Sudden Loss of Range

[apacheguy]

I've been puzzling over a sudden unexplained loss of 3 miles of rated range. I'm not talking about 'Decreasing rated range' as I am very familiar with that thread - this is something different. In over 2 years of ownership, I have never seen this behavior before. While 3 miles alone is not that big of a deal, I'm concerned should this happen again in the future. Also, it compounds the gradual decreasing range I have observed in a little over 24 months of ownership.

Over the past few months, my car has repeatedly achieved 200 miles at 80% and 225 at 90% - until I went on a trip last week. On that trip, my car appeared to charge normally (see below), but since coming back, both my 80 and 90% charge numbers have consistently been 3 miles lower. I am very surprised at the rapid loss of range - usually it takes several months to a year to see a loss of 3 miles. In my case, it essentially happened over 1 weekend. This is not normal.

Fortunately, I track data from the API and store it on my home server. I pulled the logs and am showing an excerpt below:

10/22 (80%) - 200.42
10/23 (50%) - 200.79
10/24 (90%) - 225.01
---Begin trip---
10/24 (90%, SpC) - 225.39
10/26 (90%, SpC) - 225.0
---After trip---
10/27 (80%) - 197.78 Note: 3 miles lower
10/31 (80%) - 197.11
11/1 (90%) - 221.70 Note: Tried to restore range by doing 90% charge. Still 3 miles lower.
11/2 (90%) - 222.20
11/3 (90%) - 222.04

Thus, it seems that both my 80 and 90% charges are 3 rated miles lower than they were just a few days earlier. Anyone care to explain how that could be? Anyone seen this behavior before?

 

[qwk]

This exact thing happens with roadster CAC numbers. Since the range displayed is only an estimate that is less accurate with shallow cycles, shallow cycles don't display changes like deep discharges every once in a great while do.

 

[golfski]

I am familiar with most of what has been in the "Decreasing Rated Range" thread as well, but I am starting to wonder if there is some sort of 'adjustment' being made to the rated range algorithm based on temperature, driving habits, etc. I have seen my rated range decrease from 213 @100% (191 @90%) to 199 @100% (175 @90%) in the 9,000 miles I have put on my car in almost 5 months of ownership. Lifetime I am at 342 wH/mi and average temperatures have dropped 25-30 degrees over the past few months.

I noticed this morning that my "rated" line (thicker solid line) on the energy app has moved above the 300 Wh/mi (thinner solid) line, where it used to be below that mark. I was trying to find the exact number by hitting my average (dotted line) on the rated line and it came out to be 307 Wh/mi. Given that, it seems that I haven't really lost much range at all - but rather my "Rated Range" has adjusted to a 307 Wh/mi range.

Note this first image shows the rated line above the 300 Wh/mi, and then the lines engulfing one another @ 307 Wh/mi.

 

[apacheguy]

This exact thing happens with roadster CAC numbers. Since the range displayed is only an estimate that is less accurate with shallow cycles, shallow cycles don't display changes like deep discharges every once in a great while do.

Interesting theory. My logs show that the pack made it down to the low teens % SOC during the trip, but dipped into single digits on the return trip. Thus it seems that it needs < 10% SOC to recalculate the estimated range.

I wonder what this says about used Tesla sales a few years down the road. Are potential buyers going to demand that we run the car down to rock bottom SOC and then charge back up to 100%? I know I sure wouldn't be happy if I bought a car w advertised 250 miles of range and then a few days later found it was down to 240 because I did a deep discharge.

---updated---

Actually, about a month ago I definitely ran it down to <10% SOC and it still charged up to the normal range numbers. Seems weird that doing the same thing only a month later would yield 3 fewer miles.

 

[randompersonx]

Keep in mind that Lithium Ion batteries have some strange properties as far as capacity goes. At lower / temperatures, less of the stored charge is accessible, however at higher temperatures, more damage to the pack is done.

Also, if you try to pull power from the battery at a very low rate (say, set your cruise control to 25MPH on the highway and just keep on going for 24 hours), the amount of KWH you will be able to pull will be much higher than if you are aggressively driving with frequent sprints from 60MPH to 120MPH.

Perhaps you did this last drive on somewhat cooler conditions, with somewhat more aggressive driving behavior? Another 100% -> 5% run with gentle drain charachteristics will perhaps get some of those miles back (or not).

 

[R²B]

Change in weather?

 

[apacheguy]

Perhaps you did this last drive on somewhat cooler conditions, with somewhat more aggressive driving behavior? Another 100% -> 5% run with gentle drain charachteristics will perhaps get some of those miles back (or not).

Cooler, not really. This is So Cal and the winter hasn't fully set in yet. Aggressive? Yeah probably. Very hilly terrain on the return trip. Can't remember what my numbers were but I'd guess upwards of 350 W/mi.