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Trip meter in the cold, totally wrong.

Discussion in 'Model S: Battery & Charging' started by AWDtsla, Jan 26, 2016.

  1. AWDtsla

    AWDtsla Active Member

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    I decided to discover just how bad the trip meter is. It seems to be basically garbage. Even the "since last charge" is lying, even by the car's own measure, even taking out vampire losses, which should be included in there regardless. It is "since last charge" after all.

    So if you do short trips, and you preheat the car, it seems NONE of that usage is included. By how much? Let's say 4 short trips over 8.1 miles, and 14 hours total time. The first trip of which is after charging/preheating on shore power. Reported usage is 6.1 kWh and 672 Wh/mi. Actual usage went from 189.7 to 162.7 RM, as reported by VisibleTesla. What does that come out to? ~8.4kWh. Actual energy usage over 1000Wh/mi. My napkin calculations got 1077 with vampire, 1002 without. This is not included charging efficiencies, this is only what the car is reporting. If I take out the charging efficiency I've measured previously, actual achieved is a whopping 1158 Wh/mi!

    That's A LOT of error. If I wasn't doing the math, I could be convinced that this was saving money. But since I can do math, I can see this is about 30% more expensive that the same drive done in an ICE that's getting 14mpg of premium fuel at current prices.
     
  2. stopcrazypp

    stopcrazypp Well-Known Member

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    There are conflicting goals. The in-car display is supposed to represent DC kWh from battery. This is helpful for math on how far you can travel at a given kWh in the battery. However, for pricing out how much it costs you in AC kWh, measuring at the EVSE (or even more upstream) is the correct way to determine this.

    This is the same reason why on the EPA results, the MPGe (kWh/100mi) math does not work out compared to rated range when you use the rated or usable battery capacity. The MPGe is measuring AC kWh consumed at the EVSE, not the DC kWh of the battery pack.
     
  3. trils0n

    trils0n 2013 P85

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    Would you want the trip meter to include the energy when you're not driving (preheating)?

    I think I'd prefer a separate energy graph to show climate control usage (including when not driving), and keep the trip meter just my energy usage for the trip.

    The Leaf can display the energy usage for the motor and for climate control separately -- I'd like that for the Tesla, as it would make these situations clearer.
     
  4. AWDtsla

    AWDtsla Active Member

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    Yes, I think the trip meter should include preheating you've done for the trip. But that's debatable. The "Since last charge" count should in NO WAY be lying.
     

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