There is no doubt that the 0-60 performance of the P85D is something to behold. It's absolutely amazing. I'm just throwing that out for those that keep badmouthing me because I'm not calling the car perfect.
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[updated with *] P85D 691HP should have an asterisk * next to it.. "Up to 691HP"
- Thread starter krisg81
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- Driving Dynamics Model S
There is no doubt that the 0-60 performance of the P85D is something to behold. It's absolutely amazing. I'm just throwing that out for those that keep badmouthing me because I'm not calling the car perfect.
Don't have time to do the charts yet but did several more runs. So far, these are the peaks KWs for each SOC:
90% = 413 KW
89% = 411 KW
81% = 396 KW
70% = 383 KW
66% = 376 KW
60% = 366 KW
A nice linear drop off.
Although that 90% corresponds to about 553 hp, 90% is not a daily charge for me. The only time I go above 80% is for a long trip and in that case I'm not going to be driving fast or aggressively as I'll be trying to maximize my range.
I wonder if these numbers are KW off the battery or coming out of the inverter? I'd like to think the latter. Also, it's probably true that the drive line losses aren't as high with Tesla's driveline going through a simple reducing gear rather than a transmission, torque tubes, and in the case of autos, a torque converter and further in teh case of AWD, an additional transfer case. A typical AWD car is going to lose 20 to 25% by the time the power gets to the wheels while the Tesla is going to be much less. A front wheel drive ICE is in the 10% range and a P85D should be less than that as there's no transmission to go through. Would it be too conservative to estimate only a 5 to 7% total drivetrain loss? If so, any motor or inverter losses would a lot less than typical ICE drivetrain losses. Additionally, Tesla has a far fatter power curve than an ICE.
But even giving Tesla credits for less power lost in the driveline as a way to compensate for less than advertised power and still call it equivalent, it's no where near close enough. For typical states of charge for daily driving the P85D is putting out way less than advertised power.
I'll wait for a real trip before trying 100% but if the relationship holds, 100% would be about 434 KW.
90% = 413 KW
89% = 411 KW
81% = 396 KW
70% = 383 KW
66% = 376 KW
60% = 366 KW
A nice linear drop off.
Although that 90% corresponds to about 553 hp, 90% is not a daily charge for me. The only time I go above 80% is for a long trip and in that case I'm not going to be driving fast or aggressively as I'll be trying to maximize my range.
I wonder if these numbers are KW off the battery or coming out of the inverter? I'd like to think the latter. Also, it's probably true that the drive line losses aren't as high with Tesla's driveline going through a simple reducing gear rather than a transmission, torque tubes, and in the case of autos, a torque converter and further in teh case of AWD, an additional transfer case. A typical AWD car is going to lose 20 to 25% by the time the power gets to the wheels while the Tesla is going to be much less. A front wheel drive ICE is in the 10% range and a P85D should be less than that as there's no transmission to go through. Would it be too conservative to estimate only a 5 to 7% total drivetrain loss? If so, any motor or inverter losses would a lot less than typical ICE drivetrain losses. Additionally, Tesla has a far fatter power curve than an ICE.
But even giving Tesla credits for less power lost in the driveline as a way to compensate for less than advertised power and still call it equivalent, it's no where near close enough. For typical states of charge for daily driving the P85D is putting out way less than advertised power.
I'll wait for a real trip before trying 100% but if the relationship holds, 100% would be about 434 KW.
Approximately how much cooldown time between runs. Also, what (roughly) was the ambient temperature?
SomeJoe7777
Marginally-Known Member
I plotted those and yes, it's a nearly perfect linear dropoff.
This tells me that the power limitation is not the motor or inverter, but it's the battery discharge rate. As the voltage linearly drops along with the state of charge, the discharge current limit is kept constant, resulting in a linear power decrease.
If Tesla does more battery testing, they could raise the discharge rate limit in software and allow higher power. The P85D is new, I would speculate that they need to collect some real-world data from the P85D's in the field to ensure the safety and longevity of the battery pack before allowing higher discharge rates.
If that's an exact match for the voltage curve with SoC, that tells you it's a current limit somewhere, yes. I don't think that's evidence that it is in the battery, though.
The motor windings will have a maximum current rating, and so will the inverter, and even the connecting wiring. I don't know how you would figure out which one of these current limits is driving the car's behavior.
Walter
SomeJoe7777
Marginally-Known Member
From the various dyno curves that have been posted (example), the Model S has 3 ranges of operation:
1. 0 to about 40 MPH: This is the constant high torque range. Power linearly increases with increasing motor RPM, applied motor current is maximum and constant. The limitations in this region are physical -- torque on reduction gears and axles, possibly motor current as well.
2. 40 to about 80 MPH: This is the constant power range. Power is at maximum and constant, torque begins to exponentially decrease along with current. Limitation in this region is a power limit, either in the inverter (AC side) or battery (discharge rate or discharge power).
3. > about 80 MPH, this range is voltage limited. Power begins to decrease as the inverter cannot raise the motor voltage any further to compensate for the back-EMF at high RPM. All parameters including power, torque, and current decrease. RPM still goes up, but at a slower and slower rate.
Given that the decrease in peak power proportional to the state of charge is occurring in range 2, I believe you have to conclude that the limitation is on the DC side. The inverter still has enough headroom to deliver more voltage (therefore more power) to the motor, but the software is stopping it from doing so. This means that either the inverter's elements are at maximum (which means they're probably heat limited), or the battery discharge rate is at maximum. But the inverter's limitations wouldn't change with the state of charge, so I conclude that the power limit must be on the DC side.
With that in mind, since the battery terminal voltage decreases approximately linearly with the state of charge, which matches the linearly decreasing power limits, we can conclude that the discharge current on the DC side is approximately constant across different states of charge, which to me indicates that is the limitation.
Your logic is persuasive.
A current limit anywhere in the battery or between it and the inverter would act this way, right? It could be something as simple as reaching the maximum allowable current through the high voltage contactors...
Walter
Cottonwood
Roadster#433, Model S#S37
Close, but here are a couple of corrections.
In region 1, the torque is mostly limited by tire traction. The traction control limits torque to be just short of the tires slipping, better traction produces higher torque.
Region 2, as you say is constant power. Because power is the product of torque times RPM, or force times speed, torque drops inversely with RPM and speed.Exponential is an often over and mis-used term. If "Exponential" applied here, current would drop as e[SUP]-x[/SUP], but that is not the case here.
thegruf
Active Member
It seems increasingly clear to me that the P85D is simply the model that has the two largest motors fitted that Tesla make at this time, the 85D has the next largest combo.
Equally clear is that the battery and/or inverter as the limiting factor, and most likely the battery as Tesla could always have upgraded the inverter within the +$20K over the 85D
I, for one, doubt there are more significant improvements to come, although Tesla can always surprise, I think we are at the (working) limit of the battery pack.
It would be great to see the 85D times/P85D comparison as I suspect that from >30mph the P85D will be quicker but not by much.
Not only that but the 211hp motor is supposedly a newer design with "lessons learnt" from the 470hp motor so could maintina better thermal efficiency in use.
Sorka's figures above actually go all the way back to the first post of this thread, and support that the performance drops off vs SoC, though in-line with battery voltage as you would expect.
Hopefully even more data for lower SoC can map this out further still
Equally clear is that the battery and/or inverter as the limiting factor, and most likely the battery as Tesla could always have upgraded the inverter within the +$20K over the 85D
I, for one, doubt there are more significant improvements to come, although Tesla can always surprise, I think we are at the (working) limit of the battery pack.
It would be great to see the 85D times/P85D comparison as I suspect that from >30mph the P85D will be quicker but not by much.
Not only that but the 211hp motor is supposedly a newer design with "lessons learnt" from the 470hp motor so could maintina better thermal efficiency in use.
Sorka's figures above actually go all the way back to the first post of this thread, and support that the performance drops off vs SoC, though in-line with battery voltage as you would expect.
Hopefully even more data for lower SoC can map this out further still
SomeJoe7777
Marginally-Known Member
Yes, you're correct that tire traction can also be a limit in region 1. In ideal conditions (i.e. good/new tires, dry pavement), this shouldn't be an issue, and torque should be limited by the other items listed in region 1.
You're right, exponential isn't the correct term. I was looking for a more generic term to describe the decrease in torque and emphasize that the shape is non-linear.
Cottonwood
Roadster#433, Model S#S37
Even on dry pavement with good tires, if you disable traction control by allowing tire slip, the P85D will smoke the tires. This tells me that tire traction is the limiting factor to initial acceleration and the car has more than enough torque to overcome the tire traction limit.
In the constant power region, because power is proportional to the product of torque and rpm (speed), then torque is inversely proportional to rpm (speed). That seems pretty generic and non-linear to me. :wink:
Kalud
Active Member
Yes its a mistake, I did multiple runs to compare each cars and got older results. These are the latest best observed values.
P85D: 414kW (555hp)
P85: 352kW (472hp)
S85: 330kW (443hp)
But overall, the peak value doesn't means much as the ramp-up speed is the most important thing to show here. I added little red arrows to show where the car hits 60mph. I don't think the 691hp thing is much more important than achieving the stated 0-60mph figure, repeatably over and over again. Given SOC is about 90%.
Updated graph:
Gizmotoy
Active Member
Wow, no kidding. Because with only a 29hp advantage peak, the P85 shaves more than a second off the S85's 0-60. Huge area between the curves, though. Are the arrows from the actual 60mph point from the plotted data or from the published 0-60 times?
Also interesting from maybe 45mph on up the P85D only has another ~60hp on the P85. Cool graph, thanks.
Kalud
Active Member
Yes those arrows are where the car really gets to 60mph in the actual data. I will get another graph giving time vs speed for the 3 cars, its also eye opening. The area under the curve is key in the power graph. Maybe I should make a integrated of the power over the period but I think its quite obvious already.
Two missing tests are the new 70D and 85D, I'd like to include those too...
thegruf
Active Member
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