so the car will just match the car in front of you, so most of the time it is "zero pedal driving". You have to hit the brake pedal when you are the front car at a red traffic light or at a stop sign.