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where does the extra acceleration come from in 85/P85 vs. 60?

where does the extra acceleration come from in 85/P85 vs. 60?

This is just a technical question out of curiosity -

Where is the extra acceleration coming from in the 85 and P85? For the 85, is it that the additional batteries (I assume) are dynamically switched to run the motor in series, and therefore you get that much more voltage to the system? And then for the P85, is there actually a larger motor?

Thanks.

DJung | September 15, 2013

the P85 has a different inverter and if I have heard correctly, the 85 and 60 are about the same speed. Tesla likes to jack up the 0-60 times to keep insurance rates down

omarsultan.ca.us | September 15, 2013

The P has a different inverter. It is hand wound which apparently allows for denser windings. The 85s can deliver more current than the 60s so are slight faster for 0-60 times per the Tesla website.

O

ian t.wa.us | September 15, 2013

It's the motor in the P that is supposedly hand wound. The inverter is higher capacity so it can pass along more juice to the hand wound motor.

Cheers!

jat | September 15, 2013

When you have fewer cells (the voltage is the same, so the difference is in the number of parallel cells), the power available at a given discharge rate is lower.

Ie, if you have 17 cells in parallel supplying 1A each, you get 17A at the cell voltage. If you have 12 cells in parallel, you only get 12A. Now you might be able to draw more current from the smaller pack, but you are then discharging at a higher rate which causes greater degradation and builds up more heat in the batteries.

diegoPasadena | September 15, 2013

@ goneskiian : During the factory tour I asked specifically if there was a difference between the 60 and the 85 motors, and if so what it was, and I was told it's the same motor. So that leaves the inverter as a source for the difference.

jat | September 15, 2013

@diegoPasadena - I am pretty sure the inverter is the same as for S60 and S85, and is different only in the P85 and P+.

Brian H | September 16, 2013

jat, yes, this was settled long ago. Inverter is upgraded on the P85. All Tesla sources confirm.

May not be handwound in volume production, the Roadster Sport had those, and perhaps the first Ps.

nickjhowe | September 16, 2013

85 and P85 is well understood - definitely a different inverter, and allegedly a hand wound motor.

60 to 85 has not been confirmed (to my knowledge). If the 60 is indeed slower to 60mph and down on power, then that implies fewer kW. If the motor and inverter are the same, then the 60 must be lower on voltage, current or both. This could be fewer cells, or same # of cells but different chemistry.

chrisdl | September 16, 2013

I think the baterry voltage is likely always 360 VDC to correspond with the Superchargers.

The S60 and S85 may easily have the same inverter with a different inverter firmware onboard, effectively limiting the power of the S60.

jat | September 16, 2013

@chrisdl - if the voltage is the same, which I believe to be the case, lower kWh storage capacity means lower peak current output.

chrisdl | September 16, 2013

jat: That makes sense.
You'd still need an adjusted inverter (firmware or otherwise), or you'd fry your battery.

yodasminion | September 16, 2013

I talked to the advisor in Fremont and he explained.

All three cars have the exact same motor. The S60/85 both have the same inverter, while the P's have a high powered inverter. The S60 is software limited in its acceleration, though the limitation is fairly minimal (only a fraction of a second), so telling the difference between a 60 and an 85 would be fairly hard to do, even driving them back to back. The high powered inverter on the P provides a larger pipe for electrons to flow, thus allowing faster acceleration. To be clear though, he was very clear that the S60 is neither firmware nor hardware limited, it's software, not hardware/firmware.

chrisdl | September 17, 2013

Hum... Firmware = Software :-)

chrisdl | September 17, 2013

yodasminion:
The difference between an S60 and S85 is a fraction of second for which acceleration? 0-60 mph, I guess? Official number is that an S80 is half a second faster than an S60. I agree that you'd be hard-pressed to feel that difference in practice.

When driving the car, the difference between 302 and 362 bhp should be noticeable though. We're talking about a 20% uplift in power, after all.

Benz | September 17, 2013

This is interesting stuff. I guess that about 40% of the buyers will choose a 60 kWh Model S, and about 40% of the buyers will choose a 85 kWh Model S, and about 20% of the buyers will choose a Performance or Performance + 85 kWh Model S. That's just a rough guess, by the way.

Navi | September 17, 2013

Don't think so, as far as i can tell most have the P version, then 60, then 85.

jat | September 17, 2013

@Navi - in the ATL group, there are about 3 P85s, 1 P+, 1 S40, 2 S60, and over 25 S85s (a couple of those are signatures).

Benz | September 17, 2013

Tesla Motors have never mentioned about this. Elon Musk once mentioned that the demand for the 40 kWh Model S was only 4% of the total of all Model S demand.

Is that ATL group a good and reliable source? What exactly is ATL group?

Benz | September 17, 2013

Maybe Tesla will undisclose this information in 2014, when the full year of 2013 will have been ended.

eddiemoy | September 17, 2013

the s60 and s85 both have power limit of 240kw, the p85 has power limit of 320kw.

don't know why the s85 is faster than the s60. think it may have to do with more cells allowing power to be pulled out quicker. but peak for both the same.

shop | September 17, 2013

Guys, you're all wrong - THIS is the difference:

http://www.youtube.com/watch?v=3S4_1z50rqs

chrisdl | September 17, 2013

eddiiemoy:
Where do those numbers come from?
From the Tesla spec page:

Peak Power (Vehicle specific power when battery is taken into account):
60: 225 kW
80: 270 kW
80P: 310 kW

Brian H | September 17, 2013

Long term, Elon originally thought the 60s would be the most popular. So far, 85s are in the lead.

GDH | September 17, 2013

lmao @shop

jat | September 17, 2013

I have achieved 318kW peak in my S85 at the track, as reported by the streaming API and confirmed roughly from the power gauge (though it gets cramped at the top end since it is log-scale so it is hard to be accurate).

jat | September 17, 2013

@Benz - ATL = Atlanta

chrisdl | September 18, 2013

Typo in my post: 80 = 85 and 80P = 85P ... Duh! :)

chrisdl | September 18, 2013

What have we learned so far:
(Side note: Some numbers are approximate (but all are based on actual specs!), however they still give quite an accurate idea of what you can do with each motor / battery combo.)

1) S60 and S85 have the same motor, but different batteries.
P85 has another, more powerful motor.

2) Motor specs (from Tesla website)
Power:
S60: 285 kW - S85: 285 kW - P85: 350 kW (WITHOUT taking battery into account = theoritic)
S60: 225 kW - S85: 270 kW - P85: 310 kW (power WITH battery taken into account = realistic)
Torque:
S60: 440 Nm - S85: 440 Nm - P85: 600 Nm

3) Number of cells per battery (each cell has a capacity of approx. 10 Wh, rounded for simplicity's sake)
=> 60 kWh battery has about 6000 cells.
=> 85 kWh battery has about 8500 cells.

4) Battery is charged at 360 VDC at supercharger
=> About 100 (one hundred) 3.6 V battery cells in series in a single bank.

5) Number of banks per battery
* 60 kWh battery has about 60 banks of 100 cells
* 85 kWh battery has about 85 banks of 100 cells

6) Maximum discharge current
Maximum discharge current is approx. 10 A per cell.
=> 10A per bank of 100 cells
=> 60 x 10A for 60 kWh battery = 600 A
=> 85 x 10A for 85 kWh battery = 850 A

7) Maximum discharge power, at 360 V per bank
* 60 kWh battery: 600 A x 360 V = 216 kW
* 85 kWh battery: 850 A x 360 V = 306 kW

Considering my rounding errors, this sounds like a pretty accurate calculation.

Conclusion:
* S60 is limited by maximum battery discharge level of 60 kWh battery
* S85 is limited by maximum power of motor
* P85 is limited by maximum battery discharge level of 85 kWh battery

There you go :-)

jat | September 18, 2013

@chrisdl - I agree with your conclusion. One thing you don't consider is that resistive losses become quite large at high currents. Ie, at 320kW output you are losing about a quarter of the power to waste heat (which is also why it heats up quickly when driving at the track). A 60kWh car will have this problem worse, as the current per cell is higher at lower overall power levels as well.

http://www.teslamotors.com/en_GB/forum/forums/analyzing-car-efficiency-d...

chrisdl | September 19, 2013

jat:
Thank you, that's excellent info. I'll try to incorporate that as well.
It seems that Tesla draws a seriously high current out of the cells under full load. Probably more like 14 A instead of my initial estimate of 10 A. Wow! I need to recalculate :-)

chrisdl | September 19, 2013

I gathered a lot of data (thank you everybody who helped me), so here's a more accurate calculation. The conclusion stays the same.
Note that the amount of heat generated by the battery pack is enormous at full power output (up to 86 thousand watt!).

1) S60 and S85 have the same drivetrain, but different batteries.
P85 has another, more powerful drivetrain.

2) Motor specs (from Tesla website)
Power:
S60: 285 kW - S85: 285 kW - P85: 350 kW (WITHOUT taking battery into account = theoritic)
S60: 225 kW - S85: 270 kW - P85: 310 kW (power WITH battery taken into account = realistic)
Torque:
S60: 440 Nm - S85: 440 Nm - P85: 600 Nm

3) Number of cells per battery (each cell has a capacity of approx. 12 Wh, rounded for simplicity's sake)
=> 60 kWh battery has about 4992 cells.
=> 85 kWh battery has 7104 cells (confirmed information from Tesla)

4) Battery is charged at 360 VDC at supercharger
=> 96 3.6 V battery cells in series in a single bank

5) Number of banks per battery
* 60 kWh battery has 52 banks of 96 cells
* 85 kWh battery has 74 banks of 96 cells

6) Maximum discharge current
Maximum discharge current is 12.5 A per cell
=> 12.5 A per bank of 96 cells
=> 52 x 12.5 A for 60 kWh battery = 650 A
=> 74 x 12.5 A for 85 kWh battery = 925 A

7) Power loss in battery cells (dissipated heat)
The internal resistance of a fresh battery cell is about 100 mOhm (0.1 Ohm)
=> 60 kWh battery: 650^2 x 0.1 = 42 kW
=> 85 kWh battery: 925^2 x 0.1 = 86 kW

8) Maximum discharge power, at 346 V per bank:
=> 60 kWh battery: 650 A x 346 V = 225 kW
=> 85 kWh battery: 925 A x 346 V = 320 kW

9) Total energy usage in battery (power output + heat loss):
=> 60 kWh battery: 225 + 42 = 267 kW
=> 85 kWh battery: 320 + 86 = 406 kW

Comparison model spec power output versus battery power output:
* S60: 225 kW vs 225 kW
* S85: 270 kW vs 320 kW
* P85: 310 kW vs 320 kW

Conclusion:
* S60 is limited by maximum battery discharge rate of 60 kWh battery
* S85 is limited by maximum power of drivetrain
* P85 is limited by maximum battery discharge rate of 85 kWh battery

chrisdl | September 19, 2013

Correction to this section (scratch the one above):

Comparison drivetrain spec power output versus battery power output:
* S60: 285 kW vs 225 kW (battery limited)
* S85: 285 kW vs 320 kW (drivetrain limited)
* P85: 350 kW vs 320 kW (battery limited)

jcaspar1 | September 19, 2013

The sales person I talked to at Santana Row said the motors were all the same for the 3 models, only the inverter was different for the P models. He told me the motor has the potential for nearly 900hp, but is limited by the inverter and current flow from the battery. 85 and 60 difference he said was simply how fast you could safely draw current from the battery.
FWIW

chrisdl | September 19, 2013

jcaspar1:
Yes, I've heard the same told by multiple people, although it is the first time I hear the 900 hp line, so I have no reference frame for that. There's an article on the internet referring to a 900 A inverter for the S60/S85 and an 1200 A inverter for the P85, but I have to reference frame for that either. Much to learn!

fyi: in my lingo the drivetrain (aka powertrain) is the motor-gearbox-inverter shrink wrapped package. I want to avoid the motor vs inverter discussion altogether, because in the end it makes no difference. Therefore I'll use drivetrain from now on.

omarsultan.ca.us | September 19, 2013

I specifically asked about this on the factory tour. They said the motors are the same across P and non-P. The difference is in the inverter. The P models get a hand wound inverter because they can get greater winding density that way. The tour guide said it was good there were still some things humans could do better than the robots. :)

O

chrisdl | September 19, 2013

omarsultan:
Oops, sorry, but I find that confusing. An inverter has no coils, so it doesn't have to be wound, also not by hand :-)
So I guess they were referring to the motor. But then again, many people (the force of the people!) have indicated already that there is no difference in the motors of an S60/S85/P85. The difference is allegedly only in the inverter. And then perhaps even only in the firmware of the inverter. Or the software, as some people call it. And I've also heard that only the Roadster motor is hand-wound, not the Model S motor. I guess that makes sense, since it wouldn't scale that well at a production of hundreds a week.
Anyway... color me confused.
Perhaps the tour guide equally was confused :-)

chrisdl | September 19, 2013

Quick, before anyone complains! An inverter does have coils, of course... and capacitors, and transistor, and a crapload of other electronics. But not those kind of coils like the windings in an electric motor, just to be 100% clear.

eAdopter | September 19, 2013

@chrisdl

Regarding:
"1) S60 and S85 have the same motor, but different batteries.
P85 has another, more powerful motor."

Where did you find information (from TM) regarding motor power? I know there's been plenty of speculation and hearsay, but I haven't seen anything official from TM. Can you post a link to the TM reference?

eAdopter | September 19, 2013

Sorry, I posted after taking too long and not reading the current information.

But, same question for the inverter.

While it's possible a different inverter is used in the P85, there's strong evidence the whole system is software limited.

For example:
1. A recent software update changed the kWh utilization scale on the dashboard.

2. If you drive the car to a point with less than 10 miles of range remaining (I have), the software imposes a kWh throttle maximum.

slipdrive | September 19, 2013

This is why these forums are so great. I learn more than I ever imagined. I'm a Chemical Engineer and can tell you where your gasoline (used to) come from, but chasing electrons is a challenge. thanks for the lesson and details about these great cars!

chrisdl | September 20, 2013

eAdopter:
Yes, the thread is a bit messy due to the forum's limitations, so I understand your confusion.

To be clear:
I don't know whether the motor, inverter, firmware, or software make the difference between a P85 and the other models, but it is most certainly one or multiple of those aspects. For the discussion of what limits the power this luckily has been irrelevant so far. From now on, I try to refer to the whole of motor/gearbox/inverter block as "the drivetrain". I'm open for suggestions for a better name. Powertrain, could be another option, for example.