Performance Anxiety. (any engineers out there?)

Performance Anxiety. (any engineers out there?)

I just put my deposit down for a P85, and am at peace with the price difference (since the features I want account for a lot of the price). My only concern is whether or not the higher throughput P85 drive inverter is any more likely to poop out or have issues earlier than the standard MS85 inverter. I don't know if this is analogous to my first turbo engine (an ill-fated Mitsubishi Eclipse), whose build tolerances were no match for its heavy breathing. Sorry if this is an amazingly ignorant question, but I just happen to be, well, amazingly ignorant in terms of engineering.

Also, please excuse me if this issue has been addressed before. I tried my best to do my due diligence and VOLKERIZED the heck out of the topic; I found some great threads about the price versus performance gain, but nothing on longevity and dependability. Many thanks in advance!

negarholger | 5 juli 2013

How many times do you use the "performance" ? Atfer three month I still have to floor my P85 once. For 99.9% of my driving it doesn't make a difference ( got the P for different reasons ).
If you drive a car that is maxed out at 70 miles per hour at 70 miles per hour all the time then you stress the engine at 100%. A 200 hp engine that is run at 40 hp is only stressed at 20%... guess which car will have more engine issues?

NomoDinos | 5 juli 2013

Kleist - Thanks so much for the insight! That makes a lot of sense.

PatT | 5 juli 2013

NoMoDinos -- so you ran your Mitsubishi Eclipse flat out most of the time and it died early?

Actually I agree with Kleist that it is unlikely that you will use all the power that your motor can consume, very often. But I also believe that putting more power to the motor will stress it more than if you were NOT able to cause it to put out an additional 20% of horse power. You will stress other drive train components as well, including the tires. The key is -- how often and how long? After a few blast offs your smile muscles may get tired and that issue may influence the frequency of using full power. If not, blue lights will -- definitely.

Tâm | 5 juli 2013

I am no engineer but the way I see it, there's no "break in" period. As soon as the car is assembled, they just "floor" the heck out of of the accelerator!

Wait till you get your brand new car and watch the energy graph history! They factory-test-drive the car and torture it to the maximum.

Thus, I don't see any difference whether yours is a standard or performance.

Just enjoy the car and the only thing to worry about is pre-mature worn out tires (not inverter, not motor).

lolachampcar | 5 juli 2013

I do not have experience with induction motor controllers but do have some with DC permanent magnet controllers (similar in many respects). The difference between S85 and P85 controllers is primarily peak current capability (the battery voltage is not changing so the added power comes from more current drawn from the battery, through the inverter and to the motor). In BDC inverters, current is switched to each phase using FETs (Field Effect Transistors). Larger power inverters typically use more of the same rated FET to achieve higher power throughput.

I suspect Tesla has done a similar thing in that they have either used the next size up FET (unlikely as usually high power designs are already using the most capable device) or more of the same FET in addition to increasing wire diameter to accommodate the extra current. Applying that to reliability and you simply have a few more points of failure with an extremely low failure rate. Yes, there is theoretically a reduction in lifespan but I think you will find that most inverters will outlive the rest of the car. There is also and increase in thermal loading but there is ample evidence that Tesla has done their homework WRT thermal management and there will be no issues their either.

I had absolutely no reservations going from S to P85 on my MS'.

lolachampcar | 5 juli 2013

in addition, you can bet that Tesla designed the inverter using the same philosophy used with the battery. Both have multiple points of failure (FETs on one, cells on the other) so I suspect one or more FETs failing may slightly derate power throughput but would not bring the inverter down.

Bubba2000 | 5 juli 2013

I read that the motor on the P85 has upgraded winding in the stator and I suspect the rotor is upgraded too. Besides the inverter being upgraded, I think the rest of the components including the gearbox must be the same.

In terms of manufacturing economies of scale, I think it makes sense to standardize everything. Just upgrade the inverter for the P85 versus S85. The cost of extra Copper for wiring, etc is minimal compared to the cost of having separate manufacturing lines. I wonder if the economies of scale that apply to electronic components like inverters would makes sense just to have a P85. I know Tesla needs to segment the market with different versions and price.

I was thinking of the Model T. You could have any color you wanted as long as it was black! Worked for a while till the competition caught up.

defmonk | 5 juli 2013

Actually, this is a very good question. A friend has an AMG MB, which shredded its engine mounts after 50k miles or so due to the increased torque (and a heavy foot, I'm sure). Unlike MB AMG, or most other performance sedans, the base Model S is actually designed "down" from the performance model. Consequently, I would think that every element of the P85, from the inception, is engineered to handle its higher output and loads. To your point about the Mitsubishi, reliability problems often arise when base models are tuned for higher output without considering the impact on other systems (e.g., suspension, electrical, brakes/hydraulics, bushings/sets, drive shafts, etc.).

carlk | 5 juli 2013

@defmonk That's a very good point. Clutch/transimision on my Porsche seems to last forever while I had to replace the clutch three times for my 120K mile Honda Prelude. Even though the Honda was otherwise a very reliable car, it was just not designed for very aggresive driving. I hope like you said Tesla has designed MS from the performance model down.

@Kleist Do you mind to share your "different reasons" for getting the performance model?

TikiMan | 5 juli 2013

I think the easy way to explain it would be by asking the question... Have you ever owned a big powerful electric fan that just stopped working. On the flip side, have you ever had a gas lawnmower that crapped out after ten years?

Just think of the Model S's motor as a Big electric fan.

NomoDinos | 5 juli 2013

Wow, thanks to everyone for the great responses. I feel like I'm back in college physics getting help from my IEEE buddies trying to explain angular momentum to me.

@ PatT - yes, I was younger and dumber with a heavier foot, and it pooped out. The mechanic blamed it on the turbo. I drive like a grandma most of the time nowadays, so I don't think excessive stress will be a problem anymore.

@ Tam - looking forward to seeing my car's trauma history :)

@ lolachampcar - thanks! The 60% of your post that I understood was very enlightening :) (I'll try to get up to C- comprehension level on the next couple read-overs)

@ Bubba2000 - my favorite model T quote :) Would be interested to see how much more it actually costs them to make the P drive inverter. Maybe you should help out their CFO!

@ defmonk - makes a lot of sense. Putting a 200 hp engine on my nephew's Huffy proooobably wouldn't be the best idea (although probably pretty fun)

@ Tikiman - got it, thanks for the analogy (it's seeming more and more that my brain doesn't have much room for completely new concepts anymore :)