200 kWh Roadster Pack: How is Tesla Pulling This Off?

[Yggdrasill]

In the current Roadster the limitation is the PEM (AC/DC Inverter) and motor itself, not the battery. Tesla has a patent for liquid cooling the rotor on the motor but hasn't implemented it. Perhaps it's been too expensive to do but they can justify it on this car since it's more expensive. Or perhaps they're going to use IPM motors instead of async AC which I have read are easier to cool. The 250+ mph claim leads to believe they think they have the cooling problem solved as it takes awhile to get to 250+ mph so the car would need to maintain peak output for much longer than any current Tesla model.

All of that being said, VERY few supercars/hypercars ever see a race track. They're usually driven on public roads by pudgy rich guys seeking attention. In that realm (public roads) the v4 Roadster will destroy any comer.

I think they'll have sorted out the cooling issues. I'd expect it to use three Model 3 motors with beefed up inverters, and they are reportedly PM motors. Sustained output in the 750-900 kW range should be possible.

The battery heating should be no issue at all. With twice the capacity of a S100DL, it'll have half the internal resistance, and close to twice the effective thermal mass. So the heating issue should be roughly a quarter at the same power output. Or put differently, the pack should be able to sustain speeds at more than 1.5 times what the Model S can do without having any issues. So, at least around 400 km/h.

 

[daniel]

The v4 Roadster is exactly as I have been saying. They went straight after the top end 911 market, right down to the 2+2 seating, which I believe is the right target market for this car. From what I can gather with a quick web search, Porsche sells about 1,500 911 Turbo S's per year so there is a market there. A 911 Turbo S convertible starts at $203,000, hard top at $191,000 so they are right in there with WAY better performance (911 Turbo S is 2.8 to 60). Tesla needed/wanted a halo car and that's what they made.

I think the massive range is a byproduct of needing enough cells to flow the power required for 1.9 to 60, not a goal in and of itself.

I think the mid-life crisis car will be a Performance S or 3. It wouldn't take much to do a coupe version of the 3 with the existing SP100DL drivetrain (I'm assuming improvements in battery tech will allow them to put 100kWh in the 3) and voila, very quick but not stupidly expensive and still practical car.

That makes a lot of sense. I guess I'm just not a customer for a $200,000 car. But competing head to head with the Porsche, if it can match or exceed the handling, and if it can handle the heat, as 12Pack mentions, that acceleration and range will blow the Porsche out of the water. The only reason left to buy the Porsche would be for the noise.

 

[e-FTW]

This researcher from Carnegie-Mellon thinks all the numbers are plausible, from pack size to acceleration. And he thinks the pack may be 1800 pounds.
https://jalopnik.com/heres-what-a-battery-researcher-told-us-about-the-tesla-1820558723

 

[Dutchie]

I need a Model 3 with 500 miles of real-life summer range at highway speed.

Why?

 

[Evbwcaer]

Just some ideas I’ve had, and seen:

-A double stack would be less than twice as heavy and less than twice as tall. You eliminate two layers of casing, reducing weight and height.

-What about horizontal cells? If you think double stack, then horizontal arrangements could come into play. You could run cooling/heating circuits in a straight horizontal runs, giving each cell contact on four sides and conceding zero space to cooling/heating.

-Doesn’t 200kwh seem like overkill? This thing would supercharge like an animal and probably perform better overall with 150,for example. A 200 pack could presumably charge to 250 miles in about 20 minutes, if the Superchargers can hit 200-250kw by then. Crazy

 

[mongo]

-Doesn’t 200kwh seem like overkill? This thing would supercharge like an animal and probably perform better overall with 150,for example. A 200 pack could presumably charge to 250 miles in about 20 minutes, if the Superchargers can hit 200-250kw by then. Crazy

Agree with your first two points.
Dropping pack capacity had a direct linear relationship with dropping available power. However, the vehicle mass reduction is ratiometrically less due to the non-pack weight. If the pack is half the weight of the vehicle say 4 units and the rest is 4 units. You have a 1:2 force to weight ratio. If you drop 25% of the pack, you now have a 3:7 ratio, or a loss of acceleration of 15%.

If the pack is third of vehicle weight, 4 vs 8. the base is 1:3, reducing 25% is 3:11 a loss of 19%.

I'm guessing it's the pack size need to get < 2 seconds.

 

[Electroman]

https://jalopnik.com/heres-what-a-battery-researcher-told-us-about-the-tesla-1820558723

I also asked Viswanathan whether he thought the 620 mile range was feasible. He responded, “definitely...a 200kWh battery pack can easily go 600 miles.”

Huh? Of course 200 kWh can easily give 620 mile range for car of Roadsters profile. I think the question that was implicitly asked is if the car can have a 200 kWh battery?

 

[Evbwcaer]

Agree with your first two points.
Dropping pack capacity had a direct linear relationship with dropping available power. However, the vehicle mass reduction is ratiometrically less due to the non-pack weight. If the pack is half the weight of the vehicle say 4 units and the rest is 4 units. You have a 1:2 force to weight ratio. If you drop 25% of the pack, you now have a 3:7 ratio, or a loss of acceleration of 15%.

If the pack is third of vehicle weight, 4 vs 8. the base is 1:3, reducing 25% is 3:11 a loss of 19%.

I'm guessing it's the pack size need to get < 2 seconds.

That all makes sense, but available power is different than useable power. Are the tires limiting 0-60, or is it the available power? And how much better would the car handle if it was 500lbs lighter?

All that being said, it makes sense to me that they build the car to impress numerically and more people know about and care about a 1000km range than a Nuremberg time.

 

[daniel]

Why?

See my earlier posts.

 

[Cory151]

I already have an EV for everyday use. (Tesla Roadster.) But it can't make the long drive without stopping to charge, and there are no superchargers on the secondary roads. (ETA: Any car I could rent where I live would burn a lot more gas than my Prius.)

Turo has pages full $28 per day Prii you could rent near you. Most camping and RV destinations have a 220v hookup you can use to plug into as well. Not to mention when I go from San Diego to the top of Mt. Laguna I use about 33kwh. Going back I only use 11kwh, downhill regeneration is a huge range boost that you're likely not calculating in.

Lastly, Ive owned 5 Prii and I would rather bring my Honda generator than leave my P85D at home on those twisty mountain roads. Getting in my Prius now feel like being made to eat my vegetables.

 

[mongo]

That all makes sense, but available power is different than useable power. Are the tires limiting 0-60, or is it the available power? And how much better would the car handle if it was 500lbs lighter?

All that being said, it makes sense to me that they build the car to impress numerically and more people know about and care about a 1000km range than a Nuremberg time.

Good point. I'll counter with: at what SOC does the car provide the specified performance? If the car is designed to meet spec at 50%, then the top 50% is excess the rest of the time (acknowledging that lithium batteries have a gentle SOC to voltage curve), but if you remove that 50%, you only meet spec above say 80%(accounting for less weight). At the top speed, the weight is less critical than aerodynamics, so if 50% less capacity means 50% less force, and thing go as the square, you drop your top speed by 75%.

I think?

 

[Jason S]

Until the whole car starts to slide, which is already the problem with the Model S. It'll turn without rolling, but you still hit a point where the tires just can't deal with the side-loading from the weight of the car pushing to the outside of the turn.

If the tires are sticky enough for 0-60 in 1.9s then they can handle side-loading too. Won't be a rally car, but it'll stick and 50/50 weight ratio.

Of course the real trick for an electric performance car is if it can routinely lap around a track where it’s continually being asked for hard accelerations. My Model S doesn’t make it through a single lap without power being limited due to battery heating.

BTW this is not a troll - I have a deposit on the roadster. But won’t go through with the purchase unless this is demonstrated to be not be an issue.

If you are looking for a track car there are much cheaper alternatives. A Roadster would make for a wonderful weekend car tho, like the 911 or 370z, etc

 

[daniel]

Turo has pages full $28 per day Prii you could rent near you. Most camping and RV destinations have a 220v hookup you can use to plug into as well. Not to mention when I go from San Diego to the top of Mt. Laguna I use about 33kwh. Going back I only use 11kwh, downhill regeneration is a huge range boost that you're likely not calculating in.

Lastly, Ive owned 5 Prii and I would rather bring my Honda generator than leave my P85D at home on those twisty mountain roads. Getting in my Prius now feel like being made to eat my vegetables.

I suppose I could rent a car, but honestly, I don't trust the availability of rental cars. This is a very high-value trip to me, and I'm disinclined to risk that at the last minute the car I counted on may not be available. Turo lists exactly one Prius available for rent in Spokane. Easier to keep mine.

As for RV parks, I addressed that: I figure that it would take about 4 hours to get the needed charge at 8.8 kW. I am just not willing to turn a 6-hour drive into a 10-hour trip with four hours of twiddling my thumbs and nothing to do but read a book in an RV park.

There's very little net elevation difference between where I live and where I drive to. (Getting from town to the lodges is either by helicopter or else by 4WD truck and hiking.) There are no twisty mountain roads, either. There are some mountain passes, but the roads, though they are secondary highways unlikely to get superchargers any time soon, are good.

A 500-mile-range Model 3 would be perfect.

 

[Yggdrasill]

That all makes sense, but available power is different than useable power. Are the tires limiting 0-60, or is it the available power? And how much better would the car handle if it was 500lbs lighter?

You will start off traction limited, and will only need the full power towards the end of the acceleration. And the average acceleration needed for a 1.9 second 0-60 mph is around 1.4G. Now, the required power for a 1750 kg car to accelerate at 1.4G at 60 mph is:

1750 kg x 9.8 x 1.4 = 24 kN
24 kN x 26.82 m/s = 644 kW

Adding 30% losses in the drive train, you'd need 920 kW to sustain 1.4G all the way up to 60 mph. At max 5.5C, I'm thinking a 200 kWh is actually required. Pretty close to it, at least.

 

[Yggdrasill]

Just toying with some numbers, and if they could manage 1.5G up to 40 mph, and then drop it down to 1.2G, you could get away with a smaller battery and still make 1.9 seconds.

1750 kg x 9.8 x 1.2 = 20.6 kN
24 kN x 26.82 m/s = 552 kW
552 kW / 0.7 = 780 kW
780 / 5.5 = 142 kWh

I think that would have to be pretty much my lowest figure for the prototype. Any less than 142 kWh and it wouldn't be able to do sub 2 seconds.

 

[ecarfan]

The point of the big battery wasn’t to have a 600 mile range (that’s fairly pointless in a 2+2 seater). The reason for the big battery was to have enough power for 1.9s launches.

...and to be able to sustain the claimed top speed of 250+mph for more than a few minutes.

 

[Cosmacelf]

...and to be able to sustain the claimed top speed of 250+mph for more than a few minutes.

Yeah, that’s another niggling question I had. How can it do 250 mph without gears? Those motors would be spinning way out of their power band by then...

 

[triakter]

I’m enjoying the very well thought out technical speculation in this thread, but for me the question of how they pull this off technically pales to the one of how they pull it off financially.

Even with a small windfall from reservations, even if the Model 3 production woes were magically fixed tomorrow, and even if everything goes perfectly with the semi, I don’t see how Tesla can have this car in production anywhere near 2020 with the cash they have, or can get by taking on more debt. 2023 would still seem ambitious, but believable.

 

[Cosmacelf]

As lots of companies have proven over the years, as long as you have a steady pipeline of desirable future products, Wall Street will line up to give you money.

 

[brucet999]

The Electrek editor who took a ride said the floor felt 6-8 inches higher than the original Roadster, so it could be a conventional double-stack pack.

The original roadster felt to me like I was sitting inside the frame, below the door sill. Seems like even a single-pack skateboard would feel 6-8" higher.