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Regen Poll - What technique is best (let off at last second or coast)

Discussion in 'Model S: Driving Dynamics' started by Racerx22b, Aug 2, 2017.

?

To get the most of our your regen what technique is best (creates most regen power)?

  1. Time it perfect and use max regen braking for as short of a time as possible

    40.0%
  2. Left slightly and coast as long as possible creating minimum regen braking for longer duration

    60.0%
  1. Racerx22b

    Racerx22b Member

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    I am sure someone has done extensive comparisons of this so I figured I would ask.

    To get the most of our your regen what technique is best (creates most regen power)?

    Try to time it perfect and completely let off the go pedal until you hit 8mph then apply brake at stop light

    Lift go pedal slightly and try to create regen as long as possible as you approach a stoplight
     
  2. mal_tsla

    mal_tsla Member

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    Slowing the same car from the same starting speed to the same slowest speed will generate the same energy whether you do it quickly with a full lift or slowly with a long fade.

    I know which driver I'd rather be stuck behind :)
     
  3. Racerx22b

    Racerx22b Member

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    Yeah... I meant to add a 3rd option of it doesn't matter. Darnit. I forgot and now I can't edit. Oh well.
     
  4. BerTX

    BerTX Active Member

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    So you're not asking what is the most efficient, but what generates the most regen, even if it uses more energy?
     
  5. Blup85

    Blup85 Member

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    Easy question I think.. If my understanding of the electric regen motor is correct, the motor has to convert AC energy from the regen back to Dc for the battery, where the losses come from (%10??). So obviously it would be better to leave that energy as coasting than to convert to Dc just to accelerate again( although fun!)
     
  6. mal_tsla

    mal_tsla Member

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    If overall efficiency is the goal, then whichever method is slower will be more efficient. That means the long fade coast will be more efficient, unless you're going downhill.

    But I believe the question was purely about the Regen performance. That should be roughly equal in both rapid slow and slow slow scenarios.
     
    • Informative x 1
  7. BerTX

    BerTX Active Member

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    What you really want to avoid is stopping for the light. Accelerating from a stop trumps any differences in regen between the two choices in the poll. Slowing down early for a light where cars are already stopped to try to avoid stopping is the correct answer (although unpopular).
     
    • Like x 2
  8. scottm

    scottm Active Member

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    I have a slightly different view on this... charging the batteries is more efficient when done with higher Amperage (proven). Regen is just charging for short periods of time.. so I'm going to say: lift off the pedel completely at the last moment possible that you think will result in meeting your new slower desired objective at the chosen point ahead.
    Don't undershoot your desired speed by allowing regen to continue too hard then try to regain up to desired speed. Instead, feather pressure back into the pedal to reduce regen up to the matched power point of what it takes to drive at that constant speed. This means you don't lose on loss of momentum, which is the best thing to do for conservation.
     
  9. Racerx22b

    Racerx22b Member

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    Wow, I thought someone would've had some math equation and would've known this for sure.

    Just to clarify what I am asking and apologies for not being more clear with my initial post...

    The goal is to "charge up" the battery or lower your watt per mile avg as much as possible using the regen braking when coming to a complete stop. So my question is what technique gets the most power back to the battery and maximizes the benefit of regen braking?

    Completely lift off pedal and only apply the brakes once regen is done (around 8mph) OR lightly lift up on pedal at a further distance back and have a lesser regen effect but for a longer period of time. Or when all is said and done both essentially send back the same exact amount of charge back to the battery. Both situations are assuming you apply NO brakes during regen, you are creating regen power the entire time (your power use bar is always green), are on flat ground, and you time your regen braking so that you only apply brake at the very last moment (roughly the last 20' or so) as you approach the place you need to stop.

    I hope that clears up any confusion.
     
  10. Missile Toad

    Missile Toad Member

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    Steps when stopping:
    1. From a neutral position, lift foot well before the stop, targeting a full stop with about 3 car lengths buffer;
    2. Regen is engaged, then disengaged as you approach about 4 MPH
    3. Spend the next 20 seconds rolling at 0.25-0.5 MPH across those 3 car lengths -- never touching the friction brake
    4. Get that constant feeling of motion, while the ICE drivers are going, "what is he doing?"
    I still don't know if other drivers are annoyed or amazed by #4.

    Incidentally, I have the 'creep' mode turned off. But I swear, in a dead level location, from a stop, without any brake applied, the car will still try to move at 0.1 MPH.
     
  11. mal_tsla

    mal_tsla Member

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    If your goal is to lower the wh/mile, then the further back you start slowing down/coasting, the more you'll lower it. You'll also go slower, take longer to get to the stop, and annoy cars behind you.

    If your goal is to maximize your gains from regen while arrive at the stop sign in the same amount of time, no slower/no faster, then it won't make any measurable difference whether you use a more abrupt, high G-force "full regen" fast lift vs. a gentler longer regen. It's the same amount of power, whether it is all at once or a little at a time, assuming the total time from cruising to stopped at the stop sign is held constant.
     
  12. Racerx22b

    Racerx22b Member

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    #12 Racerx22b, Aug 3, 2017
    Last edited: Aug 3, 2017
    @mal_tsla

    If you say abrupt lifting is the same amount of power created as partial lifting (all while constantly producing regen power - never going flat or into orange) then wouldn't the amount it affects your watt per mile avg also be equal. I don't think it would matter to your range if your battery got 5kwh of power in 10secs or 20secs. It's still 5kwh at the end of the day.

    I know these are not real numbers but just for example, if you regen for 10secs at 10kwh (full pedal lift) or for 20secs at 5kwh (partial pedal lift) your net power regen is 100kwh. Right?

    I am not saying your wrong. I just trying to make sense of this.

    EDIT - Just had a realization... If you lift sooner and regen longer you would save slightly more energy overall cause you wouldn't be using battery to propel the vehicle.

    So if you partially lift and create regen for 200yrds vs waiting until doing a full lift and create regen for 100yrds you would save the battery use for 100yrds. I know it would be a very minor difference but that would make sense.

    Thoughts...
     
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  13. mal_tsla

    mal_tsla Member

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    Correct. It's the same power. However, some care would need to be taken to prevent going slower, which invalidates the scenario. If you have two identical cars stopping at the exact same time from the same starting speed, then yes no matter what you're regenerating about the same energy. Physics.

    However, what is more likely to happen with a longer Regen cycle is that you'll get to the stop sign after the fast Regen car. Moving a car the same distance in more time always takes less energy than doing it faster, assuming flat ground.
     
  14. scottm

    scottm Active Member

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    #14 scottm, Aug 3, 2017
    Last edited: Aug 3, 2017
    You're getting the hang of it now. It really depends on the driving scenario.
    Don't think of regen as a method to "charge up", it's a method to consume less by scavenging what you were about to waste.
    It's compensating for your error and making the best of a bad situation: having to slow down. EVs love to roll.
    Avoiding getting into positions of waste makes you a more aware and better EV driver, maybe even a graduated hypermiler!

    Don't worry about packing power back into battery. Think about using less in the first place.

    So you have to stop, eh? Shucks. Here's how I'd rank power use efficiency.

    Scenario: City driving, regen on standard setting, as soon as you see or realize an imminent stop is needed ahead.

    In order of efficiency (from least to most efficient):

    1. move foot from accel to brake at last possible moment to make a comfortable stop. I bite my lip when my wife is driving and she's does this.
    2. begin gliding (gear to N position) move foot to brake increasing pressure to stop the roll
    3. if you have the space ease up on accel and begin regen at a pace that will see you come to almost a complete stop, then brake to stop
    4. if you don't think you have space immediately full regen... if it turns out you did have a little more space and are going to agonizingly come up a bit short of the stopping point, glide it out (see 2) so you come to natural stop with no brake at the stopping point. Take a bow.

    Not all driving scenarios support all options. For the scenario above most people are going to (3). Trying to (4) would become a royal pain for city.

    For other driving scenarios, do different things. For example, for highway cruising... I set regen to LOW and really really try to avoid decelerating, favoring inertia of the car to cover ground as the best use of energy. Keep the power gauge out of the green zone.

    I do not want to put any fuel back into the pack if I can get the rolling distance out of what I've already added as inertial potential to the car. I do find myself flicking gear into N on the highway to glide instead of regen down medium hills... gaining speed for free. ... blah blah we're getting into hypermiling.
     
  15. BerTX

    BerTX Active Member

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    I hadn't thought of changing the regen setting to low for highway driving. I wonder how that would affect cruise control actions? How hard will TACC work to slow the car down going down a hill? Will it apply the brakes? I've never driven without full regen (other than when the car cuts it back).
     
  16. mal_tsla

    mal_tsla Member

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    If we had to think about things like putting our car into N to save power, we'd still have a gas car!

    Luckily our driving habits vs. battery capacity doesn't require that level of optimization. I guess we are not early adopter EV types. :(

    Shouldn't you be able coast perfectly equivalent to putting the gear selector into N just by pressing on the accelerator the appropriate amount to keep the energy meter at zero?
     
  17. scottm

    scottm Active Member

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    #17 scottm, Aug 3, 2017
    Last edited: Aug 3, 2017
    I know, it's just hypermiling games to play on long drives when I'm bored... sometimes I draft a semi too. Even when I don't need the range.

    Usually, I do just that - control the Neutral use of power using just the accel pedal. I'm lazy and it's a long hill, flick it to Neutral.

    I do wish Tesla had a cruise mode that wasn't based solely on ground speed, but would consider trying to achieve more of a constant energy use by varying the speed a little bit either way of the set point. You know, like when you going up over small rises on the highway and you see the cruise hammering in more power to keep up speed when you know you'll be over that rise soon enough and now pointing downhill ... car regens. I'd rather cruise would just allow speed dropping a few MPH going up the hill, reacting much more sluggishly with the accel as it tests to see how long this hill is going to be. And coming down the hill it wouldn't get fully off the pedal as soon as set point speed is exceeded, but rather allow the car to speed up while holding a neutral energy input... hate to say this, but like an ICE car glides picking up speed with Cruise on but going downhill -- it doesn't apply brakes, nor should Tesla immediately apply regen braking.. To a limit. Like if you're now doing 10 over then throw the regen anchor out. I'd like this settable... call it "Slack Cruise" or whatever.

    Another foot-game you can play is "hold a constant energy line" using the accel pedal, regardless of resulting affects that has on speed. If I hold the orange bar at 200 and try to keep that constant... the car does slow a bit going up small rises and hills and overachieves speed when coming down.. similar to Slack Cruise.. But it's hard for me to emulate going Neutral with my foot each time the car has regained the desired cruising speed on the way down... I usually undershoot and see green regen. This is where I wish I had Slack Cruise to do that for me.
     
  18. fc12

    fc12 New Member

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    I agree. And the heat loss is P=I²*R, therefore the losses are over proportionally higher with higher regen, I don't think that it really matters though.
     
  19. AmpedRealtor

    AmpedRealtor Well-Known Member

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    It's basic physics. Every time you use regen, you are losing about 20% of the potential energy recapture to frictional and resistive losses. It's always better to coast than to regenerate, unless you are coasting downhill and need regen to limit your speed. Some have said that there comes a tipping point when going downhill where the added wind resistance negates any advantage to coasting. At that point, using regen and slowing down will get you farther. However, knowing where that tipping point occurs is the question.
     

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