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Why do diff battery packs have diff 0-60mph times?

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The difference between the Roadster and the Roadster sport is that the Roadster has extra battery horsepower available that it can't use because the motor and/or PEM is limiting it. I said that you build the motor to use all your available battery horsepower because the motor is cheap compared to the battery. Tesla discovered that they got it wrong the first time and the motor was limiting the car, so they made a better motor and charged more money for it.
I am an acceleration junkie and was not willing to pay $20k for the marginal improvement of the sport even though I do regret not getting the adjustible suspension.

$6K and a phone call solves that :)
 
Has anyone already done the math on what the Roadster would do with 6,831 of the cells used in the 85 kWh pack in terms of 0-60?

The motor is the limiting factor, so even with higher capacity cells and pack (which would be 79 KWh) in the roadster; the 0-60 will not change much.
 
The difference between the Roadster and the Roadster sport is that the Roadster has extra battery horsepower available that it can't use because the motor and/or PEM is limiting it. I said that you build the motor to use all your available battery horsepower because the motor is cheap compared to the battery. Tesla discovered that they got it wrong the first time and the motor was limiting the car, so they made a better motor and charged more money for it.
I am an acceleration junkie and was not willing to pay $20k for the marginal improvement of the sport even though I do regret not getting the adjustible suspension.

Do we know if all Model S' have the same exact motor? I have read multiple articles stating otherwise.
 
Thanks all - very helpful in understanding the two questions posed.

I heard something really interesting from an EV drag racer, and I will attempt to paraphrase.

The batteries in the Model S probably are used at around 4C when bursted. This means the 40kWh battery delivers 160kW ( 215 hp ) and the 85kWh battery delivers 340kW ( 456 hp )

There are batteries that can be used at much higher C rates ( like 25C or even higher ) in bursts, and that is what EV drag racers use.
So a 20kWh pack can deliver 670 horsepower. However they tend to be much less energy dense.

That's a good point - my understanding was that Tesla uses a battery chemistry that has relatively low power output but higher density compared to say the A123 batteries in the Fisker which have higher power but lower energy density. Maybe this is a bit naive, but why wouldn't manufacturers create a (for lack of a better term) hybrid battery which has say, 5 KWh "high power, low density ala A123" and the remaining 35Kwh of "lower power, higher density." For high power, peak horsepower exercises (e.g. like accelerating onto a freeway), the battery would pull energy from the 'high power' portion of the battery...then during low power applications like cruising at 55mph, the other 'lower power, higher density' cells in the battery would be used to power the motors and recharge the 'high power' portion of the battery. If you think about it, rarely do cars use all of their rated horsepower. I read on FiskerBuzz, for example, that the Karma only uses about 70 hp to maintain highway speed cruising. The A123 batteries are designed for much more charge/discharge cycles (which as Elon said, make them well suited for PHEVs), while Tesla's batteries aren't designed for that many cycles. A hybrid approach would combine these benefits into one killer battery with high peak power output and best in class energy density!
 
Some kind of "hybrid pack" could be coming in the future. Using Ultra-Capacitors/Super-Capacitors on the "front end" has also been suggested.

Another thing to consider is the regen. In stop and go traffic you are doing a lot of cycling with high input and output power. Small packs could not only limit acceleration, but also max regen capture. If you had something with high power density and high cycle life in front of the energy dense "range extension pack section" then you could probably do heavier (short term) acceleration and regen without hurting things too much.
 
By the way, lots of good info in this thread. I don't know definitive answers on this, but from what I have read before I think:

#1: Yes, Roadster Sport is "enhanced" (from base Roadster) to have more low end torque, but not necessarily any more high end horsepower.
So, it has an advantage in 0-60, but no real advantage above that. The pack may not see a max C rate any higher than in the base Roadster since the torque boost is only at lower RPMs, so max HP doesn't really change.

#2: Performance Model S vs base is a bigger boost than Roadster Sport vs Base Roadster. It makes a lot more peak horsepower, so is a more substantial sort of change.

#3: (At least initially) Roadster used commodity laptop cells mostly optimized for high energy density. With the new Model S cell formulation, Tesla worked with the battery manufacturer(s) to create a battery better suited to automotive use. Not sure what exactly is better (0ther than higher energy density for longer range), but I gather they would try to improve C rates as well since they need a lot of power to meet performance targets in the much bigger/heavier Model S. If the eventual base Model S (40kW) uses old style cells (to keep costs down) it might be power limited by cell chemistry too (not just because of lesser # of cells.)

A sign that the C rates could be higher in new cells for 85kWh model S is that they will do high kW SuperCharging on that pack, but not on the base pack, and not on Roadster.


The idea that the entry model would be "detuned" to offer less performance in an attempt to get people to want to spend more on the top line models makes sense from a marketing standpoint, but I do suspect there are reasons why the technology is also limiting what they can do. Perhaps the marketing folks are grateful that they are forced to offer a product with built-in up-sell features...
 
The idea that the entry model would be "detuned" to offer less performance in an attempt to get people to want to spend more on the top line models makes sense from a marketing standpoint, but I do suspect there are reasons why the technology is also limiting what they can do. Perhaps the marketing folks are grateful that they are forced to offer a product with built-in up-sell features...

In marketing parlance, nothing is ever "detuned." ;)
They simply found ways to engineer the 85kWh unit give even more juice than the 4okWh design. And then some engineer said, "Hey, we can do better still, and build a Performance model that really flies with just a few more tweaks!"

At least being a brand marketing guy, that's how I would describe it.
 
In marketing parlance, nothing is ever "detuned." ;)
They simply found ways to engineer the 85kWh unit give even more juice than the 4okWh design. And then some engineer said, "Hey, we can do better still, and build a Performance model that really flies with just a few more tweaks!"

At least being a brand marketing guy, that's how I would describe it.
And there's the cpu example...

Design them to run at 66 MHz. The ones that fail in testing, you throttle them to 50 MHz and sell them cheaper. Similarly with non-functional FPUs.

This turns a refuse product ("failed high-end cpu") to a discounted "value" product.
 
In that case, why didn't Tesla just use a smaller inverter for the 40kW? Would it get even more range?

In order to get more range the inverter needs to either be more efficient or lighter.
The inverter is already 90%+ efficient so there is little room to improve and making it smaller probable would make it less efficient not more.
Then weight, it probably only weighs in the ballpark of 50 pounds so there is little room to improve there either.
 
In order to get more range the inverter needs to either be more efficient or lighter.
The inverter is already 90%+ efficient so there is little room to improve and making it smaller probable would make it less efficient not more.
Then weight, it probably only weighs in the ballpark of 50 pounds so there is little room to improve there either.

Anyone know how much the combined inverter/motor unit weighs?
 
Has anyone already done the math on what the Roadster would do with 6,831 of the cells used in the 85 kWh pack in terms of 0-60?

Reducing the number of cells and reducing the weight would help the 0-60 a lot.
4554 of the best Model S cells would produce about the same power and shave off 300ish pounds.
That could cut the 0-60 by 3 or 4 tenths. Done right it could also lower the CG which would be great for handling.

Utilizing more battery horsepower might require a new PEM and/or motor.
 
Reducing the number of cells and reducing the weight would help the 0-60 a lot.
4554 of the best Model S cells would produce about the same power and shave off 300ish pounds.
That could cut the 0-60 by 3 or 4 tenths. Done right it could also lower the CG which would be great for handling.

Utilizing more battery horsepower might require a new PEM and/or motor.

Thanks. I think this is still on topic but since there is talk about maybe someday offering a PEM/Motor and battery upgrade for the Roadster, maybe this is possible.

I wonder for the Model S if going from a 40 kWh to 85 kWh pack years from now will offer the performance bump (without supercharging access though) since the motor seems to be the same across all cars.
 
In fact Tesla has patents on hybrid batteries. Perhaps we will see them in a future vehicle.

Note that the hybrid batteries will likely be most interesting in the smaller and lower range cars.
If the big car long range battery can deliver 450+ hp without hybrid shenanigans then don't bother.
If a short range battery can only deliver 150ish hp then you choose to do the hybrid thing or use all higher C cells or a bigger battery.