[Karter2]

There is a lot of outdated and incorrect information in that report and video.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.

 

[Karter2]

??? 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.

 

[Karter2]

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.

 

[Karter2]

Several power tool manufcturers are also using 21700 cells now.

 

[Karter2]

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.

 

[Karter2]

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.

 

[Karter2]

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 !

 

[Karter2]

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).

 

[Karter2]

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.

 

[Karter2]

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

 

[Karter2]

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.

 

[Karter2]

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 ?

 

[Karter2]

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 !

 

[Karter2]

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.

 

[Karter2]

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 )

 

[Karter2]

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.

 

[Karter2]

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/

 

[Karter2]

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 ?

 

[Karter2]

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.

 

[Karter2]

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 !