Elon said "We test drove some initial units and it just wasn't a good product."
That tells me they were already well on their way to developing it. And I am sure that the acceleration performance factored as much into his judgement as range.
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40kwh Model S canceled
- Thread starter gobagheera
- Start date
That tells me they were already well on their way to developing it. And I am sure that the acceleration performance factored as much into his judgement as range.
Very interesting - I wasn't aware of that. I do know that I test drove the RAV4 electric and it was very sporty to me. As everyone knows, the RAV4 has a 42 kWh battery and a "detuned" Tesla motor. Of course nothing like the MS I test drove but certainly better than my current car. I wonder if the MS just wasn't meeting it's performance spec's then. The announcement did suggest that they were saving mony by not developing the 40 kWh. If one was built and tested, perhaps that really means they didn't want to sped the time to optimize the design. Another possibility is that the cell chemistry they were planning to use for the 40 kWh was sub-par and 'development' refers to formulating a different chemistry and/or pack design with similar cells used in the 60 kWh.
rlpm
S P85 | Sig X _P90D_
Nice. I wonder who will be the first to unlock the bonus levels post-production.
I'm absolutely sure that the very low sales rate was the prime factor in the cancellation. "Less than 4%" of reservations is less than 800 a year at planned production rates, and given the low margins on the 40 kWh car, they probably decided that the margins didn't actually cover the cost of the required engineering work.
(Apparently they were having some trouble with it. Either they had to use different battery chemistry, which requires reprogramming a lot of powertrain-related stuff, or they had to have a lighter pack, which has complicated effects on the suspension and behavior of the car, or both. While these are solveable engineering problems, the question was, are the profit margins on <800 cars a year actually worth doing the engineering? )
With the RAV4EV having the same size battery pack, the people who would have bought the 40kWh may be buying Tesla powertrains anyway.
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Regarding the "software options" thing: Tesla does have an incentive to remove hardware from cheaper cars. Metal costs money. I suspect the difference between the P85 and ordinary 85 is something as dopey as larger-gauge copper wiring, but copper costs money.
Also, regarding the 40s which are "software limited" 60s -- probably some of them will be "unlockable", but don't be at all surprised if Tesla carefully uses the slightly-defective parts which didn't pass QC, but were good enough for 40kWh and for lower acceleration, to build your powertrain. Elon always has an eye for profit.
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I somehow doubt that Tesla thought that part through. :biggrin:
If any hackers successfully get into the car -- and given these incentives, someone will -- I'd appreciate it if you'd contact me. I have some questions about the open source software which Tesla is using in violation of its licenses, and you'd be able to answer those questions.
According to who?
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But they did need it. To drag people like you in.
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But the cars are all just software limited. Top Speed, 0 to 60 and now range. Is there some technical reason a properly wired 40 kWh car could not do the same 0-60 as the 85? (beside draining the bathtub too quickly?)
What a fun prize Tesla could offer here. First N "40 kWh" vehicle owners to travel 200mi. on a single charge gets an "unlock" achievement that makes the full battery available. (Assuming N is > 0.)
Great to throw the RAV4 into the mix. Watching that video it seems like Elon would not be happy with that as a Tesla product. His standards are high. So high he dropped a product that was not up to his standards. (OT) So what does that level of perfectionism mean for the Bluegen3
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But they never marketed it. We never saw or drove one. All the cars reviewed were either P85s or P85s with the new performance package. Where was the Leaf VS Tesla 40kkWh head to head. Where were the stories from happy budget Tesla owners? Without a car out there it's not suprising they sold few. It was a Tesla for $50K. Who would not love that?
Is this inside info or can you show links?
JRP3
Hyperactive Member
Stress on the cells. Example to get 85 KW of power from the 85kWh car takes less current from the cells than getting 85 KW of power from the 60kWh car. You get more voltage sag and the cells need to put out more current to hit the same level of power.
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The software limited "40's" have the same acceleration as the 60's, so no.
Neither. That was personal communications from random people inside Tesla who I was talking to on the phone for other reasons. They casually mentioned the difficulties with 40kWh design as internal company rumor.
Edit: the effects of a lighter-weight pack on the car design were specifically mentioned as difficult.
For a $10k prize, I'd put the car on a mobile dyno and drive it around on the back of a truck.
stopcrazypp
Well-Known Member
Peak battery power is lower. Peak battery power is proportional to the capacity. You basically multiply the capacity number by 4 (the peak "C-rate") to get the rough peak power. You get:
40kWh -> 160kW
60kWh -> 240kW
85kWh -> 340kW
Given Tesla was planning to make the 40kWh pack have 175kW of peak power, that's already stressing the cells more than the ~4C rate Tesla has been using.
The RAV4EV's 41.8kWh pack is has a peak output of 129 kW (peak motor output is 115kW). 0-60 is 7 seconds in sport mode. Model S 40kWh (which BTW is now completely removed from the site) was slated to have 0-60 in 6.5 seconds.
The RAV4EV was originally designed as an ICE car and got converted. The addition of the 42kWh pack under the floor lowered the center of mass compared to the ICE version and likely improved the handling characteristics. The Model S motor gives it that EV torque curve, which I found very satisfying during a test drive. It was fun to tool around in a little SUV with that much pep and not feel like you were going to roll over.
I believe the Model S was essentially designed around the 85kWh pack. The suspension was designed with that low center of mass in mind. A 40kWh pack with the same type of cells has significantly lower weight, and would effectively raise the center of mass. So the handling would be impaired. To avoid redesigning the suspension you'd have to add ballast mass, which would just be wrong when the goal is efficiency. The smaller pack also means lower peak power is available. So it definitely is a lower performance vehicle. These are the things I would think make it a "hobbled horse", not really the range.
VFX is right, though, that it wasn't really marketed except perhaps for the "$50K base price" soundbite. And Tesla did things to make it even less desirable. No matter how early you ordered, 40kWh reservation holders got pushed to the back of the production line. Also, as far as I can tell, there is no technical reason the 40kWh packs couldn't have used the superchargers. They would have charged at a lower rate, but would be done charging in about the same time as the other pack sizes. So that limitation seems to have been driven more by marketing than anything else.
I believe the Model S was essentially designed around the 85kWh pack. The suspension was designed with that low center of mass in mind. A 40kWh pack with the same type of cells has significantly lower weight, and would effectively raise the center of mass. So the handling would be impaired. To avoid redesigning the suspension you'd have to add ballast mass, which would just be wrong when the goal is efficiency. The smaller pack also means lower peak power is available. So it definitely is a lower performance vehicle. These are the things I would think make it a "hobbled horse", not really the range.
VFX is right, though, that it wasn't really marketed except perhaps for the "$50K base price" soundbite. And Tesla did things to make it even less desirable. No matter how early you ordered, 40kWh reservation holders got pushed to the back of the production line. Also, as far as I can tell, there is no technical reason the 40kWh packs couldn't have used the superchargers. They would have charged at a lower rate, but would be done charging in about the same time as the other pack sizes. So that limitation seems to have been driven more by marketing than anything else.
Perhaps you might call it marketing, but "at a lower rate" might make it not "supercharging" as originally intended -- thus watering down the whole concept of supercharging. But this has been discussed before, at length.
An extreme example: "My vehicle totally 'supercharges' at 220V/30A at the Tesla site, it's awesome!" is not something Tesla would want ever uttered.
It would be CHAdeMO level charging and done in the same amount of time as the other packs. If multiple Model Ss are supercharging, the power is shared anyway. At the same C rate this would be 40+kW (twice the rate of an HPWC), not the 6.6kW as in your example. A CHAdeMO adapter would have been quite useful for that size back, assuming the car had the DC hardware and firmware. At any rate, the issue is moot.
I guess what I have trouble with, hence the reply with example, is assertions such as "no technical reason" when it's easy to offer a simple example of a technical reason: Tesla is defining supercharging at a certain threshold and they don't consider the rate that could safely be used for 40 kWh as meeting that threshold.
You may call it a marketing reason, but I don't. Cell phones offer a simple example: some people would like to see things like "4G" have a numerical performance description rather than a marketing description. Just because Tesla hasn't publicly disclosed the numerical threshold doesn't mean they don't have one in mind.
Again, you may consider that marketing alone but that doesn't mean we have to agree on that.
In short, don't make assertions that aren't supportable and I won't push back.
We're all aware that this forum gets randomly quoted, so leaving unsupported assertions unchallenged does Tesla a disservice.
You may call it a marketing reason, but I don't. Cell phones offer a simple example: some people would like to see things like "4G" have a numerical performance description rather than a marketing description. Just because Tesla hasn't publicly disclosed the numerical threshold doesn't mean they don't have one in mind.
Again, you may consider that marketing alone but that doesn't mean we have to agree on that.
In short, don't make assertions that aren't supportable and I won't push back.
We're all aware that this forum gets randomly quoted, so leaving unsupported assertions unchallenged does Tesla a disservice.
That's not what I would call a technical reason. Charge rate by necessity is variable, regardless of the size of the pack. They'd all get the same percentage of charge as a function of time. And as I already pointed out, if more than one car is plugged in, the power is distributed. It's like you're saying if two cars are charging, neither is actually supercharging because they are now getting half the power.
??? I supported my opinion with technical reasoning. You're not actually pushing back with anything of substance and 4G is a marketing term (as is "Supercharging" of course). We don't have to agree. I appears to me that your objection is mainly because you think saying "marketing reasons" sounds bad. I don't. I think it sounds like reality.You may call it a marketing reason, but I don't. Cell phones offer a simple example: some people would like to see things like "4G" have a numerical performance description rather than a marketing description. Just because Tesla hasn't publicly disclosed the numerical threshold doesn't mean they don't have one in mind.
Again, you may consider that marketing alone but that doesn't mean we have to agree on that.
In short, don't make assertions that aren't supportable and I won't push back.
We're all aware that this forum gets randomly quoted, so leaving unsupported assertions unchallenged does Tesla a disservice.
There are plenty of reasonable marketing or even logistical reasons why the 40kWh pack cars were not given supercharger access, so I'm not necessarily saying it was a bad decision. But in my opinion there is no physical technical (i.e., electrical engineering) reason those cars couldn't have made use of the superchargers.
At any rate the simple point I was making, for the purpose of this thread topic, is that the demand for the 40kWh pack could have been higher if not for things I mentioned a few posts back.
boilerbots
Member
The power that a pack contains doesn't give you enough technical information to figure this out. Since watts = voltage X amps but a battery pack can be wired in parallel or series you can't really determine what they planned for the 40 kW pack.
Looking at the original specs for the motor output the 40 kW was supposed to have equal torque but lower HP output at lower RPMs. This would seem to indicate that the pack was originally going to have a lower voltage (less cells in series). The motors torque output is directly related to current. Horse power is directly related to torque X RPMs and the speed that a motor can spin is based on the voltage at the motor (back EMF).
Someone asked why a lower power battery could perform the same as the 85. There are several reasons. First there are most likely less cells in parallel in the smaller packs. When you put cells in parallel you can draw more current out of them. When you draw more current then you get more torque and more torque means faster acceleration to start and ultimately more HP at higher RPMs. Of course you have to keep on accelerating until you reach 60 mph or a 1/4 mile so eventually without enough volts in the pack the motor will hit it's voltage limit and thus quit accelerating. Anyway this is a mess to explain in a forum but to put it lightly, NO, you can't just make a small battery perform like a big battery especially when you are trying to not destroy the batteries life.
Can you super charge a smaller battery pack? Perhaps but this is also complicated and depends on a large number of factors which I don't have time to discuss right now.
Looking at the original specs for the motor output the 40 kW was supposed to have equal torque but lower HP output at lower RPMs. This would seem to indicate that the pack was originally going to have a lower voltage (less cells in series). The motors torque output is directly related to current. Horse power is directly related to torque X RPMs and the speed that a motor can spin is based on the voltage at the motor (back EMF).
Someone asked why a lower power battery could perform the same as the 85. There are several reasons. First there are most likely less cells in parallel in the smaller packs. When you put cells in parallel you can draw more current out of them. When you draw more current then you get more torque and more torque means faster acceleration to start and ultimately more HP at higher RPMs. Of course you have to keep on accelerating until you reach 60 mph or a 1/4 mile so eventually without enough volts in the pack the motor will hit it's voltage limit and thus quit accelerating. Anyway this is a mess to explain in a forum but to put it lightly, NO, you can't just make a small battery perform like a big battery especially when you are trying to not destroy the batteries life.
Can you super charge a smaller battery pack? Perhaps but this is also complicated and depends on a large number of factors which I don't have time to discuss right now.
This discussion highlights that the two main problems of a 40kWh pack in a Model S were lower peak charge/discharge power and impaired vehicle dynamics due to higher center of gravity. Both could be addressed by using higher power cells with less energy density. More power and more weight in the pack. plus supercharging at 60kW a possibility. We don't know if Tesla tried, if they tried hard enough, or if they pulled the plug prematurely while looking at just 4% of the early reservations asking for the 40kWh pack.
IMO the $50k price tag served very well to stir interest in Tesla Model S. People sold themselves up as they delved further into the EV topic.
My conclusion is, it would have been wise for Tesla to keep the entry model even if gross margins take a hit.
IMO the $50k price tag served very well to stir interest in Tesla Model S. People sold themselves up as they delved further into the EV topic.
My conclusion is, it would have been wise for Tesla to keep the entry model even if gross margins take a hit.
JRP3
Hyperactive Member
Boilerbots,
Your post is a bit confusing. First, the pack is 40kWh, not 40KW. The problem with using lower voltage means the operating voltage of the drive components, BMS, and charging components will be lower. This can be dealt with of course but it means more changes. Using the same operating voltage but limiting current draw is easier and more efficient. You also contradict yourself by first saying the cells in parallel are the same, then you say there are most likely less cells in parallel, so you're arguing opposite points. You may be correct that Tesla lowered the pack voltage but kept the same current, or was going to, but that's the more difficult and expensive way to go, IMO.
It's true that torque is related to current, but voltage keeps the torque up at higher RPMs. Back EMF is what limits torque at higher RPM's, and that limit comes sooner with a lower operating voltage.
Your post is a bit confusing. First, the pack is 40kWh, not 40KW. The problem with using lower voltage means the operating voltage of the drive components, BMS, and charging components will be lower. This can be dealt with of course but it means more changes. Using the same operating voltage but limiting current draw is easier and more efficient. You also contradict yourself by first saying the cells in parallel are the same, then you say there are most likely less cells in parallel, so you're arguing opposite points. You may be correct that Tesla lowered the pack voltage but kept the same current, or was going to, but that's the more difficult and expensive way to go, IMO.
It's true that torque is related to current, but voltage keeps the torque up at higher RPMs. Back EMF is what limits torque at higher RPM's, and that limit comes sooner with a lower operating voltage.
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