A look at the new Tesla cells

11989 Views 124 Replies 14 Participants Last post by Kevin Sharpe, Dec 1, 2017

PhantomPholly

Discussion Starter · May 28, 2017

2170 cells replaces 18650 standard at the Gigafactory.

Doubtful they will be available to DIY community, though. The big boys will probably contract full production.

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Duncan

· #101 · Nov 29, 2017

Modern manufacturing drives prices down towards the material costs
So $65/kwhr in materials - sounds a bit high to me
$100/kwhr total cost - if materials are $65 then that is a bit conservative as well

Musk has a history of under promising and over delivering on everything except time frames

Kevin Sharpe

· #102 · Nov 29, 2017

Duncan said:
Musk has a history of under promising and over delivering on everything except time frames

Many examples where that's untrue... one obvious example is the Roadster 3.0 upgrade, the majority of which never happened, and the one that did (battery replacement) looks like a $30,000 disaster

https://teslamotorsclub.com/tmc/posts/2402353/

Kevin Sharpe

· #103 · Nov 29, 2017 (Edited)

aeroscott said:
Energy density is a given with time at this point.

Do you believe that Tesla will deliver a 200kWh battery, that occupies less volume than today's Model S battery, in two years time?

aeroscott

· #104 · Nov 29, 2017 (Edited)

Kevin Sharpe said:
Do you believe that Tesla will deliver a 200kWh battery, that occupies less volume than today's Model S battery, in two years time?

Thanks for getting my clumsy statement.
It doesn't have to get much better . Say the truck losses 2000 lbs do to battery weight , but saves on fuel,maintenance, etc. The loss of some cargo $ wouldn't be big deal. The State could come in and say if ev powered you could go 82,000 lbs.
With less vibration ,more even distributed power to the road and a safer truck, everybody would win including better road conditions.
Incremental increases , yes always. 2x in 2 years not likely. But 2x my not be needed incremental my be enough.
Volume is not the issue, look space under the trailer

brian_

· #105 · Nov 30, 2017

aeroscott said:
... The State could come in and say if ev powered you could go 82,000 lbs.
With less vibration ,more even distributed power to the road and a safer truck, everybody would win including better road conditions.

I doubt engine vibration has any relevance to load limits; I don't think regulators even care whether an axle is driven or not.

More even power distribution? I don't think so: conventional trucks use simple differentials in each axle so both drive wheels get the same drive torque; the two axles are connected directly so they run at the same speed regardless of traction. While individual motors per wheel (or dual wheel set) are a good thing, there's nothing about the conventional setup which hurts the road. I find it interesting that Tesla chose not to power the front axle, a configuration which is problematic with a engine but would be easy (but not so cheap) in a battery-electric vehicle.

I don't think there's a precedent for allowing higher (and thus more destructive to the road) axle loads as a reward for a safer vehicle. For instance, ABS doesn't earn a higher limit, as far as I know.

With more axles, total combination weight can be increased without exceeding the allowed axle weight, and this is already considered by the various limits allowed for various truck and trailer configurations. Perhaps some heavier combinations could be allowed with stability control, but individual control of drive wheels on the tractor is unlikely to be enough to be significant to the stability of multi-trailer trains. When there are 9 axles on a rig and one is steering, improved control of two of them probably isn't as important as control of the other six.

aeroscott said:
Volume is not the issue, look space under the trailer

I would agree, except that the trailer is not the truck. Even if high-voltage high-current wiring connections were acceptable between them, the tractor (truck) and trailer are often not even the property of the same owner. Only select specific operations could tolerate having to use expensive specialized trailers to make the tractor workable.

Of course there are also trailers which do not have space under the deck which is suitable for a battery pack - primarily some types of bulk carriers, and the lowest of lowboy equipment carriers.

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Karter2

· #106 · Nov 30, 2017

Kevin Sharpe said:
I think that's the problem

All of this would be so much more believable if Tesla actually demonstrated a significant improvement in capacity rather than a change in packaging which, while important, cannot deliver the 200kWh Roadster 2 battery

Do we know for certain that the preproduction R2s as demonstrated do not have 200kWh packs ?
And if not, what size pack do we think they have ?

Karter2

· #107 · Nov 30, 2017 (Edited)

aeroscott said:
If the batteries are as cheap as I think and Elon hinted at, and mining and refining and production taking advantage of $.05/w solar cells . That will drive the cost of the batteries lower without improving cell energy density. Energy density is a given with time at this point.

$0.05/W solar cells ?... Where do they come from ?
(Solar City i guess ?...and explains why they lose so much money !)
No such cell cost is available commercially.
Oh and didnt you hear?.... The solar roof on the GF has been scrubbed.!
The last time we had a significant increase in energy density, was probably 6 years ago ..when Panasonic pushed the 18650 cell capacity up to 3.4Ah from 3.1Ah (+10%)
Energy density increase has only ever been an incrimental progress, major changes of 20%+ have never been seen,...even from Tesa.
So, unless Musk is going to Pull a rabbit from his hat,...i wont be holding my breath !

aeroscott

· #108 · Nov 30, 2017

In construction equipment they use rubber tired vibrator equipment compress asphalt and sub strait . Add vibration to a load it will increase compression .
I had a 10' wide truck crane ,it was allowed more weight(buy cal trans inspector) because of the increased distance between loads (width) ,same applies to axles , more spread more weight per axle.
The Cal trans job is to manage the roads and protect them from undo damage and save lives, they study every aspect that they can think of .
I've taken a class from their metallurgist.
This takes critical thinking .

aeroscott

· #109 · Nov 30, 2017

Karter2 said:
$0.05/W solar cells ?... Where do they come from ?
(Solar City i guess ?...and explains why they lose so much money !)
No such cell cost is available commercially.
Oh and didnt you hear?.... The solar roof on the GF has been scrubbed.!
The last time we had a significant increase in energy density, was probably 6 years ago ..when Panasonic pushed the 18650 cell capacity up to 3.4Ah from 3.1Ah (+10%)
Energy density increase has only ever been an incrimental progress, major changes of 20%+ have never been seen,...even from Tesa.
So, unless Musk is going to Pull a rabbit from his hat,...i wont be holding my breath !

That was EVTV on the $.05 solar cells for huge projects. I pay $.90'watt for 2 panels.

brian_

· #110 · Nov 30, 2017

aeroscott said:
In construction equipment they use rubber tired vibrator equipment compress asphalt and sub strait . Add vibration to a load it will increase compression .

Sure, but I hope a truck's diesel engine doesn't vibrate like a compactor!

aeroscott said:
I had a 10' wide truck crane ,it was allowed more weight(buy cal trans inspector) because of the increased distance between loads (width) ,same applies to axles , more spread more weight per axle.

Yes, axle spacing, axle width, and tire size all matter. Tesla is not changing any of these features, and electric drive doesn't inherently change any of them, so that doesn't let them carry more battery weight (to get us back closer to the "new Tesla cells" topic, rather than "Tesla's new truck")

aeroscott said:
This takes critical thinking .

Yes, we could use more of that around EV announcements.

brian_

· #111 · Nov 30, 2017

Karter2 said:
Do we know for certain that the preproduction R2s as demonstrated do not have 200kWh packs ?
And if not, what size pack do we think they have ?

Given the demonstration time of a few seconds of acceleration at a time, and presumably minutes of driving for the event, the demo car could have any production battery (including the promised 200 kWh pack), right?

aeroscott

· #112 · Nov 30, 2017

Brian, you said both axles are powered at the same time . There is a air valve (to engage 2nd drive axle) on every 3 axle tractor( road), never engage on dry/hard roads . This is true of all 2 driven axle machines, unless they have a 3ed differential .

brian_

· #113 · Nov 30, 2017

aeroscott said:
Brian, you said both axles are powered at the same time . There is a air valve (to engage 2nd drive axle) on every 3 axle tractor( road), never engage on dry/hard roads . This is true of all 2 driven axle machines, unless they have a 3ed differential .

Hmmm... the second axle may be disconnectable more commonly that I thought, but certainly they are driven a substantial amount of time (truckers don't like to pay for equipment that they don't use), and when disconnected you just have a 6x2 configuration... which isn't a problem for the many vehicles operated that way (such as every intercity coach).

Looking at the Dana Spicer lineup (a typical major axle supplier), it appears that all of their tandem drive sets have an interaxle differential, so instead of being locked in speed (both axle the same) when engaged they equally distribute torque... so they're even better than I thought.

Thanks for the tip.

Being a 6x4 full-time just doesn't seem like a feature which would matter to road load limits, and doing it with separate motors seems even less relevant now. No free ride for the extra-heavy electric truck.

Kevin Sharpe

· #114 · Nov 30, 2017 (Edited)

Karter2 said:
Do we know for certain that the preproduction R2s as demonstrated do not have 200kWh packs ?
And if not, what size pack do we think they have ?

brian_ said:
Given the demonstration time of a few seconds of acceleration at a time, and presumably minutes of driving for the event, the demo car could have any production battery (including the promised 200 kWh pack), right?

I don't think we know anything for certain about the battery used in the Roadster prototype demonstrated at the event.

Lot's of interesting work going on trying to calculate the size of the Roadster... several people have used pixel counting and know references like size of tyre fitted... the attached image (from here) seems to be typical of the end results

Ultimately this all hinges on whether you believe what Musk said on the day

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aeroscott

· #115 · Nov 30, 2017

Could just be a S with 2 100Kwh packs. give it 3 big motors and a hipper cooling system. Nothing stoping them from using lipo battery.
A Lotus type tub is a easy one off build with enhanced S parts,CC brakes.
If it's a little heavy so what , add more power.

Kevin Sharpe

· #116 · Nov 30, 2017 (Edited)

aeroscott said:
Could just be a S with 2 100Kwh packs.

Most people have concluded that the Roadster prototype does not have enough height for a double layer battery based on 18650/2170 cells... some people reported "sitting high up" during the test drive so maybe some batteries are under the seats but IMO this car does not have enough space for 200kWh today.

aeroscott said:
If it's a little heavy so what , add more power.

How much power do you need *today* to get a 200kWh battery, three motors, and four people to 60mph in 1.9 seconds, 100mph in 4.2 seconds, and then top out above 250mph without (presumably) shifting?

With enough time and resources almost anything is possible but I think this car requires a step change in battery technology that Tesla may or may not have achieved. Personally I'll be keeping my cash in my pocket, especially until we see the reality of Model 3 production

Solarsail

· #117 · Dec 1, 2017

One theory is that there is no gear-changing transmission - just each of the two rear motor having a different reduction ratio - one for low speed high torque, and the other for high speed. Of course with a differential.

I think even at the predicted capacity of 4.9Ah for a 2170 cell (which would be the same energy density as the 18650 cell), it should be possible to place the 2nd 100 kWh in the R2. Also note that for best performance, you do not want to have 200 kWh capacity, but rather 100 kWh capacity to save on weight - as long as the 100 kWh battery can produce the required power.

But if you had to fit 200 kWh with today's cells, there is room in the frunk, and also the trunk, and also double layering under the rear passenger seats. It won't be pretty, but I think it is doable.

brian_

· #118 · Dec 1, 2017

I find it interesting that the explanation of unlikely battery performance is a series of mechanical design ideas... in a thread specifically about the battery cells.

Solarsail said:
One theory is that there is no gear-changing transmission - just each of the two rear motor having a different reduction ratio - one for low speed high torque, and the other for high speed. Of course with a differential.

If I understand this correctly, you are suggesting two motors geared (at different ratios) to the same input of a differential... just so that each motor can be used at different road speeds, while the other one serves as very expensive and rapidly spinning ballast. Both motors would need to handle the highest road speed (assuming that no clutch is used); the one which has more gear reduction would spin faster... and that's the one which would presumably be expected to be more effective at low speed.

I hope (and expect) that Tesla has a better solution than that.

It seems certain that there will not be a multi-speed transmission - Tesla Motors failed miserably when they tried that the first time, and has even had trouble with their single-ratio gearboxes. I've never seen a suggestion from Tesla Motors that they are changing their approach, but perhaps someone who watches them more closely has.

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Solarsail

· #119 · Dec 1, 2017 (Edited)

Yes, except that all three motors will be powered simultaneously when high torque is required. The rear two motors having different reduction ratios, will provide best torques at different vehicle speeds. There will be considerable overlap between the two rear motors. The front one will be mid-range, while the two rear motors will supply low-speed and high-speed torque and power, due to their different reduction ratios. Both will drive the differential.

With a 2-speed gearbox, it is possible to eliminate the rear differential, and obtain even more torque because both motors will avoid the high-speed inefficient region. But then two gearboxes would be required. So I am a bit skeptical that they would take this approach. If they were going to use just one gearbox in the rear, then why have two motors? Conceptually a 2-speed gearbox using a planetary gearset is simple. But if Tesla is already having difficulty with the reduction gearbox, then woe be on them to attempt a 2-speed box.

I wonder if it is beneficial to mechanically disengage the high-reduction ratio motor at speeds of let's say above 150 mph. This would allow the two rear reduction ratios to diverge. Assume in the current Model S, the ratio is 10. In the R2, they could be 14 and 7. But if the high-ratio motor could be disengaged, then they could take it to 16 and 6, and cover a wider operating range with more torque at the low end.

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brian_

· #120 · Dec 1, 2017

Solarsail said:
With a 2-speed gearbox, it is possible to eliminate the rear differential, and obtain even more torque because both motors will avoid the high-speed inefficient region. But then two gearboxes would be required.

Yes, separate motors for each wheels means separate transmissions (one per motor). If two ratios are needed, that's two 2-speed transmissions... and that's just one end of the car. This is what Rimac does in the rear of the Concept_One.

Solarsail said:
So I am a bit skeptical that they would take this approach.

I, too, doubt they're doing this (separate motors, each with a 2-speed gearbox), just because I don't see them doing any two-speed transmission.

Solarsail said:
If they were going to use just one gearbox in the rear, then why have two motors?

I don't know why they would use two motors into a common gearbox. Two motors have been mentioned in some publications, but is there any reason to believe there is a common gearbox, or a two-speed gearbox? Other than belief that their new motors (presumably the PM design, shared with the Model 3) will be unable to deliver the claimed performance... or would demand too much f the battery (thus the gearing discussion in the battery cell topic)?

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