Model S on the Track - A Review

[walla2]

Perhaps someone handy with cars could design a liquid nitrogen blast to the undersurface of the car to cool the pack down. Could be done while pitting or perhaps while on the go (better).

 

[WarpedOne]

I'm sure it would be no biggie for Tesla's engineers to design a more powerful cooling system. They probably don't do it on Model S for cost considerations (and maybe also cosmetic design considerations - it has rather small radiators).

It is not the cost and it is not the size of radiators - it is the air/radiation cooling of the motor rotor.
To improve on it, they would need to totally redesign the motor to include oil cooling like Rimac has done to enable prolonged highpower output:

Permanent magnet motors achieve the highest power-to-weight ratio of any motor type. Most PM motors are water-cooled. In such motors, coolant fluid circulates through a jacket around the stator. Such motors deliver good short-term performance but their rotors tend to overheat during continuously demanding conditions such as race-track use. Besides of the inconvenience of a time-limited performance, such motors are in danger of demagnetization which can permanently damage the motor. Rimac motors are rotor and stator cooled with low viscosity oil which is pumped by an integrated pump. The integrated heat-exchanger transfers heat to the external water/glycol circuit which is circulating through the vehicle and radiators (the oil stays always inside the motor and does not circulate through the vehicle). This unique design is the guarantee for flawless performance even during very demanding race-conditions.

Tesla doesn't use PM magnets in their motors hence there is no danger of demagnetization and rotor is allowed to reach higher temps without damage (multiple hundreds of degrees) but still there is a point where hot turns into too hot and rotor is not strong enough anymore for them to guarantee no problem operation at +250 Hz.

Oil-cooled rotor also has higher friction (i.e. losses) than air-cooled one. Such track-ready Model S would have significantly lower range even at everyday usage. IMHO it is not worth it to Tesla to spent RD on such motor at least not for the time being.

 

[strider]

Great stuff, Doug_G! Love the profiles idea!

One of my ICE-loving, "you-greens-are-idiots" friends has been challenging me to race against his Corvette at the Infineon Raceway in Sonoma. I'll keep the race to one lap Or, take him to the neighboring drag strip instead. There are unfortunately no charging stations there, I believe.

Garage 1 at Sonoma has a NEMA 6-50 but that is the only publicly accessible (and you typically have to pay to rent a garage for the day) high voltage outlet I know of. All the Laguna Seca garages have 6-30's, and Thunderhill has a bunch of 14-50's. I have been scouring track facilities when I'm there in preparation for an electric motorcycle in a year or so.

Does anyone recall from last year's REFUEL event at Laguna Seca if the Tesla Engineering MS's were power-limiting as quickly as the production cars? Curious if they were using more liberal thresholds than customer cars.

 

[Doug_G]

Maybe I missed this, what was the temperature outside during your run?

Wore a sweater all day. Started downright cold, improved somewhat during the day. High was a very windy 17C.

 

[Kaivball]

Nice write up.

When they get a super charger at Thunderhill race track I will do the same.

 

[Grendal]

As part of the Performance + package Tesla should have the ability to "supercool" the pack and motor to allow for sustained fun at the track.

I really hope that Tesla figures this one out before the "Top Gear" guys get ahold of one. They will thrash it around the track and the moment it goes a little weak they will spend 15 minutes of air time complaining about how electric cars don't work.

 

[Aussie]

Oh dear, just came across this now. So with this problem we can only hope that Jeremy Clarkson will not get his hands on a Model S.

 

[JRP3]

It is not the cost and it is not the size of radiators - it is the air/radiation cooling of the motor rotor....


Oil-cooled rotor also has higher friction (i.e. losses) than air-cooled one. Such track-ready Model S would have significantly lower range even at everyday usage. IMHO it is not worth it to Tesla to spent RD on such motor at least not for the time being.

Model S has a liquid cooled motor and inverter. I'd bet the inverter heat is causing the limiting, since the motor can handle higher temps than the inverter components. I think the answer is larger radiators, and maybe more powerful radiator fans. There might be room in the front to add more cooling capacity, maybe a custom radiator or something.

 

[djp]

Model S has a liquid cooled motor and inverter.

I think WarpedOne is referring to the rotor itself which is air cooled and not immersed in oil. The liquid cooling is a jacket around the motor.

Damn it, so much for my hopes for a liquid cooled Roadster motor solving the power limits on a track. Sounds like it wouldn't help much since the heat is tough to dump with or without a water jacket.

 

[stopcrazypp]

(Some on these forums have speculated that the car was deciding to limit power based on Projected Range. I have to disagree - it's pretty clear that the limiting factor is drive train temperature. Without readouts I can't tell if it was the motor or power electronics... but you can tell by how fast it happens that it's one of the two. Based on my Roadster experience the battery pack has way too much thermal inertia for it to be the cause.)

So I take it you monitored your projected range and it never fell below 30 miles or so? At 1200Wh/mi, you only have 71 miles of projected range with a full charge, so at about 42% SOC you would fall under that number with that consumption.

 

[Doug_G]

So I take it you monitored your projected range and it never fell below 30 miles or so? At 1200Wh/mi, you only have 71 miles of projected range with a full charge, so at about 42% SOC you would fall under that number with that consumption.

I stopped watching it long before it got that far. I was charging at 70A whenever my run group was off so it took quite a while to drop that much. Before then I was convinced that it was thermal limits. The proof was that simply pausing for a few minutes got full power back. That is consistent with the thermal limits hypothesis and inconsistent with the projected range hypothesis.

 

[JRP3]

I think WarpedOne is referring to the rotor itself which is air cooled and not immersed in oil. The liquid cooling is a jacket around the motor.

Are you sure? Tesla has patents for liquid cooling the rotor of an AC induction motor.

 

[stopcrazypp]

I stopped watching it long before it got that far. I was charging at 70A whenever my run group was off so it took quite a while to drop that much. Before then I was convinced that it was thermal limits. The proof was that simply pausing for a few minutes got full power back. That is consistent with the thermal limits hypothesis and inconsistent with the projected range hypothesis.

Could both be at play? You may have hit the thermal limits, while others have not. Hard to tell right now where the limit is without battery/motor/inverter temp gauges. For the Roadster, the inverter was by far the main limiter, but the battery sometimes heats up too (charging the car heats up the battery too, so that might contribute also). The motor actually doesn't heat up that easily in the 2.0 version (with new fans).

I think the Model S's inverter is now liquid cooled, so it should fare better than the Roadster.

 

[richkae]

For the Roadster, the inverter was by far the main limiter, but the battery sometimes heats up too (charging the car heats up the battery too, so that might contribute also). The motor actually doesn't heat up that easily in the 2.0 version (with new fans).

Have you had your Roadster on the track? I have and can say with 100% certainty that my Roadster ( 2.0 with new fans ) was power limited because of heat in the motor and not the PEM.
I can dig up log files if necessary.

 

[brianman]

As part of the Performance + package Tesla should have the ability to "supercool" the pack and motor to allow for sustained fun at the track..

What does this desired behavior have to do with the Plus package?

- - - Updated - - -

So I take it you monitored your projected range and it never fell below 30 miles or so?

During autocross, my projected range got around or below 30 when I started to see the acceleration limiter.
During lapping, I saw the limiter with a projected range well above 30.

 

[Doug_G]

Could both be at play? You may have hit the thermal limits, while others have not. Hard to tell right now where the limit is without battery/motor/inverter temp gauges. For the Roadster, the inverter was by far the main limiter, but the battery sometimes heats up too (charging the car heats up the battery too, so that might contribute also). The motor actually doesn't heat up that easily in the 2.0 version (with new fans).

I think the Model S's inverter is now liquid cooled, so it should fare better than the Roadster.

I've had the Roadster out to Shannonville a few times. Roadster's thermal limits are definitely due to the motor, not the PEM. The new fans don't seem to make any difference.

Also I never had issues with the Roadster's battery temperature at the track.

I saw no evidence of my Model S power being limited by the projected range. At the end of the day I had 98 Rated Km left, so I would have had negligible Projected Range, yet I was still able to restore full power with a pit stop.

 

[stopcrazypp]

Have you had your Roadster on the track? I have and can say with 100% certainty that my Roadster ( 2.0 with new fans ) was power limited because of heat in the motor and not the PEM.
I can dig up log files if necessary.

I don't own a Roadster, but in many threads I have read, the PEM overheating seems to come first and more often than the motor overheating. Maybe this is flipped on the track.
http://www.teslamotorsclub.com/showthread.php/4773-PEM-motor-gets-too-hot-fans-failed/page34
http://www.teslamotorsclub.com/showthread.php/6065-Vitals-What-do-those-temperature-bars-mean
http://www.teslamotorsclub.com/showthread.php/4383-Roadster-Sport-RED-vs-WHITE-Performance-modes

Cottonwood also said the PEM was the limiter in the Roadster during his track comparison.
http://www.teslamotorsclub.com/showthread.php/10986-Model-S-vs-Roadster-on-the-Track

The motor temperature reading may be higher than the other temperatures, but the motor can tolerate much higher temperatures than the PEM and batteries (~50°C). The lowest rated induction motors can tolerate up to 105°C (221°F), the highest can tolerate up to 180°C (356°F).

 

[djp]

Are you sure? Tesla has patents for liquid cooling the rotor of an AC induction motor.

Neat, I'll have to pull up that patent. The motor I saw at the store didn't have any plumbing that could have brought coolant to the rotor and I've always heard the liquid cooling described as a jacket, but I guess anything's possible. Anyone want to disassemble their motor to find out?

I don't own a Roadster, but in many threads I have read, the PEM overheating seems to come first and more often than the motor overheating. Maybe this is flipped on the track.

My experience matches Doug's and Rich's. On a hot day the PEM can hit a thermal limit from "spirited" driving, but on a track the motor overheats first.

 

[WarpedOne]

Are you sure? Tesla has patents for liquid cooling the rotor of an AC induction motor.

They may have patents, that does not mean they have such motors, it just means they thought about it and filed a patent.
I am sure Tesla would mention liquid rotor cooling out loud if they had it. It is a big thing in electric motors, very few of them have it.
They were specific about the copper in rotor that is also a bit unusual (but still less unusual as liquid cooled rotors).

Model S' PEM has liquid cooling, roadster' PEM is air-cooled therefore Model S is capable of higher average power output.
It is not a big thing to strengthen liquid cooling and/or increase radiators. Plus already costs $7,5k or even more to retrofit, additional grand or two would not be a problem if that enabled them to claim "track readiness"!

R&D for totally different motor with liquid cooled rotor is a whole new ballgame. It doesn't pay off.

Model S motor:

and rotor

Rotor looks similar to 'run-of-the-mill' copper rotors here.

 

[JRP3]

The hollow shaft on the Tesla rotor in the National Geographic picture would lead me to think it's there for liquid cooling.
Article mentioning the liquid cooled rotor: Car News and reviews, videos, wallpapers, pictures, free games and more. - Top Speed
Tesla patent showing the open ended rotor shaft: Patent US7489057 - Liquid cooled rotor assembly - Google Patents