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A look at the new Tesla cells

11958 Views 124 Replies 14 Participants Last post by  Kevin Sharpe
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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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.
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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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%...
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.
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.
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.
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.
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.

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.
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.
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.
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... 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.
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 , 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.
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? :confused:

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

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: ; 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. :rolleyes: To be fair, this claim was likely for a shorter-range version, not the 500-miler.
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.

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...
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:
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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... 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.

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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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!

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")

This takes critical thinking .
Yes, we could use more of that around EV announcements. ;)
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?
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.
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.

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.:confused: 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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