Tesla blog post: AWD Motor Power and Torque Specifications

[wk057]

I seriously can't believe that I'm wasting more time on this yet again, but I can not sit here and let you spread additional non-information without additional reputable opposition.

I think what I point out is the core point of my analogy that you responded to originally. The crux of the issue here is whether horsepower standards must reflect the system as a whole, so I gave an example where it doesn't: SAE Gross hp. That horsepower standard characterized the engine, not the system as a whole. I hope we have agreement with that. I see this as an exact parallel with "motor power" in this case (which characterized the motor/inverter and not the system). And it also happens that the end effect in terms of percentage is very similar.

We do not have agreement on anything apparently. I consider making sure the fuel use (gasoline, diesel, propane, hamsters in wheels, or batteries) by the motors for testing to be a vital part of running a motor/engine and for an accurate measurement of a motor built for a specific application, such as in a a car. You apparently do not.

I see the fuel analogy as kind of a side point and a very imperfect one. In your original example, you said diesel and gasoline. If you put diesel fuel in a gasoline engine and vise versa, will likely not even work (and will damage the engine). An ICE can tolerate some fuels, but it will run completely differently even if you put the fuel with the same equivalent amount of energy. It is very hard to match up such an analogy with a DC power source, where what matters is the voltage and current (not the characteristics of the DC supply other than that).

Not sure where I ever said to put diesel in a gasoline car or vice versa. lol. Seems to be some more fluff for you to throw out to make it, again, appear like these arguments actually have merit.

At least we agree that an ICE will run differently if given different fuels. Extend that to the motors behaving differently with a different power source and we're finally getting somewhere. The former isn't permitted, or would immediately be seen as fraud if used to inflate numbers. You want to allow the latter even though it's the exact same thing as the first for the platform at hand.

I've been in arguments over ECE R85, the power rating standard Tesla uses in the EU, which doesn't specify that the motors must be tested with the DC source as installed in the car (while it does for the accessories attached to the drivetrain). I have been waiting to be corrected on this point, but it appears to be 100% true, esp. after Straubel's statements.

In fact, a poster pointed out a line on page 9 that seems to suggest that the standard does not expect the manufacturer to use the factory installed battery during test:
"Note: If the battery limits the maximum 30 minutes power, the maximum 30 minutes power of an electric vehicle can be less than the maximum 30 minutes power of the drive train of the vehicle according to this test."
http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2013/R085r1e.pdf

That statement seems to match with Straubel's statements:
"Since the battery electric horsepower rating varies it is not a precise number to use for specifying the physical capability of an EV. The motor shaft horsepower, when operating alone, is a more consistent rating. In fact, it is only this (single or combined) motor shaft horsepower rating that is legally required to be posted in the European Union."

While your (and Tesla's) interpretation of ECE R85 is definitely in question as far as I'm concerned, I fail to see the relevance of anything I just quoted above. We know how Tesla came to the numbers now thanks to JB Staubel's admission. They tested the motors, individually and independently of the battery and simply summed up the numbers. I'm pretty sure this had been accepted as the official source of the 691 HP number. So I'm not sure the point of the above excerpt. No one is questioning how they arrived at the number anymore, since it has been explained. The problem is the fact that the method they used to arrive at the number is complete BS when used as a spec for the P85D, the car. Again I point out that we bought *cars* from Tesla. Not motors. If I had bought the front and rear motors from Tesla... just the motors... and they gave me an invoice saying they sold me 691 HP worth of motors, I would have no argument. But they sold me a 691 HP *car* that can not produce 691 HP. How is this even in question, especially after admitting it in their own blog?!

I have seen the claim by others that electric motors can always output their peak power in the low rpm ranges, but I don't believe this to be true. Horsepower is a factor of torque and rpm. At low rpms, the peak torque of the motor limits the amount of power it can output. And given the torque is a direct function of input current, which is in turn limited due to inverter and the current limit of the motor windings, it would be impossible for the motor to output peak power at the lower rpms.

This is more readily shown with a power curve of a car that is not traction nor battery limited (the Roadster; if you doubt that, you can look up a Leaf power curve too):
(graph)

Here is the power curve of a UQM Powerphase motor (not installed in a car):
(graph)

In both cases, the peak power is not reached until later in the power band and it does not appear to have anything to do with traction, but rather because the motor is hitting its maximum torque limits at the lower rpms (the graphs seem to make that clear).

At least for this, I think we both misunderstood each other. I was not saying that the motor would output max HP at any RPM. JB was referring to the summed motor power ratings, which is a static number, which makes the sentence in question false. (515 kW < 415 kW)

However, building on that, let's say the car was bolted to the ground, all four tires and the drive units unable to spin at all. The inverters were then commanded to produce maximum power. Now, the motors are not able to spin, but they can exert a force against their entrapment equal to the amount of power input... at 0 RPM... likely ending with the death of some components. This seems counter intuitive, but it doesn't change the definition of 1 HP (electric) being ~746W. The input power doesn't just disappear because the shaft isn't turning. Exactly how much power could be input in this situation I don't know for sure, but I'm damn sure it's far more than represented by the graphs you posted.

Look at the history. Car manufacturers did not switch to net power ratings in the 1970s because they wanted to be more honest. They switched because during the fuel crisis, it was bad to be seen as making a car with irresponsible amounts of power (it was the time when CAFE fuel economy standards were introduced). Switching to net power gave them a convenient way to adjust their advertised power numbers down without having to reduce it in real world use.

I'm not sure if this is true or not, admittedly, because history is definitely not my field. Second hand, a reliable source (real world older friend who is very knowledgeable in auto history) tells me this is nonsense.

Logical thinking, however, is a pretty strong suit of mine. So logically, even if the reasoning for adoption were in fact to under advertise power due to a temporary fuel crisis, why maintain and utilize the same standard for 40+ years after the situation had passed? I mean, people want cars with high horsepower regardless of fuel economy these days when buying a powerful vehicle. No one looks at horsepower ratings as a measure of fuel economy these days, so why doesn't everyone just use SAE gross again to make the numbers look better if that's acceptable? Oh, because inflating the numbers isn't actually acceptable. DOH!

 

[flathillll]

you are still missing the point. It would be more misleading/confusing for Tesla to advertise battery hp for the average customer. Many would not understand why they are paying so much more money for the same battery hp. Motor hp represents value better than battery hp. Also note long-term the battery hp will be increased. In 8 years the new pack may come with higher capacity and be able to output more hp and your car will be faster with the same motors. You are not likely going to upgrade your motors but it is simple to swap out the battery.

 

[wk057]

you are still missing the point. It would be more misleading for Tesla to advertise battery hp for the average customer. Many would not understand why they are paying so much more money for the same battery hp. Motor hp represents value better than battery hp.

By that logic Tesla should spend an extra couple $k to make the motors on the car rated for 130 more HP. That way they can advertise a 1000HP+ car, even though the battery is in no way capable of producing this power. Far cheaper for them to do this to up the HP numbers than it is for them to upgrade the battery to actually be able to produce 1000 HP worth of power.

That would be acceptable? I think not.

 

[dsm363]

When I buy a *motor* from Tesla, this is the rating I'm going to want to see.

When I buy a *car* the numbers they advertise should reflect what the *car* does at least somewhere on the power train. Therefore the methodology they used is flat out wrong and a flat out lie since they know the car can not make this power, yet it was touted everywhere as the headline of the car.

Give me a break.

I feel a little guilty about leaving sorka and the few others in the trenches to fend off crap like this on their own.

'Crap like this'. Thanks. Given their definition they've now released it is not crap. It may not be useful in a car but that's what they did. Yes it's misleading. So is hard drive capacity. So is almost anything else advertised. If that single metric is vital to survival you should make sure the manufacturer lives up to its claims.

Don't feel bad. I'm sorry they have to deal with crap like this without you.

 

[Sad]

you are still missing the point. It would be more misleading for Tesla to advertise battery hp for the average customer. Many would not understand why they are paying so much more money for the same battery hp. Motor hp represents value better than battery hp.

No, you are. Many P85D owners do not understand why they paid so much more money for car hp (i.e. power that actually gets used to propel the car) which is not that much higher than the P85. Those are average customers equating hp with power at the wheels + some loss along the way, not some virtual figure not representative of the performance of the car. They ended up paying 20-30K more for a faster 0-30 mph realized thanks to higher engine torque (and thus higher power, but below the battery threshold given the low rpm, so achievable), and not much more than that.

 

[dsm363]

You mean in ideal conditions where the power supplied is from some source other than the battery that is supplied with the vehicle. Really??? Or did I just misread your statement?

Yes. 'Motor power' is what they advertised. Did anyone upset bother to get a definition in writing before they bought since this was so important?

In an ideal world all manufacturers would be forced to only advertise hp at the wheels in the actual car. I'd love this. We all know there is this arms race to have the more impressive states. Sure it's sad Tesla decided to play this game but anyone who has ever bought any car before should have known this is possible. Especially if such lofty hp numbers come out with no independent verification on a new dual motor EV.

 

[wk057]

Lied implies intent. The two motors added together under ideal test conditions do make 691 motor hp. Tesla never said 691 hp at shaft or wheels. Yes, it was vague and misleading anyway.

When I buy a *motor* from Tesla, this is the rating I'm going to want to see.

When I buy a *car* the numbers they advertise should reflect what the *car* does at least somewhere on the power train. Therefore the methodology they used is flat out wrong and a flat out lie since they know the car can not make this power, yet it was touted everywhere as the headline of the car.

Give me a break.

I feel a little guilty about leaving sorka and the few others in the trenches to fend off crap like this on their own.

'Crap like this'. Thanks. Given their definition they've now released it is not crap. It may not be useful in a car but that's what they did. Yes it's misleading. So is hard drive capacity. So is almost anything else advertised. If that single metric is vital to survival you should make sure the manufacturer lives up to its claims.

Don't feel bad. I'm sorry they have to deal with crap like this without you.

My post was pointing out the uselessness of yours. Your post was the 'crap' I was referring to. As mentioned above, no one is questioning how they arrived at the 691 HP number since the methodology has been admitted by Tesla through the recent blog post (and was already pretty much assumed to be this anyway). Reiterating that as a defense of itself is pointless and is the 'crap'.

So we know that the summed output of the motors tested under bench conditions from a power supply were used to get the 691 HP number. So what? Does that explanation all of a sudden make the 691 HP number an actual useful and comparable metric which to use against say, the P85's ~417 HP? Or any other vehicle's performance? No. No it does not.

The 'crap' is the regurgitation of the same non-explanation over and over again as if it somehow changes the situation.

Edit: OT, but as for hard drive capacity, I don't find that in the slightest bit misleading as the methodology is published and well known, and their ratings actually do fit the definitions of the terms used.

 

[WarpedOne]

to advertise battery hp for the average customer.

There is no such thing as "battery hp" described by a single number.

People started to somewhat grasp that battery hp is dependent on SOC.
And temperature.
And "age".
And power it output a second before, a minute before looking, etc.

It is a dynamic system and no single number would ever tell the complete story or be comparable with HP rating of an ICE engine in any meaningful way.

I am still waiting for the one who will tell me how long a dynorun must last for meaningful result.
20 seconds? Why not a single second? In real driving power demand burst are short, quarter-mile takes 11 seconds, typical overtaking takes three seconds, 0-60 run takes three seconds.

Why should we look at 'average' power over some arbitrarily long run? Dynoruns take 20 seconds or even more, but there is no realworld driving situation where one can output 300kW for 20 second straight. It is completely arbitrary demand.

ICE cars have this technique of 'revving' the engine and dropping the clutch. Revving the engine means energy gets accumulated in rotational energy of various rotating parts. When clutch is dropped all that accumulated energy is spent in a very short burst of power that far exceeds engine rated Hp. And there is no dyno that can measure it.

 

[30seconds]

Just in case anyone is curious

EUR-Lex - 42006X1124(03) - EN - EUR-Lex

"5.3. Description of tests for measuring the net power and the maximum 30 minutes power of electric drive trains
The electric drive train shall be equipped as specified in Annex 6 to this Regulation. The electric drive train shall be supplied from a DC voltage source with a maximum voltage drop of 5 per cent depending on time and current (periods of less than 10 seconds excluded). The supply voltage of the test shall be given by the vehicle manufacturer.

Note: If the battery limits the maximum 30 minutes power, the maximum 30 minutes power of an electric vehicle can be less than the maximum 30 minutes power of the drive train of the vehicle according to this test

5.3.1. Determination of the net power

5.3.1.1.

The motor and its entire equipment assembly must be conditioned at a temperature of 25 °C ± 5 °C for a minimum of two hours.

5.3.1.2.

The net power test shall consist of a run at full setting of the power controller.

5.3.1.3.

Just before beginning the test, the motor shall be run on the bench for three minutes delivering a power equal to 80 % of the maximum power at the speed recommended by the manufacturer.

5.3.1.4.

Measurements shall be taken at a sufficient number of motor speeds to define correctly the power curve between zero and the highest motor speed recommended by the manufacturer. The whole test shall be completed within five minutes."

 

[scaesare]

You didn't answer the question: how long must it stay on the dyno at full power?
If you say one second (assuming a dyno with enough resolution) the result will differ from a dyno that needs 5 seconds to assess the power.

Peak for any measurable period of time with typical automotive testing equipment.

"Any" being any time longer than what?
Don't say you looked at it at microsecond resolution?

The standard sampling resolution of typical automotive testing equipment

Is it really that hard to understand?

No, but you seem to be making it that way.

 

[flathillll]

By that logic Tesla should spend an extra couple $k to make the motors on the car rated for 130 more HP. That way they can advertise a 1000HP+ car, even though the battery is in no way capable of producing this power. Far cheaper for them to do this to up the HP numbers than it is for them to upgrade the battery to actually be able to produce 1000 HP worth of power.

That would be acceptable? I think not.

yes that would be acceptable. see my example about a 4 motor version of the model s with torque vectoring. that car would have over 1000 motor hp but the same battery hp as the 2 motor version. advertising peak car hp (aka battery hp in a application where the battery limits the system power) would be utterly stupid

 

[wk057]

And for my non-snippy post... (Edit, damnit mods... why is my snippy post not in snippyness!? Oh, it's back... not snippy enough?!)

There is no such thing as "battery hp" described by a single number.

People started to somewhat grasp that battery hp is dependent on SOC.
And temperature.
And "age".
And power it output a second before, a minute before looking, etc.

It is a dynamic system and no single number would ever tell the complete story or be comparable with HP rating of an ICE engine in any meaningful way.

Neither do peak power numbers for any other car, numbers that you rarely see in real use. But they *are* achievable somehow in the car.

I'm pretty sure everyone would have been fine if the HP rating of the P85D were the maximum power the battery pack could output under ideal conditions. This would have been a more reasonable number to use than the imaginary 691 HP that has no bearing on the car's performance whatsoever.

I am still waiting for the one who will tell me how long a dynorun must last for meaningful result.
20 seconds? Why not a single second? In real driving power demand burst are short, quarter-mile takes 11 seconds, typical overtaking takes three seconds, 0-60 run takes three seconds.

Why should we look at 'average' power over some arbitrarily long run? Dynoruns take 20 seconds or even more, but there is no realworld driving situation where one can output 300kW for 20 second straight. It is completely arbitrary demand.

I don't know what you don't understand about this not being relevant at all to the situation with the P85D. At *no* point *anywhere* in the car for *any* amount of time is 691 HP produced. Averaged, super small time frame, super long time frame, whatever. It doesn't do it.

ICE cars have this technique of 'revving' the engine and dropping the clutch. Revving the engine means energy gets accumulated in rotational energy of various rotating parts. When clutch is dropped all that accumulated energy is spent in a very short burst of power that far exceeds engine rated Hp. And there is no dyno that can measure it.

And... yeah I'm just not going to bother responding to this. When the P85D gets a clutch and flywheel, let me know. Until then, OT.

 

[scaesare]

The problem with specifying just motor shaft HP independent of what the entire system can produce, is that it becomes meaningless.

Tesla could swap a new 650+HP motor in the back of the current cars, and advertise 900HP, and be "correct". Yet the car wouldn't perform any better, as a result of the bottleneck being somewhere up the line (battery, fuse, wiring, inverter, etc...).

Swapping a 500HP-capable engine in to your muscle car doesn't make it a 500HP car if the fuel pump can only deliver fuel at a rate that supports 350HP...

(see also: VW faces customer class-action lawsuits if they permanently enable their emissions controls as it would lower HP ratings for the car.... despite the engine being capable of full HP, it's being limited by some other component in the vehicle makes it false advertising to tout a HP number the car cannot deliver)

 

[qwk]

I think what I point out is the core point of my analogy that you responded to originally. The crux of the issue here is whether horsepower standards must reflect the system as a whole, so I gave an example where it doesn't: SAE Gross hp. That horsepower standard characterized the engine, not the system as a whole. I hope we have agreement with that. I see this as an exact parallel with "motor power" in this case (which characterized the motor/inverter and not the system). And it also happens that the end effect in terms of percentage is very similar.


I see the fuel analogy as kind of a side point and a very imperfect one. In your original example, you said diesel and gasoline. If you put diesel fuel in a gasoline engine and vise versa, will likely not even work (and will damage the engine). An ICE can tolerate some fuels, but it will run completely differently even if you put the fuel with the same equivalent amount of energy. It is very hard to match up such an analogy with a DC power source, where what matters is the voltage and current (not the characteristics of the DC supply other than that).

I've been in arguments over ECE R85, the power rating standard Tesla uses in the EU, which doesn't specify that the motors must be tested with the DC source as installed in the car (while it does for the accessories attached to the drivetrain). I have been waiting to be corrected on this point, but it appears to be 100% true, esp. after Straubel's statements.

In fact, a poster pointed out a line on page 9 that seems to suggest that the standard does not expect the manufacturer to use the factory installed battery during test:
"Note: If the battery limits the maximum 30 minutes power, the maximum 30 minutes power of an electric vehicle can be less than the maximum 30 minutes power of the drive train of the vehicle according to this test."
http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2013/R085r1e.pdf

That statement seems to match with Straubel's statements:
"Since the battery electric horsepower rating varies it is not a precise number to use for specifying the physical capability of an EV. The motor shaft horsepower, when operating alone, is a more consistent rating. In fact, it is only this (single or combined) motor shaft horsepower rating that is legally required to be posted in the European Union."


I have seen the claim by others that electric motors can always output their peak power in the low rpm ranges, but I don't believe this to be true. Horsepower is a factor of torque and rpm. At low rpms, the peak torque of the motor limits the amount of power it can output. And given the torque is a direct function of input current, which is in turn limited due to inverter and the current limit of the motor windings, it would be impossible for the motor to output peak power at the lower rpms.

This is more readily shown with a power curve of a car that is not traction nor battery limited (the Roadster; if you doubt that, you can look up a Leaf power curve too):

Here is the power curve of a UQM Powerphase motor (not installed in a car):

In both cases, the peak power is not reached until later in the power band and it does not appear to have anything to do with traction, but rather because the motor is hitting its maximum torque limits at the lower rpms (the graphs seem to make that clear).


Look at the history. Car manufacturers did not switch to net power ratings in the 1970s because they wanted to be more honest. They switched because during the fuel crisis, it was bad to be seen as making a car with irresponsible amounts of power (it was the time when CAFE fuel economy standards were introduced). Switching to net power gave them a convenient way to adjust their advertised power numbers down without having to reduce it in real world use.

JB himself wrote that you can't compare gasoline cars with EV's, and that is exactly what you are doing with your strawman. That comparison is silly at best.

 

[qwk]

you are still missing the point. It would be more misleading/confusing for Tesla to advertise battery hp for the average customer. Many would not understand why they are paying so much more money for the same battery hp. Motor hp represents value better than battery hp. Also note long-term the battery hp will be increased. In 8 years the new pack may come with higher capacity and be able to output more hp and your car will be faster with the same motors. You are not likely going to upgrade your motors but it is simple to swap out the battery.

You have no point. With the right fuses, and battery cables, the regular Tesla 85kwh batteries WOULD provide enough power to make 515kw and make Tesla's advertised numbers. The reason this isn't happening is that there are software limits due to the main fuse not being able to handle the power, and software limits to prevent the faster battery degredation that come along with those much higher discharge rates.

The main difference is with an EV, the battery is detuned vs. the engine in the ICE. Same effect on power, different detuned components. Tesla took advantage of the semantics,and now they have this mess....

 

[AnxietyRanger]

you are still missing the point. It would be more misleading/confusing for Tesla to advertise battery hp for the average customer. Many would not understand why they are paying so much more money for the same battery hp. Motor hp represents value better than battery hp. Also note long-term the battery hp will be increased. In 8 years the new pack may come with higher capacity and be able to output more hp and your car will be faster with the same motors. You are not likely going to upgrade your motors but it is simple to swap out the battery.

While we're at advertising theoretical HP output, why not advertise theoretical NOx output too.

Come on. We can not seriously give Tesla a pass on something we would not give others. That doesn't just bring the conversation down - it brings us down as a community.

And eventually Tesla and the mission would suffer from dishonesty.

 

[AnxietyRanger]

This was not mocking. I was literally laughing as I read the post I replied to. I honestly had no words when I read that someone was seriously trying to say that Tesla should be allowed to overstate the actual horsepower of the vehicle by such a ridiculous margin and that be perfectly acceptable. Laughter was the only thing that came to me initially, and I wanted to convey how ridiculous it really sounded to me.

While I can *almost* understand the position of a few being willing to accept the 20% discrepancy the HP rating of the P85D, extending this to say the same battery that can produce at most ~550 HP worth of power be extended to a car with a rating of 1000 HP+ literally is just funny.

The apparent defense of flathillll's comment left me speechless. I'm glad I could still write a response, though.

If defense was not intended, then FYI, that's what it looked like and that is one of those things that seem odd. How could anyone defend flathilll's comment is beyond me.

 

[qwk]

The apparent defense of flathillll's comment left me speechless. I'm glad I could still write a response, though.

If defense was not intended, then FYI, that's what it looked like and that is one of those things that seem odd. How could anyone defend flathilll's comment is beyond me.

His comment basically states that its okay to false advertise, as long as you are the underdog. Just wow.

 

[AnxietyRanger]

His comment basically states that its okay to false advertise, as long as you are the underdog. Just wow.

This is exactly why I often feel Tesla and the mission are sometimes identified too strongly with and that has questionable consequences. It looks certain way when it happens and when it receives what looks like support in the reaction.

IMO we absolutely can not, as a community, start encouraging or giving Tesla a pass on bad things. Or even act as a community in a manner that would encourage such behavior. The fact that wk057's LOLs got more attention than flathillll's suggestion of dishonesty by Tesla is baffling to me. If I had to pick which one was more important for attention, I would pick differently.

 

[bonnie]

The apparent defense of flathillll's comment left me speechless. I'm glad I could still write a response, though.

If defense was not intended, then FYI, that's what it looked like and that is one of those things that seem odd. How could anyone defend flathilll's comment is beyond me.

Obviously you're referring to me.

You might want to read what I wrote again. I defended no one, nor did I agree with anyone. What I asked for was for response to be made without putting other people down. And of course, you knew that.