2020, 2019, 2018 Model 3 Battery Capacities & Charging Constants

[AlanSubie4Life]

@AlanSubie4Life I notice in comparing posts #27 and #39 that you've added a row for 2018 Model 3 LR RWD 310, in addition to RWD 325. Can you tell me what happened when the existing fleet of RWDs was updated to 325 miles of range--was it simply a change in the formula to read a higher range, or was there a change in the firmware that actually wrung more miles out of the existing hardware?

Separately, I'm astonished that the 2020 Model 3 P 18" now has a higher range than my 2018 LR RWD. Clearly there have been drive train improvements along the way (which may be revealed to us in April).

I don't have good answers for you.

Well...I actually removed that row (I replaced the picture...). The 310 rated miles LR RWD is a point of confusion for me, and I'm still trying to work it out/reconcile all the available data.

All of the stuff below on the LR RWD may be wrong. It's a bit of a mystery to me.

I was not paying attention to this stuff at that time, but my guess/understanding is that the rated range constant has never changed on the RWD. I suspect they once had a much larger bottom buffer on the RWD vehicle, or they did more "expansion" of the existing 310 rated miles (so those vehicles would have taken forever to show degradation - see elsewhere, and here, for my unproven theory on how that is managed). I have no idea really. It's possible it was paired with an efficiency improvement - but they've never retested the vehicle in 2019 or for 2020 so we have no idea really.

That being said, what I do know: The EPA requires the energy measured in the test to be made available to the consumer, as I understand it (lockout of an unusable buffer is not allowed, though a usable buffer below 0% is allowed). (However, I don't know what is allowed if you do voluntary reduction...) If that energy were all available, it would have been 79.3kWh. So the 310 mile to 325 mile update probably did not change the available energy.

If I work this out, I will publish the data in a spreadsheet. There are a lot of numbers that don't align in the various data files, unlike for the other vehicles. So it makes it confusing.

Yes, on the Model 3 P it is pretty amazing how much it has been improved. Part of that is due to the efficiency improvement of the rear motor drive (you can see that on the SR+ efficiency increases), the rest is from something else.

 

[ElectricIAC]

I don't have good answers for you.

Well...I actually removed that row (I replaced the picture...). The 310 rated miles LR RWD is a point of confusion for me, and I'm still trying to work it out/reconcile all the available data.

I was not paying attention to this stuff at that time, but my guess/understanding is that the rated range constant has never changed on the RWD. I suspect they once had a much larger bottom buffer on the RWD vehicle, or they did more "expansion" of the existing 310 rated miles (so those vehicles would have taken forever to show degradation - see elsewhere for my unproven theory on how that is managed). I have no idea really. It's possible it was paired with an efficiency improvement - but they've never retested the vehicle in 2019 or for 2020 so we have no idea really.

That being said, what I do know: The EPA requires the energy measured in the test to be made available to the consumer, as I understand it. (However, I don't know what is allowed if you do voluntary reduction...) If that energy was all available, it would have been 79.3kWh. So the 310 mile to 325 mile update did not change the available energy.

Yes, on the Model 3 P it is pretty amazing how much it has been improved. Part of that is due to the efficiency improvement of the rear motor drive (you can see that on the SR+ efficiency increases), the rest is from something else.

The newest iteration is more efficient and it’s not just number shell games? Oh well. $11K buys a lot of electricity. Makes me wonder though what they’ll be able to do with a new build LR RWD..

 

[AlanSubie4Life]

newest iteration is more efficient

It's entirely possible (and likely, given that it would be in keeping with their company objectives) that any efficiency improvements made to the 2020 Performance are applied retroactively to the other 2018/2019 Performance vehicles (and other vehicles), to the extent possible. Remember that things as simple as a Michelin tire formulation change would also affect the range test results. It's not necessarily all drivetrain efficiency improvements. Some users have reported noticing efficiency improvements (I would never notice and have not noticed). Ironically, better drivetrain efficiency necessarily reduces heat generation, and probably makes the limited regen problems worse. Maybe that is why everyone is complaining this year. Depending on whether they are stressing switching inverter devices with higher voltages or not during shutoff, better efficiency might reduce warranty costs as well (due to reduced heat). Could also make warranty costs higher - it depends!

But anyway, even if they did this, there would be no obligation (and it would break precedent, except for that one exception of the RWD range change) to change the rated range numbers on older vehicles. It would be likely to piss people off because it wouldn't actually be changing the energy available (which is what matters, and many people know this), even if efficiency improvements came with it. People would accuse Tesla of trying to hide capacity loss, even though the rated miles cannot be used in isolation to determine capacity loss (it is the rated miles & the constant that matter).

A new build LR RWD would likely have a rated range of over 345 miles. It's already at 335 rated miles before any efficiency improvements.

 

[AlanSubie4Life]

After others pointed out that there was some 5-cycle data available, I added it to my spreadsheet. I've tried to cut down the number of columns to make it more readable. Again, once I sort out the LR RWD numbers (looks like it might not be consistent or possible), then I'll probably post this spreadsheet in original form.

But, this should be ok for now.

A few notes:

Note that the Model 3 Performance 20" got two tests with full discharge with different capacities - an indication that that buffer should not be counted on - probably cut out early on one test! It's interesting because it shows there can be a fair amount of variance in efficiency from test to test (looks like 2-4%).

For cold weather:
You can see available pack energy is reduced at 20 degrees F. And you can see just how high that usage goes even for that not too stressful test (it's the FTP test which is basically UDDS). It consistently adds about 110Wh/mi at an average speed of 20mph for the FTP, so we're looking at ~2kW of additional usage at 20F (which is surprisingly low to me).

 

[Wreckless316]

After others pointed out that there was some 5-cycle data available, I added it to my spreadsheet. I've tried to cut down the number of columns to make it more readable. Again, once I sort out the LR RWD numbers (looks like it might not be consistent or possible), then I'll probably post this spreadsheet in original form.

But, this should be ok for now.

A few notes:

Note that the Model 3 Performance 20" got two tests with full discharge with different capacities - an indication that that buffer should not be counted on - probably cut out early on one test! It's interesting because it shows there can be a fair amount of variance in efficiency from test to test (looks like 2-4%).

For cold weather:
You can see available pack energy is reduced at 20 degrees F. And you can see just how high that usage goes even for that not too stressful test (it's the FTP test which is basically UDDS). It consistently adds about 110Wh/mi at an average speed of 20mph for the FTP, so we're looking at ~2kW of additional usage at 20F (which is surprisingly low to me).
View attachment 509808

I’m thinking you might appreciate this. Hoping you can help me make sense of the numbers.

Since Friday evening (5 days) I traveled 243 miles from 100% charge. Take a look at both pics below for the story. Can you run the numbers for me and explain the capacity loss so far? I know I only used 43kwh, with the remainder being the 9 miles (4%) plus the buffer. Can you lay out the math for that? Also thought you might want to validate the charge constant using the energy screen. Please see pics.

 

[AlanSubie4Life]

Can you lay out the math for that? Also thought you might want to validate the charge constant using the energy screen.

Your battery contains 245rmi*210Wh/rmi = 51.5kWh.

For a continuous 100% to 3.7% discharge you would expect to see:

51.5kWh*0.955*0.98*(0.963)= 46.4kWh.

You see 42.95kWh. This does not count any use while in park.

So you have lost 46.4kWh-42.95kWh = 3.5kWh to vampire drain. Very reasonable for 5 days (~3 rated miles per day, quite low).

Without that drain, you’d be at 26 rated miles remaining. You’d have to track each drive ending and starting rated miles, or use an app to track those drains while in park, if you wanted to check the math on that.

That efficiency is amazing. I can’t use it to calculate the constant because it only has one significant figure (9 rated miles)...but it coincidentally works out to be 210Wh/rmi assuming perfect precision. Pictures have to be captured at a relatively high SoC.

 

[Wreckless316]

Your battery contains 245rmi*210Wh/rmi = 51.5kWh.

For a continuous 100% to 3.7% discharge you would expect to see:

51.5kWh*0.955*0.98*(0.963)= 46.4kWh.

You see 42.95kWh. This does not count any use while in park.

So you have lost 46.4kWh-42.95kWh = 3.5kWh to vampire drain. Very reasonable for 5 days (~3 rated miles per day, quite low).

Without that drain, you’d be at 26 rated miles remaining. You’d have to track each drive ending and starting rated miles, or use an app to track those drains while in park, if you wanted to check the math on that.

That efficiency is amazing. I can’t use it to calculate the constant because it only has one significant figure (9 rated miles)...but it coincidentally works out to be 210Wh/rmi assuming perfect precision. Pictures have to be captured at a relatively high SoC.

Thank you! What is the formula for calculating the continuous discharge? You used figures like .98 and .955? Can you explain

 

[AlanSubie4Life]

Thank you! What is the formula for calculating the continuous discharge? You used figures like .98 and .955? Can you explain

0.955 accounts for the buffer not being included in the 51.5kWh. (Converts from 210Wh/rmi charge/EPA, to 200.5Wh/rmi, displayed.)

0.98 is approximate (might be a bit closer to 1 for you) because the trip meter seems to miss some energy. At these consumption levels it might miss less. Or more. I don’t know. Empirically determined. (Converts from 200.5Wh/rmi displayed to ~197Wh/rmi (trip))

 

[Wreckless316]

0.955 accounts for the buffer not being included in the 51.5kWh.

0.98 is approximate (might be a bit closer to 1 for you) because the trip meter seems to miss some energy. At these consumption levels it might miss less. Or more. I don’t know. Empirically determined.

But I thought when using Charge constant to calculate kwh capacity, that included the buffer ?

 

[AlanSubie4Life]

But I thought when using Charge constant to calculate kwh capacity, that included the buffer ?

That’s correct - the calculation using the rated miles at 100% does include the buffer (you can’t directly use the charge constant at any other % to calculate remaining energy). But remember the rated miles from 0 to 246rmi (displayed) do NOT include the 4.5% buffer. Otherwise there would be no buffer!

So that means that 95.5% of that 51.5kWh is available from 246rmi to 0rmi(displayed).

For 2020 SR+, it’s 210Wh/rated mile, EPA
200.5Wh/rated mile, displayed
~197Wh (trip)/rated mile, displayed

I track this in my table.

 

[Wreckless316]

That’s correct - the calculation using the rated miles at 100% does include the buffer (you can’t directly use the charge constant at any other % to calculate remaining energy). But remember the rated miles from 0 to 246rmi (displayed) do NOT include the 4.5% buffer. Otherwise there would be no buffer!

So that means that 95.5% of that 51.5kWh is available from 246rmi to 0rmi(displayed).

For 2020 SR+, it’s 210Wh/rated mile, EPA
200.5Wh/rated mile, displayed
~197Wh (trip)/rated mile, displayed

Ahhh...and that’s because what is displayed becomes increasingly pessimistic, so by the time it reaches 0 miles, the real constant for displayed range becomes 200wh/mi? Get that right ?

 

[AlanSubie4Life]

Ahhh...and that’s because what is displayed becomes increasingly pessimistic, so by the time it reaches 0 miles, the real constant for displayed range becomes 200wh/mi? Get that right ?

The real constant for displayed rated range is always about 200Wh/rmi for 2020 SR+.

As far as pessimism is concerned, it depends on what you mean. If you assume that you do not want to touch the buffer at all, the display is actually very optimistic! In your specific case, you have 9 rated miles left, and we know that you would use all of that when driving 9 miles at 197Wh/mi. At your recent rate of 135Wh/mi, you’d make it 13 miles - not the 14 it predicts.

It’s optimistic in this view because it is always using 210Wh/rmi for the energy per rated mile, and furthermore it is using your trip meter Wh/mi value which we know reads a little low. So it is getting you both ways with optimism.

However, if you include the use of the buffer, then obviously it is a bit pessimistic. Even if you were only able to use 1/4 of the buffer (0.6kWh), that would give you 4 additional miles, so you’d make it 17 miles not 14.

Depends on your perspective. Trying to use the buffer can result in getting stuck by the side of the road. Or the middle of the road.

When you reach zero rated miles the prediction will be that you have zero range remaining. But presumably you could travel a couple miles carefully (maybe as many as 10 - plenty of videos of this but it is really really risky). So it is arguably pessimistic in the prediction if you decide to push into the buffer.

EDIT: fixed some numbers above...

 

[KenC]

Your driving is very efficient for LA.

 

[Wreckless316]

Your driving is very efficient for LA.

I mean I'm in traffic most of the time. Where can I really go and wherever it is, it wont be fast!

 

[Wreckless316]

That’s correct - the calculation using the rated miles at 100% does include the buffer (you can’t directly use the charge constant at any other % to calculate remaining energy). But remember the rated miles from 0 to 246rmi (displayed) do NOT include the 4.5% buffer. Otherwise there would be no buffer!

So that means that 95.5% of that 51.5kWh is available from 246rmi to 0rmi(displayed).

For 2020 SR+, it’s 210Wh/rated mile, EPA
200.5Wh/rated mile, displayed
~197Wh (trip)/rated mile, displayed

I track this in my table.

Ok I think I've understood most of it now. My confusion was centered around concept of capacity vs rated miles and how its calculated to display.

Last question. So is it safe to say the concept of discharge constant vs charge constant exists solely due to the buffer. If there was no buffer than things would be streamlined and we would really only be looking at the charge constant, as the rated miles would be "discharge" at the same rate of the charge constant?

 

[AlanSubie4Life]

So is it safe to say the concept of discharge constant vs charge constant exists solely due to the buffer. If there was no buffer than things would be streamlined and we would really only be looking at the charge constant, as the rated miles would be "discharge" at the same rate of the charge constant?

Yes. This confused me for a while. I don’t want to complicate things, but honestly it may be simpler to forget about the “charge” constant except when you want to know your battery capacity at 100%. And even then you don’t need it (you can just use 200Wh/rmi and divide by 0.955 instead...). It’s really only there to match the EPA results.

The easiest way to think about it is you have a buffer (which you never want to use) of 4.5% of your full capacity (about 2.3kWh for you at the moment), and each rated mile (for your 2020 SR+) contains ~200Wh (a nice easy round number for calculations!).

Finally - to resolve one point that confused me - ignore the “kWh added” on the screen in the car from charging events. That number is bogus, as it is just a simple calculation using the charging constant (the correct value to use is the ~200Wh/rmi number). You can’t arrive at the very official 88.4% charging efficiency (Tesla published - see the chart) with 7.7kW charging unless you use that 200Wh/rmi number.

That is all you need to know I think.

 

[Wreckless316]

Yes. This confused me for a while. I don’t want to complicate things, but honestly it may be simpler to forget about the “charge” constant except when you want to know your battery capacity at 100%. And even then you don’t need it (you can just use 200Wh/rmi and divide by 0.955 instead...). It’s really only there to match the EPA results.

The easiest way to think about it is you have a buffer (which you never want to use) of 4.5% of your full capacity (about 2.3kWh for you at the moment), and each rated mile (for your 2020 SR+) contains ~200Wh (a nice easy round number for calculations!).

Finally - to resolve one point that confused me - ignore the “kWh added” on the screen in the car from charging events. That number is bogus, as it is just a simple calculation using the charging constant (the correct value to use is the ~200Wh/rmi number). You can’t arrive at the very official 88.4% charging efficiency (Tesla published - see the chart) with 7.7kW charging unless you use that 200Wh/rmi number.

That is all you need to know I think.

So what would be the best way to convert from Kwh to rated miles? For example converting 3.5kwh (Vampire drain in 6 days, not 5 ).

Is it 3.5kwh divided by 210wh/mi? That would equal to 16.7 miles for 6 days....or 2.78 miles per day vampire.

Did i get all that right?

 

[AlanSubie4Life]

So what would be the best way to convert from Kwh to rated miles? For example converting 3.5kwh (Vampire drain in 6 days, not 5 ).

Is it 3.5kwh divided by 210wh/mi? That would equal to 16.7 miles for 6 days....or 2.78 miles per day vampire.

Did i get all that right?

No. I've also done this wrong in the past, but for vampire drain, you're looking at displayed rated miles.

It's ~200Wh per displayed rated mile, as mentioned above, so you should use that value. In fact, for any calculation, use the value for Wh per displayed rated mile (not the charging constant). As I said above, it may well be easiest to just ignore the charging constant. It's kind of unnecessary noise, though it is directly related to the per rated mile/discharge constant...and it shows up on the charging screen indirectly...so we carry it around and track it...

So, If you lost 3.5kWh of energy (untracked as mentioned above): that is 17.5 rated miles in 6 days, 2.92 miles per day.

The miles on your screen each are worth ~200Wh from your battery. It's that simple. If you drive up 1000 feet, that's about 1.4kWh potential eneergy in addition to the driving. So that's going to require at least 7 rated miles (slightly more due to drivetrain inefficiency) more than driving the same distance on the flat.

 

[Wreckless316]

No. I've also done this wrong in the past, but for vampire drain, you're looking at displayed rated miles.

It's ~200Wh per displayed rated mile, as mentioned above, so you should use that value. In fact, for any calculation, use the value for Wh per displayed rated mile (not the charging constant). As I said above, it may well be easiest to just ignore the charging constant. It's kind of unnecessary noise, though it is directly related to the per rated mile/discharge constant...and it shows up on the charging screen indirectly...so we carry it around and track it...

So, If you lost 3.5kWh of energy (untracked as mentioned above): that is 17.5 rated miles in 6 days, 2.92 miles per day.

The miles on your screen each are worth ~200Wh from your battery. It's that simple. If you drive up 1000 feet, that's about 1.4kWh potential eneergy in addition to the driving. So that's going to require at least 7 rated miles (slightly more due to drivetrain inefficiency) more than driving the same distance on the flat.

I guess the only use for charge constant for the average joe like myself is to calculate remaining battery capacity only at 100%?

 

[AlanSubie4Life]

I guess the only use for charge constant for the average joe like myself is to calculate remaining battery capacity only at 100%?

Yes. It is useful for calculating your full remaining battery capacity, which includes the buffer, at 100%, and is predictive of what the CAN bus readback would tell you.

Or you can just use the discharge constant, multiply by your rated miles at 100%, and divide by 0.955. It will give you the same value.