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Method to calculate/extrapolate battery capacity from trip consumption

willow_hiller

Active Member
Apr 3, 2019
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Maryland
This is what I was wondering too, but it’d need to be pretty far off to drop it from 240 to 192.

But it seems like in all Model 3 there’s definitely some weirdness going on with the screen indication of what’s usable verses what the EPA application says. No one is seeing 55kWh nor 78kWh.

Is it possible there's a large bottom buffer? Elon tweeted this in May 2018: Elon Musk on Twitter

"A Tesla has a usable reserve of 5 to 15 miles range even after the battery reads “empty”. This will not hurt the pack."
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
9,665
11,616
San Diego
Is it possible there's a large bottom buffer? Elon tweeted this in March: Elon Musk on Twitter

"A Tesla has a usable reserve of 5 to 15 miles range even after the battery reads “empty”. This will not hurt the pack."

Yes. He had another Twitter post (for some reason I've been quoting 6 miles but I guess it's 5, I was misremembering):

Elon Musk on Twitter

Still, it doesn't explain the atrocious results. He should try someone else's car.
 

Zoomit

Active Member
Sep 1, 2015
2,197
4,117
SoCal
Is it possible there's a large bottom buffer?
I theorized the Model 3 has a large bottom usable buffer, probably a year ago now. But in this SR+ example it’d need to be 48 mi to bring the test result back up to the EPA range. That’s ~10kWh and just doesn’t make sense.

Edit: Found it, I was thinking a 5.6kWh reserve, but that still seems exorbitant. This was Feb ‘18 and we don’t seem to have learned much since then. Supercharger speed: 116kW
 
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Zoomit

Active Member
Sep 1, 2015
2,197
4,117
SoCal
@AlanSubie4Life Not sure if you realize it or not but 78,269 Wh / 333.8 mi = 234.5 Wh/mi. Those numbers are from the first published 3 LR RWD EPA test. Calculating a ~234 Wh/mi constant from the car would make me infer that’s the source.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
9,665
11,616
San Diego
@AlanSubie4Life Not sure if you realize it or not but 78,269 Wh / 333.8 mi = 234.5 Wh/mi. Those numbers are from the first published 3 LR RWD EPA test. Calculating a ~234 Wh/mi constant from the car would make me infer that’s the source.

That would make some sense, as for why Tesla chose this constant. I can't really say it's exactly 232Wh/rmi due to rounding errors; it could be closer to this 235Wh/rmi. And that's just the way it behaves on my car; I don't know whether other variants behave the same way.

I noticed there is a massive thread on what is the "actual capacity" of the Tesla batteries. It is quite contentious. :) Fortunately I don't really care about that. (There's a big debate whether you can get the since last charge meter to show 78kWh used with zero net elevation loss.) Anyway, I just want to know what Wh/mi (indicated) I need to get to achieve the rated range, and the constant makes that possible. The constant may or may not be "real" Wh/rmi, but I don't care.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
9,665
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San Diego
In the video Alex states that he routinely goes over a 2000’ pass for his commute. I wouldn’t read anything into the 267 Wh/mi number.

I did not bother to watch the video, just read his article. How many miles does he have with that 267Wh/mi number?

It has not really been that cold, so I would not expect it to be pushed up that much by heating use, but maybe he runs the car warm.

I have a lifetime of 285Wh/mi and 265Wh/mi over the last 300 miles in a P3D+ and I am not really trying that hard to be efficient, and I have ~800’ of hills every day.

Tires cost me about 30Wh/mi. I figure the AWD costs me another 20Wh/mi. And then the SR+ is lighter. So I’d expect it would be possible to routinely get 220Wh/mi with a little bit of care, even with those hills. Without the hills I doubt that 200Wh/mi would be that difficult.

So to me 267Wh/mi seems very high unless of course it includes a lot of winter use...but it is an SR+ so it is brand new.

Surprised there isn’t a whole thread about this somewhere here...maybe there is...?
 

willow_hiller

Active Member
Apr 3, 2019
3,152
15,019
Maryland
I did not bother to watch the video, just read his article. How many miles does he have with that 267Wh/mi number?

It has not really been that cold, so I would not expect it to be pushed up that much by heating use, but maybe he runs the car warm.

I have a lifetime of 285Wh/mi and 265Wh/mi over the last 300 miles in a P3D+ and I am not really trying that hard to be efficient, and I have ~800’ of hills every day.

Tires cost me about 30Wh/mi. I figure the AWD costs me another 20Wh/mi. And then the SR+ is lighter. So I’d expect it would be possible to routinely get 220Wh/mi with a little bit of care, even with those hills. Without the hills I doubt that 200Wh/mi would be that difficult.

So to me 267Wh/mi seems very high unless of course it includes a lot of winter use...but it is an SR+ so it is brand new.

Surprised there isn’t a whole thread about this somewhere here...maybe there is...?

Just under 1000 miles. He also states that he keeps regen on low for his commute, so that may be a contributing factor. But for his range test he said the regen was on standard.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
9,665
11,616
San Diego
He also states that he keeps regen on low for his commute, so that may be a contributing factor.

With a 2000 foot hill on his commute, I would think that would be a contributing factor... I am sure he explains why, but it seems completely nonsensical. And I can’t think of a good reason.
 

willow_hiller

Active Member
Apr 3, 2019
3,152
15,019
Maryland
Just noticed his lifetime wh/mi matches up pretty well with the test. Lifetime of 263 wh/mi, and in real-life range test his table shows 3.85 mi/kWh which translates to 259.7 wh/mi.

So somehow his commute with a mountain pass has the same efficiency as a flat range test?
 
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willow_hiller

Active Member
Apr 3, 2019
3,152
15,019
Maryland
Dug up this old thread to post an additional "real world" range test as reported by InsideEVs: Tesla Model 3 Standard Range Plus Real-World Highway Range Test

272 miles from the SR+ on 78 mph cruise control with the AC set to 68. Alex on Autos really has some explaining to do...

Edit: Just watched through the video, he used 125% of the battery to go 272 miles. So for 100% he got 217 miles.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
9,665
11,616
San Diego
For the first leg he averaged 70mph (most freeway done at 78mph), did 140.3mi @ 248Wh/mi, went from 95% to 28% battery (67%). Trinidad & Colorado Springs are the same elevation. Looks like he had minimal traffic so no significant drafting. Really quite an excellent result - that's as fast as you really would ever need to go without getting a ticket. (Obviously you can go slightly faster in some parts of Nevada where speed limits are 80mph...)

I didn't bother to watch the rest because it was too confusing; he wasn't trying to show what the range was as far as I could tell.

From the first leg, without entering the reserve, it looks like you could do:

140.3/0.67 => 209 miles on a 100% to 0% discharge, without entering the reserve.

Alex DEFINITELY has some explaining to do. I think if you drop the freeway speed to below 70mph you'll hit 240miles without the reserve. Just a rough estimate. To get only 192miles...I have no idea.

An additional conclusion: 140.3mi*248Wh/mi / ( 0.67 * 240rmi) = 216Wh/rmi

This is the constant I will use for the SR+ from now on. The constant in the P3D & AWD is 230Wh/rmi.

So, if you can get to 216Wh/rmi on the display, you'll get 240 miles of range...and to do that I would guess you'd need to drop your speed to below 70mph.
 

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