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What's wrong with the Tesla regen? Or my car? (Chart)

Discussion in 'Model S' started by tedsk, Mar 15, 2017.

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  1. tedsk

    tedsk Member

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    #1 tedsk, Mar 15, 2017
    Last edited: Mar 15, 2017
    I've been driving BMW i3 for couple years and recently traded it for Tesla Model S. Right away I noticed difference in regenerative braking behavior. First Tesla doesn't stop completely like BMW but starts coasting at around 5mph - forces to use friction brakes which wasn't necessary in BMW. Second and more annoying one is non-linear deceleration (it makes it very hard to predict where car will stop and forces me to depress accelerator closer to the end of braking). My butt-dyno was screaming - something fishy is going on at the end off deceleration right before regen gives up at around 10mph. My assumption was that it is software glitch in regen rate limiter and I decided to check exact metrics. It showed that my assumption was incorrect (regen current to battery pack was linear) but butt-dyno didn't lie. So what is the heck going on there?
    Need help from gurus and have complete CAN3 log for the measuring period. I highlighted 4 specific periods: 1 - linear deceleration, current (what one may expect); 2 - deceleration kicks-in while regen current stays constant; 3 - regen gives up and car starts coasting at around 5mph; 4 - I hit friction brakes.
    What is happening on in period #2? If regen doesn't increase what makes car brake 2 times more heavily?
    Legend: Green line is calculated and scaled deceleration rate to fit on the screen, it lags a little since it is 1 second moving average; Yellow - pack current in Amperes; Blue - speed in mph;
    Regen.jpg
     
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  2. ivolodin

    ivolodin Member

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    Regarding first question about Tesla not completely stopping, I believe this is due to the creep. You can disable creep under driving settings. I also noticed that regenerative braking is not linear. It's noticeable when you are slowing down for an exit on the highway. Deceleration rate at around 70mph seems to be a lot lower then at 30mph.
     
  3. Livver77

    Livver77 Member

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    You will get use to how it reacts and have it down to a science real quick. I would suggest using the actual breaks atleast once per drive as some people have had caliper issues due to the fact they never use them or use them very little. Also if you are in a cold climate the regen is not available when the battery pack is cold and you can see this when you have the energy chart on the dash selected.
     
  4. croman

    croman Active Member

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    I'm not sure any EV can actually regen brake to a full stop. The LEAF acts very similarly to the Tesla and will also kick out regen at 5mph. I noticed that the Tesla is not linear like the LEAF but its close enough that it usually isn't an issue other than in cold due to limited regen.
     
  5. Az_Rael

    Az_Rael Supporting Member

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    I believe the i3 is different in this regard - my understanding is it has a much more aggressive regen than a Tesla and can be used down to 0mph. The new Bolt also has regen down to a full stop as well. So there are at least a few EVs that have implemented regen in this way.
     
  6. cantdecide

    cantdecide Member

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    The Tesla behavior is independent of creep settings. We have Tesla and an i3 so I do know what you mean... On a slight downslope the Tesla will never come to a complete stop with no pedals pressed.
    For your first question as to what is the difference between the cars I believe the i3 adds in fiction breaking at low speeds to keep the user experience constant.

    For the Tesla experience (nice chart btw) I guess it is starting the obvious that in the first section it is current or wattage limited (I expect the limitation is the ability of the battery itself to take up charge at that charge level and temperature).
    After that there is a short patch of constant deceleration (likely for ux reasons) then perhaps it switches to an engine torque limitation or similar?
     
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  7. Socalcommuter

    Socalcommuter Member

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    I've disabled creep and it still does not completely stop.
     
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  8. hiroshiy

    hiroshiy Supporting Member

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    I read somewhere in the TMC that below 5mph, there is no electricity generated so no regen. i3 seems to apply reverse power from motor or friction brakes to bring the car from 5mph to complete stop. At least that's what I heard.
     
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  9. JohnnyG

    JohnnyG Weee!

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    This is great data; nice chart! I would love to see this charted with actual vehicle speed (numbers). Then, run multiple logs: starting at 25MPH, 45MPH, 65MPH, etc... I'm curious to see if the pronounced increased rate of deceleration always starts at the same vehicle speed....
    From a physics perspective; under a constant rate of resistive force, the rate of deceleration will increase in a non-linear fashion as the object slows. Maybe this is what we're experiencing?
     
  10. davinci2017

    davinci2017 Member

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    I actually like that it doesnt completely stop. I also like that it is non-linear. It takes some getting used to but the push pull is more elegant and smooth and its easier to drive the car in traffic and keeping the movement smooth compared to linear regen that comes to a stop which feels a bit too aggressive in stop go traffic.
     
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  11. croman

    croman Active Member

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    This must be how the i3 and Bolt do it. There is no way to slow an EV down beyond 4-5mph through inductive resistance. I'm not an EE, so take my response with a grain of salt as an enthusiast only.
     
  12. tedsk

    tedsk Member

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    Thanks for the guess but it is not creep - I turned it off.

    Exactly, it ranks up at around 30mph. My opinion - it is a serious issue.

    That is not my question. On can get use to live under the bridge. Irrelevant, sorry.

    Brakes you mean? I do use it all the time since I forced to. It is impossible to stop at traffic light without hitting brakes in Tesla. It was possible in BMW i3.

    You are wrong. It actually can. Thing is that for Tesla motor in order to generate electricity it should consume some electricity too. At speeds below 5mph it consumes more than generates so makes it inefficient as generator. But I want it continue to work as brakes even below 5mph till complete stop and do it linearly. It should be adjustable in settings for sure but I want this option. BMW does it by default and it is amazing. One pedal driving is something I quickly got use to and don't want back. BMW even holds the car still at stop with motor. No brakes needed unless emergency.

    Kind of. It is not more aggressive it just doesn't give up and makes its job as brakes, not only as recuperator.

    It doesn't. It uses electric motor for that. Truth to be told it indeed engages friction brakes during regen but in very particular case - it emulates regen with friction brakes if battery is completely charged and can't accept more charge. Nice thing actually - BMW got it right. Consistency in braking is the key! Tesla's implementation is a fail.

    Thanks! But your interpretation is not correct. There is only one limiting thing here - max current battery can accept (due to converter or temp limitation but it doesn't matter). In this particular case current was limited to around 48A. Adding battery voltage it was limited to 16KW. Since power was constant what made car decelerate faster? Brakes engaged?

    Exactly. I like it the BMW way but it is just half of the issue.
     
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  13. tedsk

    tedsk Member

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    Not true. It is possible. It will not generate power but consume it though.
     
  14. croman

    croman Active Member

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    Its not regen braking if it uses energy to accomplish what a friction brake does. Thanks for clarifying because now I understand what BMW is doing to stop from <5mph.

    I'm not sure I like the BMW approach but I won't knock it until I've tried it.
     
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  15. tedsk

    tedsk Member

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    I would suggest to do a test drive. Worth time.

    It is still braking but doesn't regenerate energy below 5mph.

    As for me I'd prefer convenience and pay with energy instead of friction brakes wear and moving my foot between pedals.
    Give me choice Tesla!
     
  16. m2140

    m2140 Member

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    I too did the switch from an I3 to a Tesla and at first I did not like the difference.

    The i3 is far more aggressive and allows for true single pedal driving. But like others stated, under 5 mph the i3 is just doing some cleaver programming and actually using the motor on power to slow down (not regenerating) and then holds the car with the brakes on its own.
    Also, on the i3 you never have access to more than 80% of the battery available so the regen braking is always consistent no matter the charge.

    Tesla on the other hand does no regenerative braking under 5 mph and needs you to perform the work. Disabling Creeps does not affect this behavior. But depending on the model you have 85kw or higher battery, your regen braking changes based on your battery level. 95% or higher has reduced regenerative braking to protect the battery. Once under 95% regen braking is back to normal.
    Tesla also requires you to use the brake pedal to stop & enable auto hold. the i3 does it for you.


    I recently took a chevy Bolt on a test drive and I really hated the Regen braking on that thing. Unlike other EV's in order to get regenerative braking on the Bolt I had to steps on the brake pedal. It was really odd. Of course the guy on the test drive had no clue if there was a mode to change that. But the Bolt forced me to drive with 2 pedals. When I pressed the brake the software in the car makes the decision if the motor or the brakes are being used. I guess they did it to allow the car can coast and work like a regular gas car and reduce the learning curve.
     
  17. jmsurpri

    jmsurpri Member

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    I believe the bump in deceleration in phase 2 is caused by the front motor regen kicking on.
     
  18. derekmw

    derekmw Member

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    The way I drive the Model S, I am able to do single pedal driving as well. Coming from a Leaf, I learned to pay attention much further out on what's happening (light changing, cars slowing down) to where I do not have to constantly go back and forth on pedals. Even in stop and go traffic, I time my acceleration to match the traffic conditions and do not have to actually brake. There are the occasional unavoidable cases where traffic stops longer than I anticipated but for the most part, I am mostly doing 1 pedal driving except at lights and stop signs.

    In my opinion, I think this approach is better as it teaches me to avoid unnecessary acceleration where I need to depend on harder regen that requires braking.
     
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  19. Az_Rael

    Az_Rael Supporting Member

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    The Bolt has one-pedal driving. You probably needed to put the car in L instead of D with the shifter. Its too bad the sales rep had no clue.

    Bolt EV Goes the Distance…With One Pedal
     
  20. jelloslug

    jelloslug Active Member

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    The i3 does, or at least the 2014 BEV I used to have did.
     

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