Can someone PLEASE explain how rated range is calculated.

[wormhole]

Please look at the above photo. When I unplugged my car and got in for the trip, I had 180 rated miles left in the battery. As you can see, I drove 81.4 miles, used 24.1 kWh, and averaged 296 wh/mi. Yet when I finished I had 93 rated miles of range left. I still lost 5 miles of rated range vs actual range despite averaging less than the 308 wh/mi i thought went into the 265 rated mile range calculation.

I have asked [email protected] numerous times about this, using numerous trips with similar results. I have never gotten a straight answer, and in most cases the 'response' has been to highlight logs for an entire day which is completely irrelevant to the question. For clarity, again, I unplugged the car and drove off, there was no vampire loss. Any explanation would be greatly appreciated. Thanks.

 

[jerry33]

As far as I know, rated range is just the EPA number. The way it works for me is:

1. Charge car to some amount e.g. 210 miles.

2. Drive a bit say 50 miles.

3. Subtract some vampire e.g. 5 miles.

4. Add some gains e.g. 8 miles.

5. Balance at the end of the day 163 miles.

If we use your numbers to obtain the vampire loss:

1. 180 miles

2. minus 81.4 miles = 98.6 miles

5. minus 93 miles

3. equals 5.6 miles vampire loss.

 

[wormhole]

As far as I know, rated range is just the EPA number. The way it works for me is:

1. Charge car to some amount e.g. 210 miles.

2. Drive a bit say 50 miles.

3. Subtract some vampire e.g. 5 miles.

4. Add some gains e.g. 8 miles.

5. Balance at the end of the day 163 miles.

If we use your numbers to obtain the vampire loss:

1. 180 miles

2. minus 81.4 miles = 98.6 miles

5. minus 93 miles

3. equals 5.6 miles vampire loss.

There is no vampire loss when you immediately start driving the car when you unplug it. Plus you 'added gains' to your calculation, not sure what that is, or why you'd end up using less rated miles than actual miles driven while I would use more...

 

[stopcrazypp]

This owners only thread is supposed to explain it:
http://www.teslamotors.com/forum/fo...rmation-about-rated-miles-and-projected-miles

But paraphrasing others that have access to it:

if you charge your car up to 265 miles and then drive at exactly 306/308 Wh/mi, you will not make it to 265 miles when you hit 0, rather you will have driven about 249 miles.

http://www.teslamotorsclub.com/show...stimate/page27?p=411509&viewfull=1#post411509

Here's another reference that tries to explain the situation (although it's not 100% certain):
https://docs.google.com/document/d/1nlZhDYtCinX_Wkb9OST-QBzervVp5yABMVBS266Q3W4/pub#h.1e9ai734m71s

 

[wormhole]

https://docs.google.com/document/d/1nlZhDYtCinX_Wkb9OST-QBzervVp5yABMVBS266Q3W4/pub#h.1e9ai734m71s

hadn't seen this, this helps explain it, thanks.

 

[yobigd20]

Can someone PLEASE explain how rated range is calculated.

it's a calculated algorithmic guess and it's near impossible to be 100% accurate.

To learn more about the actual calculation itself, you're going to want to read these thoroughly:
Patent 20100138178: "Battery capacity estimating method and apparatus" Battery capacity estimating method and apparatus - Patent application
Patent 20110156641: "STATE OF CHARGE RANGE" http://www.faqs.org/patents/app/20110156641

In order to accurately estimate the remaining capacity of a battery, it is critical that the full capacity of the battery be accurately known. Unfortunately, under normal use conditions such as those encountered in an electric vehicle or other battery-power device, it is difficult to accurately ascertain battery capacity. For example, in one method of determining battery capacity, the initial capacity of the battery is gradually decreased based on a variety of factors such as battery age, the number of charge/discharge cycles to date, and temperature. Unfortunately this technique does not provide a very accurate assessment of battery capacity, both because some factors are not properly taken into account (e.g., historical temperature profiles, load conditions, depth of discharge prior to each charging, charge/discharge rates, etc.) and because the effects of the errors accumulate as the battery ages. Another method of determining battery capacity is to allow the battery to become fully discharged, and then determine the capacity of the battery during charging. Although this technique can be used occasionally, using it on a routine basis can have serious repercussions since deep discharging a battery, and in particular fully discharging a battery, can dramatically shorten its lifetime. Additionally, for most battery-powered devices, especially electric vehicles, it would be extremely inconvenient to require that the user allow the battery to become fully discharged prior to charging. This would be similar to requiring that a conventional car be driven until the gas tank was dry before refilling, simply in order to determine the gas tank's capacity.
...
what is needed is a method of accurately estimating battery capacity that is less susceptible to, or more accurately takes into account, the many factors that can influence a battery's capacity.
...
[0005]The present invention provides a method and apparatus for accurately estimating battery capacity based on a weighting function. The disclosed system monitors battery current and uses the monitored battery current to calculate the state of charge (SOCbyAh) of the battery.
...
weighting calculation are based on sensor accuracies and control loop timing. These constants, like many non-linear real-world systems, are difficult to model and therefore are generally tuned based on real-world experimental data, the intended use of the device, and how much overshoot and response time can be tolerated. Typically, the initial settings for the constants are based on sensor accuracy and usage assumptions. For instance, in an EV application where the consequences of overshoot are severe and there are frequent rests (e.g., when the driver stops at the grocery store, school, restaurant, etc.), these constants are set high to give a low weighting.
...

While the charging profile from process 215 works in a near best-case scenario, it is desirable to provide some operational margin on top of the profile determined based upon just the target range and some value for vehicle efficiency. There are deviations from range and efficiency that may be determined in many different ways, as well as some predetermined (e.g., factory or user preset value) range safety margin to ensure that the vehicle has extra capacity to reduce chances of prematurely running out of charge. Control 200 provides deviations for range and vehicle efficiency in process 220. Control 200 then, at process 225, modifies the optimized SOC-cycle-preserving profile from process 215 by re-optimizing the SOC-cycle preserving profile when considering the range and efficiency deviations from process 220.
...
Vehicle efficiency is not constant and varies based upon different factors and energy consumption from the battery. When the user is driving more aggressively, vehicle efficiency will be less than when the user is driving more conservatively, other factors being equal, and the user will require more energy to travel one mile.
...
As the battery cells age, capacity declines. Practically, this means that a wider SOC range is desired to meet the same vehicle range targets as was met by a narrower SOC range when the battery cells were newer. Electric vehicles have other variable power needs besides providing the primary mission of mileage. User needs/desires for temperature and humidity control are preferably factored in and added as appropriate margin to the base level SOC range. Temperature and humidity control are specific examples of auxiliary uses for the charge stored within the battery cell pack. Other auxiliary uses may include battery cell pack cooling and heating and other environmental factors controlled by the user (e.g., internal/external lights, audio systems, and other charge using loads in the vehicle.) A user's actual or historic use informs the establishment of the margin and the actual SOC range.

or, rather, my simplified explanation - "it's complicated". lol.
but honestly, 5 miles range loss? that's a hell of a lot better than mine. It takes me 135 rated range miles to drive 100 actual miles. but I don't drive anywhere near the speed limit either.

 

[scaesare]

I started THIS THREAD a while back to discuss this. It might shed some light on the discrepancies we see...

 

[jerry33]

There is no vampire loss when you immediately start driving the car when you unplug it.

To put a nice face on it, lets call it auxiliary system use.

Plus you 'added gains' to your calculation, not sure what that is, or why you'd end up using less rated miles than actual miles driven while I would use more...

If I start with 210 miles, drive 50, and end up with 170 miles (for ease of calculation), I've gained ten miles over the rated range.

The reason that one person might use more and the other one less is how many Watt hours per mile they use. If 308 Wh/mi is equal to rated range, then someone using 340 Wh/mi would get less and someone using 255 Wh/mi would get more. If you use exactly 308 and get less than rated range then either the calculation is out, the Auxiliary systems are using some, or a combination of both.

 

[wraithnot]

The slightly screwy method to calculate rated range makes a lot more sense if you consider that there is some uncertainty in calculating exactly when the car will need to shut down, but people will be REALLY unhappy if the car stops when there is 5 miles left on the gauge and that people will also be very unhappy if they pay a whole lot of money for a car with 265 miles of range, but the gauge shows significantly less when they fully charge it.

If a fully charged car shuts down on average after 265 miles of 308 wh/mi that means sometimes it will shut down after a few more than 265 miles and sometimes it will shut down after a few less than 265 miles. So you have to make the gauge show zero after less than 265 miles of 308 wh/mi so you can be really confident it will never strand someone with more than zero on the gauge. But you can't do that simply by subtracting miles from the gauge or it will never show the full 265. Thus the strategy of showing 265 when full, but removing miles from the gauge faster than you would for 308 wh/mi.

The most accurate way to do things would be to show 265 when full, remove miles of range corresponding to 308 wh/mi, and somehow represent the uncertainty of when the car will actually stop moving. But that would probably confuse the hell out of people. So they do something slightly sneaky that gives them the behavior they want and will only confuse the hell out of people if they really try to dig into the details ;-)