Are Dual Motor 3 rear motors basically RWD 3 rejects?

[MP3Mike]

Do you think people with AWD delivered already could upgrade to Performance with a simple software update? That’s a hard pill to swallow.

Now, that will only work if he made all the AWD models Performance to eliminate producing multiple variants, then software limited it in hopes of you asking for the upgrade later for tons more cash like he did with the Model S batteries.

The rear AWD motor is rated for 11% less than the RWD and Performance models. (188kW instead of 211kW)

What we don't know is if that is due to:

1. Binning and the motors performing more poorly.
2. Eliminating some of the MOSFETs on the inverter.
3. Completely done in software.

If it is because of #1 or #3, then they probably could upgrade to the Performance model specs via just software. (Though that could increase the failure rate.) If it is because of #2 then software ain't gonna help.

 

[adaptabl]

Do you think people with AWD delivered already could upgrade to Performance with a simple software update? That’s a hard pill to swallow.

Now, that will only work if he made all the AWD models Performance to eliminate producing multiple variants, then software limited it in hopes of you asking for the upgrade later for tons more cash like he did with the Model S batteries.

No different that EAP. The hardware and software is there but you have to pay a fee to have in unlocked. Most likely one byte in a control setting.

 

[TurnFast]

Even if the lower rated rear motor 188 vs 211 is due to hardware differences like a few mosfets removed from the inverter, that 11% difference does not explain how the performance is a full second faster. There has got to be software limiting going on as well.

After watching some videos of people trying to modify the RWD with lighter wheels, summer tires, and a staggered setup and still reporting the same 5.1s 0-60, I suspect Tesla is software limiting the performance of both the RWD and AWD to protect sales of the PAWD.

 

[mongo]

But how much power is being lost in those MOSFETS? The total drive unit efficiency is very high and probably only a very small amount of power is being lost in the switching transistors. Is there a teardown that shows the heatsink size for them, that would give you a good idea.

The impact is not on the overall system efficiency, it's in the maximum sustainable power the electronics can handle before hitting their thermal limit.
Take the ST part, the junction to case temperature coefficient is 0.45 C/W, assume 0.55 C/W for mounting and cold plate, total of 1 C/W. The max junction temperature is 175C, if the coolant loop is running at 35C, then there is a 140C delta to work with, that works out to 140W of dissipation.
For the nominal part (at 25C), the sustainable current level is i^2*R=140, with 18 mOhm resistance, that's 88.2Amps. For the worst case, the resistance is 28 mOhm and the current limit is 70.8 Amps.
Now look at what happens as the die heats up: the 175C nominal resistance is 25 mOhm, a 39% increase from 25C and a limit of 74.8A
If that trend holds for the worst case part (Figure 12 indicates a 50% change for 25 to 175), the hot resistance is 39mOhm with a current limit of 60 Amps.
Thus a max temp nominal part has better current/ power handling ability as an ambient worst case part. At the hot end, it provides 18% more current. However, it runs cooler, so for the same power profile it will be at a lower temperature and thus more efficient/ more power available.

So a worse performing part gets hotter faster and even less capable faster. Not a big deal for street use, but for a P on the track, it can definitely affect things.

 

[mattk926]

Even if the lower rated rear motor 188 vs 211 is due to hardware differences like a few mosfets removed from the inverter, that 11% difference does not explain how the performance is a full second faster. There has got to be software limiting going on as well.

After watching some videos of people trying to modify the RWD with lighter wheels, summer tires, and a staggered setup and still reporting the same 5.1s 0-60, I suspect Tesla is software limiting the performance of both the RWD and AWD to protect sales of the PAWD.

It would be interesting to know how they limit that. If the assumption is the tires weren't sticky enough to the point the stock setup is losing traction being the limiting factor then swapping to stickier tires for more traction should make the car accelerate faster. If the stock setup tires were sticky enough then that would explain why stickier tires didn't result in any performance gains from a stand still. Power output could be capped, but if we are assuming the tires weren't sticky enough then that wouldn't be the case i would think... If somehow they leveraged the traction control system/speed sensing system etc to software limit power dynamically that would be a whole new level of trickery. I doubt that would be the case as the easier solution would be to limit the max amps to the motor through the controller effectively lowering the rated kW rating of the motor...

 

[Daniel in SD]

The impact is not on the overall system efficiency, it's in the maximum sustainable power the electronics can handle before hitting their thermal limit.
Take the ST part, the junction to case temperature coefficient is 0.45 C/W, assume 0.55 C/W for mounting and cold plate, total of 1 C/W. The max junction temperature is 175C, if the coolant loop is running at 35C, then there is a 140C delta to work with, that works out to 140W of dissipation.
For the nominal part (at 25C), the sustainable current level is i^2*R=140, with 18 mOhm resistance, that's 88.2Amps. For the worst case, the resistance is 28 mOhm and the current limit is 70.8 Amps.
Now look at what happens as the die heats up: the 175C nominal resistance is 25 mOhm, a 39% increase from 25C and a limit of 74.8A
If that trend holds for the worst case part (Figure 12 indicates a 50% change for 25 to 175), the hot resistance is 39mOhm with a current limit of 60 Amps.
Thus a max temp nominal part has better current/ power handling ability as an ambient worst case part. At the hot end, it provides 18% more current. However, it runs cooler, so for the same power profile it will be at a lower temperature and thus more efficient/ more power available.

So a worse performing part gets hotter faster and even less capable faster. Not a big deal for street use, but for a P on the track, it can definitely affect things.

Absolutely. I just suspect that they have plenty of cooling on the inverter and when you average all the switching transistors the actual variation is minimal. The cooling system is shared between all components, what's the biggest source of heat?

 

[mongo]

Absolutely. I just suspect that they have plenty of cooling on the inverter and when you average all the switching transistors the actual variation is minimal. The cooling system is shared between all components, what's the biggest source of heat?

Those number assumed an infinite ability to remove heat from the coolant (it would likely go above 35C), but that heat still has to get from the die to the coolant and the motor windings likely have a higher temperature rating than the FET.

I agree, the variation of an averaged set is more concentrated that the individual items, but the variation does have a direct impact on available performance.

 

[djgarrett21]

I don't believe the act of binning motors has anything to do with increased output. Rather, it probably has more to do with the behavior of the motor under load. The "better" motors most likely perform closer to the ideal than others. IMO binning is related more to reliability and an ability to sustain operation under higher load. Having said that, I'd bet a large sum of money that the binned motors are fractionally better than the non-binned ones and the real discriminator has much more to do with software rather than hardware. Another way to think about this; if binning equated to higher outputs then the performance of Ps from one vehicle to another would vary depending upon how "good' a motor it got. That doesn't appear to be happening.

Remember we are talking about a true mass-produced vehicle with the Model 3. Reducing part count and producing high volumes is the name of the game. Hardware commonality between variants saves tons of $. In that regard the Model 3 is apples-to-oranges when comparing to the S or X.

 

[Revelate]

Well, someone (SteveWin1, and apologies for putting basically the same post in two different threads) did some analysis of the VIN's registered and if it were a software limitation they'd just be producing both concurrently... but the data seems to suggest that it's the same line building either P or AWD, but not both concurrently.

That suggests a swap of at least one part, probably the motors.

AWD.jpg
PvsNonP.jpg

 

[mongo]

I don't believe the act of binning motors has anything to do with increased output. Rather, it probably has more to do with the behavior of the motor under load. The "better" motors most likely perform closer to the ideal than others. IMO binning is related more to reliability and an ability to sustain operation under higher load. Having said that, I'd bet a large sum of money that the binned motors are fractionally better than the non-binned ones and the real discriminator has much more to do with software rather than hardware. Another way to think about this; if binning equated to higher outputs then the performance of Ps from one vehicle to another would vary depending upon how "good' a motor it got. That doesn't appear to be happening.

Remember we are talking about a true mass-produced vehicle with the Model 3. Reducing part count and producing high volumes is the name of the game. Hardware commonality between variants saves tons of $. In that regard the Model 3 is apples-to-oranges when comparing to the S or X.

Part's individual specifications fall in a bell curve. Conservative (reliable) design calculations are based on the worst case values (or a blended Monte Carlo) and applying a derating on that. The software limits would typically be set such that even in the worst case, the module life meets the longevity criteria. This is likely the base motor case.

However, most parts are better than worst case and 50% are above the median value. So by testing the finished product,Tesla can tell which units can operate at a higher performance level. These get the Performance software limits.

So the software limit depends on the tested performance which depends on the individual part characteristics, but there are only two sets of limits. Within those two groupings, there will be better units than others, but the better will not show up in terms of acceleration because that is based on torque/current which is a software limit. Where it will likely show up is in how much power the drive unit can put out before it hits its thermal limit (and maybe in Wh/mile, but drive electronics loss is small compared to total power and motor losses so an improvement there doesn't shift things much).

Speaking of apples to oranges, the difference in design between the 3 drive electronics and the S/X inverter is amazing.

 

[mongo]

Well, someone (SteveWin1, and apologies for putting basically the same post in two different threads) did some analysis of the VIN's registered and if it were a software limitation they'd just be producing both concurrently... but the data seems to suggest that it's the same line building either P or AWD, but not both concurrently.

That suggests a swap of at least one part, probably the motors.

AWD.jpg
PvsNonP.jpg

Given the semi to line part handling system on GA4, that makes a lot of sense. GF1 may be shipping motor types grouped by pallet or truck.

 

[djgarrett21]

Well, someone (SteveWin1, and apologies for putting basically the same post in two different threads) did some analysis of the VIN's registered and if it were a software limitation they'd just be producing both concurrently... but the data seems to suggest that it's the same line building either P or AWD, but not both concurrently.

That suggests a swap of at least one part, probably the motors.

AWD.jpg
PvsNonP.jpg

I'm not trying to say that I don't believe the binning process is happening, and I bet there are some minor differences (someone pointed out fuses). Just saying that the difference in the power output between the non-P and P is mainly a function of software, not the motor itself. RWD (252hp) vs P (283hp) is quite the delta.

RWD (283hp) and P rear drive unit (283hp) are the same. I think it is reasonable to assume that all three variants (RWD, AWD, P) have the same drive units with different mapping. My contention that the binned motors contribute very little to the difference in performance.

Circling back to the OP - AWD motors are not rejects, they're just throttled.