How is current to the motor limited? Electronically or physically?

[Sticky]

Hi guys, new member looking into the Tesla Model S from a purely performance car standpoint.

I come from a background modifying BMW's for big power and the Model S has me thinking about taking a "new school" approach to modifying cars.

Now, from what I read here if the Performance Model S had 4.375C like the 40kWh model was supposed to have output would be in the 506 horsepower range. That's a boost of almost 100 hp and a good amount of torque to boot likely putting the 1/4 mile time and trap speed on par with something like a Panamera Turbo S or the upcoming all wheel drive version of the E63 AMG.

The Tesla is respectably quick as it sits but to truly perform like the top guys more torque/power is necessary. I also understand the motors in the cars are basically the same with the inverter being different in the performance model.

So is it just software that is holding the car back? Tesla simply chose between the best balance of range and power? I wouldn't mind a high performance mode with less range and replacing the battery earlier wouldn't bother me earlier for more performance.

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Hmm can't edit my post meant to say "wouldn't bother me either" whoops.

 

[brianman]

Welcome to the forum. Don't worry about the editing until you've got a handful of posts with typos.

I'd try to help answer your questions but I'm useless on this particular area.

 

[Sticky]

Welcome to the forum. Don't worry about the editing until you've got a handful of posts with typos.

I'd try to help answer your questions but I'm useless on this particular area.

No worries I've searched and it seems there isn't too much info on this topic.

How cool would it be to simply load in a different file allowing more current and have more power? A sport mode of sorts.

 

[TEG]

I am not an expert on this, but I think the current going to the motor is completely under electronic control being managed by software.
They have software developers "program" the car to specify fairly precise amounts of torque at different RPMs. The accelerator pedal position being one major input to this.

They impose limits to manage things like heat, and battery health.

I think they have more precise control over the performance than you would find in a typical gasoline engine car.

 

[SCW-Greg]

+1 to TEG here... as past interviews with JB have eluded to his early discovery that raw output from the motor was (too) instant.

Here's the reference...
"It was soon clear that the extreme torque provided by electric motors can be a problem, especially in a high-powered car. Without a well-tuned motor controller, the torque can jerk the driver around, says Andrew Baglino, one of the engineers Straubel hired. What's more, the complex interplay between the driver's application of the accelerator, the conditions of the road, and the electronic characteristics of the battery and motor can have unexpected consequences."

Innovators under 35 (2008)

 

[Sticky]

I am not an expert on this, but I think the current going to the motor is completely under electronic control being managed by software.
They have software developers "program" the car to specify fairly precise amounts of torque at different RPMs. The accelerator pedal position being one major input to this.

They impose limits to manage things like heat, and battery health.

I think they have more precise control over the performance than you would find in a typical gasoline engine car.

So if tuners can get access to the electronics I'm guessing they can then program the car to offer more power? If it's all software, this would be awesome.

I'm sure it is more precise control but that isn't the issue. The issue is in figuring out exactly how Tesla is limiting the current and "setting" the car at the horsepower/torque it is.

 

[SCW-Greg]

So if tuners can get access to the electronics I'm guessing they can then program the car to offer more power? If it's all software, this would be awesome.

I'm sure it is more precise control but that isn't the issue. The issue is in figuring out exactly how Tesla is limiting the current and "setting" the car at the horsepower/torque it is.

Fyi, I just added an edit above with ref to this tuning.

 

[Sticky]

+1 to TEG here... as past interviews with JB have eluded to his early discovery that raw output from the motor was (too) instant.

Here's the reference...
"It was soon clear that the extreme torque provided by electric motors can be a problem, especially in a high-powered car. Without a well-tuned motor controller, the torque can jerk the driver around, says Andrew Baglino, one of the engineers Straubel hired. What's more, the complex interplay between the driver's application of the accelerator, the conditions of the road, and the electronic characteristics of the battery and motor can have unexpected consequences."

Innovators under 35 (2008)

This is pretty interesting. Seems the motor controller would then be where this is all controlled? The throttle inputs, current, power at rpm, etc.?

 

[Todd Burch]

I don't believe a Model S is going to be as easily tunable as an internal combustion engine car, especially with all of the proprietary stuff going on. There is far more complicated and less tangible stuff going on here than in a gas car. We might see tuners with PhDs in electrical engineering and computer science...but it will probably be rare, if we see it at all.

Just my guess.

 

[PaceyWhitter]

And unfortunatly, any tuning would likely require an illegal hack of Tesla's software.

 

[JRP3]

There are also physical limitations of the motor. Increase current too much and you start melting the windings. Performance then drops to zero.

 

[scaesare]

There are also sorts of physical constraints in addition to the one JRP3 mentioned: current ratings for the transistors and other semiconductors in the inverter, conductor gauge in the wiring, cooling capacity for the batteries, motor, and inverter, resistance at the connection points, etc...

Now it MAY be that there is margin for additional performance in some, or even all, of these components, but just because software is controlling the process doesn't mean that it's not a system without physical limitations.

(I, for one, have wondered if the difference in the perfomance models is really a software imposed one...)

 

[NielsChr]

AFAIK
The motor is frequence controlled - e.g. spin speed is controlled by AC - the motors rpm are not controlled by the current, the current is drawed when needed - also when speed is low. This s why we have this high torqe even at low speed.

It could/would be posible to fine tune the software to allow faster acceleration or even higher top speed.
right now I asume 0.60 is limited be the traction control, I asume it could be posible along the road map to make it even better and allow faster times - but Im not shure faster times are needed (more/faster tire wear)

but it could be that they will provide a "switch" like how handling the cars performance: (Long range, Standard, Fast performance)
then the use can select wich mood they are in.

 

[qwk]

(I, for one, have wondered if the difference in the perfomance models is really a software imposed one...)

I have driven the performance and own a regular 85 Model S. The main difference is the power available right from the initial pedal mash. It's a very slow ramp up on my car, and much faster on the P85. Once you get going about 35mph, both cars perform very similar. I'm about 99% sure that the performance upgrade is just software, or at the very least the regular 85kwh car is severely held back by software below about 35mph.

 

[scaesare]

I have driven the performance and own a regular 85 Model S. The main difference is the power available right from the initial pedal mash. It's a very slow ramp up on my car, and much faster on the P85. Once you get going about 35mph, both cars perform very similar. I'm about 99% sure that the performance upgrade is just software, or at the very least the regular 85kwh car is severely held back by software below about 35mph.

Undoubtedly the software tune has to be different for the P85 car... but if the software commands the system to ramp up to power levels the inverter (or other components) can't deliver, then it obviously won't work.

Given that is is apparently cheaper to build 60KWH battery packs and software-limit them to 40KWH output, I wonder if it's also more economical to build only one flavor of inverter, and simply software limit it's output.

Of course, it was stipulated that only 4% of battery packs would have been 40's... whereas there appear to be a significantly greater percentage of P-models out there... so engineering, building, and supporting two different configurations there may make more sense...

 

[Zextraterrestrial]

There were positively 2 different sets of drive train units at the factory during my second tour. performance and regular. Most of the Performance were gone (dec 1st)
During my third tour - end of january. there were way more of all of the supplies for all types of car versions and different options

drive train units w/ motor / inverter combo should have higher peak capabilities for the inverter and bigger wire to the motor.
It is just a big RC car with Tesla having the controller (but probably limited, I hope)

 

[metafor]

There are also sorts of physical constraints in addition to the one JRP3 mentioned: current ratings for the transistors and other semiconductors in the inverter, conductor gauge in the wiring, cooling capacity for the batteries, motor, and inverter, resistance at the connection points, etc...

Now it MAY be that there is margin for additional performance in some, or even all, of these components, but just because software is controlling the process doesn't mean that it's not a system without physical limitations.

(I, for one, have wondered if the difference in the perfomance models is really a software imposed one...)

I believe it was mentioned that the performance model has a beefier inverter than the normal 85kWH, thus allowing it to provide higher current to the motor.

 

[mknox]

I have driven the performance and own a regular 85 Model S. The main difference is the power available right from the initial pedal mash. It's a very slow ramp up on my car, and much faster on the P85.

Very slow? Like you, I drove both a Standard and a Performance and ended up buying the Standard. I've mashed the pedal and had the rear end start to break free before the TC or Stability Control reigned me in and left everyone in the dust. I get that the Performance model is even quicker, but I wouldn't characterize the Standard as "very slow" to ramp up.

 

[qwk]

I believe it was mentioned that the performance model has a beefier inverter than the normal 85kWH, thus allowing it to provide higher current to the motor.

It's certainly possible, but the current delivered in the 30+mph range is about twice as much(according to the dash gauge) as the initial burst. Once you drive the car, you can definately see what I'm talking about. The question is, how much software limiting is happening?

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Very slow? Like you, I drove both a Standard and a Performance and ended up buying the Standard. I've mashed the pedal and had the rear end start to break free before the TC or Stability Control reigned me in and left everyone in the dust. I get that the Performance model is even quicker, but I wouldn't characterize the Standard as "very slow" to ramp up.

Maybe it's just my car? I dunno. The performance model at the Get Amped event had a very violent takeoff. Not so with my car. My car does however have very good acceleration once you get going.

 

[mknox]

IMaybe it's just my car? I dunno. The performance model at the Get Amped event had a very violent takeoff. Not so with my car. My car does however have very good acceleration once you get going.

Probably just a relative thing and it depends on your frame of reference. Before I got mine, I drove a non-Performance at the Get Amped event in Toronto (because that was what I intended to buy), but then drove a P85 in California when I was visiting my brother who lives there. I was hard pressed to tell the difference, but then my driving style usually isn't super aggressive to begin with.

I do recall it being mentioned that one of the earlier software updates had changed the whole "throttle" response of the cars, so maybe that's a factor too.