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Rated Range Survey Results

Thanks to the 62 people who filled out my survey trying to understand Rated Range.  The long detailed analysis is available here including the graphs:

http://teslaowner.wordpress.com/2013/07/30/rated-range-results/

For purpose of discussion, the executive summary is the following:

Rated Range Varies for the Majority of Cars in the Following Bands:

175-195 for 60kWh Batteries
220-245 for 85kWh Batteries

The rated range appears to have no correlation between energy used over long periods of travel.
The rated range appears to have no correlation between miles driven.  Since the cars are so new there is unlikely to be much battery degradation yet.

I think this survey almost asks more questions than it answered.  There is clearly not a clear correlation between long term driving habits and rated range.  Perhaps immediate short term driving habits?  Perhaps the car simply cannot measure the amount of energy in the battery very accurately?  How accurate, reliable and useful is this rated range number?  Why is there so much variation in the rated range number in the Model S?

What I would personally like to see is an accurate consisted rated range that I could understand and also a simple energy measurement.  I would like to see a gauge that simply said 55kWh left in my battery.  I would find this more straightforward.  I can do the simple math in my head to convert that to "can I drive to X without recharging"

I am also wondering if part of the problem with giving these accurate numbers is that historically cars do not give you accurate measurements of remaining fuel.  All of the cars I have owned have had crude analog gauges or digital readouts that were stepped scales and not a simple readout "12.1" gallons left.

I am looking forward to any comments on this survey and if there are any suggestions on other things to look at.

I took a look at the early spreadsheet over the weekend but there weren't enough responses to draw the numbers you did out of the data. I found there to be less difference between the 60 and 85kWh batteries than I expected.

Unfortunately, we didn't have a statistically significant sample at the time I looked so the standard deviation was pretty big. However, using a median, people are driving 307 Wh/mi. I used median to filter out the noise that would otherwise have been injected by those of you who drive very very fast and those of you who somehow can eke every last mile out of each electron.

Still, I agree with the conclusion that this data does not answer the question "can I drive to X without recharging?" But give yourself a break. When did you ever develop this quality of data for an ICE automobile?

By the way, I only saw one P+ but there didn't appear to be much variance among the 85, p85 and p85+ models. Unless more data has come in to show that false.

@sxross I am perplexed by your statement "there wasn't enough responses to draw the numbers you did out of the data". There actually was only a couple of additional responses over this last weekend.

Also, the survey did not distinguish between "85, p85 and p85+ models" as that is pretty much irrelevant as they all have the same battery pack.

You must have been looking at another survey.

It seems that Rated Range does not scale up linearly with the battery size. If 60 KWh battery can have rated range 175-195, I expect 85 KWh will have rated range 248-276. Model S 60 KWh seems to have more value in terms of mileage than 85 KWh.

@adyc100

Your comment is very interesting! I had not noticed that. When I look at the data both the average and the median of the 60kWh batteries is 182.5

The 85kWh battery is 232.5

Using the 60/85 ratio, the data from the 60 would suggest the rated range of the 85 should be 258, and visa versa, the 85 data would imply the 65 should be only 164.

Since I still don't really understand what the rated range really means, I'm not sure what this really means either!

Any Limited 60 kWh range data?

@ramtaz. Yes

"The two data points for the 40kWh battery was 140 and 143 rated range." in the long report

Perhaps I was looking at different data. I was looking at e Google doc that appeared a few days ago. I was hoping to draw some commonalities out of the data but I only had a few more than 20 rows and a lot of variance.

Was I, indeed, looking at different data?

Different 'scaled' ranges might be caused by different car weights and/or different motor efficiencies at different speeds/load levels - the 60, 85 and P85 all have different motor powers, peak power rev ranges and torques.

@sxross - yes you were looking at different data. I did a survey monkey. I don't think the raw data is public. I just transferred it manually to a spreadsheet.

For all the gory details (minus raw data)

http://teslaowner.wordpress.com/2013/07/30/rated-range-results/

@nickjhowe

Actually the cars generally weigh the same. They only crash tested one car weight. The 60 is filled with dead battery cells weighing the same as the 85. I'm sure there are minor other weight difference but that is not the reason for the rated range changes.

My detailed survey shows that the overall energy difference, which is primarily due to how someone is driving and where they are driving than smaller things like options, showed how rated range had no correlation to this. I was quite surprised by the lack of correlation.

Different motors = different results. Higher HP output eats range.

@Iowa92x - yes, but I compared energy output vs. range and could not find any correlation.

Some here in this thread may have been referring to the spreadsheet of results from the separate survey that I created trying to understand how the Model S converts kWh remaining to rated range remaining.

For those who haven't seen it, there is a detailed explanation of how rated range is calculated, in this new thread, based on an email from Tesla, including some explanation of why the rated ranged displayed after a standard charge "dropped" after 4.5 was installed.

Hmm, bit.ly links seem to have been blocked or suppressed. Let see if this works:

Survey: http://bit.ly/teslasurvey1
Results: http://bit.ly/teslasurvey1results

To preview the redirect, use http://bit.ly/teslasurvey1+ and http://bit.ly/teslasurvey1results+ .

I had not seen that earlier thread as I mostly read the other forum, this one is much harder to follow and to post into.

If it is solely a fixed value, why is there so much "range" in "rated range" for all these cars with the same battery? I doubt that 85% of the 85kWh batteries have significantly degraded...

@OP - "What I would personally like to see is an accurate consisted rated range that I could understand and also a simple energy measurement. I would like to see a gauge that simply said 55kWh left in my battery. I would find this more straightforward. I can do the simple math in my head to convert that to "can I drive to X without recharging"

How is that different from ideal range. ideal range is directly proportional to State of Charge of battery. You can achieve the ideal range by driving at 279 KWh/m rate. That is exactly what we did one time we found ourselves 100 miles from home with 125 ideal range left. We drove the car around the ideal range line all the way home and arrived with 20 mi ideal range, radio on, AC set to 72 deg. The temp was in the high 90s with little to no wind and mostly flat road.

@July10Models

I just think it is easier to think in kWh. I could know for a particular path A->B I need X amount of energy. Any range value is dependent upon the road. Where I could remember. Oh over that mountain pass it took me X kWh to get there.

I know I can do the math from the data available, but it is more complex.

Also it is clear from the stats, that rated range is related to SoC also, just a less conservative number.

I've never driven at 279 KWh/mile!

"I would like to see a gauge that simply said 55kWh left in my battery."

One problem with that is the energy a battery can deliver starting from a particular state of charge is not constant. It depends on several variables, including temperature and rate of discharge. You can see graphs for this in the 18650 data sheet.

I don't know how the range meter works. But I suspect it is based on measurement of both the voltage and temperature of the battery, and possibly other variables as well. The algorithm that combines these measurements into a projected range is probably more complex than you might imagine.

I don't think your problem is with units (kWh vs. miles). I think your problem is the range meter is not as predictable and deterministic as you would like. I agree that is an issue. But the alternative is a simplistic meter that would be easy to understand but would likely be highly inaccurate in certain situations. Would that be an improvement? I don't think so.

Ideal range, rated range, kwH are all interlinked and somewhat inaccurate. I don't see the problem with having all of them listed since they are all probably equally undeterministic.

But I still think kWh could be useful for planning unusual road conditions. I very often travel on non-flat roads. I think for example going up an obscure mountain pass in the Sierras it would be more useful to think in terms of kWh. If I already knew it took 52kWh to get up I80, 33kWh to get up another road, I would be fine on X road. I think this is harder to think of in terms of rated and ideal ranges, but could be easily done either way. But also, these numbers in kWh would translate to either 60 or 85 batteries to share with others but rated/ideal would be battery size dependent.

What is the 18650 data sheet?

The 18650 data sheet is at

http://www.panasonic.com/industrial/includes/pdf/Panasonic_LiIon_CGR1865...

This is not the exact battery in Model S but the specs are pretty close.

As I said, I don't think units is your problem. You can work in rated miles or you can work in kWh, or just go crazy and work in rated km. I suspect most people will find it easiest to think in terms of a familiar distance measurement. But as you say, there is a problem in that the rated range meter only works in miles (or km) whereas the trip meter only works in kWh. This is confusing. I would probably prefer if the trip meter showed rated miles used.

I don't think kWh numbers for a given trip are the same for the 60 and the 85. The 60 is more efficient; I don't know why, but it is. Rated miles used on a trip probably do translate from the 85 to the 60 (i.e a trip that reduced rated range by 100 miles in an 85 probably will reduce rated miles in a 60 by 100 miles also).

Looking at what is really different (assuming a 60 driven exactly like a 85 which is in itself unrealistic) I assume that the inverter having to be able to handle an output of 45 kW more in the 85 might be a little less efficient at the same instant power throughput.

I would bet on the human factor. People who decide for a 60 might be "wired" a little different than those who go for the 85 or P85 and so I would expect to find a systematical higher use of energy / mile in the 85 population, even if you (in a double blind setup) would give them 60s ;-)

No offense to both populations, P85+ myself...

My limited 60 kWh battery is at 134 rated range from a delivery rated range of 147 .. May 29
Loses 4-6 miles of range per 8 hours at the office.


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