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Larger battery size around the corner?

DarkHelmet

Member
Aug 10, 2018
81
123
West Coast
There’s a diminishing return on increasing the battery pack. As weight goes up, the energy required to move that weight goes up exponentially... it’s not linear.

A combination of lighter weight materials, engineering, battery chemistry improvements, etc will all combine to create much bigger improvements than simply slamming more cells in. A lot of the same principles apply to aviation... aerodynamics, weight, power plants, materials, etc.

There was a great NOVA special recently, which is on Netflix about the looming battery technologies, and there’s some really promising stuff around the corner!!!
 

DoctorVenkman

Member
Jul 29, 2018
428
578
Los Angeles
There’s a diminishing return on increasing the battery pack. As weight goes up, the energy required to move that weight goes up exponentially... it’s not linear.

Care to elaborate more on this? From what I remember of high school physics, mass is linear factor in most formulas.

F = m * a
E = 1/2 * m * v^2
P = m * a * v

etc...

Those would all imply a linear relationship. Unless I'm missing something I don't think there are diminishing returns on weight vs energy.
 

Dirk

Member
May 8, 2017
35
59
Sunnyvale, CA
I don't think bigger batteries are chasing a necessary dream at this point — a 120D would just be wasteful. I think now we have to make the motors more efficient, and find better ways to charge & cool the batteries. That would pay off more than going from 300 to 360 miles on a charge.
I don't think those things would help much.
Electrical motors are already extremely efficient (with % efficiency in the mid 90's). So, with heroic efforts, you might go from 95 to 98% but that's rather immaterial. Electric motor design is now focused on making them cheaper to manufacture, use more or less rare earth metals and improve their durability, torque characteristics, etc. As a comparison, an ICE engine barely reaches 25% efficiency! This by the way is probably a reason most ICE manufacturers are so scared of electrical motors: where is the differentiation? No more fine-tuned dual turbos to make your "driving machine" different from some Korean import. Pretty much everybody can have the same motor with excellent performance.

Cooling of batteries is already quite sophisticated in a Tesla with, I would assume, very little to improve on.

Charging speed and capacity of batteries are important though but both would require some major breakthroughs and new cell chemistry. The time to charge your Tesla or the time to charge your phone or portable are pretty much the same: the Li-Ion chemistry defines a maximum charge rate and it does not make a difference whether you have one small battery or 8000 of them, wired together. That's why I just have to laugh when I see those press releases where some company claims to charge their (future, not yet built, but great looking on a render) car in "10 minutes".
 

DarkHelmet

Member
Aug 10, 2018
81
123
West Coast
Care to elaborate more on this? From what I remember of high school physics, mass is linear factor in most formulas.

F = m * a
E = 1/2 * m * v^2
P = m * a * v

etc...

Those would all imply a linear relationship. Unless I'm missing something I don't think there are diminishing returns on weight vs energy.

Simple math using a model X...

Using round numbers, It’ll go let’s say 250 miles on 100kwh at 6000lbs. That’s 400 wh/mile or 15wh/lb/mile

If you double the battery capacity to 200kWh, that’s another 1400 lbs all things being equal. 7400 lbs at 15wh/lb/mile is now 494.3 wh/mile with a 200kWh battery nets you 404 miles of range.
 

NoBeard

Member
Jun 18, 2018
328
501
McLeod HIll, NB
So what kind of battery pack are they putting in the Semi? If it's such a direct line between weight and range, I wonder how that can work without putting some redonkulous battery pack in there, but that creates the same problem all over again. Isn't the formula more complicated and related to acceleration required from stop, power for climbing, regen when decending and less about straight weight to range?
 

XHabjab

Helping to end the ICE Age
Feb 25, 2018
665
1,392
Georgetown TX
I don't think bigger batteries are chasing a necessary dream at this point — a 120D would just be wasteful. I think now we have to make the motors more efficient, and find better ways to charge & cool the batteries. That would pay off more than going from 300 to 360 miles on a charge.
I totally know how you feel, but the truth is the majority of Americans' round-trip commutes are less than 300 miles a day.
The majority of Tesla cars (MS and MX at least) are not commuter cars.

My car only goes about 240 miles between charges and I'd by far prefer at least 400, on par with typical ICE vehicles. If there was a 500 mile option, I'd buy it. I am a traveller, not a commuter.

This is partly a marketing decision, but mostly requires changes in battery technology. It is not achievable with motor or electric/electronic changes.
 

cwied

Member
Jan 13, 2015
887
643
San Mateo, CA
Simple math using a model X...

Using round numbers, It’ll go let’s say 250 miles on 100kwh at 6000lbs. That’s 400 wh/mile or 15wh/lb/mile

If you double the battery capacity to 200kWh, that’s another 1400 lbs all things being equal. 7400 lbs at 15wh/lb/mile is now 494.3 wh/mile with a 200kWh battery nets you 404 miles of range.

Off the top of my head, here are the actual forces you have to counteract to move the car:
1. Air resistance - proportional to frontal area and square of speed.
2. Rolling resistance - proportional to weight and speed
3. Drivetrain friction - proportional to speed and torque
4. Road gradient - proportional to weight and speed
5. Acceleration - proportional to weight

If you drive at a constant speed on a flat road, only the rolling resistance is proportional to weight. The biggest factor - air resistance - is not dependent on weight at all.

It's clear that adding weight adds energy cost, but I think it's less than linear, not to speak of exponential.
 
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DarkHelmet

Member
Aug 10, 2018
81
123
West Coast
Off the top of my head, here are the actual forces you have to counteract to move the car:
1. Air resistance - proportional to frontal area and square of speed.
2. Rolling resistance - proportional to weight and speed
3. Drivetrain friction - proportional to speed and torque
4. Road gradient - proportional to weight and speed
5. Acceleration - proportional to weight

If you drive at a constant speed on a flat road, only the rolling resistance is proportional to weight. The biggest factor - air resistance - is not dependent on weight at all.

It's clear that adding weight adds energy cost, but I think it's less than linear, not to speak of exponential.

You’re right, all those things are factors as well, but between the two cars I postulated aerodynamics is a constant (power power required is a square of the speed gained, double the speed quadruple the power required). The rest would take way too much physics to compare but also increase in a non-linear fashion with weight, which is why I broke it down into energy consumed per lb/mile. This is all assuming 7400 lbs didn’t break your model X :)

FWIW I was an aeronautical engineering major in college.
 
Last edited:

Kenriko

Former Vendor
May 5, 2016
1,050
1,398
Bay Area, Austin, Miami
This is my guess/speculation.

Elon said they had a new design for the standard range Model 3 pack that is 1) lighter 2) longer range.

I'm thinking that they are going to make horizontal bandoliers which will make the pack vertically shorter in the Model 3 SR and at the same time allow them to use those same modules in the current S/X packs since the 2170s are taller than the 18650s the only way for them to fit them without a drastic pack redesign (and resulting height/clearance issues) is to place them horizontally.

Total KWH might stay the same or get a slight bump but by using 2170s will allow faster charging on V3 superchargers which have already been confirmed to require the newer batteries and maybe end up with a weight reduction which would also increase range.
 

Peteski

Active Member
Oct 2, 2017
3,539
2,403
UK, Milton Keynes
Tesla is trying to move all their inventory also saying that free unlimited supercharging is going away in September. Also from experience, when I was purchasing my MS 85D a few years ago I heard there was a 90kW battery that will be offered as standard as they were phasing out the 85 and it was just a rumor. All Tesla employees sore it was just a rumor and sure enough 3 months after my purchase the 990 is available.

Not much of a basis for a 120 kWh battery other than pure speculation. I could come up with dozens of alternative speculative rumours based on this. But I think the main reason why a larger battery is unlikely (at least in the short term) is down to weight and cost. When a 120 kWh pack can be made for the same cost, size and weight as a current 100 kWh pack then it might well appear. Most likely on an all new MX/MS platform around 2022. Until then I think 100 kWh is the benchmark and that's pretty much in line with all the upcoming competition in the next few years. I haven't heard of anyone planning a bigger battery than 100 kWh, have you?
 

bob_p

Active Member
Apr 5, 2012
3,734
2,943
There is a point of diminishing returns on battery pack size, with a decreasing number of potential customers needing the extra range - and willing to pay for it.

For S & X, there are two groups of customers that could use a larger battery pack:
  • Round trips that are beyond the range of the battery pack, without a supercharger on the route. With the expanding supercharger network, this is likely a pretty small percentage of potential customers.
  • Model X owners towing trailers (no more than 5000 lbs), which reduces the range by 30-50%. Based on forum posts, this appears to be a very small percentage of Model X owners.
For the Roadster 2.0, there's a 3rd group of customers needing a larger battery pack - who want a car that can drive for a reasonable distance and very high speeds (which quickly consumes the charge).

Musk made a comment when the 100 packs were introduced that they may not introduce larger packs. Another manufacturer appears to have reached the same conclusion.

While there are some Tesla customers who could use a larger battery pack in the S & X, what's more likely is a change in battery packs to reduce manufacturing costs (by shifting to the Model 3 battery design) and supporting faster charger (V3 supercharging could be introduced in the next 6-12 months).

We've looked at purchasing a travel trailer with our Model X - and having a larger battery pack would be nice, though with the reduced speeds when towing a trailer (typically 55 MPH), a 100 battery pack will still go about 3 hours of driving between charges, which is about as long as our human passengers are willing to go between stops...

For anyone considering delaying an S/X purchase to get a larger battery pack - you may have a long wait. However, if V3 supercharging is released soon - and that requires a change in the battery pack, that might be worth waiting for.
 
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spectrum

Member
Jun 17, 2018
482
515
Atlanta
The majority of Tesla cars (MS and MX at least) are not commuter cars.

Lol. I can't believe you are so self-centered that you think all Tesla owners are travelers like you. Every Tesla owner I've ever known (dozens) use it as their daily driver and their work commute. I don't think I've ever seen a Tesla (other than the Roadster, of course) that was used for only recreation.

The world doesn't revolve around you, and disagreeing with my posts doesn't change that.
 

AMPUP

Member
Mar 27, 2014
638
230
Dunn Loring, VA
Lol. I can't believe you are so self-centered that you think all Tesla owners are travelers like you. Every Tesla owner I've ever known (dozens) use it as their daily driver and their work commute. I don't think I've ever seen a Tesla (other than the Roadster, of course) that was used for only recreation.

The world doesn't revolve around you, and disagreeing with my posts doesn't change that.

Whilst I use my S for commuting I also use it to travel to family 350 miles away, that requires a stop for 45 mins or more whereas my wife’s Ice can get there in one go.. Utilizing the 3 battery tech with a 100 pack and the 3’s more efficient drivetrains I’m pretty sure they can get the S/X to 400+ miles, that’s the magic number for all people to not worry about range anxiety (especially in the winter) and If they upgrade the interior then they are at the true tipping point of attracting all Lexus and 5/7 series BMW drivers. They will have to do something soon else sales of the S/X will drop off. Americans like to travel the roads holidays, long weekend getaways, vacations etc. those people aren’t commuting they are traveling 400+ miles to see family. Spending years rolling out the 3 could cost them on the S/X. I for one have considered trading ‘down’ to a P3D, it has better range, is faster than my current S (now), the interior is refreshing and it’s half the price of a P100D... However, I just can’t get past how unattractive it is from the back. My 0.2 of course...
 

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