Running out of charge

[ajdelange]

Range in miles is a finer granularity. It is the exact same, only showing range in miles is a more accurate value as it as 300 steps vs 100 steps.

You are a victim of what is called "empty precision" or "empty resolution" when it is used to sell cheap telescopes and microscopes. Consider the percent display. It ranges from 0% to 100%. Can we increase the accuracy by expressing remaining capacity is permille instead of percent? No. The accuracy of the estimates is so poor that Tesla, in accordance with good engineering practice, does not display it to more than two significant digits. Expressing the capacity in figures ranging from 0 ‰ to 1000 ‰ does not tell you anything more than you knew when it was expressed in %. The error in these figures is about 0.3% (or 3 ‰) if you prefer which translates to about a mile of rated range.

The issue is that the car shut down showing 16 miles remaining. That should never happen and indicates a issue with the battery for sure. Just recently an owner in Texas had this issue. Tesla claimed all is normal and later replaced the battery under warranty.

The funny thing is that we don't see reports that the car shut down when the battery showed 5% remaining but we do see reports that it shut down when it had 16 miles remaining. What kind of miles? Rated or average or instantaneous? When I ask "what did the energy display show when this happened?" I never get an answer. Can a battery just fail with 4% estimated usable charge? Yes, it can but I really suspect that the real problem here is that people aren't monitoring their usage as they go. When I see an energy graph boxcar (especially if I see it on my own display) I'll believe the problem is otherwise.

 

[David99]

It's arbitrary saying 100 divisions is as accurate as it goes, and anything finer is 'empty resolution'. If that was the case, the car would not be able to calculate single digit range numbers, yet it does. When you look at the CAN bus data you can see the car calculates remaining capacity much more accurately. I have done that for 4 years and I can see it adding and subtracting energy at 0.01 kWh increments. I can see it accurately measure single digit Watts. It is perfectly capable of measuring and calculating with very small amounts of power and energy. Very small amount of power draw are accurately measured and shown. Definitely not 'empty resolution'.

The fact that people say the car shut down at x amount of range only says that people like to display 'range' more than % because it relates to their driving. Percent is a random number that doesn't tell you how far you can go. There is no user error. 14 miles left is far far more than misjudged energy usage can explain. Even at 50% higher energy usage the actual remaining range would be 9 miles instead of 14. Still far away from shutting down.

The battery has a buffer of 4 kWh which is usually not accessible. It is there to protect the battery from being discharged all the way which is bad. But, according to a Tesla engineer, the car will allow to use the buffer partially if the range calculation comes in wrong towards the end. The BMS allows driving into the buffer (to some extend) to prevent the car from shutting down before it shows 0. So if the car does shut down at 14 miles left, something dramatic has gone wrong because it is supposed to have 14 miles left plus some emergency buffer. Usually its individual cells/bricks that have degraded more than the rest and show a sudden voltage drop causing the BMS to do a premature shutdown. Again, there have been several cases exactly like this and Tesla has replaced the battery under warranty.

 

[ajdelange]

It's arbitrary saying 100 divisions is as accurate as it goes, and anything finer is 'empty resolution'.

No, it isn't. If you quantize something to 1 unit you introduce an error with standard deviation of 1/sqrt(12). Look up "quantizing"

If that was the case, the car would not be able to calculate single digit range numbers, yet it does.

Nonsense 0.41*295 = 120.95.

When you look at the CAN bus data you can see the car calculates remaining capacity much more accurately. I have done that for 4 years and I can see it adding and subtracting energy at 0.01 kWh increments. I can see it accurately measure single digit Watts.

When I calculate pH from an electrodes temperature and voltage readings I use floating point and get an answer to floating point resolution. But as I know pH expressed to more than two decimal points is meaningless I only display two. Or put another way, if my ADC has resolution of 0.1 mV then I know the accuracy of any reading is at best 0.1/sqrt(12). That number may get converted to floating point (very precise) but it is still not accurate to better than 0.1/sqrt(12). That error gets propagated throughout the rest of the arithmetic, mixed in with the error from the temperature reading and magnified by the "geometry" of the problem and the final answer that comes out while it may have 12 digits beyond the decimal point is only accurate to 2 so I only display 2.

It is perfectly capable of measuring and calculating with very small amounts of power and energy. Very small amount of power draw are accurately measured and shown.

The problem is that coulomb counting does not give very good estimates of SoC. To determine SoC by coulomb counting you have to know where you are counting from. That is if you want to know what the SoC is after adding Q coulombs you have to know what the state was before you added the Q. In order to do that you need to estimate the the OC voltage of the cells and have the detailed charge/discharge curve for the temperature at which the measurement is made. This is pretty complicated and the "geometry" of the problem thus pretty hairy. Thus coulomb counting only gives a relatively rough estimate and even if you do the arithmetic in floating point (which I gather they do) the answer is not accurate (though it may be precise). Do you understand the difference between accuracy and precision? I suspect not. I've run into lots of engineers who don't let alone lay people.

Definitely not 'empty resolution'.

Thus precision in an SoC estimate beyond two significant digits or at most perhaps 3, even though it come from coulomb counting and voltage measurement combined in a Kalman filter, is definitely empty resolution. And guess what? The engineers at Tesla know that and that's why they show the driver two significant digits.

When you look at the CAN bus data you can see the car calculates remaining capacity much more accurately.

No, it calculates it with more precision. You really need to understand this before trying to draw conclusions about the displays.

Percent is a random number that doesn't tell you how far you can go.

Whaaaa? The displayed value of how far you can go is calculated from the estimated SoC. How far you can go is the available charge (really energy) divided by the energy estimated to be required to go one mile (or km). The problem is, of course, that that range is an estimate and its numerical value depends on how it was estimated. Thus a range estimate contains both the error incurred in trying to estimate SoC and the error inherent in the Wh/mi estimate.


What % tells you is how much usable battery you have left. That is the most important piece of information to you. If I see battery dipping below 5% I know I'd better find charge tout suite. I know that that nominally means I have 15 miles left and I know that I can stretch that out if I hypermile. I'm not really trying to push % displays because I think people should use whatever they are comfortable with. But evidently people get lulled into thinking that they have 14 miles range left when their SoC is 0 % available.

There is no user error. 14 miles left is far far more than misjudged energy usage can explain.

I don't think there was ever a suggestion that user's were making calculation errors. The observation was that people who use the % display rather than the miles display don't seem to be reporting this pickle.

Even at 50% higher energy usage the actual remaining range would be 9 miles instead of 14. Still far away from shutting down.

Well I have no idea as I never use the miles range setting but I think it might be the other way round. IOW you get down to 5% usable but as you have been rolling downhill with a tail wind your car is measuring 100 Wh/mi (I actually saw -146 on a drive the other day). Assuming your car has the 100 kW battery that means about 5000/100 = 50 miles estimated range when in fact your rated range is more like 15 miles which is what you will experience when you come to the bottom of the hill or 7 if you then have to go back up the next hill. The problem with this thesis is that I don't know that the little battery gauge displays estimated miles or just rated. If it's just rated then there is, in effect, no difference in what the display tells you be it in miles or km or %.

So if the car does shut down at 14 miles left, something dramatic has gone wrong because it is supposed to have 14 miles left plus some emergency buffer. Usually its individual cells/bricks that have degraded more than the rest and show a sudden voltage drop causing the BMS to do a premature shutdown. Again, there have been several cases exactly like this and Tesla has replaced the battery under warranty.

I am not saying that there cannot be battery or BMS failures. If I see a utilization graph that shows the actual utilization tracking the predicted nicely to some point at which the actual curve plummets below the 0 line then I agree that there is something awry in the battery system. That's why I keep asking "what did the utilization curve show?" But I never get an answer. That tells me that either people don't understand what I am asking or that they don't monitor that graph. If there is any good to come out of this thread it would be that people would have gotten the idea that they should monitor that graph.

 

[Rocky_H]

Your dismissiveness of this as just a "fancy display" makes it sound like it's a damn screen saver animation!

Again you know full well that this is not what I said or implied.

It wasn't implied. You explicitly said it:

No need for the fancy display though it is fun to watch.

 

[Rocky_H]

But rated range is just a fixed number multiplied by % and thus equally as accurate or inaccurate. This assumes that % = available kW/capacity and that the BMS doesn't decide that the battery capacity has changed.

I see this misunderstanding come up pretty frequently. It is not a straight conversion back and forth between % to rated miles. They are measuring different things.
The % is a "fullness" measurement--not an amount of energy measurement. So no matter how old the car is or how degraded the battery is, it will still continue to show 0 to 100 percent.
However, the rated miles number is converting from the car's measurement of the amount of energy, and then dividing by that fixed EPA efficiency constant to state it using a different unit.

This has been covered a lot in the other discussion threads on people's preference of using % or rated miles, but they do measure different things. A car that has degraded and lost 10 or 15% of its capacity will still show you 100% full when it is holding all of the energy it can take--it is "full". But the rated miles will show a lower number, because it does show a lower amount of kWhs, which it then converts to rated miles.

 

[ajdelange]

I explicitly said that the fancy display is a damn screen saver? Where did I say that.

I'd really prefer that we stick to discussion of the technical aspects of the matter.

 

[North75]

Showing percentage vs range in miles is not the issue.
Percentage is simply 'capacity' / 100.
Range is 'capacity' / 300. (using a range of 300 rated miles)

Range in miles is a finer granularity. It is the exact same, only showing range in miles is a more accurate value as it as 300 steps vs 100 steps.

The issue is that the car shut down showing 16 miles remaining. That should never happen and indicates a issue with the battery for sure. Just recently an owner in Texas had this issue. Tesla claimed all is normal and later replaced the battery under warranty.

I agree. In my opinion, this is more analogous to your car breaking down than running out of gas. Maybe like an ICE fuel pump breaking or something. (I've never had that happen, but I've had 2 or 3 ICE breakdowns over the years that have left me stranded on the side of the road)
It's slightly nebulous of course as you are able to recharge the car and drive again, but I agree it's indicative of an abnormal failure.

 

[Silicon Desert]

wow what a nightmare situation for sure. on trips i am too paranoid to run it down to under 30 miles left. even 20-25 remaing gives me the shakes. So when i charge at sc i always wait till it says i will have at least 30% left after i arrive to the next charger. Cant trust any gauges.

yes, that is pretty much what I do on trips. Not due to being paranoid either, just being cautious because you never know what is going to happen. The best examples I have is one time I drove to a charger in Colorado that was temporarily out of commission. The car map indicated that, but since it was close off the interstate, I thought I would check anyway as sometimes the map isn't perfectly accurate. Sure enough, it was dead and repair people were there. Fortunately I had enough juice to make it to the next SC.

Then on a second problem 2 years ago, I was driving down the interstate and the CHP was turning around traffic due to the Paradise CA fire. Again, enough to get to a recently passed SC. Sure I could also stop at a destination charger somewhere, but those things are slow compared to a super charger. Lastly, I can never trust those winds up in Kansas (and elsewhere for that matter). Once I had to slow down to make it to the next charger due to 30 mph head wind.

 

[Silicon Desert]

It's phrased in a way that's a little misleading. If you are following a navigation route, and it has already calculated your Supercharger stops, it will only show those stops in your display. If you cancel the route, all Superchargers will show up. So it's not that it hides them overall, it's just that if you have a programmed route in the navigation, it only wants you to see that plan. I'm really not sure why that is, and I would agree with @Rocky_H that they really should just show them regardless. It's possible the developers thought that seeing a Supercharger might entice some people to stop when they didn't need to do so, or maybe they had some other intent with it. I believe you can still show them by hitting the charger icon on the map as well, even during navigation.

Nicely stated. About that last comment, hitting the charger icon on the map to display all chargers..... recently I did that and it did not show all chargers, so maybe I did something wrong as I do remember it working as you said... previously clicking on it even with a planned route, it showed all the superchargers. I had to cancel my route to see them all. Again, maybe I didn't click the right icon.

I also would prefer to see ALL superchargers even if I have a planned route. They could do something as simple as showing them a different color, or putting a small tag on ones I don't need to stop, or just put up a temporary message saying it will be bypassing the next supercharger that isn't needed, but I can obviously stop if I want. And yes, I'm sure you folks have even better ideas than mine about this. Bottom line is that for us, there are MANY times we want to stop for some reason before reaching the next needed supercharger. If there is one not far away, we would prefer to stop at one of them while eating, going to the restroom, or just getting some quick exercise out of the car.

 

[ajdelange]

I see this misunderstanding come up pretty frequently. It is not a straight conversion back and forth between % to rated miles. They are measuring different things.
The % is a "fullness" measurement--not an amount of energy measurement.

I realize that I am addressing a man who thinks multiplying by 3 is intimidating mathematics but think about what you just said. A measure of fullness, yes. But what is fullness? It is the fraction of something in a container relative to the capacity of the container. If I give you an empty 1L volumetric flask, pour 333 mL of vermouth into it in your presence and ask you how full it is you can answer you can answer "1/3". If we repeat the exercise with a 500 mL flask your answer would be "2/3". If you tell me that you have a 1L flask that is 1/3 full I know it contains 333 mL. If you tell me that you have 0.5 L flask that is 2/3 full then I know that you have 333 mL. Thus if you tell me how full the flask is and its capacity I can tell how much vermouth is in it and I can tell how many martinis I can make if I know how many mL of vermouth are required to make one martini.

Now if you bring a flask of vermouth into my lab and ask how many martinis we can make from it and you say you don't know how much vermouth is in there then to answer your question we'd need to figure that out. How would we do this? Well we could pour the vermouth into a graduated cylinder and read it but we really don't want to empty the flask and dirty other glassware (in the case of a battery it's not practical to empty it just to find out how much charge is in it) so we look for an indirect measure. With the flask we could weigh it (if we knew the tare) or we could measure the height of the liquid. That would work if we had a plot or table of liquid volume vs surface height. Or, you could say it was full yesterday and you made two martinis since then. I hope its clear that the height measurement is analogous to the voltage measurement on a battery and that keeping track of the number of martinis you made since it was full is equivalent to coulomb counting. Note that neither method really gives an accurate measure of how much is in the flask because the rate of change with height is much smaller in the fat part than it is in the neck. Also note that if someone else snuck a martini out of the flask without you knowing it your estimate of how much is left based on how many martinis have been made would be in error. Thus we need to recalibrate the 0 level in the withdrawn volume counter from time to time.

The important aspect of this is that if you know the size of the flask and how full it is (0 to 100%) then you know how many mL of vermouth are in it and can get to what you really want to know which is how many martinis you can make or from another perspective if you will run out of vermouth before you have made a certain number of martinis. Thus percent full and number of martinis convey the same information. The only caveat is that with percent full you need to know capacity. As the car ages the capacity becomes smaller but barring catastrophic failure that doesn't happen over night and the BMS is continuously estimating capacity.

This has been covered a lot in the other discussion threads on people's preference of using % or rated miles, but they do measure different things.

I hope it is clear from the discussion above (but very much doubt it is) that they do not convey different information. Knowing % full and capacity allows you (or the car's computer) to calculate miles to go.

A car that has degraded and lost 10 or 15% of its capacity will still show you 100% full when it is holding all of the energy it can take--it is "full". But the rated miles will show a lower number, because it does show a lower amount of kWhs, which it then converts to rated miles.

Yes, QED. My X is newish. Call capacity 100 kWh. Call the rated consumption rate 3 miles per kWh. Fully charged its rated range is 300 mi. If the battery is half full (50%) that's about 50 kW hrs available and my rated range is 150 mi. A couple of years down the road if my capacity has degraded 20 % to 80 kWh the fully charged rated range is 240 mi (80% of 300 mi). At 50% reported capacity I would have about 40 kWh in the tank and my rated range would be about 120 mi (which is 80% of 150 kWh.)

In my car at the present there is a 1:1 mapping between miles driven and average battery consumption and I can estimate range remaining quite simply just by multiplying the percent remaining by 3 (but please, lets not get back into the question of how difficult that may or may not be - the car's computers can handle it). As my car ages that mapping will change. When the battery has aged to 80% I will only get 2.4 miles per percent. The 1:1 mapping will remain.

 

[Rocky_H]

You are talking about doing division problems with 2 and 3 digit numbers

This is at the heart of your misunderstanding of what I am saying. I am asking people to to do division by a number close to 3.

I realize that I am addressing a man who thinks multiplying by 3 is intimidating mathematics

Can you please try to be mature and knock off the insults and the dishonesty?

I will determine my margin at Brattleboro based on 420 Wh/mi (what I get in wet weather) rather than 310

You were talking about selecting 420 or 310 for your consumption factors, neither of which is "3", nor is even that which would be the factor that would approximate "3" (333 Whrs per mile).

 

[David99]

The problem is that coulomb counting does not give very good estimates of SoC. To determine SoC by coulomb counting you have to know where you are counting from.

If you imply that Tesla isn't good at calculating SoC then go ahead. It's been very accurate for my car driving for more than 5 years under very different conditions. It is generally accepted that Tesla has the best BMS out there. I have driven my car down to single digits range left countless times and it has never ever been off. It is incredibly accurate and even keeps track of degradation very precisely. After 240k miles on my car and 5 years I have significant degradation. Still the BMS very accurately shows the SoC and I can drive it down to 0 miles left. It has never shut down before it was zero. It has never shut down on my even going beyond that point. Looking at the car's own data shows clearly where the precision limits are. They are way better than 1/100. Your theoretical explanations are not wrong, but you base it off assumptions that are just incorrect. Do yourself a favor had get the tools to read CAN bus data from your car and spend a few months with it. You will see how accurate the system is.

To loop back to the original question, could the use of rated miles instead of percentage introduced enough inaccuracy to cause a driver to be confused and the car to shut down? Absolutely not. Showing percentage in this case would have indicated there is at least 6% left. So can we close the case that showing percentage has anything to do with the car shutting down prematurely in this case.

Again, there are many cases of users that had their cars shut down at similar states and in all cases Tesla replaced the battery as defective (granted it was still under warranty).

 

[ajdelange]

Can you please try to be mature and knock off the insults and the dishonesty?

If it is insulting I cannot help that. As to dishonesty have you not espoused with great determination and made multiple statements to the effect that multiplying and dividing by single digit numbers will be intimidating to many people?

You were talking about selecting 420 or 310 for your consumption factors, neither of which is "3", nor is even that which would be the factor that would approximate "3" (333 Whrs per mile).[/QUOTE]

If my car has a kW/h of charge added the % indicator goes up by 1%. If I drain 1 kWh the % indicator goes down by 1%. In the entire history of my car's driving it has averaged 299 Wh/mi. Therefore, I get, on average 3.34 mile per kWh or 3.34 miles per %. Without doing much I can see that if I have to go 127 miles I'll probably use about 3.34 times 127 miles (42%) which is, more easily obtained by dividing 127 by 3 (because the reciprocal of 3.34 is 0.299) than by multiplying 127 by 3 to get 38.1 and then adding 3.81 to that to get 42%. All percentages rounded to the nearest % because that's what the display shows. And all assuming average consumption. It isn't always. But when I get into the car if I have to go 127 miles I know I'll use about 42% of the battery. If I have, say, 52% then I know I'm probably good for the trip as I have, nominally, 10% margin.

If I'm sailing along with 127 miles to go and it starts to rain I know that the power consumption will go up from 300 Wh/mi to around 420. Clearly I am going to consume, at that rate, 4.2/3.34 = 1.26 ~ .3*4.2 times as much energy i.e. 1.4 times as much so we take 42% add a quarter of that to it and estimate about 52% consumption.

The message here is if you know a few tricks you can do a lot of what may seem to be complex computations in your head. When I was an embryo engineer we didn't just whip out our cell phones and call up the app. We had to learn how to make "engineering approximations" and were trained in this art. That's where this all comes from.

You can keep trying to shoot holes in this technique all you like and I'll keep coming up with instructions on how to do it but I think that is a waste of time as I think you are determined not to accept it. And you don't have to. You don't like it, don't use it. Just don't try to convince me, or others, that it isn't valid.

 

[ajdelange]

If you imply that Tesla isn't good at calculating SoC then go ahead.

I have never implied, or meant to imply, that Tesla's BMS is anything other than the most sophisticated in the world. But I spent many years on estimation theory, error propagation, Kalman filtering and such like so I know there are limitations. Since I have gotten this car I have come to learn something about the problems of SoC estimation in Li ion batteries. As we used to say when I was practicing "I'm an expert. I read a book". Just to be clear, that's a joke. I am not an expert though I have done some reading.

It's been very accurate for my car driving for more than 5 years under very different conditions.

Yes, I have found it to be very accurate too.

It is generally accepted that Tesla has the best BMS out there. ...

I don't disagree.

Looking at the car's own data shows clearly where the precision limits are. They are way better than 1/100

I'll ask again. Do you understand the distinction between precision and accuracy?

Your theoretical explanations are not wrong, but you base it off assumptions that are just incorrect.

Can you tell me which assumption those are.

Do yourself a favor had get the tools to read CAN bus data from your car and spend a few months with it. You will see how accurate the system is.

I would love to do that. Where do I get these tools?

To loop back to the original question, could the use of rated miles instead of percentage introduced enough inaccuracy to cause a driver to be confused and the car to shut down? Absolutely not. Showing percentage in this case would have indicated there is at least 6% left.

You have no idea what the percentage display would have indicated as no one will tell us that.

So can we close the case that showing percentage has anything to do with the car shutting down prematurely in this case.

No because we don't know what the percentages displayed were. And we didn't say that switching to a percentage display would solve the problem. We merely noted that people who use the percentage display don't seem to experience this problem so much if at all.

You assume that whenever someone runs out of juice there has been a major failure in some system or systems. In fact several of these guys have reported charging the car, taking it to the SC, having it checked out and continuing as if nothing had happened. I have to conclude from these cases the problem came from not interpreting the available data correctly or not looking at it at all.

Again, there are many cases of users that had their cars shut down at similar states and in all cases Tesla replaced the battery as defective (granted it was still under warranty).

Again, I don't doubt that but we seem to have cases here where that was not the case.

 

[ohmman]

So much passion for range estimation! It’s great that everyone has strong feelings but I doubt it’s worth facing off so aggressively about minor differences in interpretation. What works for one may not for the other. I’ve never run out of range even while towing, but I’m sure there are conditions where I might be taken off guard. I don’t see the need to denigrate others on a forum where we are just discussing the nuances of our cars.

 

[DigAdrenaline]

No, it isn't. If you quantize something to 1 unit you introduce an error with standard deviation of 1/sqrt(12). Look up "quantizing"

Nonsense 0.41*295 = 120.95.

When I calculate pH from an electrodes temperature and voltage readings I use floating point and get an answer to floating point resolution. But as I know pH expressed to more than two decimal points is meaningless I only display two. Or put another way, if my ADC has resolution of 0.1 mV then I know the accuracy of any reading is at best 0.1/sqrt(12). That number may get converted to floating point (very precise) but it is still not accurate to better than 0.1/sqrt(12). That error gets propagated throughout the rest of the arithmetic, mixed in with the error from the temperature reading and magnified by the "geometry" of the problem and the final answer that comes out while it may have 12 digits beyond the decimal point is only accurate to 2 so I only display 2.

The problem is that coulomb counting does not give very good estimates of SoC. To determine SoC by coulomb counting you have to know where you are counting from. That is if you want to know what the SoC is after adding Q coulombs you have to know what the state was before you added the Q. In order to do that you need to estimate the the OC voltage of the cells and have the detailed charge/discharge curve for the temperature at which the measurement is made. This is pretty complicated and the "geometry" of the problem thus pretty hairy. Thus coulomb counting only gives a relatively rough estimate and even if you do the arithmetic in floating point (which I gather they do) the answer is not accurate (though it may be precise). Do you understand the difference between accuracy and precision? I suspect not. I've run into lots of engineers who don't let alone lay people.

Thus precision in an SoC estimate beyond two significant digits or at most perhaps 3, even though it come from coulomb counting and voltage measurement combined in a Kalman filter, is definitely empty resolution. And guess what? The engineers at Tesla know that and that's why they show the driver two significant digits.

No, it calculates it with more precision. You really need to understand this before trying to draw conclusions about the displays.


Whaaaa? The displayed value of how far you can go is calculated from the estimated SoC. How far you can go is the available charge (really energy) divided by the energy estimated to be required to go one mile (or km). The problem is, of course, that that range is an estimate and its numerical value depends on how it was estimated. Thus a range estimate contains both the error incurred in trying to estimate SoC and the error inherent in the Wh/mi estimate.


What % tells you is how much usable battery you have left. That is the most important piece of information to you. If I see battery dipping below 5% I know I'd better find charge tout suite. I know that that nominally means I have 15 miles left and I know that I can stretch that out if I hypermile. I'm not really trying to push % displays because I think people should use whatever they are comfortable with. But evidently people get lulled into thinking that they have 14 miles range left when their SoC is 0 % available.

I don't think there was ever a suggestion that user's were making calculation errors. The observation was that people who use the % display rather than the miles display don't seem to be reporting this pickle.


Well I have no idea as I never use the miles range setting but I think it might be the other way round. IOW you get down to 5% usable but as you have been rolling downhill with a tail wind your car is measuring 100 Wh/mi (I actually saw -146 on a drive the other day). Assuming your car has the 100 kW battery that means about 5000/100 = 50 miles estimated range when in fact your rated range is more like 15 miles which is what you will experience when you come to the bottom of the hill or 7 if you then have to go back up the next hill. The problem with this thesis is that I don't know that the little battery gauge displays estimated miles or just rated. If it's just rated then there is, in effect, no difference in what the display tells you be it in miles or km or %.


I am not saying that there cannot be battery or BMS failures. If I see a utilization graph that shows the actual utilization tracking the predicted nicely to some point at which the actual curve plummets below the 0 line then I agree that there is something awry in the battery system. That's why I keep asking "what did the utilization curve show?" But I never get an answer. That tells me that either people don't understand what I am asking or that they don't monitor that graph. If there is any good to come out of this thread it would be that people would have gotten the idea that they should monitor that graph.

Ok. I disagreed with you earlier in this thread, but on further reading and reflection, I decided to try it. (I’m 1000 miles from home with lots of driving in the next short while). What I found is, you’re right.

-Converting percent to miles (or KMs) is easy.
-The errors introduced but having the car convert it to range is the best explanation I’ve heard yet (it was showing rated distance, but the energy graph was displaying average range over 50kms, but I was watching instant range too. All 3 were within 1km of each other).
-You’ve made and justified a persuasive argument for percent over mileage.
-Testing it for a couple of hundred miles today raises no legitimate objections and partially invalidates some of my own.

Consider me a convert. Pride makes it hard to admit this, but you really are right here.

Thanks for taking the time to explain all of this, Ive benefited from it.

Kev

 

[ajdelange]

...but on further reading and reflection...

That's all I am asking for. Thanks for posting this.

 

[meomyo]

Why would you run it to even 13 miles left? No offence but that seems risky with an ev. I hate this fact about ev as you never know what that battery gauge really means.Like on a laptop.

i agree with any software pc/ev thing the battery meter never ever is truely accurate and can change daily. Risky and stressful.

 

[meomyo]

Your post makes it seem like there's a Supercharger on every corner like a gas station or California or something. You live in Colorado. You know better. We stayed at the Supercharger we were at until lit said we were good to go to get to the next one. We even stayed an extra 20 min beyond that just to make sure we had more than enough since we weren't in any hurry. Not really sure how you presume we could have avoided that as if it was operator error. In hindsight it's really easy to say "well, should have just stayed there longer" but is that really the solution is that everyone sit at Superchargers a full hour beyond when it says you're good to go to make it to the next one?

Sorry didnt mean to say your fault-sorry if i infered that.
All i know is i do stay way longer then they say at sc when traveling because i am paranoid and know so many things can affect the range that to me there are so many variables that i totally spend way more time at a sc then it tells me to.

 

[meomyo]

Sigh. Why do you assume there is only one knob to twist to manage this? You're talking about how long you stayed at the Supercharger, but then nothing about how fast you drove for the next couple of hours along your way. A few miles per hour speed difference over the course of a couple of hours makes significant differences in your remaining range. Tweak your speed to continue to leave yourself enough margin.

You want to talk I-70 in Colorado? Great. Because last year, I had to deal with quite this difficulty there on I-70 in February at freezing outside temperatures. I was at Grand Junction, and I put in a nav destination farther over in Kansas, and the stupid car trip planner selected that I would go all the way straight through to Silverthorne(!), which is mostly uphill, in freezing temperatures, 209 miles, with my old S85. It was saying I needed to fill up to 100% and arrive with only 7%, which I knew seemed like an unrealistic prediction, given the cold temperature. That is when I learned about its other terrible behavior as I scanned carefully along the route to see if there was a closer Supercharger in the middle. It HIDES the Superchargers it thinks you should skip!!!!! So I didn't know Glenwood Springs was available right there halfway in the middle until days later. So...I made it work. I kept my heat low, and my cruise control at some stupid 10-15 mph below the speed limit, which extended the range enough to make it happen. It sucked a little, but I thought I didn't have another choice, so I did what was necessary. You didn't have it that bad, so probably should have kept more than a 13 mile (about 5%) margin.

Sorry, that this is kind of a rabbit trail that is a little about planning for the future, with not going with 5% margins. I do still agree with you that this should not be normal or expected that the car shuts off with 5% still showing available. When it's down to the last 1 or 2%, though, the risk level is just getting really high for counting on measurement accuracy to be that precise. It's a little unrealistic.

This situation is my nightmare-moreso in freezing weather where milage is all over the place depending on heating/speed ect . May times the sc network tells me to charge x amount of minutes and then arrive at 7% which i never follow as thats too low for me to feel comfotable. What it there is a storm or standstill traffic for hours or steep inclines ect. No way the sc /car profile takes all those things into considereration ..does it? Now that would be a killer amp in the car to take temp..speed and inclines into consideration on the route to be more accurate.