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Contribution of regenerative braking?

Discussion in 'Model S: Battery & Charging' started by skynet, Sep 20, 2015.

  1. skynet

    skynet New Member

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    Has Tesla published data defining how much energy (or miles) are generated via regenerative braking? I’m interested if my dogmatic focus on optimize regenerative braking makes a material difference.
     
  2. CHG-ON

    CHG-ON Still in love after all these miles

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    Yes. Check out their site and blog.
     
  3. voyager

    voyager Member

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    Can you be more specific where to find data on regenerative braking? Also in general.
    Especially considering that those are pretty mighty big disks the Model S is featuring on all four wheels...

    Tesla-Chassis-Frame.jpg
     
  4. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    The brakes really have nothing to do with regeneration because you control how much to use them. The Tesla is not like the Prius where most of the regeneration is on the brake pedal. In the Tesla every bit of regeneration is on the accelerator pedal and the brakes are just the brakes. This system has several advantages: 1) The brake control system can be much simpler. 2) You get almost one pedal driving. 3) There is no transition feel (which feels like your brakes have gone) because the system has decided to stop regeneration. This happens on expansion joints and rough surfaces while braking in non-Tesla cars with regen.

    As far as the miles given by regen goes, that depends upon the driving style and the terrain. It's hard to give a number that would work in the majority of cases. A few things to note: Regeneration takes kinetic energy and converts it into electricity and heat. This is better than friction braking which turns all of the kinetic energy into heat. Therefore it's more efficient to modulate the accelerator pedal so that no regeneration is used whenever possible because all the kinetic energy (less rolling resistance) is turned into motion. Bear in mind there are energy conversion losses every time energy is moved from one form to another.
     
  5. Johann Koeber

    Johann Koeber Member

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    I would really like to know how many kWh are gained by regeneration.

    The electricity gained by regeneration goes right back to the battery. So this contributes to the cycling of the battery.

    The way I see it, the batteries take a lot more cycling than is obvious. But the regeneration is usually of shallow amplitude and thus does not degrade the battery much.

    Does anyone have a guess of the amout of regen we are getting (like in % of the power used)? I really wish there was a meter somewhere, probably there is and we cannot access it.
     
  6. scottm

    scottm Active Member

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    #6 scottm, Jan 1, 2016
    Last edited: Jan 1, 2016
    There is a meter on my car, a green arc that shows how much juice is being generated in the moment.
    And on the trip meter consumption graph, the area under the chart, where it goes green shows what you've packed back in over time... dont all S's have this?

    Take a trip up a big mountain range, then back down... the same route.
    Don't touch the brakes on the way down. Nor the accelerator.
    Go as far as the car will by coasting to a stop at the bottom.
    Note the total distance travelled. And energy used.
    Observe the SOC, at the outset, at the top, at the bottom after the return trip.
    Repeat, but this time turn regen setting to low.
    Finally, find a nice flat stretch and drive the distance obtained above, at the average speed it took you to do the round trip. And for good measure, drive back on the flat route that distance again to rule out wind and altitude.

    Draw your conclusions, and share with the group here.

    I'll share my conclusion: regenerative braking is a waste of energy that would have been better conserved by not having to slow down in the first place, I.e. the best power consumption target is flat. Regenerate nothing, and don't use the brakes. I wish I could turn regen completely off on the highway, but at best I can only turn it to low. I view each use of the brakes as a failure, bad planning on my part. Except of course, when you need to use the brakes.

    For me, the massive brakes on the car are mostly wasted, but there when needed because the car is so heavy. The regenerative technology is also mostly wasted, my commute is highway. But the regen is free, doesn't add weight, and is better than fricton braking when you do need to slow down - so I'll take it. Dont forget regen is still braking, which is a waste.
     
  7. nwdiver

    nwdiver Active Member

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    If you're concerned about regen causing battery degradation... don't be. Cycling the battery 90% once is worse than cycling it 10% 20 times... The tiny cycles that the battery experiences due to regen likely extend battery life slightly if anything...
     
  8. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Regeneration tops out at 60kW. If you're using it to slow the car from 80kph to 10kph, the deceleration takes about 15 seconds and regen tapers from 60kW to zero. Rough numbers: average 30kW for 15 seconds is 0.125 kWh.

    The largest single dose of regen I ever see comes when descending from a mountain pass, gaining nearly 3kWh during the 11 mile descent.
     
  9. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Mostly agree. However, there is a point when going down a long steep grade where more kinetic energy is used to push air than is converted to heat during regeneration. As far as I know, no one has done the calculation to say at what speed this is, but I expect it to be around 120 km/h (75 - 80 mph).
     
  10. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    You can control regen - with your right foot. If you keep your foot in the middle, essentially neutral, the car will coast.
     
  11. kejsermad

    kejsermad Member

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    I can answer your question quite precisely. I use a programme called linkmytesla. It shows you how much energy is regenerated and over the last 24.000 km I have regenerated 17% of the total energy consumption. In genereal this value will be between 15-20 % depending on driving habits if you keep regen in standard mode.
     
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  12. Johann Koeber

    Johann Koeber Member

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    Thank you very much. This is what I was after.

    So the Model S uses 17 % more electricity for propulsion than the power meter will tell us. But this electricity is produced in the drive train. Clever.

    The batteries are charged and discharged more than most people might believe. No measurable degrading because of the small amount of charging.
     
  13. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    It's going to depend on the driver and the terrain. You can't generalize from one data point.
     
  14. Kim.T

    Kim.T Member

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    Users from Denmark using linkmytesla.dk are reporting 15% regen
     
  15. David99

    David99 Active Member

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    While the conversion from kinetic energy to electricity into the battery is pretty good during regenerative braking (around 80%), the actual energy you get back is much smaller. Say you accelerate to 60 mph and then use regen to slow down to zero. You will get many 20-30% of the energy back that you put in to accelerate the car to 60 in the first place. Same with a mountain. If you need 10 kWh to drive up a mountain, you might be maybe 2-3 kWh back going down using regen. It's not lack of efficiency. It's just that you used the energy to move the car and traveled some distance. Wind resistance and a lot of other things 'use' up energy on the way which can't be recovered.
     
  16. voyager

    voyager Member

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    Thanks everyone. So, no general statistics. Regen is very much dependent on the way you drive and tend to come to a halt.
     
  17. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    The largest, noticeable gain is down big elevations. I regularly get 10 added rated miles in the battery coming down Wolf Creek into Pagosa Springs.
     

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