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Battery charge level in a Tesla is measured to a much higher level of accuracy than the remaining gasoline in an ICE vehicle's tank. But even with Tesla's method there are still variations and inaccuracies - but to a much smaller extent than in an ICE vehicle where the angle at which the car sits could affect the gauge.
This depends on the car. The Prius fuel system, for example, has two inclination sensors in the dash, a fuel temperature gauge, a sending sensor in the auxiliary tank, and a speed sensor.
And yet my Prius had the most inaccurate gauge of all the cars I've owned. The gauge would barely move for the first couple of hundred miles, but once low the gauge would move very quickly. I ran out of gas twice in my Prius as a result. I've never run out of charge in my Model S.
My second generation Prius has the least accurate fuel level indicator of all cars I've owned. My wife has run out of gas over a dozen times. Fortunately most of those times were close enough to a gas station that the battery would get her there.
The fuel tank is a rubber bladder that expands and contracts as fuel is put in or taken out. There is no level float inside the bladder itself. The float is in a smaller tank that sits next to the bladder and only comes into play once the bladder stops putting fuel into the smaller side tank.
When it gets down to one flashing pip, you might run out of fuel in 0 miles(we've run out before the last pip even starts flashing) or you might have 50 miles left. If the temperature changes dramatically, it can be off as much as 100 miles.
^^ exactly this! I ran out of gas within 4 miles of the gauge dropping to one pip. This happened on the freeway. All the lights started flashing and I got a big red triangle warning on the dash. I thought my car was going to blow up or something. Fortunately my spouse was on his way home, so asked him to bring me some gas. I am so thankful for having a Model S today!
My Model S has NEVER, EVER let me down let alone in such dramatic fashion.
I lost 2 or 3 more at both 90 and 100. Please let us know what they tell you. I've also talked to service about this.
MarcG
Active Member
I'm really starting to think that firmware 7.0 has something to do with this, whereby temperature does have a strong correlation to the reported rated range.
I've put together the last 130+ data points from my 90% charges (range mode was always ON) since late-January, when VisibleTesla started working for me with the new-at-the-time experimental version, and created the graph below.
I upgraded to firmware 7.0 (2.7.056) as soon as it came out, which is on the evening of 10/14/2015. My 90% charges were still very stable at around 224 miles of rated range, while temperatures were still fairly mild in the San Francisco bay area. So there was no change between 6.2 and 7.0 in calculating rated range in mild temps.
Then in late October, temperatures dropped by at least 10ºF and have stayed fairly low. I keep track of my daily commute, and my morning temps had been in the mid- to upper-60's until 10/30, at which point they dropped to lower- to mid-50's. FYI, my service center upgraded my firmware to 2.7.77 on 11/7.
I know some have seen drops unrelated to temperature, but my pack is coming up on one year and over 22,000 miles so it should have stabilized by now (you can see that from mid-May to late-October in my data).
Which reminds me, some of you 90 kWh pack owners are probably seen early drops, which are more common at first, then degradation stabilizes to a lower rate.
But what I'm seeing from my data is highly unusual drops in reported rated range, and it's highly correlated to the recent colder temperatures in my area.
I've put together the last 130+ data points from my 90% charges (range mode was always ON) since late-January, when VisibleTesla started working for me with the new-at-the-time experimental version, and created the graph below.
I upgraded to firmware 7.0 (2.7.056) as soon as it came out, which is on the evening of 10/14/2015. My 90% charges were still very stable at around 224 miles of rated range, while temperatures were still fairly mild in the San Francisco bay area. So there was no change between 6.2 and 7.0 in calculating rated range in mild temps.
Then in late October, temperatures dropped by at least 10ºF and have stayed fairly low. I keep track of my daily commute, and my morning temps had been in the mid- to upper-60's until 10/30, at which point they dropped to lower- to mid-50's. FYI, my service center upgraded my firmware to 2.7.77 on 11/7.
I know some have seen drops unrelated to temperature, but my pack is coming up on one year and over 22,000 miles so it should have stabilized by now (you can see that from mid-May to late-October in my data).
Which reminds me, some of you 90 kWh pack owners are probably seen early drops, which are more common at first, then degradation stabilizes to a lower rate.
But what I'm seeing from my data is highly unusual drops in reported rated range, and it's highly correlated to the recent colder temperatures in my area.
About 1700 miles. Took delivery on 9/15. Originally was 288 & 258 rated miles at 100% & 90% respectively. I was losing about 1 mile per week up until early November. Now it's about a mile every two weeks. Currently at 278 & 249. So I've lost about 10 of the 16 extra miles I was supposed to get with the 6% range upgrade. I'm hoping its a software/algorithm issue and not real degradation as many have speculated on this forum but I'm tracking it and have asked the SC to do the same.
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Interestingly enough, my P85D's 100% charge has reverted to where it was 6 months ago at a loss of only 3 miles since new, now at almost 20,000 miles. I charged to 250 miles yesterday at a supercharger and to 224 miles @ 90%. I haven't seen those numbers for a while, with a recent 90% charge being 220 miles and a 100% charge being 245 miles.
Obviously my battery hasn't un-degraded itself, so I'm assuming that a lot of the range drop we see is algorithm related.
Some of it has to be real, though. At about 20,000 miles I should have done about 90 equivalent full charge cycles on the pack. Based on cycle testing graphs I should have lost roughly 6% capacity by now and be down to ~238 miles at 100% and ~214 miles at 90%, but I haven't. I think there are a few different things at play here.
<speculation>
First, at the beginning of life I do not believe that the 0-100% range Tesla allows us to use and is displayed is actually 0-100%, then as the pack degrades a bit, the actual usage range inches closer to the actual 0-100% range of the pack (with some small buffers on the ends of course). I think the algorithm drops miles at a slower rate than actual pack degradation by eating some of the buffer. I have some data that supports this, but not enough to say for certain. If I'm right, though, degradation will go through a couple of phases. Phase 1 would be the initial calibration where miles are lost quickly as the algorithm sorts things out. Phase 2 would be a mostly level plateau where degradation of miles appears very slow. Phase 3 would be when the buffer portion is eaten up and rated miles drop with actual pack degradation from this point, faster than in phase 2.
If correct, and based on some numbers I've seen from my cars of being able to utilize say, 77 kWh worth of power from the 85 pack, lets say 8 kWh of buffer total, 4 of which can be used by the algorithm. So if the pack degrades by 8 kWh, the algorithm can make this appear to be only a 4 kWh degradation in miles. The actual pack capacity would be 78 kWh, and usable pack capacity would be 73 kWh, which would look like a loss of only ~12-13 miles or so. But the next 8 kWh degradation would show as ~26 miles of loss since there would be no buffer to mitigate with.
This is the only way I seem to be able to correlate my data and other cycle life data for these cells with what we see from the range algorithm.
</speculation>
Obviously my battery hasn't un-degraded itself, so I'm assuming that a lot of the range drop we see is algorithm related.
Some of it has to be real, though. At about 20,000 miles I should have done about 90 equivalent full charge cycles on the pack. Based on cycle testing graphs I should have lost roughly 6% capacity by now and be down to ~238 miles at 100% and ~214 miles at 90%, but I haven't. I think there are a few different things at play here.
<speculation>
First, at the beginning of life I do not believe that the 0-100% range Tesla allows us to use and is displayed is actually 0-100%, then as the pack degrades a bit, the actual usage range inches closer to the actual 0-100% range of the pack (with some small buffers on the ends of course). I think the algorithm drops miles at a slower rate than actual pack degradation by eating some of the buffer. I have some data that supports this, but not enough to say for certain. If I'm right, though, degradation will go through a couple of phases. Phase 1 would be the initial calibration where miles are lost quickly as the algorithm sorts things out. Phase 2 would be a mostly level plateau where degradation of miles appears very slow. Phase 3 would be when the buffer portion is eaten up and rated miles drop with actual pack degradation from this point, faster than in phase 2.
If correct, and based on some numbers I've seen from my cars of being able to utilize say, 77 kWh worth of power from the 85 pack, lets say 8 kWh of buffer total, 4 of which can be used by the algorithm. So if the pack degrades by 8 kWh, the algorithm can make this appear to be only a 4 kWh degradation in miles. The actual pack capacity would be 78 kWh, and usable pack capacity would be 73 kWh, which would look like a loss of only ~12-13 miles or so. But the next 8 kWh degradation would show as ~26 miles of loss since there would be no buffer to mitigate with.
This is the only way I seem to be able to correlate my data and other cycle life data for these cells with what we see from the range algorithm.
</speculation>
MarcG
Active Member
Interesting speculation there Jason. I guess I can try a 100% charge tomorrow, but I have little faith it will restore my "lost" miles again. Your P85D is basically as "old" as mine and has nearly as many miles on the odo, so I'm not sure what could be causing my loss of rated range besides software algorithms. If anything, my area should see less temperature swings (and extremes) than yours...
I'd have probably passed you in miles by now if I hadn't swapped some summer drives for flights. My car sat for nearly a month in total, actually.
I doubt *a* 100% charge would have much effect, except to kick start any balancing circuits for cells that may be a little off, which wouldn't have a measurable effect for several days after at least. One of these days I'm going to get some real voltage reads from the P85D and see where things are really at...
@wk057 - I'm sure you've seen FlasherZs range numbers (266 rated at 100% for a P85 after 40,000+ miles). AFAIK, he has the best range numbers across the entire Model S fleet with equivalent mileage. Given what you have observed in cell cycle life, is there anyway that those numbers are accurate? IMO, it's pretty unbelievable that he's had 0 capacity fade with that many miles. I don't doubt the data he is collecting and reporting, but I do have serious doubts with the range algo and why it differs so greatly from what others report.
Mine is similar to yours. I have been slowly dropping and my 90% is now 221 rated miles (Range Mode OFF) at 16,949 miles. Not sure what my 100% is now - it's been a while since I've done a 100% charge (last time I did it was 249 miles but that was at about 12k miles at the Charlotte Supercharger so I could make it to Atlanta without stopping).
Mike
MarcG
Active Member
221 with range mode OFF is equivalent to 224 with it ON. That's exactly where I was seeing my 90% charges for a while until this sudden and steep drop in the last month.
Mike, was your 249 number @100% with range mode ON or OFF?
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