TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

acceleration goes down with charge level ?

Discussion in 'Model S: Battery & Charging' started by joer00, Apr 8, 2013.

  1. joer00

    joer00 Member

    Joined:
    Jan 26, 2013
    Messages:
    297
    Location:
    Tampa
    Last week when I picked up my MS from the service it had a nice full charge. After one day in my wife's ICE the first thing I had to do is floor the MS :)

    The traction control light went on at 30 MPH ! I was wondering how acceleration is affected by the battery charge. The kw/h shows the same 320 if the battery is full or almost empty (I know it gets a dotted yellow line when below 40 miles to restrict the kw/h).

    But something must go down with less battery, is it the volts ? How does the battery % measure work ? Any explanation please from you smart physicists out there :)

    Did anybody do acceleration tests at different charging levels ?
     
  2. stopcrazypp

    stopcrazypp Well-Known Member

    Joined:
    Dec 8, 2007
    Messages:
    7,047
    #2 stopcrazypp, Apr 8, 2013
    Last edited: Apr 8, 2013
    There's two types of dotted yellow lines.
    The one above the "kW" means output power is limited:
    http://www.teslamotorsclub.com/attachment.php?attachmentid=11616&d=1352953730
    The one below the "kW" means regen power is limited:
    http://www.teslamotorsclub.com/attachment.php?attachmentid=17118&stc=1&d=1361719485

    In general, the battery voltage will go down as the battery discharges. This reduces the power available to the motor and also explains why people generally get the best times at the drag strip when at or near fully charged. In contrast, the dotted lines are a software limit.
     
  3. ckessel

    ckessel Active Member

    Joined:
    Jan 15, 2011
    Messages:
    4,266
    Acceleration suffers very little with the charge level dropping. The rate at which the batteries can discharge doesn't change much as they drop in charge level so the car's performance doesn't change much. As stopcrazypp noted, the best times are with a full charge, but it's not a huge difference.

    It's the same reason your phone, ipad, laptop, etc don't start running slower as the battery gets lower. State of charge is only slightly related to rate of discharge unless you start to get very low (at which point you'll see those dotted lines in the speed console).
     
  4. bluetinc

    bluetinc Member

    Joined:
    May 11, 2009
    Messages:
    682
    Location:
    MD
    Hey Joe,

    The quick of it is that Power (kW) = Voltage * Current and as the battery level drops, the voltage of the battery drops. To keep getting the same power out of it (320kW) as the voltage goes down the amount of current goes up. At some point, both to protect the battery due to the chemistry/physics of pulling high currents from a low voltage cell you start to see the limits imposed by the software.

    I'm not sure about the acceleration test. I think I can measure a small small (sub .5 second) difference between full and say 40%, but I haven't done enough testing in a controlled way to be sure.

    Peter


     
  5. SuperCoug

    SuperCoug Model S Res #7734

    Joined:
    Mar 16, 2012
    Messages:
    225
    Location:
    Bothell, WA
    I think this may be the reason why Tesla seems to consistently report 0-60 times that are about 1/2 second slower than what owners and the car magazines are actually seeing. I think they want to be very conservative and report that slightly slower time so a car magazine can't say things like "Well, Tesla claims the Model S can do 0-60 in X.X but we were only about to achieve X.Z in our real world testing".
     
  6. vfx

    vfx Well-Known Member

    Joined:
    Aug 18, 2006
    Messages:
    14,792
    Location:
    CA CA
    When drag racing ICE cars, owners have many tricks to eeek out tiny fractions of a second.

    In the same vein, drag racing electrics always benefit from a topped off battery.
     
  7. Doug_G

    Doug_G Lead Moderator

    Joined:
    Apr 2, 2010
    Messages:
    15,852
    Location:
    Ottawa, Canada
    Traction control has nothing to do with your charge level, and everything to do with your wheels slipping. If you want better acceleration, find some better pavement!
     
  8. William13

    William13 Member

    Joined:
    Mar 19, 2011
    Messages:
    943
    Location:
    South Bend
    Acceleration is limited to protect the battery at low charge levels and when the battery is very cold. A measurable but somewhat meaningless (other than racing) drop in acceleration occurs at less than 100% charge. Mild but cumulative battery damage occurs with hot, full batteries being quickly discharged.
     
  9. joer00

    joer00 Member

    Joined:
    Jan 26, 2013
    Messages:
    297
    Location:
    Tampa
    Of course it does ! If and how much the wheels are slipping is a function of torque and grip .

    So thanks to the guys who gave a meaningful answer, the torque only goes down insignificantly with less battery.

    I am still interested how much. Since there seems to be no data I will get the Iphone acceleration app and do some tests. Of course on the same street with same condition (dry and same temperature). So we should have some data soon.

    - - - Updated - - -

    I see but WHY ? If, as others mentioned here, the volts go down but the amps up so the KW/h stays the same (which is also what the dashboard shows), why should it be slower, even if it is meaningless ? 320 KW is 320 KW, so as long as we get 320 it should be the same acceleration. (again, I am talking about >40 miles left on the battery where the limit line is off).

    Which brings me to the next questions for the non Performance owners, I assume you guys do not see the full 320 KW on acceleration ?
     
  10. William13

    William13 Member

    Joined:
    Mar 19, 2011
    Messages:
    943
    Location:
    South Bend
    The cell's voltage potential is highest at full charge and drops off a little as the charge is used. The amps stay basically the same. The inverter although nominally 320 kW likely outputs more with a higher voltage as is true of nearly all electrical equipment.
     
  11. Stoneymonster

    Stoneymonster Active Member

    Joined:
    Jan 8, 2013
    Messages:
    1,554
    Location:
    Aptos, Ca
    I have a non-perf. Flooring it pegs the meter at 320kW. Would love an explanation for that.
     
  12. stopcrazypp

    stopcrazypp Well-Known Member

    Joined:
    Dec 8, 2007
    Messages:
    7,047
    This may be the confusing thing: The display only shows the software limiter. That's the dotted line that sometimes shows up at 160kW. You can't tell the hardware limits until you floor it and look at where the green line goes up to (although even this may not be true as we don't know if the green line is mapped directly to battery/motor output).

    Keep in mind that although you can pull more amps from the battery, there's a limit to how much. This is the discharge limit of the batteries (the peak C-rate). Also, as you pull more amps from the battery, the voltage sags, which only further reduces available power. So like William13 says, the amps you pull stays basically the same (assuming you are pulling peak amps already), but the power goes down with the voltage.
     
  13. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,756
    Location:
    Texas
    To put it another way Watts equals Amps times Volts. A Watt is the measure of power. As Volts go down, so do Watts.
     
  14. johnmodels

    johnmodels Member

    Joined:
    Feb 2, 2013
    Messages:
    149
    Location:
    SoCal
    Has anyone seen it where your s85, or any model s, limit the acceleration when you have over half charge? Mine is showing the yellow dotted line between 160 and 320kw under full acceleration. The batt is showing over 130-140 rated miles left. It also is more sluggish when accelerating taking more time to hit 320kw, substantially slower. I ahve called tech support and they are working on it...
    john
     
  15. stopcrazypp

    stopcrazypp Well-Known Member

    Joined:
    Dec 8, 2007
    Messages:
    7,047
    It has happened to people, mainly at the track. Although some people have reported it also during high power demand for long periods of time (like very high speeds or uphill on steep grades). The limit there is heat (although no one has been able to pinpoint which part: motor, PEM, or battery).
     
  16. fiksegts

    fiksegts Active Member

    Joined:
    Jan 6, 2013
    Messages:
    1,049
    Location:
    Miami
    how fast were you going? did you do repeated runs? I've seen the car pull back power after repeated all out accelerations runs...

    - - - Updated - - -

    and back to the original question, the charge level does effect performance... 0-60 MPH in 3.9 on a full charge and 4.3 with 50 miles left....
     
  17. Bound466

    Bound466 Member

    Joined:
    Dec 31, 2011
    Messages:
    204
    Location:
    Rancho Cucamonga, CA
    Yes. I've noticed that too. I experience better acceleration when the battery is more than half full.

    I've also experienced the dreaded dotted line when performing multiple high speed accelerations. But what's been strange is that when I start accelerating, the orange line still goes past the dotted line anyway, and I don't notice any limitation.
     
  18. johnmodels

    johnmodels Member

    Joined:
    Feb 2, 2013
    Messages:
    149
    Location:
    SoCal
    I was going about 40mph with about 135 rated miles left in regular city driving. The minor frustrating thing is that I would like full power unless there is a good reason not to have it available, like under 30 miles left. It seems like something is not running properly. I did do a few 3 seconds acceleration runs at 40 mph and video'd it. It was 72 degrees outside. Doesn't it make since to have full performance until the batt needs to conserve itself. Or is that possible because of the technology?
    john
     
  19. Doug_G

    Doug_G Lead Moderator

    Joined:
    Apr 2, 2010
    Messages:
    15,852
    Location:
    Ottawa, Canada
    I went drag racing a couple of months ago. The car was fractionally slower each time I ran, presumably due to a slightly lower battery. I'm talking about a 0.01 second difference per run though. Yes it's so consistent you can notice something like that.
     

Share This Page