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Major discrepancy between trip meter avg energy and speedometer energy usage

Discussion in 'Model S: Battery & Charging' started by robbie380, Feb 2, 2014.

  1. robbie380

    robbie380 Member

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    In the car now and been cruising at 71 mph. My speedometer energy reading is about 350ish. My trip meter is showing over 420. The hat gives? Anyone have any ideas? I've reset it multiple times too.
     
  2. robbie380

    robbie380 Member

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    So I just made it home. I left the supercharger station with 181 miles on my range and I got home with 28 miles of rated range after driving 101.5 miles. Luckily I charged it a little longer to be safe or else I would be on the side of the road waiting for a tow truck right now. I haven't had this problem in the short time I've had the car. I'll be calling the service center tomorrow to find out what happened. The temp outside was about 34 degrees. I know cold weather hurts battery performance, but I didn't think it was this extreme.
     
  3. jerry33

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

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    1. I've found that the more you reset the counters in a car (any car), the less accurate they are.

    2. My guess is that you didn't set the tire pressure to compensate for the low temperatures.

    3. 34 F, plus 71 mph, plus low tire pressures is going to take off quite a bit of range. In a gas car you lose about one mpg for ever mph you go over 60 because the power is going mostly to push air out of the way.
     
  4. markwj

    markwj Moderator, Asia Pacific

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    Out of interest, I tried the estimator calculator on the Tesla Motors website (Your Questions Answered | Tesla Motors).

    Highway, 55mph @ 70F in a Model S standard, yields 306 miles 'ideal'.
    Increasing speed to 70mph drops estimate to 240 miles 'ideal'.
    Dropping temperate to 32F and turning on heater, still at 70mph, gives 204 miles 'ideal'.

    So, that is about a 1/3rd penalty. Of the 100 miles 'lost', it is about 60/40 to speed/cold.

    2/3rds of 181 is about 120, and you did about 101.5 with 28 left, so that sounds about right.

    Regards, Mark.
     
  5. robbie380

    robbie380 Member

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    1. I may not have adequately stated what was going on. The counter/trip meter reading clearly was accurate considering how quickly I used up my battery. The issue was that the power usage meter on the speedometer was not matching up to the trip meter reading.

    2. No I did not add air to the tires to compensate for the lower temps.

    3. Yes clearly the temp does take a massive amount off the range. This was the coldest weather that I have driven the car in, but still something seems off. Once I got in the Austin area I slowed down to 60 and I was still losing range much faster than I would have expected. If we calculate out what my range would have been on a full charge then I would have only been around 177 miles on my max range.

    Also, that point about mpg in gas cars would seem to be a bit extreme.
     
  6. scaesare

    scaesare Active Member

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    I suspect this generalization isn't really... well "true".

    Case in point:

    My SUV gets ~17MPG. I've driven it at 80MPH for expended periods of time. My mileage didn't go "​negative 3MPH" as you suggest it would have done.

    Certainly wind resistance is significant as speeds increase, but that math doesn't hold up.
     
  7. robbie380

    robbie380 Member

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    Thanks for the calculator link. I had forgot about that. I will add that I ended up turning off the heater for most of the trip back home to save power. I was kind of worried about making it home after I left the supercharger station and saw that my energy usage was much higher than I was expecting so I thought it would be best to play it safe with no heat.

    Also, like I mentioned above, I don't think the range numbers sound about right. I only would have been able to get about 177-ish miles out of a full range charge (267 mile charge). That is about 66% of ideal rated range. That is a huge difference from the numbers the calculator gives.
     
  8. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Try EVTripPlanner. I have found it to be the best estimator of an actual energy usage for a route. Also, headwinds can really suck on the batteries.
     
  9. bob_p

    bob_p Member

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    There may be a difference in how the average in the trip table is calculated vs. the energy graph - because when the car first leaves the charger - the trip average since last charge reading is extremely high (sometimes over 1000) - and this isn't shown in the energy graph.

    It's possible the energy graph calculation only includes energy consumed once the car begins moving - and the trip average may include energy consumed while the car is in park - providing total energy consumption (including the "vampire load").

    With the current software, the best option appears to be comparing the projected range on the dashboard with the long distance (30 mile) range in the energy graph - and if you're driving a long distance and the energy graph shows less range than distance to the next charger - it's time to slow down or find a closer charger.

    Because there are multiple variables affecting actual energy consumption (speed, traffic congestion, road conditions, outside temperature, wind speed and direction, elevation changes, ...) - the best prediction of actual range is probably going to be the predicted range with the energy graph.
     
  10. robbie380

    robbie380 Member

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    Just talked with a service rep. He was nice, but not very useful. He is forwarding my car data and everything I told him to the service center and I guess they will contact me. It's about 42 outside right now and I was just driving from work back home at 45 mph and I still feel like the car is using far too much energy.
     
  11. TexasEV

    TexasEV Active Member

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    I had the almost identical experience yesterday in Austin. Left the Columbus supercharger with 174 miles of range and arrived home with only 9 miles, even after slowing down to 55 for the last third of the trip when I saw the miles dropping too quickly. So that's 165 miles of rated range used, compared to the reverse trip Friday evening with temp in the 60's using 130 miles of range at speed of 75-80 most of the way. It's the cold that makes the difference. In the summer I made that trip using 120 rated miles.
     
  12. roblab

    roblab Active Member

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    In my experience, the heater sucks - the battery. I guess, dress warm, wear gloves, bring a blanket. We do.

    We are so used to having astounding amounts of waste heat that we pump into the car at will and never have to think about, that when you have to actually MAKE heat, no one understands. It's the heater, folks. It drops your range by the ton. Sure, the range calculators help, but after making it through last winter (16 months old now), even in "mild" California weather, I plan to use an extra 50% of power (350 wh/mi up to 500 with heat on) when driving in the cold.
     
  13. aviators99

    aviators99 Model S - R140

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    If I'm understanding the OP's question, I don't think anyone has tried to answer it. It seems like he is saying that the kW meter on the *speedometer* is not matching with the trip computer. Whatever extra power is required due to cold, tires, heater, etc., should certainly be reflected in the kW meter on the speedometer, so the kW there should match the trip computer?
     
  14. Trnsl8r

    Trnsl8r Blue 85kwh since 12/8/12

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    I was reading this bit from the OP's posts over and over, and I don't get it... I don't see how you can correlate the energy gauge on the speedometer to wh/mile? Am I missing something? :confused:
     
  15. jerry33

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

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    You are correct. I was thinking of a high mpg car. Pressed enter too soon and had to leave, so I didn't correct it.
     
  16. yobigd20

    yobigd20 Well-Known Member

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    Yep. This heater can use 6kWh-8kWh. So if your stuck in traffic and you go 2 miles in 15 minutes your avg Wh/mi can easily be > 1000
     
  17. jerry33

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

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    177 miles is what ChadS calculated.
     
  18. Todd Burch

    Todd Burch Electron Pilot

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    A few things to dissect here:

    Energy usage on your trip:

    1. What were the wind conditions? Winter is a windy season, with strong fronts crossing the US. Even a relatively light wintertime 10-15 MPH headwind means that your apparent speed (for purposes of drag losses) was 81-86 MPH. A 15 MPH headwind is going to play a larger factor in energy consumption than the chilly 34 degF conditions--especially if you had the heat off, as you said. Assuming you're not using heat, I achieve close to rated range at 70MPH on the highway at 35 degF (about 310 Wh/mi, S85, 19" wheels). A headwind could definitely explain, especially with TexasEV's story. Note that even a crosswind or even a crosswind with a very slight tailwind component could increase energy usage, because you have to steer into the crosswind (against it) to keep the car in the lane.

    2. You get the same kinds of energy losses in a gas car too...it's just that gas cars don't have precise enough instrumentation to measure it as accurately as the S.

    3. Using heat in a gas car doesn't seem to make much of a change, because gas cars are ALWAYS wasting tons of heat. You see much more of a difference in the S because electric drivetrains are so much MORE efficient when the heat is off, that it seems shocking when you turn the heat on.

    4. Any elevation changes? Hills?

    Dashboard energy graph Wh/mi (I assume that's what you were referring to when you said "speedometer energy reading") vs. Trip meter

    1. Differences have been noted in the past. The trip meter certainly seems to include some extra energy usage that's not in the graph--but in my experience it's generally only significant in the first few miles of driving.

    2. One potentially misleading thing is that the graph is only showing your 5/15/30 mile average, whereas the trip meter is showing "since last charge" or "since last reset". If you reset the trip meter, you have to drive 5 miles (or 15 or 30) to compare it to the graph. When I do this, they're in the ball park--although certainly not exact.

    Not sure if any of this is helpful.

    - - - Updated - - -

    By the way, the next time you go through a drive through and have to wait for a few minutes--check out your energy graph when you finally pull away. Not uncommon to see 1000 Wh/mi+ for that tenth of a mile.
     
  19. TexasEV

    TexasEV Active Member

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    There is ideal range, and there is rated range. What do you mean by "ideal rated range?" Forget ideal range, we don't live in an ideal world. For rated range, yes a 1/3 penalty in the cold is typical. That's why superchargers are being spaced no more than 150 miles apart, and usually closer to 120.

    If you really get into trouble coming back to Austin, there are ChargePoint level 2 chargers on the approaches to Austin from all directions where you can pick up a few extra miles.

    By the way if you're not on the Austin Tesla owners google group, PM me.
     
  20. cinergi

    cinergi Active Member

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    The energy graph (that I suspect you're talking about next to the speedometer) is a running average. It's customizable to 5, 15, or 30 miles -- based on the setting of the energy graph on the 17" screen. That graph and the trip meter will match after driving 30 miles (assuming the graph is set to 30 miles).

    I think I read that it was in the 40's -- which shouldn't make that much difference on range. The cold starts to noticeably affect range around the freezing mark.
    Other factors may be at play here -- like elevation changes, wind, precipitation, etc. Do you have the Tesla-provided tires on the car or do you have your own?
     

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