Extrapolation of Range and Battery Size(s)

[rEVhappy]

It'd help me understand your point if you could be specific and argue how each individual component would scale instead. I agree there is a case to be made that some parameters will rather scale with the cube-square root instead. That's 85% instead of 80%. Total power draw would then become 3332W + 2820W + 4100W. That puts us at 64kWh before brick protection. But I took a very large brick protection : 9kWh (more than the current 85 model S) partially to offset this low ball number. 6kWh is an equally likely reserve so I think my numbers in the end up hold up pretty well.



I am looking forward to your model.

Your assumption that a 20% reduction in volume will correspond to a 20% reduction in weight, which will then correspond to a 20% reduction in rolling resistance, power draw from components like AC, battery cooling, etc doesn't quite work out so cleanly in the real world. If there were a bigger sample size of ev's using Tesla's components other than the S and X, I'd gladly show you a 'model'.
And EPA testing isn't done at steady state 80 km/h cruising, so your initial premise is flawed.

Yes. My thoughts exactly.

They are not fighting to shave 5KWh off the pack.

They put in a 60 KWh pack and keep refining the car towards production. Today they know they can achieve ~215 miles with the prototypes, and think they can do better with the final production model.

I think this is more about where final range lands with a 60KWh pack, than about how much they might shave off the pack.

IMO the fight to 'shave off' 5kWh was done quite a while ago. Otherwise, why would the improvement over a S60S be a mere 7 miles. That's only a 3.3% improvement in 5 years. With lighter overall weight, better overall battery density and efficiency, better Cd, smaller footprint for less frontal area, small improvements in motors/inverters, and other incremental improvements, all they could pull off was 7 miles? That's a pretty conservative estimate, and Tesla usually doesn't do conservative. Just my 2 cents.

 

[SageBrush]

Ahh ... OK. I am wrong on the weights.
So if the M3 is about 1.4x heavier and about 0.667x lower Cd
Then if all else is equal and the energy split at 65 mph is 50% aero, then the M3 will be about 1.4*0.667 = 0.924x the i3 highway energy consumption.

At i3 of 300 Wh/mile, that puts the M3 at 277 Wh/mile.
The EPA number includes about a 15% charging loss estimate,
so the on-road energy economy works out to 277*0.85 = 235 Wh/mile

My estimates are starting to converge

 

[Rashomon]

I actually threw some numbers into a model, and only at about 30 mph or below is an i3 likely to be more efficient than a M3. Even at 40 mph, an M3 uses less power than a non-REx i3. Aerodynamics kick in quickly. The assumptions are about .47 meter-squared CdA for the M3, 0.7 meter-squared for the i3, 1250kg and 1750kg for respective weights, and 0.007 rolling resistance for both. The i3 already has pretty special tires, and what Tesla has asked Michelin for -- based on Michelin's public comments -- are likely to be at least as good. Low rolling resistance minimizes the effect of weight differences. I would bet a very large sum of money the base battery in the M3 is 55 kWh or less. And I suspect I'm a little conservative on the M3 CdA, as I'm using an A that's conservative.

This also points to the future of the MS. It's due for a substantial refresh by the time that the M3 is in production. I think a redesign will address issues addressed with the M3 (more rear seat headroom) and go for similar efficiency improvements. It is, after all, generally easier to get a lower Cd with a longer vehicle. If it gets a redone pack with the new more energy dense cells at the same time, I think the top of the line MS is likely to see a very substantial range increase, on the order of at least 25-30 percent. That will help justify the price difference with the M3.

And, guys, don't use standard assumptions that at 65 mph aerodynamic drag is half the load. With low-rolling resistance tires, the cross-over where aero equals rolling drag is more like 45 mph for a M3, and that's very dependent on weight, CdA, and tire characteristics for a given vehicle. By 65 mph, well over 60 percent of a M3's power will be overcoming aero loads.

 

[Snowdog]

IMO the fight to 'shave off' 5kWh was done quite a while ago. Otherwise, why would the improvement over a S60S be a mere 7 miles. That's only a 3.3% improvement in 5 years. With lighter overall weight, better overall battery density and efficiency, better Cd, smaller footprint for less frontal area, small improvements in motors/inverters, and other incremental improvements, all they could pull off was 7 miles? That's a pretty conservative estimate, and Tesla usually doesn't do conservative. Just my 2 cents.

Is it really 5 years, do we see example of improvements in most recent Tesla Models? They would have modern electronics, not 5 year old electronics. Results for the electronics are already great, so this is diminishing returns.

Again, (as you noted) not talking about aerodynamic dominated steady state cruising here. EPA is dominated by weight, not Aerodynamics, as even the EPA Highway test has a low average speed and many stops.

The bottom line is that a ~3600lb Tesla is unlikely to leap ahead of ~2600lb i3, on a weight dominated test like the EPA combined range.

 

[Rashomon]

These are the actual test cycles. The M3 is going to spank the i3 in the Highway cycle, even though it's much, much lower speed than current real world highway use, at least if you're not in the Northeast US or someplace like Sweden with very low speed limits. It will lose in the urban cycle to the light weight of the i3, though good regeneration helps take the edge off of weight differences. The combined is likely to be pretty close . . .

 

[Snowdog]

These are the actual test cycles. The M3 is going to spank the i3 in the Highway cycle, even though it's much, much lower speed than current real world highway use, at least if you're not in the Northeast US or someplace like Sweden with very low speed limits. It will lose in the urban cycle to the light weight of the i3, though good regeneration helps take the edge off of weight differences. The combined is likely to be pretty close . . .

There are 5 cycles. AFAIK, the AC cycle and High speed cycle combine with your link to create the highway numbers. So there are stop/accelerations mixed in as well.

When all is said and done the final EPA combined number is heavily weighted to stop and go driving, and a fairly low overall average speed.

 

[SageBrush]

There are 5 cycles. AFAIK, the AC cycle and High speed cycle combine with your link to create the highway numbers. So there are stop/accelerations mixed in as well..

Yes, 5 cycles, but IIRC only three are used for the 'highway' number. Do you remember if the cycles are equally weighted ?

 

[Rashomon]

Yes, 5 cycles, but IIRC only three are used for the 'highway' number. Do you remember if the cycles are equally weighted ?

No they're not. The old "55-mph" highway cycle seems to be about 81 percent of the highway portion, but then it's blended again with the AC test, reducing the contribution. See page 92 of: https://www3.epa.gov/carlabel/documents/420r06017.pdf. The formula is somewhat complex. The EPA also seems to allow -- at a company's discretion -- use of the original two cycles with a correction factor for the post-2009 fuel-economy ratings for EV autos, but you really have to dig through a lot of regulations to see what is actually required. And anytime there is discretion, someone will start gaming the system.

 

[aronth5]

] View attachment 170732 Interesting video put out by Teslarati showing the large 3D CAD rendering displayed behind Elon. Slowed down the video and it highlights a lot of good information.
At 7:26 is shows the cell sizes are larger using 8 battery modules going length wise compared to the S and X which are side ways.
Plus lots of other great info from the test ride earlier in the video.

 

[Thomas Edison]

So if they aren't using 18650's then what are they going to use?

View attachment 170733 ] View attachment 170732 Interesting video put out by Teslarati showing the large 3D CAD rendering displayed behind Elon. Slowed down the video and it highlights a lot of good information.
At 7:26 is shows the cell sizes are larger using 8 battery modules going length wise compared to the S and X which are side ways.
Plus lots of other great info from the test ride earlier in the video.

 

[MP3Mike]

So if they aren't using 18650's then what are they going to use?

New cells that they are designing and producing at the Gigafactory. (They said that they were sizing them to maximize the energy density.)

 

[aronth5]

So if they aren't using 18650's then what are they going to use?

New cells that they are designing and producing at the Gigafactory. (They said that they were sizing them to maximize the energy density.)

Speculation is the 18650 cell format will be replaced with something like a 20700- format (20 mm diameter, 70 mm length) so roughly 10% wider and taller.

 

[Snowdog]

Speculation is the 18650 cell format will be replaced with something like a 20700- format (20 mm diameter, 70 mm length) so roughly 10% wider and taller.

Yep and that gives you over 30% more volume, and thus 30% more capacity. Depending on current spacing they might have enough room to squeeze in nearly the same amount of cells, or say 10% less cells, they still get a net win.

 

[Thomas Edison]

Interesting

 

[SageBrush]

Back to the drawing board ...
Comment deleted

 

[LargeHamCollider]

Some good discussion, I ran my own M3 numbers well before the reveal under the assumption that Tesla's EPA range target was around 230mi. I calculated a ~55kwh battery was needed to hit that figure.

Rather than present my own numbers I'll second Rashomon's, they're very good, and I'll add that much of my data was adapted from this Tesla document (and yes it is data straight from Tesla): Roadster Efficiency and Range Excel File

Also by way of speculation I'm guessing that tesla goes from 18650 cells to 18750 cells, it's the height that constrains Tesla and keeping constant radius minimizes the reduction in cell power density that comes with increasing cell size. 8 Model S modules of 18750s would get you ~50kwh which is what I guess M3 will start with.

The argument that Tesla will want to match Bolt's 60kwh pack has some merit though.

 

[MP3Mike]

Also by way of speculation I'm guessing that tesla goes from 18650 cells to 18750 cells, it's the height that constrains Tesla and keeping constant radius minimizes the reduction in cell power density that come with increasing cell size.

They have actually said that the new cells will be ~20% larger in both directions to maximize energy density. So expect them to be something like 20750 cells.

 

[Jayc]

Can someone summarize the best guess so far with regard to battery size and price ?

I am probably going to go for the lowest spec AWD version, any thoughts on what the battery size and price of entry AWD will be ?

In the UK, from April 2017 there is going to be an annual surcharge tax imposed for cars over £40,000 and I am hoping I can just about get into Model 3 AWD and also avoid the tax.

 

[LargeHamCollider]

Can someone summarize the best guess so far with regard to battery size and price ?

I am probably going to go for the lowest spec AWD version, any thoughts on what the battery size and price of entry AWD will be ?

In the UK, from April 2017 there is going to be an annual surcharge tax imposed for cars over £40,000 and I am hoping I can just about get into Model 3 AWD and also avoid the tax.

You will be fine unless the pound seriously plummets, base plus AWD will be less than $40,000 USD per Elon tweet on AWD price.

There exists significant disagreement on base battery size, personally I'm quite confident it will be 50-55kwh; but who knows what it will be marketed as...

 

[Ubbe]

The argument that Tesla will want to match Bolt's 60kwh pack has some merit though.

That, and most important of all -to enable decent Supercharger charging times. I don't believe Tesla will settle for "good enough" when it comes to key features like that.