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Regen braking and brake lights
- Thread starter Jeffruby
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- Driving Dynamics Model S
I had wondered the same--how come I haven't been rear ended yet? yes the brake light does come on.
-m
-m
I was wondering why anyone would want to 'break" their lights??? Then I realized you were talking about "brake" lights. They come on whenever you regen greater than 30.
mknox
Well-Known Member
My sense is that the brake lights flash on and off as you re-gen more than what would be typical in a regular car. In fact, the other day I was driving in heavy freeway traffic where the speed would range up and down from about 40 MPH to 70 MPH with the ebb and flow of traffic. There was a guy fairly close behind me and I could see him waving his hands wildly at me in the rear view mirror and I think he thought I was being an ass and tapping the brakes constantly.
NigelM
Recovering Member
mknox
Well-Known Member
For sure the guy was tailgating, but unfortunately that is the norm around here. My point was that I think the lights flick on and off more than what might be considered "normal". A gasoline car will decelerate a bit when you let off the gas due to engine braking, but not flash the brakes. The lights should and do come on under full re-gen, but I'm talking about moderate deceleration.
It is only an assumption, because I don't want to be staring at the 17" screen to verify this or not when I should be looking at the road.
NigelM
Recovering Member
If that makes folks who are tailgating me pay attention, I'm fine with it. It's much better than someone plowing into the back of me because I slowed faster than they expected.
We have to remember that as EVs become more prevalent so other drivers will get used to the regen brake lights.
mknox
Well-Known Member
Nope, there aren't even amber lights on the back of North American Model S cars. It's just the regular brake lights coming on... the same ones that come on when you hit the pedal.
I haven't done a serious study of this but did check things out to satisfy my own (limited) curiosity. The brake lights come on, it seems, at varying regen values depending on the speed (amount?) you are decelerating. So at highway speed and slowing down, I noticed it was around -30. At city road speed (50-70kph or 30-40mph), it was somewhere around -15. Then after that it's a real challenge to get them to light up at all without the brake pedal. Since I often modulate the fun pedal coasting up to a red light, I think that means my brake lights are often NOT displayed even though I'm slowing down somewhat. However I also watch the behaviour behind me and change my deceleration rate depending on what the other driver is doing (i.e., delay any regen braking until closer to the stopped traffic, etc).
I'm still getting used to estimating exactly when to fully release the fun pedal so that a) I come to the near-stop on regen only at the perfect distance behind the stopped traffic or at the red light, and b) I get maximum regen on the car. Not concerned about refilling the battery charge; it's just a fun challenge for me. Yes, I'm easily amused - comes from all those schoolroom times of being told to go sit in the corner. :tongue:
I'm still getting used to estimating exactly when to fully release the fun pedal so that a) I come to the near-stop on regen only at the perfect distance behind the stopped traffic or at the red light, and b) I get maximum regen on the car. Not concerned about refilling the battery charge; it's just a fun challenge for me. Yes, I'm easily amused - comes from all those schoolroom times of being told to go sit in the corner. :tongue:
More likely he was excited to see a Model S.
It's easy to tell when the brake lights are on when you drive at night with the rear camera on. I doubt that your brake lights are constantly flashing. Regardless, the opinion of tailgaters is their problem, not mine.
mknox
Well-Known Member
Trust me, the hand gestures I was seeing are generally not meant to convey glee and excitement :smile:
It was daytime, but that is a good tip. I may try that for a bit just to see. I have used the Charging screen where you can kind of see the brake lights go on and off (as well as headlights, turn signals and so forth). I agree 100% with your comment on tailgaters, but it seems around here provoking them with jabs of brake lights does not generally make things better.
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I wonder if the car is pre-wired for the amber turn signals used in the European markets???
Brass Guy
Active Member
I'm reasonably sure that at a high enough speed, the brake lights don't turn on with regen alone.
The deceleration from max regen feels less pronounced at higher speeds. My guess is that the higher rotational speed of the rotor (higher frequency) provides higher kW regen with less decelerating force. Some EE can reply and confirm or refute.
Then when you slow enough that the decelerating force crosses a threshold, the brake lights turn on. I think this is still at a highway speed, certainly above 50mph.
The deceleration effect seems to increase to a maximum, I think around 30mph or so, then the regen slowly tapers to maintain a constant deceleration as you slow further.
Then the deceleration effect decreases as well, presumably to provide a smoother stop. The decrease in deceleration crosses the threshold again, probably around 10mph, and the brake lights turn off unless you're on the brake pedal by then.
Well, that's my take anyway.
The deceleration from max regen feels less pronounced at higher speeds. My guess is that the higher rotational speed of the rotor (higher frequency) provides higher kW regen with less decelerating force. Some EE can reply and confirm or refute.
Then when you slow enough that the decelerating force crosses a threshold, the brake lights turn on. I think this is still at a highway speed, certainly above 50mph.
The deceleration effect seems to increase to a maximum, I think around 30mph or so, then the regen slowly tapers to maintain a constant deceleration as you slow further.
Then the deceleration effect decreases as well, presumably to provide a smoother stop. The decrease in deceleration crosses the threshold again, probably around 10mph, and the brake lights turn off unless you're on the brake pedal by then.
Well, that's my take anyway.
jamieb
Member
User interface suggestion:
Would be nice to have the ring around the speedometer glow red when the brake lights come on. Could be made quite subtle and user-selectable to be on or off depending upon personal preference. Would help folks know (without looking down at the speedometer or glancing at the center screen) when their brake lights are coming on. Might be nice for new drivers to get a sense of brake lights & regen, then turn off if they don't like it.
Would be nice to have the ring around the speedometer glow red when the brake lights come on. Could be made quite subtle and user-selectable to be on or off depending upon personal preference. Would help folks know (without looking down at the speedometer or glancing at the center screen) when their brake lights are coming on. Might be nice for new drivers to get a sense of brake lights & regen, then turn off if they don't like it.
The kinetic energy isn't linear with speed. It's exponential. In other words, the same amount of regen (let's say 20 kW) will slow the car down less at higher speeds vs lower speeds. This is why regen at 20 kW feels less when going 75 mph than 20 kW at 20 mph. To reduce this effect (it feels unnatural and is uncomfortable in normal driving) the Model S is reducing regen as the car slows down. It basically tries to even it out.
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