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Preconditioning Car Yield Full Regen Capability?

jsmay311

Active Member
Apr 22, 2016
1,179
1,695
Chicago suburbs
I’m on 2020.48.30 in my 2018 LR RWD. I was surprised yesterday when I got in the car to leave in the morning and had full regen in 20 degree weather. I went on to my TeslaFi logs and sure enough the car woke up 2 hours before I left and burned through 10% battery heating the battery and then the cabin. I charge at work and don’t plug in at home so I was surprised. I changed the scheduled departure time on the screen and checked again this morning and sure enough I had full regen when I left this morning. I had no idea the car would warm up without being plugged in until now. Not sure if it’s a bug or a feature.

Man, that’s a lot of wasted energy. I hope that’s not typical behavior. Preconditioning should not be designed to be so dramatically wasteful.

Jeez… it really is as bad as Gforce1 described.

I finally got around to trying an unplugged “scheduled departure” preconditioning with my cold-soaked Model 3 LR RWD. It started heating the battery 2 hours and 10 minutes in advance of the scheduled departure time, during which it used 10% of the battery, 8-9% of which went into heating the battery and only 1-2% into heating the cabin. (Data gathered from TeslaFi.)

Background details:
The car was left unplugged and cold-soaked outside in overnight/morning temps that got down around 15F-20F. The car was not driven or charged the previous day, so the battery temp was probably down pretty close to ambient.

I had set a scheduled departure time w/ preconditioning turned on for 12pm and a cabin temp of 70F. The car started warming the battery at 9:50am, at which point the battery level was 83%. According to TeslaFi, it drew ~3kW of power continuously until 11:27am (97 minutes) by which time the battery level had dropped to 75% (an 8% drop). Then it sat idle for another 13 minutes until 11:40am when it started warming the cabin. It only took ~5 minutes to heat the cabin, which used another ~1% of the battery. Over the next 15 minutes, it drew modest amounts of power (1-2kW), presumably to maintain cabin and battery temperatures, which used up another ~1%

TeslaFi data summary:
  • 9:50am; battery at 83% (77% usable): Car starts drawing a reported 3kW continuously for the next 97 minutes. (The kW figure is rounded to the nearest whole kW, so, presumably this is the 3.5kW battery heater/stator heating the battery).
  • 10:18am; battery at 80% (79% usable): Difference between actual and usable battery level is down to ~1% after 28 minutes of battery heating, but battery will continue heating itself for another 69 minutes.
  • 11:27am; battery at 75% (75% usable): Car stops drawing power.
  • 11:40am; battery at 75%; cabin temp 31F: Car starts warming the cabin. Power draw = ~6kW.
  • 11:45am; battery at 74%; cabin temp 70F: Cabin temperature reaches target temperature.
  • Power draw fluctuates between 1kW and 6kW for the next 15 minutes, presumably to maintain the cabin and battery temperatures.
  • 12pm (scheduled departure time); battery at 73%: I get in the car. There are zero “reduced regen” dots on the display.
So, in summary, 10% of the battery used up to heat the battery and cabin when only ~1% would be needed to heat the cabin alone (and maybe another ~3% for heating the battery if you wanted to get a decent amount of partial regen).

It’s hard to view this programmed behavior as defensible when the waste is so great and the benefit (full regen instead of partial regen) is so minor, especially given that owners are given no way to toggle off battery preconditioning without also disabling cabin preconditioning.
 

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