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I miss the full power regenerative braking when using my Tesla in the cold. Like, I really miss it and don’t like driving the car as much when it just coasts wh

by zaroth 8y ago

I miss the full power regenerative braking when using my Tesla in the cold. Like, I really miss it and don’t like driving the car as much when it just coasts when I lift the accelerator. I actively dislike pressing the brake pedal anymore, and feel cheated whenever I have to touch it except to activate Hold at a stop. If supercaps could give me full regenerative braking at 0°F then I’d pay an extra $1-2k for the feature absolutely. In warm climates I can absolutely see brake pads never being replaced. The only time I use the brake pads to slow down is in sub-freezing temps and once in an emergency. For those who haven’t driven an EV with strong regen braking, you drive with a single pedal. “Neutral” is the accelerator slightly depressed. Lift your foot to slow down, fully lifting your foot is a strong braking down to about 10 mph. I should look up how fast you get 60-10 with a warm Tesla on regen alone. You drive with a single pedal, and you can dart in and out of traffic very nimbly because over-accelerating for a lane change and then regen’ing back to cruising speed is very efficient and fun and you don’t have to move your foot to another pedal. But regen degrades as the battery cools. A frozen battery will barely regenerate at all, at 0°F it’s actually disconcerting when you lift your foot and the car just... coasts. The display does have a gauge showing how much regen is available, so it’s not a surprise but it literally feels weird.

castratikron 8y ago
Why not use resistive braking to warm up the battery pack? This is how locomotives implement braking; the drive motor operates in regen and the current goes to massive grid resistors. There are no brake pads.
- toomuchtodo 8y ago
  The Model S and X have a dedicated battery warmer, the Model 3 does not as a cost cutting measure (it uses the motor windings to heat the coolant loop, but it appears this solution, while clever, is inadequate).
  - Scoundreller 8y ago
    Why not resistively heat that cooling loop? Or release it to the cabin? Turn on the de-frost? I kinda wish my ICE car would crank everything up while engine-braking down a hill to reduce brake and fuel use. It shouldn’t be that expensive...
    - zippy 8y ago
      that's what the model 3 does. it induces resistance in the motor at 0 rpm to generate heat which is then transferred to the coolant loop to heat the battery. but in order to warm up the very large battery pack, on a cold morning you need to turn the car on (well) before you start driving to have it warm enough for full regen.
      - Reason077 8y ago
        You can, of course, do this from the Tesla app. It’s not like an ICE car where (usually) you have to physically be in it to start it.
    - ummonk 8y ago
      With my ice car in the summer I often only turn on the AC only while going downhill or exiting the freeway.
      - Scoundreller 8y ago
        I just wish it was more automatic. Hard to say if I'm saving pennies or dollars, but a $1 chip to do it should pay for itself quickly.
    - Itsdijital 8y ago
      Just about every modern car cuts fuel when you're engine braking.
    - handzbagz 8y ago
      An modern (Last 20 years) ICE engine shouldn't use any fuel while engine braking. The ECU should just cut the fuel to the engine and allow it to run under vacuum. My 15 year old Golf does and engine braking is why I've still got the original brake pads after 180K miles.
- bluGill 8y ago
  There are brake pads in a train, each car has them. I'm assume the engine does too but I'm not an expert. You are correct that the resistive braking is preferred - the energy to stop a train would eat brake pads if that is all they used. (I suspect air brakes don't allow as much control - but again here I'm outside my expertise)
- wil421 8y ago
  I’m not so sure this is how locomotives brake. After living beside a train track for 4 years I can tell you the cars are not using regenerative breaking to slow down. They use air brakes that are audible due to the brake pads and air.
  - darkpuma 8y ago
    https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_braking https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_bra... This specifically addresses the air brakes you're hearing: >Dynamic braking alone is insufficient to stop a locomotive, as its braking effect rapidly diminishes below about 10 to 12 miles per hour (16 to 19 km/h). Therefore, it is always used in conjunction with the regular air brake. This combined system is called blended braking.
    - Animats 8y ago
      That's improved with AC locomotives. Regenerative braking now works down to zero speed, if desired.[1] Locomotive motors today are three-phase variable frequency synchronous motors, run as servomotors. Like other servomotors, they can be controlled all the way down to a stop. At some point the friction brakes are applied, but that's usually done only at slower speeds. Large modern locomotives often have "wings" with ventilation slots and fans. That's where the heat from the braking resistors gets dumped. This is a big win when moving heavy freight down long mountain grades. Friction brakes tend to overheat, but fan-cooled resistor banks can dump heat all day. It's amazing that semiconductors for that kind of power not only exist, but are not that big. [1] http://www.republiclocomotive.com/ac-traction-vs-dc-traction.html http://www.republiclocomotive.com/ac-traction-vs-dc-traction...
piker 8y ago
> A frozen battery will barely regenerate at all, at 0°F it’s actually disconcerting when you lift your foot and the car just... coasts. The display does have a gauge showing how much regen is available, so it’s not a surprise but it literally feels weird. Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle.
- dsfyu404ed 8y ago
  >Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle. When you're buying a high end vehicle "quirky" is the preferred adjective. 20yo $1500 German cars are "unreliable". Chinese EVs are "buggy". When you buy a Tesla, a new high end Mercedes or some other status symbol it's all just part of how it goes. Unreliability or odd behavior is not a negative at that price point. It's all part of the ownership experience. You don't get to complain about it. It's implied by the price point that you knew what you were getting into and can handle it.
  - dharmab 8y ago
    I think warranty support and dealer network plays a role in that.
    - dsfyu404ed 8y ago
      Warranty coverage is not that great and dealers are few and far between once you get into exotic stuff. The German stuff available at the Model S price points is not much better (in terms of warranty). The line between exotic and not gets kind of blurry because a lot of the lower end exotic stuff shares a platform with something else so most service can be done at that dealer network. In any case, price determines whether technology is given the benefit of the doubt when it fails. Someone breaks a Harbor Freight tool and everyone blames the tool. Someone breaks a Mac or a Snap On and everyone blames whoever broke it. When Walmart has to recall food it's Walmart's fault for not choosing better suppliers. When Whole Foods has to trash a bunch of lettuce people blame the lettuce makers. When cheap things break, act weird or somehow go wrong they get blamed. When expensive things break or act funny that's how they were meant to be and if you don't like it you were using it wrong or your expectations were wrong. People will do all sorts of mental gymnastics to avoid making expensive things look bad.
Shivetya 8y ago
To each their own. I like my TM3 and enjoy regenerative braking but there really is not reason to use a blended braking system which keeps with the current petrol car model of, use the brake pedal to slow down. It also may be safer since your foot will be over the brake when needed. Chevrolet used this on the Volt for normal driving, you press the brake pedal and it decides how much hydraulic brakes you need over what regeneration can provide. Audi is going this route too. What makes it even better is they can totally mask the loss of regeneration in cold weather which can be disconcerting. If anything I think Tesla should make it an option, the loss of regen braking even when the pack is only saturated to 40F is bad enough and just useless below freezing. They can do wonders with OTA so there is no reason to not offer all options, low to regeneration, high regeneration, maximum, and blended. Again, blended doesn't mean it uses the disc brakes, only that it can when it has too and this is safer than relying on one pedal driving.
- m_mueller 8y ago
  Your point about safety raises an idea: Why not do the inverse? Your driver assist tells the car how fast it can drive (GPS, signage), break pedal as well as a configurable level of assistance tells it how much to stop. Steering is still mine, and I won't give it up until full autonomous cars with zero driver responsibility are mass produceable.
  - fastball 8y ago
    Because I want to drive over the speed limit.
    - m_mueller 8y ago
      I'm not saying take away the gas pedal - it could still be there as a 'boost' pedal, intended for overtaking for example.
      - fastball 8y ago
        My car already does this with radar-informed cruise control, except it doesn't force a certain speed on the driver. You just set it like normal cruise control.
dsfyu404ed 8y ago
>For those who haven’t driven an EV with strong regen braking, you drive with a single pedal. “Neutral” is the accelerator slightly depressed. Lift your foot to slow down, fully lifting your foot is a strong braking down to about 10 mph. So basically like an old pickup from back when 4.xx was a typical rear end ratio and transmissions didn't have overdrive so you were doing 3000+rpm at 60.
tlb 8y ago
Me too. I live at the top of a steep hill, so if I charge fully I can't regen all the way down in the morning, and I have to press this large pedal that hydraulically clamps some friction pads around steel disks attached to the wheels. So I set it to charge a little less than full, and gain about 6 miles of range on the way down. A resistive dump of 20-30 kW would improve the cold weather deceleration experience, but that's a big honking resistor that'd need forced air cooling.
- Scoundreller 8y ago
  Why not 2-4 kw to heat the cabin really fast when it’s cold? Pre-heating the cabin instead of the brakes would save cabin heating energy later.
  - tlb 8y ago
    The model S already has a 6 kW cabin heater, which is presumably fully on when starting out cold. Electric heat is great -- the cabin starts warming up immediately. Braking normally goes up to 60 kW. Another 2-4 kW would barely make a difference.
    - Scoundreller 8y ago
      I’m making up numbers, but I think braking is like insurance: most payouts/utilization is at the low end. You need the 60kw available for hard braking, but what percentage of the area under the curve is below the 5kw mark?
      - tlb 8y ago
        60 kW isn't hard braking -- that's the normal level you get in a model S when you take your foot off the accelerator anywhere above 20 mph. So coming to an anticipated red light, you'd normally brake at the full 60 kW tapering down to zero at about 10 mph, then use the mechanical brake. That's makes for a comfortable stop and wastes the minimum power. Hard braking, like slamming them on at 80 mph, can exceed 1000 kW.
njarboe 8y ago
This is the same experience one has with an ICE engine and manual gear box at higher RPM. Much easier to drive aggressively in that mode for reasons you state.
- zaroth 8y ago
  Yes, it’s like the joy of a stick but without any gears or RPMs it means the feel of it is much smoother and very easy to attenuate. I’ve never driven a high performance stick shift, only a cheap beater stick as my first car, but I found high RPM stop and go in 1st or 2nd gear was always somewhat hard work and jerky. The TM3 is absolutely not hard work or jerky, the single pedal driving is actually quite a joy IMO.
stefan_ 8y ago
It seems like the cases where regenerative braking doesn't work coincide perfectly with the season where you want simple resistive loads for fast acting interior heating.
ThePhysicist 8y ago
Naive question: Couldn't they "just" simulate the regenerative braking effect by automatically engaging the brakes when you lift the foot from the accelerator, so that the behavior would be identical over all temperature ranges?
- azhenley 8y ago
  Or by using some sort of capacitor/resistor. Elon has made claims about the longevity of brakes in Teslas due to rarely touching the brake pedal. And I agree, I don't want my brakes wearing out just to simulate the effect.
rladd 8y ago
Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate. This seems safer to me and also easier to control: you press the brake and it brakes. If it can regen, it regens, if not, it uses the disks. If you hit the brakes hard and the regen won't be enough to slow you down, it will use disk to the extent it needs to (or just switch to disk entirely). Coasting is also good: no reason to regen if what you really want to do is coast, and no reason to have to keep your foot on the accelerator in that case either. Prius do regen slightly in coasting mode, but it's not very noticeable.
- masklinn 8y ago
  > Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate. It also makes way more sense: your drivetrain can't be perfectly efficient so being unable to coast (and regen-braking every time you would be) is a double energy loss, first waste energy converting kinetic to electric, then you waste energy again converting back from electric to kinetic. Regen-braking instead of coasting only makes sense in an "engine braking" analogue: have the car regen-brake to try and keep below some set speed on downhills.
- mywittyname 8y ago
  You can turn on full engine-braking in a Prius and it works fairly well (but also uses the ICE). It's enough that I use it entirely in most cases to get down to coasting speeds.
  - serpi 8y ago
    I drove a Toyota CR-V and was really amazed how it manages to burn fuel while decelerating. It is a disgrace of a hybrid vehicle.
    - nitrogen 8y ago
      Does it actually burn fuel? I've coasted an ICE car down a mountain in the winter and the temperature gauge didn't budge (and thus the heater never warmed up), implying no fuel was used. Surely a hybrid could do the same?
barkingcat 8y ago
This advice is dangerous. You still need brakes for emergencies (and in modern day driving, there are tons of cases where you need to have the car come to a full stop, without the delay of regen braking)
- elif 8y ago
  Agree... intentionally getting in front of another driver with "over-acceleration" then slowing faster than normal torque converter coasting levels without activating your braking lights is asking for a rear-end collision. Not to mention, it is delusional to consider this style of driving "efficient" because of regeneration. You're paying a premium for acceleration speed, and then being taxed by regneration efficiency...
  - Bedon292 8y ago
    Regenerative breaking does activate your brake lights though, at least in the Tesla. I would assume it is the same in all EVs, as it would be a massive safety issue and asking for rear-end collisions otherwise.
  - zaroth 8y ago
    I may have overstated it. What I meant was simply when changing lanes you need to accelerate faster than cruising speed to make up for the distance of the lane shift if you want to stay evenly separated from the cars around you, versus drifting backward about a car length as you move between lanes. In addition I like to have some forward movement while changing lanes on a highway, so that if there is someone (several car lengths) behind me in the adjacent lane they know they won’t have to slow down. So you can add a bit of speed as you make the lane change and then bleed it off in regen to return back to that lane’s cruising speed. It should not be enough of a delta to involve any kind of brake light. The energy loop is extremely efficient e.g. if you are going 60mph to bump up to 65mph and then back to 60mph, like 90% is reclaimed, from the energy chart display, you get a spike up and then down in consumption whichs appear to be symmetrical. Actually, if you lane change in AutoPilot I believe it will do something similar. It does not change (semi-)autonomously lanes without applying some power.
etaioinshrdlu 8y ago
Other commenters have similar thoughts but here it is said more directly: the car should not drive differently at all depending on temperature. There is no reason it has to be that way. The motor can regen fine at any temperature. The battery cannot, but dumping power resistively into air heat is one of the easiest things to do electrically, and they could definitely do it. With one counterpoint being that maybe this is a feature, not a bug, and may save drivers from excessive non-productive braking.
- semi-extrinsic 8y ago
  I checked around, and a 2 kW dump resistor is about 3" diameter by 20" length. You'd need, say, 16 of those at a packing fraction about 0.5 for sufficent air flow, so you're looking at a cuboid which is 20" long and 4*3"/sqrt(0.5/0.9) = 16" to a side, or 2560 cu.in. Then you add the fans and the intake and outlet ducting etc. you can probably figure 3500 cu.in. total volume. For comparison, the Model 3 "frunk" seems to be 28" x 15" x 9" = 3780 cu.in. So you'd have to sacrifice the entire frunk for your resistor pack.
  - extropy 8y ago
    How about just dumping that heat into the battery coolant loop. Oh wait.
  - deleted 8y ago
    [deleted]
  - etaioinshrdlu 8y ago
    I think there are still some reasonable solutions: * smaller resistive heaters with higher airflow * dump the heat into resistively heating the battery. Then use the battery again! * Just use disk brakes to achieve the same feel. Which is also, basically, dumping heat. Remember that the problem to solve is that a car shouldn't drive differently at different temperatures...
    - therein 8y ago
      Now where could one get this said airflow in a vehicle moving through a medium that is commonly referred to as air? :) Heating up the battery with this airflow for a certain amount of time should warm them up relatively quickly and evenly since done via convection too. Now I genuinely wonder if there is a reason why Tesla didn't go with that.
taneq 8y ago
Having your car's braking behaviour change so markedly seems poor. Couldn't they just use the regenned power to run the battery heaters?
walru 8y ago
>starting a sentence with like. Hate me all you want. This is HN. I would enjoy a elevated level of grammar.
jac_no_k 8y ago
2018 Nissan Leaf owner here driving with e-pedal, essentially a single pedal driving from movement to complete stop. I've driven from summer conditions down to -10dC (14dF) conditions. For winter, the car is on squishier winter tires. This confuses the traction control unit enough to cut out regen on full pedal lift off and switch over to caliper brakes, still single pedal. The car still slows and comes to a complete stop, but deceleration is much stronger with regen. I've adapted to no longer fully lift off the pedal, expecting a more gentle deceleration, providing a more consistent stopping distance. The brake pedal still responds normally and it gets used in surprise situations. Even at -10dC (14dF), the regen operates similar compared to warmer temps with the Leaf. At -30dC (-22dF) the battery heater supposedly kicks in, but have not taken the car into those kinds of conditions. I would think it's a software update on the Tesla to kick on the battery warmers in colder climates for consistent regen. Or software update to engage the brakes when regen isn't available.
fpoling 8y ago
I had Toyota Yaris hybrid and after 3 years I had to replace brake pads twice due to rust. Apparently with regenerative braking I had not used them much. This prevented them from heating that normally removed any water buildup. Granted that was in Bergen, Norway where it rained a lot, but I learned that even in dryer climates this was a problem. After the first replacement I was asked to brake hard periodically to heat the pads. I started doing that, but it did not help much.
nubslayer 8y ago
Coasting is better then regen'ing, pretty sure. If you regen, you have to slow down, only to have to speed back up again, but at a worse efficiency loss than just coasting.
- greglindahl 8y ago
  What do you think happens if the car in front of you is coasting, and you're trying to match its speed?
  - nubslayer 8y ago
    wut It's possible to get in an 'envelope' behind another car and get pulled along with it.
    - greglindahl 8y ago
      I wasn't talking about drafting. I was just saying that you can "coast" in a one-pedal car by pressing on the pedal by an appropriate amount... and most drivers will do that every time they drive, because they'll be behind other cars that are coasting.
      - nubslayer 8y ago
        I'm saying that harvesting energy while coasting is probably not efficient.
burfog 8y ago
This is kind of odd. You mean that the battery can't take the power when cold? The obvious fix is to use that power first for heating the battery. You'd still slow the car via power generation, giving the exact same braking feel. Trains often do something similar, except that they dump the power as heat to the air. That would work too.
londons_explore 8y ago
Tesla could totally fix your concerns with software only changes. By changing the motor drivers to have a much higher current in all coils of the motor, the I^2 R losses are much higher, and the car will slow down while heating the motors up. Then run the cooling pumps and the heat will go into heating the battery.

by zaroth 8y ago

castratikron 8y ago

Why not use resistive braking to warm up the battery pack? This is how locomotives implement braking; the drive motor operates in regen and the current goes to massive grid resistors. There are no brake pads.

toomuchtodo 8y ago
The Model S and X have a dedicated battery warmer, the Model 3 does not as a cost cutting measure (it uses the motor windings to heat the coolant loop, but it appears this solution, while clever, is inadequate).
- Scoundreller 8y ago
  Why not resistively heat that cooling loop? Or release it to the cabin? Turn on the de-frost? I kinda wish my ICE car would crank everything up while engine-braking down a hill to reduce brake and fuel use. It shouldn’t be that expensive...
  - zippy 8y ago
    that's what the model 3 does. it induces resistance in the motor at 0 rpm to generate heat which is then transferred to the coolant loop to heat the battery. but in order to warm up the very large battery pack, on a cold morning you need to turn the car on (well) before you start driving to have it warm enough for full regen.
    - Reason077 8y ago
      You can, of course, do this from the Tesla app. It’s not like an ICE car where (usually) you have to physically be in it to start it.
  - ummonk 8y ago
    With my ice car in the summer I often only turn on the AC only while going downhill or exiting the freeway.
    - Scoundreller 8y ago
      I just wish it was more automatic. Hard to say if I'm saving pennies or dollars, but a $1 chip to do it should pay for itself quickly.
  - Itsdijital 8y ago
    Just about every modern car cuts fuel when you're engine braking.
  - handzbagz 8y ago
    An modern (Last 20 years) ICE engine shouldn't use any fuel while engine braking. The ECU should just cut the fuel to the engine and allow it to run under vacuum. My 15 year old Golf does and engine braking is why I've still got the original brake pads after 180K miles.
bluGill 8y ago
There are brake pads in a train, each car has them. I'm assume the engine does too but I'm not an expert. You are correct that the resistive braking is preferred - the energy to stop a train would eat brake pads if that is all they used. (I suspect air brakes don't allow as much control - but again here I'm outside my expertise)
wil421 8y ago
I’m not so sure this is how locomotives brake. After living beside a train track for 4 years I can tell you the cars are not using regenerative breaking to slow down. They use air brakes that are audible due to the brake pads and air.
- darkpuma 8y ago
  https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_braking https://en.wikipedia.org/wiki/Dynamic_braking#Rheostatic_bra... This specifically addresses the air brakes you're hearing: >Dynamic braking alone is insufficient to stop a locomotive, as its braking effect rapidly diminishes below about 10 to 12 miles per hour (16 to 19 km/h). Therefore, it is always used in conjunction with the regular air brake. This combined system is called blended braking.
  - Animats 8y ago
    That's improved with AC locomotives. Regenerative braking now works down to zero speed, if desired.[1] Locomotive motors today are three-phase variable frequency synchronous motors, run as servomotors. Like other servomotors, they can be controlled all the way down to a stop. At some point the friction brakes are applied, but that's usually done only at slower speeds. Large modern locomotives often have "wings" with ventilation slots and fans. That's where the heat from the braking resistors gets dumped. This is a big win when moving heavy freight down long mountain grades. Friction brakes tend to overheat, but fan-cooled resistor banks can dump heat all day. It's amazing that semiconductors for that kind of power not only exist, but are not that big. [1] http://www.republiclocomotive.com/ac-traction-vs-dc-traction.html http://www.republiclocomotive.com/ac-traction-vs-dc-traction...

piker 8y ago

> A frozen battery will barely regenerate at all, at 0°F it’s actually disconcerting when you lift your foot and the car just... coasts. The display does have a gauge showing how much regen is available, so it’s not a surprise but it literally feels weird. Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle.

dsfyu404ed 8y ago
>Nondeterministic regenerative braking as described here seems like a serious bug in a vehicle. When you're buying a high end vehicle "quirky" is the preferred adjective. 20yo $1500 German cars are "unreliable". Chinese EVs are "buggy". When you buy a Tesla, a new high end Mercedes or some other status symbol it's all just part of how it goes. Unreliability or odd behavior is not a negative at that price point. It's all part of the ownership experience. You don't get to complain about it. It's implied by the price point that you knew what you were getting into and can handle it.
- dharmab 8y ago
  I think warranty support and dealer network plays a role in that.
  - dsfyu404ed 8y ago
    Warranty coverage is not that great and dealers are few and far between once you get into exotic stuff. The German stuff available at the Model S price points is not much better (in terms of warranty). The line between exotic and not gets kind of blurry because a lot of the lower end exotic stuff shares a platform with something else so most service can be done at that dealer network. In any case, price determines whether technology is given the benefit of the doubt when it fails. Someone breaks a Harbor Freight tool and everyone blames the tool. Someone breaks a Mac or a Snap On and everyone blames whoever broke it. When Walmart has to recall food it's Walmart's fault for not choosing better suppliers. When Whole Foods has to trash a bunch of lettuce people blame the lettuce makers. When cheap things break, act weird or somehow go wrong they get blamed. When expensive things break or act funny that's how they were meant to be and if you don't like it you were using it wrong or your expectations were wrong. People will do all sorts of mental gymnastics to avoid making expensive things look bad.

Shivetya 8y ago

To each their own. I like my TM3 and enjoy regenerative braking but there really is not reason to use a blended braking system which keeps with the current petrol car model of, use the brake pedal to slow down. It also may be safer since your foot will be over the brake when needed. Chevrolet used this on the Volt for normal driving, you press the brake pedal and it decides how much hydraulic brakes you need over what regeneration can provide. Audi is going this route too. What makes it even better is they can totally mask the loss of regeneration in cold weather which can be disconcerting. If anything I think Tesla should make it an option, the loss of regen braking even when the pack is only saturated to 40F is bad enough and just useless below freezing. They can do wonders with OTA so there is no reason to not offer all options, low to regeneration, high regeneration, maximum, and blended. Again, blended doesn't mean it uses the disc brakes, only that it can when it has too and this is safer than relying on one pedal driving.

m_mueller 8y ago
Your point about safety raises an idea: Why not do the inverse? Your driver assist tells the car how fast it can drive (GPS, signage), break pedal as well as a configurable level of assistance tells it how much to stop. Steering is still mine, and I won't give it up until full autonomous cars with zero driver responsibility are mass produceable.
- fastball 8y ago
  Because I want to drive over the speed limit.
  - m_mueller 8y ago
    I'm not saying take away the gas pedal - it could still be there as a 'boost' pedal, intended for overtaking for example.
    - fastball 8y ago
      My car already does this with radar-informed cruise control, except it doesn't force a certain speed on the driver. You just set it like normal cruise control.

dsfyu404ed 8y ago

>For those who haven’t driven an EV with strong regen braking, you drive with a single pedal. “Neutral” is the accelerator slightly depressed. Lift your foot to slow down, fully lifting your foot is a strong braking down to about 10 mph. So basically like an old pickup from back when 4.xx was a typical rear end ratio and transmissions didn't have overdrive so you were doing 3000+rpm at 60.

tlb 8y ago

Me too. I live at the top of a steep hill, so if I charge fully I can't regen all the way down in the morning, and I have to press this large pedal that hydraulically clamps some friction pads around steel disks attached to the wheels. So I set it to charge a little less than full, and gain about 6 miles of range on the way down. A resistive dump of 20-30 kW would improve the cold weather deceleration experience, but that's a big honking resistor that'd need forced air cooling.

Scoundreller 8y ago
Why not 2-4 kw to heat the cabin really fast when it’s cold? Pre-heating the cabin instead of the brakes would save cabin heating energy later.
- tlb 8y ago
  The model S already has a 6 kW cabin heater, which is presumably fully on when starting out cold. Electric heat is great -- the cabin starts warming up immediately. Braking normally goes up to 60 kW. Another 2-4 kW would barely make a difference.
  - Scoundreller 8y ago
    I’m making up numbers, but I think braking is like insurance: most payouts/utilization is at the low end. You need the 60kw available for hard braking, but what percentage of the area under the curve is below the 5kw mark?
    - tlb 8y ago
      60 kW isn't hard braking -- that's the normal level you get in a model S when you take your foot off the accelerator anywhere above 20 mph. So coming to an anticipated red light, you'd normally brake at the full 60 kW tapering down to zero at about 10 mph, then use the mechanical brake. That's makes for a comfortable stop and wastes the minimum power. Hard braking, like slamming them on at 80 mph, can exceed 1000 kW.

njarboe 8y ago

This is the same experience one has with an ICE engine and manual gear box at higher RPM. Much easier to drive aggressively in that mode for reasons you state.

zaroth 8y ago
Yes, it’s like the joy of a stick but without any gears or RPMs it means the feel of it is much smoother and very easy to attenuate. I’ve never driven a high performance stick shift, only a cheap beater stick as my first car, but I found high RPM stop and go in 1st or 2nd gear was always somewhat hard work and jerky. The TM3 is absolutely not hard work or jerky, the single pedal driving is actually quite a joy IMO.

stefan_ 8y ago

It seems like the cases where regenerative braking doesn't work coincide perfectly with the season where you want simple resistive loads for fast acting interior heating.

ThePhysicist 8y ago

Naive question: Couldn't they "just" simulate the regenerative braking effect by automatically engaging the brakes when you lift the foot from the accelerator, so that the behavior would be identical over all temperature ranges?

azhenley 8y ago
Or by using some sort of capacitor/resistor. Elon has made claims about the longevity of brakes in Teslas due to rarely touching the brake pedal. And I agree, I don't want my brakes wearing out just to simulate the effect.

rladd 8y ago

Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate. This seems safer to me and also easier to control: you press the brake and it brakes. If it can regen, it regens, if not, it uses the disks. If you hit the brakes hard and the regen won't be enough to slow you down, it will use disk to the extent it needs to (or just switch to disk entirely). Coasting is also good: no reason to regen if what you really want to do is coast, and no reason to have to keep your foot on the accelerator in that case either. Prius do regen slightly in coasting mode, but it's not very noticeable.

masklinn 8y ago
> Toyota Prius and Prius Prime also charge their batteries during braking, but use the brake pedal to decellerate. It also makes way more sense: your drivetrain can't be perfectly efficient so being unable to coast (and regen-braking every time you would be) is a double energy loss, first waste energy converting kinetic to electric, then you waste energy again converting back from electric to kinetic. Regen-braking instead of coasting only makes sense in an "engine braking" analogue: have the car regen-brake to try and keep below some set speed on downhills.
mywittyname 8y ago
You can turn on full engine-braking in a Prius and it works fairly well (but also uses the ICE). It's enough that I use it entirely in most cases to get down to coasting speeds.
- serpi 8y ago
  I drove a Toyota CR-V and was really amazed how it manages to burn fuel while decelerating. It is a disgrace of a hybrid vehicle.
  - nitrogen 8y ago
    Does it actually burn fuel? I've coasted an ICE car down a mountain in the winter and the temperature gauge didn't budge (and thus the heater never warmed up), implying no fuel was used. Surely a hybrid could do the same?

barkingcat 8y ago

This advice is dangerous. You still need brakes for emergencies (and in modern day driving, there are tons of cases where you need to have the car come to a full stop, without the delay of regen braking)

elif 8y ago
Agree... intentionally getting in front of another driver with "over-acceleration" then slowing faster than normal torque converter coasting levels without activating your braking lights is asking for a rear-end collision. Not to mention, it is delusional to consider this style of driving "efficient" because of regeneration. You're paying a premium for acceleration speed, and then being taxed by regneration efficiency...
- Bedon292 8y ago
  Regenerative breaking does activate your brake lights though, at least in the Tesla. I would assume it is the same in all EVs, as it would be a massive safety issue and asking for rear-end collisions otherwise.
- zaroth 8y ago
  I may have overstated it. What I meant was simply when changing lanes you need to accelerate faster than cruising speed to make up for the distance of the lane shift if you want to stay evenly separated from the cars around you, versus drifting backward about a car length as you move between lanes. In addition I like to have some forward movement while changing lanes on a highway, so that if there is someone (several car lengths) behind me in the adjacent lane they know they won’t have to slow down. So you can add a bit of speed as you make the lane change and then bleed it off in regen to return back to that lane’s cruising speed. It should not be enough of a delta to involve any kind of brake light. The energy loop is extremely efficient e.g. if you are going 60mph to bump up to 65mph and then back to 60mph, like 90% is reclaimed, from the energy chart display, you get a spike up and then down in consumption whichs appear to be symmetrical. Actually, if you lane change in AutoPilot I believe it will do something similar. It does not change (semi-)autonomously lanes without applying some power.

etaioinshrdlu 8y ago

Other commenters have similar thoughts but here it is said more directly: the car should not drive differently at all depending on temperature. There is no reason it has to be that way. The motor can regen fine at any temperature. The battery cannot, but dumping power resistively into air heat is one of the easiest things to do electrically, and they could definitely do it. With one counterpoint being that maybe this is a feature, not a bug, and may save drivers from excessive non-productive braking.

semi-extrinsic 8y ago
I checked around, and a 2 kW dump resistor is about 3" diameter by 20" length. You'd need, say, 16 of those at a packing fraction about 0.5 for sufficent air flow, so you're looking at a cuboid which is 20" long and 4*3"/sqrt(0.5/0.9) = 16" to a side, or 2560 cu.in. Then you add the fans and the intake and outlet ducting etc. you can probably figure 3500 cu.in. total volume. For comparison, the Model 3 "frunk" seems to be 28" x 15" x 9" = 3780 cu.in. So you'd have to sacrifice the entire frunk for your resistor pack.
- extropy 8y ago
  How about just dumping that heat into the battery coolant loop. Oh wait.
- deleted 8y ago
  [deleted]
- etaioinshrdlu 8y ago
  I think there are still some reasonable solutions: * smaller resistive heaters with higher airflow * dump the heat into resistively heating the battery. Then use the battery again! * Just use disk brakes to achieve the same feel. Which is also, basically, dumping heat. Remember that the problem to solve is that a car shouldn't drive differently at different temperatures...
  - therein 8y ago
    Now where could one get this said airflow in a vehicle moving through a medium that is commonly referred to as air? :) Heating up the battery with this airflow for a certain amount of time should warm them up relatively quickly and evenly since done via convection too. Now I genuinely wonder if there is a reason why Tesla didn't go with that.

taneq 8y ago

Having your car's braking behaviour change so markedly seems poor. Couldn't they just use the regenned power to run the battery heaters?

walru 8y ago

>starting a sentence with like. Hate me all you want. This is HN. I would enjoy a elevated level of grammar.

jac_no_k 8y ago

2018 Nissan Leaf owner here driving with e-pedal, essentially a single pedal driving from movement to complete stop. I've driven from summer conditions down to -10dC (14dF) conditions. For winter, the car is on squishier winter tires. This confuses the traction control unit enough to cut out regen on full pedal lift off and switch over to caliper brakes, still single pedal. The car still slows and comes to a complete stop, but deceleration is much stronger with regen. I've adapted to no longer fully lift off the pedal, expecting a more gentle deceleration, providing a more consistent stopping distance. The brake pedal still responds normally and it gets used in surprise situations. Even at -10dC (14dF), the regen operates similar compared to warmer temps with the Leaf. At -30dC (-22dF) the battery heater supposedly kicks in, but have not taken the car into those kinds of conditions. I would think it's a software update on the Tesla to kick on the battery warmers in colder climates for consistent regen. Or software update to engage the brakes when regen isn't available.

fpoling 8y ago

I had Toyota Yaris hybrid and after 3 years I had to replace brake pads twice due to rust. Apparently with regenerative braking I had not used them much. This prevented them from heating that normally removed any water buildup. Granted that was in Bergen, Norway where it rained a lot, but I learned that even in dryer climates this was a problem. After the first replacement I was asked to brake hard periodically to heat the pads. I started doing that, but it did not help much.

nubslayer 8y ago

Coasting is better then regen'ing, pretty sure. If you regen, you have to slow down, only to have to speed back up again, but at a worse efficiency loss than just coasting.

greglindahl 8y ago
What do you think happens if the car in front of you is coasting, and you're trying to match its speed?
- nubslayer 8y ago
  wut It's possible to get in an 'envelope' behind another car and get pulled along with it.
  - greglindahl 8y ago
    I wasn't talking about drafting. I was just saying that you can "coast" in a one-pedal car by pressing on the pedal by an appropriate amount... and most drivers will do that every time they drive, because they'll be behind other cars that are coasting.
    - nubslayer 8y ago
      I'm saying that harvesting energy while coasting is probably not efficient.

burfog 8y ago

This is kind of odd. You mean that the battery can't take the power when cold? The obvious fix is to use that power first for heating the battery. You'd still slow the car via power generation, giving the exact same braking feel. Trains often do something similar, except that they dump the power as heat to the air. That would work too.

londons_explore 8y ago

Tesla could totally fix your concerns with software only changes. By changing the motor drivers to have a much higher current in all coils of the motor, the I^2 R losses are much higher, and the car will slow down while heating the motors up. Then run the cooling pumps and the heat will go into heating the battery.