# A look at the new Tesla cells



## PhantomPholly (Aug 20, 2008)

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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## Karter2 (Nov 17, 2011)

There is a lot of outdated and incorrect information in that report and video.
3000mA vs 6000mA electrical charge ??
97cc volume capacity ??
What is all that about ?
21700s and 20700s have been available in various forms for a while in portable toolpacks, and even commercial Ebike packs ( Panasonic released in 2015).
Also available individually/loose via reputable retailers.
Samsungs 21700-30T is rated for 30 amp continuous discharge, 50 A burst. (Lygte tested)
Teslas cell will most likely again be a compromise of more capacity, longer cycle life, but without the extreme power ability.


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## PhantomPholly (Aug 20, 2008)

Karter2 said:


> There is a lot of outdated and incorrect information in that report and video.
> 3000mA vs 6000mA electrical charge ??
> 97cc volume capacity ??
> What is all that about ?


As I read it, the extra volume was minimal while the energy captured was almost doubled by tweaking both the production process and some of the materials. It isn't just about the form factor.



> 21700s and 20700s have been available in various forms for a while in portable toolpacks, and even commercial Ebike packs ( Panasonic released in 2015).


The article said 2170 more than once, which was confusing because of the missing zero on the end, but I believe you are correct that the form factor has been out there previously. However, those are NOT the same batteries as Teslas. Tesla is doing something proprietary with their Gigafactory batteries to get that energy density.



> Teslas cell will most likely again be a compromise of more capacity, longer cycle life, but without the extreme power ability.


When you have a 100Kwh pack in a car, you don't need tremendous C rates to operate the motor at peak power, so that would make sense. On the other hand, until we get all the numbers reported on their proprietary formulation it may be premature to speculate that they sacrificed power density for greater energy density - they may have managed to get both.


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## Karter2 (Nov 17, 2011)

??? Did you read the script or watch the video ?
That article , mostly transcribed from the included video is based on old info and put together by someone who doesnt know what they are talking about.
What is a charge capacity of 3000mA or how do you get a a cell volume of 97 cc from a 21700 ? (Its 24.2cc)
And "tested at 5750- 6000mA output ???.....is not 6Ah capacity, its just BS !!
There is nothing extra special in Teslas 21700, its just a larger format of their existing cells, possibly with a different Cathode for good cycle life, .
It is 50% bigger by volume, but not in energy capacity with 4.75 Ah.


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## PhantomPholly (Aug 20, 2008)

First and foremost, I am not here to make excuses for bad writing.

So I watched both stupid videos and I agree the dumb narrator was clearly pulling some stuff out of his nether regions. The numbers that seem to be "hard" are these:



Larger form-factor (1.333x volume, not 1.5x) somehow helps facilitate cheaper production and also somehow factors into stuffing more energy into a pack. Good.
Musk (his voice) and his associate on tape claim a 10-15% improvement in energy density due specifically to chemistry changes (whether from anode, cathode, or electrolyte changes not specified). Since 18,650 is specified as 250wh/kg, that would put the new cells between 275-287.5wh/kg for JUST the chemistry.
They also claim cost advantages for the larger cell, and an ability to pack more in with more battery and less structural supporting materials. This in turn implies a synergy of factors giving the final pack a higher energy density than just chemistry changes alone would provide, and at lower cost. In other words, the final installed pack might have, say, a 30% energy density than the old pack. If the old pack was 300 miles, that would be nearly a 100 mile improvement in range for similar price. Pretty good.
The numbers for 3,000mA and 5,750-6,000mA are probably meant to mean maximum usable discharge rate. If you get double the discharge rate from 1.33x the volume, that implies substantially improved energy density. Also good.

I don't see anything in these multiple incremental improvements to be derisive about other than the poor reporting.


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## Karter2 (Nov 17, 2011)

Sorry but...
21700 is 45% more volume than 18650.
Energy Capacity of the 21700 would need to be 5Ah+ to even have the same energy density. But these new cells have been reported to be 4.75 Ah.
Im sure you are aware that Teslas most recent 18650 cell , in their largest 100kWh pack, has to supply 6-7C (20A) for short periods (Ludicrous mode) and can continuously supply 10 amps.


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## evlithiumbattery (Jun 20, 2017)

21700 cells is a tremendous battery cell, when can they available on the market? another battery company would provide the similar battery very soon


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## riba2233 (Apr 29, 2015)

They are available for at least half a year now:

https://eu.nkon.nl/rechargeable/other/sanyo-ncr20700b-lithium-battery.html


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## Karter2 (Nov 17, 2011)

Several power tool manufcturers are also using 21700 cells now.


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## PhantomPholly (Aug 20, 2008)

I'd be curious to see someone do some actual comparison testing (performance, life) between the Tesla cells in that form factor and others such as the Sanyo pictured above.


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## riba2233 (Apr 29, 2015)

Panasonic bought Sanyo, and Panasonic makes cells for tesla, so they are based on the same chemistry and probably have similar life expectation.


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## PhantomPholly (Aug 20, 2008)

riba2233 said:


> Panasonic bought Sanyo, and Panasonic makes cells for tesla, so they are based on the same chemistry and probably have similar life expectation.


That is a theory. It is not fact. Tesla has patents on it's chemistry, no one else can use it.


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## riba2233 (Apr 29, 2015)

Really? Didn't tesla open their patents? Also, what you are saying could be true for these new cells, but in past they've used regular panasonic 18650be cells and they are available to anyone.


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## PhantomPholly (Aug 20, 2008)

riba2233 said:


> Really? Didn't tesla open their patents? Also, what you are saying could be true for these new cells, but in past they've used regular panasonic 18650be cells and they are available to anyone.


Well that's a fair question, and they did stop pursuing patents. I suppose that if Sanyo doesn't disclose use of a patent on the cell we can't know. On the other hand, if Tesla's chemistry is fairly new it seems pretty unlikely others are using it already - changing the guts of a battery requires some expensive changes to the assembly line and to the vendors from whom they source materials (and who would be the vendor creating Tesla-clone anodes and cathodes?) - so they might not want to pay for that unless they believe that the improvement is worth the cost of the switch over.


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## Karter2 (Nov 17, 2011)

If Tesla have any "Secret Sauce" to build into their new cells, they have been uncharacteristicly shy of even hinting about it ?
(Remember this is the guy who has said he is going to put people on Mars in the near future )
Also, since they use large capacity packs (40kWh+), Tesla will likely focus on capacity, safety, and cycle life factors, rather than any major step forward in output or charge rate, so a 3-4C rate discharge is fine for them.
However, if someone is thinking of using Tesla cells in a low capacity pack (<20kWh), then those cells may not be the best choice.


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## PhantomPholly (Aug 20, 2008)

Karter2 said:


> If Tesla have any "Secret Sauce" to build into their new cells, they have been uncharacteristicly shy of even hinting about it ?


I was going by the video, in which Musk plainly said there were changes in the chemistry which helped increase the energy density. Not being psychic, I can't tell you whether he was being honest.... 



> (Remember this is the guy who has said he is going to put people on Mars in the near future )


lol, define "near future?" You never know, he may do it...



> Also, since they use large capacity packs (40kWh+), Tesla will likely focus on capacity, safety, and cycle life factors, rather than any major step forward in output or charge rate, so a 3-4C rate discharge is fine for them.


I would hope so...



> However, if someone is thinking of using Tesla cells in a low capacity pack (<20kWh), then those cells may not be the best choice.


Absolutely agree -without spec sheets we can't know if they are "better" for a given application.


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## Karter2 (Nov 17, 2011)

With 50+% more volume in the new cell, it ought to be possible to get over 5Ah capacity in. But i am willing to bet they have not reached that figure.
Eventually, someone will get hold of a few cells to reveal all.


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## Solarsail (Jul 22, 2017)

Karter2 said:


> Teslas cell will most likely again be a compromise of more capacity, longer cycle life, but without the extreme power ability.


The only people interested in extreme power output are the RC hobbyists, and one of a kind applications. EVs have too many cells in parallel that cell power output is not an issue at all.


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## Solarsail (Jul 22, 2017)

riba2233 said:


> They are available for at least half a year now:
> 
> https://eu.nkon.nl/rechargeable/other/sanyo-ncr20700b-lithium-battery.html


But this is 20700 and not 21700.


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## Karter2 (Nov 17, 2011)

Solarsail said:


> The only people interested in extreme power output are the RC hobbyists, and one of a kind applications. EVs have too many cells in parallel that cell power output is not an issue at all.


 Not strictly true..dependig on the definition of "extreme"..
Cordless power tools put huge loads on the batterys, (previously 18650s, but now switching to The 20700 and 21700 cells).. With 15-20C not uncommon.
Ecigs and high power flashlights also demand high currents from small single cell , packs.
Even tesla push their cells beyond normal limits when they pull 1500 amps from a 74p cell group !


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## Solarsail (Jul 22, 2017)

Karter2 said:


> Even tesla push their cells beyond normal limits when they pull 1500 amps from a 74p cell group !


Well, with the 100DL, the 580 kW load will be distributed over 85 cells. That is 17 A per cell or 5C. The heat generated with a 100 mOhm internal resistance is phenomenal. It will be about 30 W per cell, or 240,000 W for the pack. This is not coolable. The pack will glow after a minute! Even at 50 mOhm, the thermal energy produced is 120 kW (plus all the heat from the connections). This can be sustained for only a few seconds.

No wonder the 100DL wins the 0-60 but loses the 1/4 mile because it has to throttle itself back or you get destroyed cells. Also the lack of a 2nd gear in the Tesla causes the motor to operate in an inefficient region, draining more current.

The average user probably never exceeds 2C.


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## major (Apr 4, 2008)

Solarsail said:


> ... Also the lack of a 2nd gear in the Tesla causes the motor to operate in an inefficient region, draining more current.
> ...


Hi Sol,

You think you could show us a quantitative analysis or reference supporting your statement?

Thanks in advance,

major


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## riba2233 (Apr 29, 2015)

Internal resistance is closer to 40-42 mohm, but yeah, still a lot heat at max power levels. That's why it can only be used as burst power, their efficiency drops to around 65%.


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## major (Apr 4, 2008)

riba2233 said:


> Internal resistance is closer to 40-42 mohm, but yeah, still a lot heat at max power levels. That's why it can only be used as burst power, they efficiency drops to around 65%.


Hi riba,

A battery's maximum power output is at half its open circuit voltage so discharge efficiency is 50%. For a resistive load that would occur when load resistance equals the internal resistance of the battery. At maximum power the power converted to heat in the battery is equal to power delivered to the load.

major


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## Solarsail (Jul 22, 2017)

major said:


> Hi Sol,
> You think you could show us a quantitative analysis or reference supporting your statement?
> major


This must be a trick question?  The torque curve is pretty flat until it reaches a threshold speed whereby it declines by speed. Namely the motor efficiency drops rather steeply with higher speeds. The decline in torque is faster than the increase in RPM and thus power drops and efficiency decreases and motor thermal energy increases.

So in order to have a faster car, the RPM must be dropped below the threshold, which means the gear should be increased. Thus we need at least two gears.

If you provide me the spec sheet for Tesla's motor, I will try to work it out.


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## Karter2 (Nov 17, 2011)

You dont need a motor spec when you have a dyno readout !...
https://teslamotorsclub.com/tmc/att...parison-graph-zoomed-to-tps-eq100-png.112464/
You can see the torque starts to drop off at about 35 mph, But the power stays virtually constant all the way up to the 95mph limit of the trace.
..but sure, even that speed is only 2/3 of the motor max rpm (18k rpm) so what happens in that rpm range is not measured, though it has been reported that the power stays at that level before starting to drop off at 120 mph (~14k rpm).


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## major (Apr 4, 2008)

Solarsail said:


> This must be a trick question?  The torque curve is pretty flat until it reaches a threshold speed whereby it declines by speed. Namely the motor efficiency drops rather steeply with higher speeds. The decline in torque is faster than the increase in RPM and thus power drops and efficiency decreases and motor thermal energy increases.
> 
> So in order to have a faster car, the RPM must be dropped below the threshold, which means the gear should be increased. Thus we need at least two gears.
> 
> If you provide me the spec sheet for Tesla's motor, I will try to work it out.


Hi Sol,

Mr. Karter2 has been kind enough to supply the data, so please provide the analysis to substantiate your statement concerning inefficient operation and draining current due to direct drive. I just don't see it.

major


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## brian_ (Feb 7, 2017)

Solarsail said:


> The torque curve is pretty flat until it reaches a threshold speed whereby it declines by speed. Namely the motor efficiency drops rather steeply with higher speeds. The decline in torque is faster than the increase in RPM and thus power drops and efficiency decreases and motor thermal energy increases.


The torque does drop after the threshold (as it does with any motor), and with a brushed DC motor it drops rapidly and all of the above applies. With an induction motor or PM AC motor the torque tends to drop in proportion to speed so power tends to be reasonably constant for a substantial range of speed above the threshold.


Karter2 said:


> You dont need a motor spec when you have a dyno readout !...
> https://teslamotorsclub.com/tmc/att...parison-graph-zoomed-to-tps-eq100-png.112464/...


Thanks - excellent illustration 

Dropping torque doesn't necessarily imply dropping efficiency. Anyone who wants to put in the effort can compare the total mechanical power (the sum of front and rear power; power for each axle is the product of torque and speed). The "power" curve on the graph must be electrical power, since it is not zero in the brake-stand stall leading up to the launch (at zero on the time scale); that means that any change in efficiency could be calculated (but not absolute efficiency, because the actual power is not known, unless you know the tire rolling radius).

I found the discussion in thread in which this graph was posted (_Chassis CAN Logging To ASCII Text Plus Graphing_, page 9), and the data appears to be all from the car's internal network, collected by CAN messages... so there's likely no real torque measurement at all.

I wondered about the validity of the torque data, since some dynamometer methods are questionable, (although I eventually realized that there's no dyno here) and in this case the torque values are inconsistent: from 415 somethings @ 35 mph to 190 @ 70 mph would make sense for the front because it would be about a 10% power drop, but from 200 somethings @ 35 mph to 115 @ 70 mph would be about a 30% power _increase_. If the real mechanical power is almost constant, the almost constant electrical power draw suggests that efficiency is roughly unchanged.

I think the torque data might be a little flaky, since the front does not drop enough with the speed increase to be plausible with constant power, although the car could be shifting power to the front with increasing speed, which makes physical sense. The electrical power data is at least plausible, because to accelerate the two-ton mass accelerating at 10 m/s2 through 50 km/h or 30 mph takes 280 kW, the car weighs somewhat more than two tons, and there is rolling and aero drag... so the 400+ kW of power consumption may be a little high but at least is in the right ballpark.

I can see why Tesla Motors gave up on multi-ratio transmissions after their first attempt failed (in the Roadster). They're now putting so much power in these cars that the speed-dependent power under the threshold (which corresponds with 30 mph in this test) doesn't matter: the constant torque at and below the threshold is probably all the tires can handle anyway (it's accelerating at over one g up to that point), and certainly it is all that is needed. With AWD and separate front and rear motors (which is the only sensible arrangement), shifting gears could be a challenge to manage well.


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## Solarsail (Jul 22, 2017)

I think what I am saying is that the Tesla motor efficiency drops at higher RPMs. Thus it would be beneficial if the reducing gearbox which I believe is reducing by a factor of 6 resulting in motor turning at 12,000 RPM at 95 mph - were to reduce to 3 over let's say 50 mph. Then there would be more power available to the wheels as opposed to heating the engine and increasing coil resistance and more work for the cooling system. Also much less noise and better comfort.

In the chart, look at 55 mph. R_Tq for the L is 255 (whatever unit) and at 75 mph 163 and at 90 mph is 130.
55*255 = 14,025
75*163 = 12,225
90*130 = 11,700
Whatever the unit may be. You can see the power to the wheels decreasing, even though power input is almost constant. Between 55 mph and 90 mph, power input drops 3.4% while power output drops 16.6%. I believe a 10% increase in power could be achieved at 95 mph if the gear ratio were dropped from 6 to 3, and the motor RPM halved.

This would also allow Tesla to increase the reduction at lower speeds, such as from 6 to 8 and get even better acceleration. Of course it should be the user's option to decide at what speed to change the gears - i.e. there should also be a manual mode.


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## dcb (Dec 5, 2009)

yah something might be up with that chart. I cant find any permutation of mph and torque and units that adds up to anything like 500kw at the wheels at the knee or the end. Assuming 27" diameter tires.

not related to gearing per-se, that is a compromise, not a bad one either, you aren't *really* concerned about efficiency if you are driving 95+ mph, the motor is maintaining power pretty well and trading torque for rpm, like a gear change would, only a hell of a lot more smoothly and reliably.

this might shed some light, same torque-ish shape but they started at 30mph so maybe that is what is off. 920ft lbs and 588 hp, p100d, the peak torque is at about 50mph


https://youtu.be/q5HgthPgzgQ?t=326


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## Solarsail (Jul 22, 2017)

brian_ said:


> I can see why Tesla Motors gave up on multi-ratio transmissions after their first attempt failed (in the Roadster). They're now putting so much power in these cars that the speed-dependent power under the threshold (which corresponds with 30 mph in this test) doesn't matter: the constant torque at and below the threshold is probably all the tires can handle anyway (it's accelerating at over one g up to that point), and certainly it is all that is needed. With AWD and separate front and rear motors (which is the only sensible arrangement), shifting gears could be a challenge to manage well.


They are putting so much power that the cells are at the limit and can only be run for a few seconds before damage sets in, and they have to cut down on power. So that is how they lose the 1/4 mile sprint. With a higher drive reduction ratio, they can get more torque for less power at the start, and then at high speeds, less power wastage which means higher speeds. I think it was a very bad decision to drop the gearbox. A dual clutch gearbox with only two gears can be designed by their engineers in their sleep. I fail to see the challenge in shifting gears with a dual dry clutch. They will kill two birds with one shot. I am certain electric supercars will all be multi-gear.

If it is true that the 100L is drawing 580 kW - I believe this is for the motor and for all base systems and cooling, including line losses - and assuming an internal cell resistance of 60 mohm (which increases with cycle life), the current drawn from the pack is 1,475 A and heat generated by the pack, not including line thermals, is 130 kW, or about 16 W per cell. Each cell is drained at 17A which is 5C - way above the spec (2C Panasonic, 3C Tesla) I believe - unless they have a new chemistry, which they have not shared. So when Musk says "will share patents", he means, I will not patent, so I won't have to share. Or more likely, they are just overheating the cells as it is doubtful that they can collect 130 kW of heat. Hence the very short duration of maximum acceleration.

With a gearbox, many of these issues can be mitigated.


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## dcb (Dec 5, 2009)

multiple gears would only slow it down, and make it less reliable. A low power vehicle could make use of it, i.e. be able to climb a hill and have reasonable top speed, but this thing already can break traction with ease on startup and go 150+mph. I wouldn't mess with it, it does 10 second 1/4 miles! a lower gear doesn't buy you anything off the line and a higher gear doesn't buy you much.

also see my previous post.


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## Solarsail (Jul 22, 2017)

It should be noted that according to the chart, the vehicle is drawing almost 40 kW at standstill. Compare this to a Leaf's 0.5 kW base load. I would guess that this may be the result of entering Ludicrous mode and the cooling system is feverishly pre-engaged to cool down the systems and the pack, prior to the sprint.



brian_ said:


> I wondered about the validity of the torque data, since some dynamometer methods are questionable, (although I eventually realized that there's no dyno here) and in this case the torque values are inconsistent: from 415 somethings @ 35 mph to 190 @ 70 mph would make sense for the front because it would be about a 10% power drop, but from 200 somethings @ 35 mph to 115 @ 70 mph would be about a 30% power _increase_. If the real mechanical power is almost constant, the almost constant electrical power draw suggests that efficiency is roughly unchanged.


That is a good point that power may be transferred to the front wheels as it speeds up. That may explain the loss seen at high speeds in the rear train. In fact the chart indicates that the front motor is getting more efficient at higher speeds!
Front Ludicrous:
55 mph 140 = 7700
90 mph 93 = 8370
So there has been a gain of 8.7%. Obviously the power is being shifted to the front. But not as much as the rear is losing power. Also note the base load of 40 kW. So that would mean that the loss is actually larger as a percentage of power consumed by the motors.


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## Karter2 (Nov 17, 2011)

Solarsail said:


> I think what I am saying is that the Tesla motor efficiency drops at higher RPMs. Thus it would be beneficial if the reducing gearbox which I believe is reducing by a factor of 6 .


 The Tesla transmission has a 9.73:1 reduction.
Efficiency related motor heating is not the issue limiting 60+ mph Teslas performance, 
...nor is the heating of the battery and inverter at the high currents (1500A) demanded for 500kW output.
The cells can output this max level of current draw (5-6C) for the 10-15 seconds needed to run a 1/4 mile , so that is not the cause of reduced performance .
(In "Ludicrous" mode, the car actually pre-heats the battery pack to improve the discharge capeability, before a run is enabled)
However , it is true that the car has power limiting safety mode for protection of the battery, inverter, and motor , but these only seem to kick in after several minutes of high performance operation.


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## major (Apr 4, 2008)

If we're talking motor efficiency then why not look at efficiency plots. I couldn't find one for the Tesla. Odd, I thought I had one stashed in my files. But it would be similar to this except scaled and likely optimized.










You can see like about a 1% efficiency point difference between maximum output at 8000 and 4000 RPM. This is what I am basing my skepticism on. The above chart is for a PM motor I think. The second attachment is for and induction motor. Typically such plots will include inverter losses along with the motor. Cooling and auxiliary system power is unknown.

When you design with sufficient motor, the shifting gearbox becomes a liability. We have numerous threads discussing this topic. 

Regards,

major


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## Solarsail (Jul 22, 2017)

dcb - I think the calculation for ICE horsepower is somewhat different than pure electric and is bloated. I have seen elsewhere that 28 HP of ICE power is equated to only 15 kW electric motor (about 20 HP). This may explain the high 588 kW figure of the dyno -- which does not include the base load which is at least 40 kW. With a 50 kW base load, it is hard to believe that 638 kW is being consumed.

The Tesla already has a reduction gear of 9.73:1. They can have two sets of these with a dual dry clutch system where only one is engaged at a time. There will be absolutely no loss in efficiency. (A clutch has other uses such as in towing or cruising.) Why not have a quicker car with more torque and a quieter and faster car at high speeds? All you need is a dual parallel reduction drive. I would choose 13:1 and 6:1 where the gear changeover is programmable (higher for sports mode).


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## Solarsail (Jul 22, 2017)

Karter2 said:


> The Tesla transmission has a 9.73:1 reduction.
> Efficiency related motor heating is not the issue limiting Teslas performance,
> ...it is the heating of the battery and inverter at the high currents (1500A) demanded for 500kW output.


Wow - at this ratio, the motor RPM is about 21,000 at 95 mph assuming 245/45R19 tires. Does this reduction include the differential? At 21,000 RPM you are smoking a lot of things, and the noise is certainly not so pleasant (if you can hear that frequency!). This is not a good idea and makes the drivetrain costlier than it should be.

Dual (or even triple) 'parallel' reduction is the way to go. Should make the gearheads happy.

Yes, the cells are the limit at 5C -- see my calculations in a post above.


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## major (Apr 4, 2008)

His dyno # was 588hp, not kW. And wheel power is measured the same regardless of the power plant; engine (ICE) or electric motor or steam engine. hp or kW are just units. Power is the same .

major


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## Karter2 (Nov 17, 2011)

That 40kW at standstill is just the launch mode holding the car against the brake prior to launch..for a fraction of a second. 
Where are you getting your figures from ?..
Tesla motor is at 18,000 rpm at 152 mph..
...so about 10,000 rpm at 95mph.

Oh and yes, power is power Hp, kW , ICE, Electric, all the same .
They may "feel" different, but when measured they are the same.That is often due to the different Torque characteristics of an electric drive.
People also get confused with dyno "correction" factors for ICE tests which are not needed for EVs


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## Solarsail (Jul 22, 2017)

Karter2 said:


> The cells can output this max level of current draw (5-6C) for the 10-15 seconds needed to run a 1/4 mile , so that is not the cause of reduced performance .
> (In "Ludicrous" mode, the car actually pre-heats the battery pack to improve the discharge capeability, before a run is enabled)
> However , it is true that the car has power limiting safety mode for protection of the battery, inverter, and motor , but these only seem to kick in after several minutes of high performance operation.


So are you saying that there is no reduced performance in 1/4 mile? I find it mind-boggling that they would pre-heat the cells. 

At 1,500A, the pack is generating 135 kW. Do you know the cooling capacity of the system for the battery pack? It would have to be at least 100 kW. So that may explain where the missing power is going. I tend to think that the limiting factor will be the cooling of the battery pack, and that should start kicking in after maybe 30 seconds. Has anyone seen the temperature chart (for the inside of the battery ) at these rates?


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## Solarsail (Jul 22, 2017)

major said:


> His dyno # was 588hp, not kW. And wheel power is measured the same regardless of the power plant; engine (ICE) or electric motor or steam engine. hp or kW are just units. Power is the same .
> 
> major


Ahh ... thanks for the correction. That is a lot better.

My point is that the dyno, made for the sports and muscle car market, will tend to overrate things. I have seen that in a slightly different context, that power by ICE is discounted when compared to electric power. By as much as a factor of 1.4. See for example Torqeedo.com. So power is not the same if marketing says so.


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## dcb (Dec 5, 2009)

Solarsail said:


> Dual (or even triple) 'parallel' reduction is the way to go. Should make the gearheads happy.


take a look at the graph I posted in #30
http://www.diyelectriccar.com/forums/showthread.php?p=885953#post885953

it stays within 15% of 588 hp from ~45mph to 110mph!

parallel clutch paths need multiple gear reductions and efficiency hits, and you are adding a high wear item in a very demanding application, so a driveline that would have lasted a million miles now needs service every 20k miles.

a lower gearing won't help anything (unless tire smoke is a thing), and it doesn't have any problems that need fixing at 150+mph on the high end, and a 10 second 1/4 mile! holds peak torque from 0 to near 60mph in 2.27 seconds, what more do you want?!? dual clutch whatsit is not gonna last or help (noise, lol). 

It could use a diet @ 5,000 lbs, and an appropriately lower ratio at the same time, that's about it.

they tried the dual speed transmission, it didn't hold up, and didn't really buy them much except headache and expense. They are hitting all the high profile performance metrics without it. And you have like 2 moving parts...

http://www.autoblog.com/2008/01/23/breaking-tesla-has-a-solution-for-their-transmission-woes-get/


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## brian_ (Feb 7, 2017)

Solarsail said:


> ...
> In the chart, look at 55 mph. R_Tq for the L is 255 (whatever unit) and at 75 mph 163 and at 90 mph is 130.
> 55*255 = 14,025
> 75*163 = 12,225
> ...


That's the approach which I was suggesting.
The problem with these values is that the output (based on torque and road speed) is for only the rear motor of this two-motor AWD vehicle, while the electrical power input is for both motors.


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## major (Apr 4, 2008)

Solarsail said:


> So power is not the same if marketing says so.


I don't care much about marketing. Never have believed a car salesman.


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## brian_ (Feb 7, 2017)

Solarsail said:


> With a higher drive reduction ratio, they can get more torque for less power at the start...


They can get more torque at the wheels below the current threshold speed - which they don't need - but not necessarily for less electrical power per unit of mechanical power.


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## brian_ (Feb 7, 2017)

Solarsail said:


> ...
> A dual clutch gearbox with only two gears can be designed by their engineers in their sleep. I fail to see the challenge in shifting gears with a dual dry clutch. They will kill two birds with one shot. I am certain electric supercars will all be multi-gear.


I agree that a dual-clutch design is the obvious solution for automated shifting of a two-speed gearbox, and especially for multiple gearboxes (due to multiple motors). The Rimac Concept_One (more of a technology demonstrator than a production car, but a more-than-million-dollar extreme performance exotic) has this type of transmission for each rear drive motor (one per wheel).

On the other hand, most electric drive motors, even in megadollar hybrids and electric concepts, drive through single-speed gearboxes. Even the Concept_One only had two-speed gearboxes at the rear, not the front. The two-speed seems easy, but manufacturers are not consistently finding it worthwhile.


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## brian_ (Feb 7, 2017)

Solarsail said:


> It should be noted that according to the chart, the vehicle is drawing almost 40 kW at standstill. Compare this to a Leaf's 0.5 kW base load. I would guess that this may be the result of entering Ludicrous mode and the cooling system is feverishly pre-engaged to cool down the systems and the pack, prior to the sprint.


It could be that the cooling system is running, but that wouldn't take anything close to 40 kW and my guess - since the chart shows substantial torque output at zero speed - is that the motors are being driven and the car is being held by the mechanical brakes. This is the electric version of the classic run-up before launching, and should be expected of a current automated launch system (which would not be expected in a Leaf). Unlike other current production EVs and hybrids, Teslas have induction motors, so the stator field is rotating (at the slip speed) with the motors stalled - it seems to me that could take substantial power.

(I see now that Karter2 already explained the launch mode, but I'll leave my longer version.)

Maybe they're running the motors at stall in part to do the pre-heating that Karter2 mentioned.


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## dcb (Dec 5, 2009)

brian_ said:


> The two-speed seems easy, but manufacturers are not consistently finding it worthwhile.


sure, just take a bulletproof existing design and throw in a couple clutches and gears that can handle the 1000 odd foot pounds and 16,000 rpm, for an imperceptible change in performance and efficiency, what could go wrong?


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## brian_ (Feb 7, 2017)

Solarsail said:


> Wow - at this ratio, the motor RPM is about 21,000 at 95 mph assuming 245/45R19 tires. Does this reduction include the differential?


The Tesla gearbox is the most common layout for production EVs, which is a two-stage helical spur gear train. The final gear is the ring gear around the differential, just like a typical transverse front-wheel-drive transaxle, so yes... that quoted reduction ratio is the motor to wheel speed ratio.



Solarsail said:


> At 21,000 RPM you are smoking a lot of things, and the noise is certainly not so pleasant (if you can hear that frequency!).


I haven't had a ride in a Tesla, so I have no idea what it sounds like, but I don't know why anyone would assume "at 21,000 RPM you are smoking a lot of things". Lots of machines run much faster than that, including gear trains and electric motors.


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## Solarsail (Jul 22, 2017)

major, thanks for the charts - they are very helpful.

Does the inefficiency also reduce the torque, or just the output power?

The first chart, running at 4000 rpm with 90 Nm of torque requires about 38 kW. Let's say this is an electric Smart car. With a tire circumference of 1.1 m and a reduction ratio of 7:1, you get 37 kph. The efficiency is 92%. At 35 kW power, you will be accelerating quite a bit. So you accelerate to 74 kph and the rpm is 8000. Your efficiency is about 93%. Now you are approaching 111 kph which is 12,000 rpm. From the chart you see that the efficiency is quickly being pushed down to 80, 70, and then 60%. The faster you go, efficiency drops dramatically.

What is causing this sudden drop in efficiency? 

It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.

BTW. my calculation for RPM was amiss. Karter2 has the correct speed.


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## brian_ (Feb 7, 2017)

dcb said:


> sure, just take a bulletproof existing design and throw in a couple clutches and gears that can handle the 1000 odd foot pounds and 16,000 rpm, for an imperceptible change in performance and efficiency, what could go wrong?


The gears are no problem, but yeah... with the clutches, the two-speed only *seems* easy. The design is actually straightforward, but dual-clutch transmissions in conventional cars have had varying success with durability of the clutches... although most work fine, even while shifting much more frequently than a 2-speed would require and slipping to get started (which the electric drive would not). It can certainly work, but most manufacturers think the risk or cost or weight or bulk or something is not worth the improvement in efficiency or available power.


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## Karter2 (Nov 17, 2011)

Lithium cells have reduced IR at certain temperatures..depending on the exact chemisty...but generally in the 30-50 deg C range.
Your heat figures are way off.
With each cell discharging 15 A @ 40mohm IR...it will generate approx 9 watts of heat.
With 8000 cells that means a total of 72kW of heat....for 10 secs !!
Do some heat theory maths and see what that means in a 600kg battery pack
...not a melt down situation.
EDIT....to save having to correct any mistakes you may make on that heat calculation, you can look up battery cell tests for this type of cell.
At a constant 15A discharge the cell increases in temp by les than 5 degC after one minute !
BUT.. The power electronics in the inverter controls may not take so well to dealing with the 500+ KW they are handling .
Teslas pack "cooling" system is dual function..cooling and heating.
Apparently it is more often used to coolthe pack during supercharging (30+ minutes at 1-2C) especially in hot climates after a high speed run.
...and also for preheating the pack in cold climates..again particularly before charging.


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## brian_ (Feb 7, 2017)

Solarsail said:


> The first chart, running at 4000 rpm with 90 Nm of torque requires about 38 kW. Let's say this is an electric Smart car. With a tire circumference of 1.1 m...


The standard rear tires for a smart are 185/60R15, which have a rolling circumference of 1.83 m. 1.1 m would be ridiculously small - 350 mm or 13.8" diameter, which is much smaller than the tires on 10" wheels of an original Austin Mini. It doesn't matter to the Telsa battery, but if you're working out examples, they won't produce realistic speeds with the wrong tire size.


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## dcb (Dec 5, 2009)

fwiw I do think that a clutchless 2 speed shifting is gonna be a thing at some point. With hi resolution control over motor speed or even gear tooth position (yes, possibly the return of sliding mesh, it is simpler mechanically and more efficient) it will be able to snick it up or down no problem. but it will be for lower powered commuters, or Bonneville. 

I really don't see where it helps looking in the graph in post #30, you drop the ratio by 10% the rpm drops to a point with %10 more motor torque (no change in wheel torque), and the power is basically flat anyway., and the performance is more than adequate as is for a road car.


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## Karter2 (Nov 17, 2011)

Im not a motor technology guy, but there was a comment on the Tesla forum suggesting that the profile of the Torque plot on that graph , ...in particular the flat constant value for the first several thousand rpm....suggests that the maximum torque available is being limited by the control systems (current limiting ?).
Implying that even more torque is potentially available via software and or harware alterations...One of which may well be a higher power capacity battery.
Major, ?..Brian ?...anyone,...any view on this ?


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## dcb (Dec 5, 2009)

yep, flat top means you are at the limit of the controller.

i.e. the flat part of the torque curve is the controller limiting motor current, and a flat top on the power curve is probably the controller limiting battery current.

i.e: http://media3.ev-tv.me/Azure300VDC-400Acurve.pdf a serious flat top.

when at the power limit, the motor behaves like a CVT, which is nice.


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## major (Apr 4, 2008)

Solarsail said:


> Does the inefficiency also reduce the torque, or just the output power?
> 
> What is causing this sudden drop in efficiency?
> 
> It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.


Hi Sol,

Doesn't seem the place to answer those two questions and you really need a study in motor design and a look at the particular one in question. The only "sudden" drops in efficiency which I see are near zero torque or zero speed, areas where the motor spends little duration and/or are of such low power that poor efficiency accounts for little loss. Obviously if you push any motor beyond its intended application you can encounter consequences.

You seem to imply that multiple ratios can buy performance at the top end, high speed & high power. I fail to follow that logic. When you have sufficient motor properly geared to handle the top end, you'll have plenty for the entire operational region in most applications. Even the drag race is better handled with one ratio.

I realize there are those who disagree. One in particular is John Metric. He occasionally visits this board. You might look at his efforts in the electric 1/4 mile. Lonestar Racing IIRC. NEDRA.com

Regards,

major

Edit:



Solarsail said:


> It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.


I reread the above statement and can't make any sense out of it. But I think it is academic anyway because nobody would operate a motor at such a condition.


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## major (Apr 4, 2008)

dcb said:


> yep, flat top means you are at the limit of the controller.
> ...


Well sure, but that limit is set to prevent exceeding or closely approaching breakdown torque in the case of the induction motor. Beyond BDT, more motor current doesn't produce more torque, less in fact.

Edit: attachment from: http://what-when-how.com/induction-...-control-constant-voltshertz-induction-motor/


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## dcb (Dec 5, 2009)

the neat thing about that graph is how much the peaks resemble a series motor torque curve.

but yah, you can't overload it on the low end like a series, cuz you are just saturating a shorted transformer at some point. 










edit, it could be a controller limit (switch rating) or pre-determined motor limit enforced by the controller.

edit2, I don't even understand armature reaction fully, so take it w/a grain of salt.


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## Karter2 (Nov 17, 2011)

Here is a little wild "internet rumour"....
http://www.teslarati.com/tesla-4416-lithium-battery-cell-model-3-next-gen-s-x/
..tesla using a "44160" format cell in the new model 3 !


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## Hollie Maea (Dec 9, 2009)

dcb said:


> fwiw I do think that a clutchless 2 speed shifting is gonna be a thing at some point. With hi resolution control over motor speed or even gear tooth position (yes, possibly the return of sliding mesh, it is simpler mechanically and more efficient) it will be able to snick it up or down no problem. but it will be for lower powered commuters, or Bonneville.
> 
> I really don't see where it helps looking in the graph in post #30, you drop the ratio by 10% the rpm drops to a point with %10 more motor torque (no change in wheel torque), and the power is basically flat anyway., and the performance is more than adequate as is for a road car.


We made a pretty sweet clutchless two speed for the Nikola truck, but they never got the damn thing running so we never got to see it in action.


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## jetpax (Oct 28, 2013)

Karter2 said:


> Im not a motor technology guy, but there was a comment on the Tesla forum suggesting that the profile of the Torque plot on that graph , ...in particular the flat constant value for the first several thousand rpm....suggests that the maximum torque available is being limited by the control systems (current limiting ?).
> Implying that even more torque is potentially available via software and or harware alterations...One of which may well be a higher power capacity battery.
> Major, ?..Brian ?...anyone,...any view on this ?


I'd have thought the flat top for the first few thousand is exactly what you'd expect from a PMSM motor see here esp. fig 8

Using this as a model predicts the S100DL performance quite accurately with published numbers, but as the model shows, more torque low in the rev range will not help as the limiting factor is tyre grip.








This model also lets you add an ideal two-speed box, but playing with that shows it doesn't seem to buy much on a road car, given the wide rev range of a Tesla motor, as dcb has said.


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## Karter2 (Nov 17, 2011)

jetpax said:


> I'd have thought the flat top for the first few thousand is exactly what you'd expect from a PMSM motor.......


 Yes, but the question is what limits it to any specific peak torque level ?....
....current, control hardware, software, ...or motor design/hardware ?
So far , Tesla have raised the peak torque simply by increasing the amps, but is there still room for more that way ?
Im sure it would be possible to squeze a little more than 7C from those cells for a couple of seconds,....but could the controller and motor convert that into more torque ??
The performance model is very good, but not 100% accurate, as it seems to predict a best 0-60mph of 2.6 secs, whilst There are reliable reports of sub 2.3 sec times on record.....Probably down to tyre and track condition.


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## jetpax (Oct 28, 2013)

Note the 2.6s number is for 0-100kmh. 0-60mph is 2.5, which I believe is the 'standard' Ludicrous number, which the parameters of this vehicle profile aim to model. Of course, there is a limit to how accurate a simple model such as this, with only a few dozen parameters, can model an entire vehicle performance!

But the beauty of having a model is that you can change the model parameters to see what it would require to get a model S to 60 in 2.3s, and thus discover exactly what Tesla are doing.

Note that I've had to assume quite high friction values (mu=1.25) even to get to 2.5s number. 

So assuming the tyres haven't changed and we are wheel slip limited in the 0-30 range, it would imply Tesla are raising the base speed somehow to extend the flat torque range higher to improve the 30-60 number.

Of course this another way of saying, they are increasing the motor peak max power. The 2.3s number could be achieved by upping the total motor power from 600kW to 700kW, but this pushes the max current from 1600A to ~2000A. This sounds astronomical, but given some of JB Straubels comments regarding their inverter, may not be so far fetched...


> The power rating increases are largely enabled by better and better power electronics – transistors or IGBTs which is what we are using. As those improve, we can continue pushing up the current rating and continue increasing performance. If we can make the inverter just half a percent more efficient, that’s half a percent less battery pack that we have to put in the car or half a percent more range that the customer gets to have so it a very strong and virtuous feedback cycle with high efficiency.


And, this could be done within the 10C discharge envelope of the pack.

OTOH if the tyres _can_ achieve mu=1.6, that would pretty much do it...


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## Karter2 (Nov 17, 2011)

jetpax said:


> I'd have thought the flat top for the first few thousand is exactly what you'd expect from a PMSM motor.......


.. I forgot to mention...
...you do know the Tesla is an Induction motor , not a PMSM. ?

( sory but i had a hitch with the forum and could not get a login for a while )


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## brian_ (Feb 7, 2017)

jetpax said:


> I'd have thought the flat top for the first few thousand is exactly what you'd expect from a PMSM motor...


I agree - basically constant torque up to a threshold point, then constant or dropping power (so dropping torque... just a matter of how steeply) is normal. That is, normal for AC permanent magnet motors...



Karter2 said:


> ...you do know the Tesla is an Induction motor , not a PMSM. ?


... and that behaviour is also normal for induction motors (although the slip speed must be controlled appropriately to get peak torque for any given shaft speed), as major's graph shows in post #58 - just follow the peaks of the slip/torque curves for each speed.


And although real Tesla fans all probably knew this long ago, I learned from another discussion that the Model 3 is using a permanent magnet motor, so just "Tesla" is not going to be specific enough for these discussions.


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## brian_ (Feb 7, 2017)

Karter2 said:


> Im not a motor technology guy, but there was a comment on the Tesla forum suggesting that the profile of the Torque plot on that graph , ...in particular the flat constant value for the first several thousand rpm....suggests that the maximum torque available is being limited by the control systems (current limiting ?).
> Implying that even more torque is potentially available via software and or harware alterations...One of which may well be a higher power capacity battery.
> Major, ?..Brian ?...anyone,...any view on this ?


The flat-torque region can be limited by current. I'm certainly no Tesla expert, but it seems like some of the performance improvements have been the result of more aggressive (less restrictive) current limiting as they have gained experience with what the battery and electronics can handle - no physical change in components involved. Of course there are limits to that, both in voltage and physically in both the motor and the battery.


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## Karter2 (Nov 17, 2011)

For anyone that missed it, the "44160" cell format rumour has been neatly killed and explained as a miscommunication during a Tesla presentation where some tech guy stated that the Model 3 would use 4416 cells......
.....he litterally meant a quantity of 4,416 cells in the pack !
The cells are , of course, the new 21700 , 5.0 Ah capacity Tesla cell.
Which puts the M3 "long range" pack right at 83-85 kWh max capacity.


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## jetpax (Oct 28, 2013)

Karter2 said:


> .. I forgot to mention...
> ...you do know the Tesla is an Induction motor , not a PMSM. ?
> 
> ( sory but i had a hitch with the forum and could not get a login for a while )



Not anymore , but as Brian says, same applies to induction motor.


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## Karter2 (Nov 17, 2011)

Yes , the M3 has gone to PM, but the Mod S that was being discussed will remain as n induction motor.....at least for now !
And some more details on the M3 pack
https://electrek.co/2017/08/24/tesla-model-3-exclusive-battery-pack-architecture/


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## jetpax (Oct 28, 2013)

Karter2 said:


> Yes , the M3 has gone to PM, but the Mod S that was being discussed will remain as n induction motor.....at least for now !
> And some more details on the M3 pack
> https://electrek.co/2017/08/24/tesla-model-3-exclusive-battery-pack-architecture/


Yes saw the M3 pack details, included it in my M3 simulator

Had to assume 4.75Ah for the 2170 cells, as published by Samsung (cf Panasonic??)

But with that assumption, the short range version comes in ~10% under the 220 mile number, so presumably they are relying on a process improvement down the road.


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## Karter2 (Nov 17, 2011)

Why use the Samsung spec ?
Tesla had to declare details of the pack to the EPA for approvals.
Those official documents declare the "long range" pack to be 230 Ah from a 46p pack....so 5.0 Ah per cell.
Presumeably Tesla are "selling" the pack as a lower capacity (4.4 Ah) to allow for a conservative operating voltage range (3.0-4.1 v ?). To ensure long working life and give some "headroom" for capacity loss compensation.
So , maybe you should use the "Tesla rating" of 4.4 Ah for the simulator ?


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## jetpax (Oct 28, 2013)

Couldn't find a definitive 20700 cell capacity (if you have please post) but from the pack details you posted the cell capacity must be ~4.75Ah.

(4.4Ah gives a pack density of 70kW and range of 288miles)


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## Karter2 (Nov 17, 2011)

Tesla are highly guarded of their actual cell specs, so until someone gets hold of a few cells and tests them ( give it a few months) we have to rely on information such as that supplied by Tesla to the EPA for certification
https://electrek.co/2017/08/07/tesla-model-3-new-details-revealed/
230Ah, 350v etc
Added to the fact that we also know its a 4,416 cell count, in a 96s, 46p pack configuration .
The rest is just maths.
Infact Tesla are being even more cagey than normal with information regarding these latest cells, and of course they will continue to develop, refine, and improve the cell chemistry , so things will likely change again in the coming months and years.


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## Kevin Sharpe (Jul 4, 2011)

Any reliable updates on the 21700 Tesla cell specs?


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## electro wrks (Mar 5, 2012)

Kevin Sharpe said:


> Any reliable updates on the 21700 Tesla cell specs?


As others have pointed out, things don't pencil out for the new Semi and R2 to be using today's battery technology. It seems like the batteries in these vehicles must have energy densities improved by a factor of ~ 2.


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## Solarsail (Jul 22, 2017)

electro wrks said:


> As others have pointed out, things don't pencil out for the new Semi and R2 to be using today's battery technology. It seems like the batteries in these vehicles must have energy densities improved by a factor of ~ 2.


Tesla could use some "real" good news. I would think even if they had improved energy density by 20%, it would be huge news. I am afraid we may have hit a hard ceiling. The 3.4Ah came out 3 or 4 years ago and there has not been any density improvement by Panasonic (or Tesla) since then.


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## Kevin Sharpe (Jul 4, 2011)

electro wrks said:


> As others have pointed out, things don't pencil out for the new Semi and R2 to be using today's battery technology.


Yeh, I get that but was more interested in the Model 3 battery and how we might use the salvage


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## Kevin Sharpe (Jul 4, 2011)

Solarsail said:


> The 3.4Ah came out 3 or 4 years ago and there has not been any density improvement by Panasonic (or Tesla) since then.


I thought the 21700 in the Model 3 was 'confirmed' as ~4.6Ah given we 'know' the long range version has 4416 cells and a capacity of either 74kWh (here) or 80kWh (here)


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## brian_ (Feb 7, 2017)

electro wrks said:


> As others have pointed out, things don't pencil out for the new Semi and R2 to be using today's battery technology. It seems like the batteries in these vehicles must have energy densities improved by a factor of ~ 2.


There is so little hard data for the Semi that this seems like a difficult conclusion to support. A battery technology improvement over the Model S/X may be necessary, but a factor of two? 

Tesla has been claiming a high content of Model 3 components in the Semi; with the gearboxes being different, and none of the cab, structure, steering, brakes, suspension, axles, wheels, or tires being shared, it seems necessary (and reasonable) that all of these components would all be straight from the Model 3:

battery modules (from this description, four in a Model 3 and about four dozen in the Semi)
inverters (one per motor)
motors (four of them in the Semi, one to two in a Model 3)
BMS



Kevin Sharpe said:


> Yeh, I get that but was more interested in the Model 3 battery and how we might use the salvage


Since Model 3 modules built of the 2170 cells are presumably superior to the 18650's in current production models, my guess is that modules which you salvage from Model 3's after they go into actual production will be the same as what will be used in the Semi (and presumably Roadster 2). Or at least the cells in them will be the same.

The Semi's requirements may have driven the shift to larger modules, so that there is not such an impractically large number of them in the 1 MWh Semi pack... or perhaps it was just simplification for production cost efficiency. Either way, those big modules are going to be a challenge for packaging in many DIY projects.


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## Solarsail (Jul 22, 2017)

Kevin Sharpe said:


> I thought the 21700 in the Model 3 was 'confirmed' as ~4.6Ah given we 'know' the long range version has 4416 cells and a capacity of either 74kWh (here) or 80kWh (here)


The 3.4Ah capacity is for a 18650. Now since the 2170 is 1.466x the volume of the 18650, one would expect the proportional capacity for the 2170 to be 4.98Ah. But if the capacity is confirmed at 4.6Ah, then that is a step backward! (Note that the 'chemically usable' volume proportion of the 2170 is actually higher - about 1.5x, which implies a capacity of 5.1Ah.)

The T3 LR pack is estimated at 78 kWh nominal (and 74 kWh usable). 78 / 4416 / 3.6 = 4.9Ah -- which I believe is more likely (than 4.6Ah).


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## Kevin Sharpe (Jul 4, 2011)

brian_ said:


> Since Model 3 modules built of the 2170 cells are presumably superior to the 18650's in current production models, my guess is that modules which you salvage from Model 3's after they go into actual production will be the same as what will be used in the Semi (and presumably Roadster 2). Or at least the cells in them will be the same.


The Tesla Model 3 battery capacities announced by Elon Musk suggest that the 2170 is 'simply' a repackaging and cost reduction exercise. Clearly a 200kWh battery will not fit in the Roadster 2 without some major improvements in energy density (at least x2). It's hard to know whether Tesla can deliver this in two years, but given Musk has never met a date I guess two years could turn into five and then maybe it's possible


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## Kevin Sharpe (Jul 4, 2011)

Solarsail said:


> The 3.4Ah capacity is for a 18650. Now since the 2170 is 1.466x the volume of the 18650, one would expect the proportional capacity for the 2170 to be 4.98Ah. But if the capacity is confirmed at 4.6Ah, then that is a step backward! (Note that the 'chemically usable' volume proportion of the 2170 is actually higher - about 1.5x, which implies a capacity of 5.1Ah.)
> 
> The T3 LR pack is estimated at 78 kWh nominal (and 74 kWh usable). 78 / 4416 / 3.6 = 4.9Ah -- which I believe is more likely (than 4.6Ah).


Thanks, that makes a lot more sense


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## brian_ (Feb 7, 2017)

Kevin Sharpe said:


> Clearly a 200kWh battery will not fit in the Roadster 2 without some major improvements in energy density (at least x2).


While the Semi's battery size and packaging are mysteries at this point (it could have five tons of battery), that's a good point about the Roadster - it's hard to see that body with double the battery volume (or mass) of a Model S.


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## electro wrks (Mar 5, 2012)

brian_ said:


> While the Semi's battery size and packaging are mysteries at this point (it could have five tons of battery), that's a good point about the Roadster - it's hard to see that body with double the battery volume (or mass) of a Model S.


The Tesla Semi main designe_r, _Jerome Guillen, said in a recent presentation in Europe that the Tesla truck weighs no more than a diesel truck. If you take a modern diesel semi (also designed by a team lead by Jerome Guillen when he worked for Daimler/ Freightliner) and pull the engine:https://freightliner.com/demand-detroit/engines/dd16/ ; transmission:https://freightliner.com/demand-detroit/detroit-dt12-transmission/ say ~1000# of tanks, radiators, non-fuel fluids, and other ICE related equipment; and 200gal(~1400#) of fuel. You save ~6000# (if I haven't left any thing out). So how much energy will ~6000#(~2700kg) of batteries give us?


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## brian_ (Feb 7, 2017)

electro wrks said:


> The Tesla Semi main designer, Jerome Guillen, said in a recent presentation in Europe that the Tesla truck weighs no more than a diesel truck.


Good info from Guillen.  The weight has been missing from most of the fluff publicity around the Semi.



electro wrks said:


> If you take a modern diesel semi (also designed by a team lead by Jerome Guillen when he worked for Daimler/ Freightliner) and pull the engine:https://freightliner.com/demand-detroit/engines/dd16/ ; transmission:https://freightliner.com/demand-detroit/detroit-dt12-transmission/ say ~1000# of tanks, radiators, non-fuel fluids, and other ICE related equipment; and 200gal(~1400#) of fuel. You save ~6000# (if I haven't left any thing out). So how much energy will ~6000#(~2700kg) of batteries give us?


And it's even worse than that, because the electric truck still needs a cooling system (although lighter than the diesel's), and - much more importantly - that 2700 kg would need to include four motors. You could delete the diesel's differentials, roughly offsetting the reduction gearing that goes with the motors. Then there's the electronics... four inverters, the chargers, etc.

This could also mean that the claim of matching diesel weight is just bunk.  To be fair, this claim was likely for a shorter-range version, not the 500-miler.


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## aeroscott (Jan 5, 2008)

Everthing can be made lighter with less vibration . Battery packaging will save weight over the multiple car batteries . Small improvements in batteries
are a given.
That's not " just bunk" it's good engineering.


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## brian_ (Feb 7, 2017)

aeroscott said:


> Everthing can be made lighter with less vibration .


I'm not sure what components might be part of this "everything", since the Semi is using the same hitch, tires, wheels, suspension, and frame design as a conventional design truck. Are the frame rails lighter? That could make a few kilograms of difference, I suppose.



aeroscott said:


> Battery packaging will save weight over the multiple car batteries . Small improvements in batteries
> are a given.
> That's not " just bunk" it's good engineering.


Continual improvements _are_ good engineering. Whether the "same as diesel" claim turns out to be the result of improved design, or is just bunk, remains to be seen...


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## electro wrks (Mar 5, 2012)

brian_ said:


> This could also mean that the claim of matching diesel weight is just bunk.  To be fair, this claim was likely for a shorter-range version, not the 500-miler.


It could be. Although in the presentation, I believe he only talks about the longer range Semi. To clarify, he does parse the weight discussion by saying the Semi has the same cargo capacity as a diesel semi. Hear for yourself at ~ 4:30:
https://electrek.co/2017/11/26/tesla-semi-vp-trucks-electric-presentation/


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## Solarsail (Jul 22, 2017)

My guess is that the unit weight for the modules, including packaging, will be 4.5 to 5.5 kg/kWh. A 1MWh pack is out of question, including by volume. A 300 kWh pack will weigh about 1,500 kg or 3,300#.


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## Karter2 (Nov 17, 2011)

Kevin Sharpe said:


> The Tesla Model 3 battery capacities announced by Elon Musk suggest that the 2170 is 'simply' a repackaging and cost reduction exercise. Clearly a 200kWh battery will not fit in the Roadster 2 without some major improvements in energy density (at least x2). It's hard to know whether Tesla can deliver this in two years, but given Musk has never met a date I guess two years could turn into five and then maybe it's possible


 I doubt Musk is in any rush to alter/improve the cell performance just yet.
They are having enough problems getting the cell/pack production up to speed as it is (one of the main bottlenecks in M3 production delays), so any more changes in that department are very risky.
Tesla has also recently lost several of their key tech guys on the battery development side including Kurt Kelly the department head , and Jon Wagner , head of battery technology !


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## brian_ (Feb 7, 2017)

electro wrks said:


> To clarify, he does parse the weight discussion by saying the Semi has the same cargo capacity as a diesel semi. Hear for yourself at ~ 4:30:
> https://electrek.co/2017/11/26/tesla-semi-vp-trucks-electric-presentation/


Thanks for the clarification. 

That's a *huge* difference. There is no single value for maximum truck weight (it depends on axle count, axle spacing, which road, where...) so it's easy to compare an eight-ton diesel tractor and an 10-ton electric tractor and say they have the same payload because they can both haul a 30-ton trailer.

Commercial trucks in North America have their tare mass and maximum gross loaded mass posted on the side of the truck. Some which operate over wide areas have quite a list of gross combination weight values listed, each annotated with where it applies. The highest values (typically a Canadian federal limit of 62,500 kg - 137,789 lb - for a B Train Double) are more than 1.5 times the lowest values (such as the general US federal limit of 80,000 lb or 36,288 kg). Even within a single jurisdiction, a truck licensed for 40 tons and one licensed for 60 tons are not wildly different in their own weight.

On the other hand, Guillen refers to only a single GVW limit (the US federal value) and says that they are *aiming* to have the same payload... so nothing has actually been achieved, and we're still talking about aspirations. Even the 800 kilometre (500 mile) range is expressed as a target, not an actual specification. By the time these numbers get from the Truck VP to the Supreme Leader (Musk), of course they become absolutes.


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## Kevin Sharpe (Jul 4, 2011)

Karter2 said:


> I doubt Musk is in any rush to alter/improve the cell performance just yet.


I agree... hard to imagine how we get from here to a 200kWh Roadster 2 battery in two years


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## electro wrks (Mar 5, 2012)

brian_ said:


> On the other hand, Guillen refers to only a single GVW limit (the US federal value) and says that they are *aiming* to have the same payload... so nothing has actually been achieved, and we're still talking about aspirations. Even the 800 kilometre (500 mile) range is expressed as a target, not an actual specification. By the time these numbers get from the Truck VP to the Supreme Leader (Musk), of course they become absolutes.


The trucking industry is a careful, conservative lot. Tesla is not going to be able to fool them for long, if they can't deliver the goods. I suspect the better cheaper batteries that we speculate must be in the Semi and R2 are here, with full production coming sometime later. I also suspect Tesla isn't bragging about it so as to not tick off the people buying the Model 3, that has the older batteries.


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## Duncan (Dec 8, 2008)

One of the things to bear in mind when looking at larger battery packs is that on the current packs a lot of the weight is armour - and also structural weight

When you go larger the structural weight and especially the armour weight do not have to go up anywhere near as fast as the "active" weight so a battery with ten times the capacity may only have six or seven times the weight


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## aeroscott (Jan 5, 2008)

That sounds right to me


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## electro wrks (Mar 5, 2012)

Here's some quick(some might say frantic!) info on the better batteries that could be in the Semi and R2 starting at ~1:20: https://www.youtube.com/watch?v=MUaEfDkzQfs


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## aeroscott (Jan 5, 2008)

Elon said $65/Kwh in materials and at another time said well under $100/Kwh for finished batteries.
It will be closer to the $65. Commodity level manufacturing which by it's nature will be continually refined in a never ending quest for improved production. 
He also said the through put is like a machine gun and they slow it down so you can see the cells.


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## Kevin Sharpe (Jul 4, 2011)

aeroscott said:


> Elon 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


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## aeroscott (Jan 5, 2008)

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.


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## Duncan (Dec 8, 2008)

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


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## Kevin Sharpe (Jul 4, 2011)

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/


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## Kevin Sharpe (Jul 4, 2011)

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?


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## aeroscott (Jan 5, 2008)

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


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## brian_ (Feb 7, 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 (Nov 17, 2011)

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 ?


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## Karter2 (Nov 17, 2011)

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 !


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## aeroscott (Jan 5, 2008)

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 .


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## aeroscott (Jan 5, 2008)

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.!
> ...


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


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## brian_ (Feb 7, 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.


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## brian_ (Feb 7, 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?


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## aeroscott (Jan 5, 2008)

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 .


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## brian_ (Feb 7, 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.


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## Kevin Sharpe (Jul 4, 2011)

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 (Jan 5, 2008)

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.


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## Kevin Sharpe (Jul 4, 2011)

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


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## Solarsail (Jul 22, 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.


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## brian_ (Feb 7, 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 (Jul 22, 2017)

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_ (Feb 7, 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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## Solarsail (Jul 22, 2017)

So if we eliminate the possibility of two 2-speed gearboxes, then in order to have two rear motors, the following architectures remain:

a) Different reduction ratios + rear (and front) differential. The Model 3 reduction ratio is close to 10. So for the R2, it would be 14 on one motor and 7 on the other motor. A further twist here is that if the 14 motor could be disengaged by a clutch, then the ratios could be wider such as 16 and 6. The front ratio would remain at 10.

b) Another possibility is just one 2-speed gearbox in the rear for one of the motors. One motor runs at ratio 14 the other at 7 but also has the benefit of the 2-speed gearbox and then can also run at 14, for low-speed high acceleration. I don't think this would be a good design.


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## brian_ (Feb 7, 2017)

Solarsail said:


> a) Different reduction ratios + rear (and front) differential. The Model 3 reduction ratio is close to 10. So for the R2, it would be 14 on one motor and 7 on the other motor. A further twist here is that if the 14 motor could be disengaged by a clutch, then the ratios could be wider such as 16 and 6. The front ratio would remain at 10.


I get that, but with two motors, two sets of gearing, and now a clutch, you're nearly all of the way to the mechanical complication simply having one motor and a two-speed transmission (and you have extra electronic complication). So, this seems very unlikely to me.

On the other hand, having somewhat different motors - and perhaps different reduction ratios - between the front and the rear is quite viable. While this is not done with the Model S and X (even when front and rear motors are different sizes they are comparable characteristics and the same reduction ratio), a moderate version can make sense. The front motor would be optimized for higher speed and used in a greater proportion to the rear at high speeds, leaving the power distribution more rearward at low speed (when acceleration is greater so load transfer to the rear is significant). Logically, in this scenario the two motors in the rear are identical to each other and simply each driving a wheel.



Solarsail said:


> b) Another possibility is just one 2-speed gearbox in the rear for one of the motors. One motor runs at ratio 14 the other at 7 but also has the benefit of the 2-speed gearbox and then can also run at 14, for low-speed high acceleration. I don't think this would be a good design.


I agree that this could be built. I also agree that it wouldn't be good. 
If using a transmission like this, then there would be no point in having two motors - just one large motor driving through the transmission would make more sense.


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## electro wrks (Mar 5, 2012)

Solarsail said:


> So if we eliminate the possibility of two 2-speed gearboxes, then in order to have two rear motors, the following architectures remain:
> 
> a) Different reduction ratios + rear (and front) differential. The Model 3 reduction ratio is close to 10. So for the R2, it would be 14 on one motor and 7 on the other motor. A further twist here is that if the 14 motor could be disengaged by a clutch, then the ratios could be wider such as 16 and 6. The front ratio would remain at 10.
> 
> b) Another possibility is just one 2-speed gearbox in the rear for one of the motors. One motor runs at ratio 14 the other at 7 but also has the benefit of the 2-speed gearbox and then can also run at 14, for low-speed high acceleration. I don't think this would be a good design.


If I'm not mistaken, the R2 has motor based torque vectoring. This implies symmetry, side to side, for the two motors and gear reduction boxes in the back. Another thing: somebody said that when the Semi was accelerating at the event in Hawthorne, they thought they heard a shift(electronic shift?). Maybe something like a shift from a Delta to a Wye stator configuration? Is this a possibility? Or, something else electronic?


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## Solarsail (Jul 22, 2017)

brian_ said:


> The front motor would be optimized for higher speed and used in a greater proportion to the rear at high speeds, leaving the power distribution more rearward at low speed (when acceleration is greater so load transfer to the rear is significant). Logically, in this scenario the two motors in the rear are identical to each other and simply each driving a wheel.


I think this would be something like two identical rear ratios at let's say 14 and a front at 7 - for a 2:1 ratio. The problem is that this will not take you up to 250 mph. The rear motors cannot deliver the power at those speeds, and the front is underpowered and too high RPM for 250 mph is required - the spread of the ratios is not wide enough. But I like the idea that at high speeds, power is mostly delivered by the front, and I think that will make for better high speed driving. So the ratios I propose are 18 for RM1 (rear motor 1), 10 for RM2, 6 for FM, for a 3:1 ratio of the reduction gears.

0 - 60 mph, 100% power on all three motors, torque ratio (RM1, RM2, FM): 60%, 35%, 5%
60 - 150 mph, power is cut to RM1, 100% to RM2 and FM. Torque ratio: 25%, 55%, 20%
150 - 250 mph, power is cut to RM1, RM2, and 100% to FM. Torque ratio: 0%, 30%, 70%

Electrowrks, what is the effect of switching from delta to wye in the stator configuration of a PM motor?


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## Kevin Sharpe (Jul 4, 2011)

electro wrks said:


> If I'm not mistaken, the R2 has motor based torque vectoring. This implies symmetry, side to side, for the two motors and gear reduction boxes in the back.


Multiple articles have stated that the Roadster has torque vectoring... I'm not sure what the original source of this is but suspect it will be required to get such a heavy car around corners.


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