Question concerning timing the end of my first 100% charge

[Duma]

Just to add to the data here, I did my first and only 100% charge a few weeks ago and using Visible Tesla captured similar results to those reported by Andyw2100. In my case, this was 6 weeks after delivery with about 1500 miles on the car. I was charging at 40 Amps with voltage steady at 242 Volts (HPWC).

Once the car reported 100%, it continued to charge for an additional 30 minutes. During this time the current tapered down to 5 Amps. The taper was not linear, with current staying at 40 amps for about 5 minutes, dropping to 20 Amps over the next 10 minutes and continuing to decrease more gradually for the remainder of the time. About an hour after the charging finished the rated range increased from 273.1 miles (at end of charging) to 275.5 miles. This is for an 85D and as best I can recall, I had range mode enabled prior to starting the charge. I was not monitoring the displays in the car or in the Tesla App as I was in bed, asleep.

I did not experience any strange screen behavior. Both the 17" and instrument cluster screens were normal when I left on my trip, which was about 4 hours after charging completed (3 hours after the last range increase).

If the 1 hour lag between the end of charging and the range update is purely calculation of the data to update the range, that would be an enormous amount of computation. This suggests that there is more to the recalibration than just number crunching. The taper during the last 30 minutes of charging appears consistent with some sort of cell rebalancing.

 

[Andyw2100]

If the 1 hour lag between the end of charging and the range update is purely calculation of the data to update the range, that would be an enormous amount of computation. This suggests that there is more to the recalibration than just number crunching. The taper during the last 30 minutes of charging appears consistent with some sort of cell rebalancing.

Thanks for an excellent post!

In your case whatever the car was doing between the time the charging stopped and the range increased took an hour, but in mine it took over four hours! Perhaps that's an indication that my pack, with much more time and mileage on it, was significantly more unbalanced than yours was. It would be interesting to see what that lag is for someone who regularly range charges. Presumably it should be shorter than yours was, with also perhaps little or no change in range. (Of course if there's no change in range we won't be able to tell when the process finished.)

Thanks for posting!

 

[Duma]

In your case whatever the car was doing between the time the charging stopped and the range increased took an hour, but in mine it took over four hours! Perhaps that's an indication that my pack, with much more time and mileage on it, was significantly more unbalanced than yours was. It would be interesting to see what that lag is for someone who regularly range charges. Presumably it should be shorter than yours was, with also perhaps little or no change in range. (Of course if there's no change in range we won't be able to tell when the process finished.)

Today I was poking around my charging behavior as recorded by VisibleTesla, investigating why my car sometimes shows 66% in the morning even though I had set the limit at 65%. In each case, the charging had indeed ended at 65%, but anywhere from 1 hour to 11 hours later (with 4 hours typical) the rated range increased by several miles, and this was enough to increase the charge percentage to 66%. This "recalibration" does not occur on every charge. Over the period of a month, I noticed 3 events, with a gap of 4 days in one case and 14 days in the other. Not enough information to determine any correlation with the nature of the charge.

The bottom line is that the battery recalibration calculation is not restricted to a range (>90%) charge but occurs on a regular basis based on some unknown factors. It looks like the charging is based on some equation (likely estimated charge as a function of current, voltage, temperature,...). There appears to be a separate analysis that adjusts the parameters of this equation based on some further analysis of measured data. Unknown whether this analysis is done locally on processors in the car or on the Tesla servers, but that large variability of the time makes it seem like it is a job that is getting queued back on Tesla servers and affected by other processing. The VisibleTesla data does not show any reductions in the charging current at the end of the charging sessions preceding the "recalibration" so there is no clear evidence of any cell rebalancing unless this is managed at full current (40 Amps in my case).

 

[Barry]

I charged to 100% only once, about a month ago. I charged to 90% overnight, then did the 100% charge in the morning, before leaving. It took about 2 hours for that last 10%. I was surprised, but shouldn't have been, when I saw the regen limited line on the speedometer, and had to use the brake pedal a few times.

 

[Andyw2100]

Today I was poking around my charging behavior as recorded by VisibleTesla, investigating why my car sometimes shows 66% in the morning even though I had set the limit at 65%. In each case, the charging had indeed ended at 65%, but anywhere from 1 hour to 11 hours later (with 4 hours typical) the rated range increased by several miles, and this was enough to increase the charge percentage to 66%. This "recalibration" does not occur on every charge. Over the period of a month, I noticed 3 events, with a gap of 4 days in one case and 14 days in the other. Not enough information to determine any correlation with the nature of the charge.

The bottom line is that the battery recalibration calculation is not restricted to a range (>90%) charge but occurs on a regular basis based on some unknown factors. It looks like the charging is based on some equation (likely estimated charge as a function of current, voltage, temperature,...). There appears to be a separate analysis that adjusts the parameters of this equation based on some further analysis of measured data. Unknown whether this analysis is done locally on processors in the car or on the Tesla servers, but that large variability of the time makes it seem like it is a job that is getting queued back on Tesla servers and affected by other processing. The VisibleTesla data does not show any reductions in the charging current at the end of the charging sessions preceding the "recalibration" so there is no clear evidence of any cell rebalancing unless this is managed at full current (40 Amps in my case).

Another very interesting find, Duma. Thanks for sharing!