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The Three Mile Regen Dead Zone; what's up (or down)

Discussion in 'Model S: Battery & Charging' started by Cottonwood, Aug 26, 2013.

  1. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Rated miles is a good metric of capacity left in the battery. I live in Colorado and vertical is just another part of driving. You go up, and you have to pay the potential energy piper; you go down and the piper pays you back. That's fine, but I wish that the Tesla cars would just display what is left and not play games.

    Games you say! For some reason, Tesla cars don't want to show an increase in rated miles until you accumulate a total of three. I first noticed this driving down Mt Evans in my Roadster in 2009 (I think that I may have been the first to take an EV over 14,000 feet.). Going down long mountain grades, there is a lot of Regen going on. The rated miles stays the same, then suddenly jump by three. If you don't get to the magic, three-mile threshold, then the rated miles just don't go away for awhile until the universe comes back into balance. Amazingly, the magic three mile dead zone is in the MS as well (well, occasionally, it is four...). My MS lives most of its life in Pagosa Springs, CO. 30 or 40 times a year, I drive up to Wolf Creek Pass and then back home. There are about 10 miles of regen in the potential energy bank driving to the west, down off of the pass. The bonus, potential energy, rated miles, always come in bursts of three...

    Why can't Tesla just tell us what is left in the battery? Why do they wait until each three mile increment to show us reality; what is there to hide?
     
  2. dflye

    dflye S Sig Perf 414, VIN 814

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    At least for me, on average I get about 3 miles from one kilowatt hour. So, maybe more of an integer vs float issue in some calculation, and it doesn't register until you've reclaimed at least 1 kWh?
     
  3. brianman

    brianman Burrito Founder

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    I wouldn't jump to an integer/float conclusion, but we definitely have several examples where the internals measure things in one unit, "simplifies" (rounds/floors/whatever), and then converts to another unit. Cruise control is another example that readily comes to mind.
     
  4. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    I had the same idea, but its the same 3-mile, regen deadzone in the Roadster and the MS. The Roadster does about 230 Wh/mi and the MS does about 307 Wh/mi. If it were an integer kWh thing, then the Roadster would have been more like 4 miles, but its 3.

    Most of the time, I have seen the display limited to integer units, but not the internal calculations. For example, look at the trip screen right after a charge; although the miles and kWhs are in 1/10ths, and start at very small values (one quanta is a very large percentage), the Wh/mi display gets a full 3 digit precision that reflects far greater precision that the displayed values of distance and energy.

    Also, if there was a kWh resolution issue, then the rated miles remaining would count down by 3 or 4's. My theory is that someone wanted to avoid too busy a miles in the battery display and put in a deadzone on regen, and this concept just rolled over from the Roadster to the MS.

    I know that I am a little obsessive, but when pushing the range to its limit and deciding whether or not to stop for that last little top-up on the battery, I keep a careful eye on the difference and ratio between the nav system and battery miles remaining. If I correct for altitude by 6 or 7 miles per thousand feet vertical, then these are very good metrics of whether I will make it to the destination or not. Having this 3 mile, regen deadzone on descents just makes those calculations more coarse. Lately, I have been pretty good at arriving at the day's destination with 10-20 miles left. That leaves me with a some margin, but without Superchargers, avoids excessive charge time mid-trip.

    Mental math is good to keep the mind alert on long drives. :biggrin:
     
  5. wycolo

    wycolo Active Member

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    I've posted this before: I like the 3 (or 4) mile-at-a-time jump as opposed to one mile at-a-time simply because it is easier for a geezer mind to keep track of as I'm doing a long downgrade. Going from 4 to 7 is something I easily notice esp when that 4 has been on the screen for a long time. Could be a geezer engineer at TM slipped this one by the committee.

    When you took your Roadster over 14,000 feet I bet you looked under it for leaking battery juice. :smile:
    --
     
  6. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Yeah, a design decision, but I hate it when the machine hides information from me...

    Yup, just like taking off in a helicopter, look around for puddles and parts before you depart the area. :wink:
     
  7. wcalvin

    wcalvin Member

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    Anyone figured out how to get it to display kwh left rather than miles?
     

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