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Tesla blog post: AWD Motor Power and Torque Specifications
- Thread starter dsm363
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- Driving Dynamics Model S
The P85D can't output a GROSS 691 hp at the motor shafts with the provided battery. Period. But it's moot. The P85D doesn't produce 691 hp under any circumstance even before accounting for losses that J1349 does for ICE cars. When I say GROSS, I mean we'd be happy with 525 KW at the battery before all the other losses that would occur on the way to the motor shafts.
But as it stands, we got SHAFTed.
Tesla has come forward and admitted that they arrived at the the combined hp rating by adding up the two motor ratings and that it is not the actual power produced by the car.
Why couldn't they have just stated how much horsepower the car actually makes?????? Why would that have been so difficult?
stopcrazypp
Well-Known Member
I am 100% aware of your argument. You are saying that because the battery does not output 515kW, Tesla does not meet GROSS power. You are using your own definition of GROSS power then, not SAE GROSS power (as the ICE industry uses) if that is what you are saying. Your definition of gross power is a number that can be measured in the car in a stock configuration with the accessory load removed (as opposed to J1349 which includes it), but that is not SAE gross.
What I'm talking about is SAE gross as discussed here: "J245 and J1995, which calculated the output of a ‘bare’ engine on a test stand with no accessories, free-flowing exhaust headers (no mufflers), and optimal ignition timing, with a correction factor for standard atmospheric conditions."
http://ateupwithmotor.com/terms-technology-definitions/gross-versus-net-horsepower/
The missing accessory load are beside the point, the more important bit is that it uses connected equipment and settings that are not stock.
Analogy is this:
SAE Net power:
EV: stock battery -> stock motor/inverter -> stock accessory load
ICE: stock header with muffler / ignition timing / carburetor/fuel injection etc -> stock engine -> stock accessory load
SAE Gross power ("motor power" analogy):
EV: power supply -> stock motor/inverter -> no accessory load
ICE: custom header with no muffler / optimal ignition timing/carburetor/fuel injection etc -> stock engine -> no accessory load
It was a decision they made back in October 2014 to switch to "motor power" for all models (a bad one with 20/20 hindsight; they should have just posted both numbers). Speculation back then (by those that noticed the change, most didn't) was it was related to upgrade ability of the cars. It was after the 691 hp thread that they added back system power numbers for other models in April 2015.
As for why they continue to leave it out for the P85D/P90D, I think the reason is obvious based on the reaction of some here. All that will do is cause more outrage for those complaining. I think eventually they will put a number back, but only after most people have gotten enough familiarity with what they meant with "motor power".
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Let me try to understand this. You are saying no car meets the rated horsepower numbers because they were all tested under ideal conditions that does not replicate the "engine/motor in car" environment?
I'm glad we agree upon something. The battery does not output 515 KW (691 hp). My definition of GROSS allows Tesla to claim MORE hp than they would otherwise be able to. My definition is as upstream as you can get at the battery under optimal conditions at the highest state of charge before any losses occur. You can twist this all you want but it won't be more than 555 hp.
It's a moot point already. Tesla has already admitted that they arrived at the number by adding up motor power ratings that this is NOT the actual horsepower produced by the vehicle as delivered. The argument is over. Those that believe Tesla was not misleading in advertising a combined hp that is not in fact the actual hp can stick to their belief. Those that believe Tesla should have advertised the actual power produced, even if they did so at the most upstream point possible, will stick by their belief as well. You already know which side I stand on. I think Tesla was misleading and wrong to advertise 691 hp when the car in fact comes nowhere near close to that.
Kilowatt
Member
Ugh... god, I've really been trying to stay out of these threads... but I'm seriously confused about what anyone fails to understand about the problem here.
The comparisons to SAE don't make any sense and are just as bad as Tesla's own obfuscation of the issue with JB's blog post. There is no "SAE Gross Power" methodology for an EV (not that's I'm aware anyway), so let's just stop assuming what that methodology will be. For SAE measurements on an ICE, does the fuel source change between SAE Net and SAE Gross measurements? Pretty sure the ICE still gets fed gasoline (or diesel or whatever fuel it's supposed to use). If it were fed something more exotic for gross testing I think people would have a problem with that. It seems pretty reasonable to figure that an eventual SAE gross vs SAE net for EVs will have the same fuel source as well: the actual battery that it will be powered from.
Saying that an EV should be tested with the motors run from a power supply, which has little to no voltage drop or power loss like a battery would have, is like saying that we should test ICE vehicles on nitrous oxide and advertise those power numbers. Would it be reasonable of an ICE manufacturer to do that? I would think not. Why should Tesla get to swap out their fuel source to get better numbers then? Seems pretty unreasonable to me, yet this blog post claims Tesla rated the car's performance without accounting for the battery... one of the most important parts of an EV's power train.
Accessory loads are negligible in an EV, specifically the Model S, so I personally don't care if they're included or not. We'll just give Tesla the full usage capability of the resistive heaters (~8kW), A/C (~5kW), and DC-DC (~3kW) combined as a handicap regardless and it's still < 20kW/~26HP. So lets shoot for 665 HP / 496 kW then. Does the car do that? Nope.
JB pretty much lost all credibility with me whatsoever when he wrote: "Defining electric power in terms of horsepower is not very intuitive." I thought this man was an engineer? Everyone with any familiarity with electrical engineering knows that 1 HP = 746W. This has been the way it's been for long before Tesla Motors was conceived. Yet it's not "intuitive" to do simple multiplication or division to convert W or kW to or from HP? This is coming Tesla's god d**n Chief Technical Officer for crying out loud.
Even from a technical perspective, stripping away the crap, this post is misleading at best. "With the P85D the combined motor shaft power can often exceed the battery electrical horsepower available." Now again, I remind you that this is Tesla's CTO. Why would he use the word "often" in this sentence? This man knows the maximum capability of the battery pack. He knows that it is never able to meet the "combined motor shaft power" of the motors. "Often" implies that it can at some point. If it can, and he can give me the conditions under which I can get my car to feed 691 HP worth of energy from the pack to the motors, by all means do so and you will never again hear from me on this topic. I'll even buy a P90D+L as part of my apology. Since I know this is impossible with the P85D's stock battery pack (and likely the P90D's), I'm pretty sure saying "often" here is a lie... misleading at best.
Overall, this blog post appears to be nothing more than fluff and obfuscation of a few key facts deliberately aimed at a target audience who isn't going to be familiar with the technical aspects and is going to just take Tesla at their word, as usual, just like we took them at their word when they sold us a car that put out 691 HP.
I do find it interesting and a bit amusing that this is the second blog post from JB addressing deficiencies of the P85D, both regarding issues I have been very vocal about (initially the efficiency issue, and more recently the horsepower issue.... neither of which has been resolved by the blog posts, although the efficiency issue is much less of an issue than it used to be).
For some data to munch on: In some testing I've done of cells from the P85 packs I have for my solar project I've been able to measure the internal resistance of the cells pretty well. So I whipped up this chart of what the maximum horsepower output of the 85 kWh pack will be at various SoC using that data and the associated voltage drops extrapolated out to the full 85kWh pack level. Interestingly enough, and essentially confirmation that the data and methodology is correct, it matches to within a few percent of all REST max kW readings I have for my P85D using the 1300A number. The P85 is limited to 1200A, for reference. I brought the graph out to the 1500A Elon Musk claimed the P85D could pull with the (so-far vaporware) Ludicrous hardware updates.
You'll see that at 100% to 60% SoC (the only ranges I have sufficient data for so far) that the P85 will always have enough power available at or below it's maximum amperage (1200A) to output 100% of it's rated and advertised horsepower (417 HP or somewhere near there). The P85D, however, never has enough power available from the battery to even get close to it's advertised power. It drops ~75HP from 100% to 60% SoC. That's ~15% of it's actual power output lost in the first 40% of the discharge of the pack. I don't have enough data to accurately show data for lower SoC's with certainty like I do with these, however the data I do have suggests that a P85D at 50% SoC or so can actually have less power than a P85 (with slightly more charge). That's pretty sad. Drive 120 miles and lose 100+ HP. lol.
Not to say that this isn't expected. This aspect of the situation I fully understood from day 1. (Max power available at 100% SoC). Granted, my testing is done at room temperature. There may be some wiggle room with heating the pack at an optimal temperature at an optimal SoC for lowering the internal resistance of the cells slightly, but it would take nearly a 100% decrease in internal resistance for the 85kWh pack to put out 515 kW @ 100% SoC voltage @ 1300A. Considering these are batteries and not superconductors, I'm going to say that this is impossible. I'm also going to point out that the same is impossible of the 1500A Ludicrous upgrade, which would get us up to about 600HP at best. (Edit: Note: I have *zero* data for the cells used in the 90 kWh pack. It is entirely possible that their internal resistance is lower than the cells in the 85 kWh pack, thus boosting performance for the 90 kWh pack per amp more than the 85 kWh pack.)
Back on topic, after filtering the nonsense, Tesla has essentially admitted that they used misleading numbers when advertising the P85D with this blog post. They posted a number they knew the car could not produce. They never made anyone aware that the car could not produce this power. An asterisk next to "691" linking to this same blog post back in October 2014 might have saved a lot of headaches... but would certainly have dulled sales for Q4'14.
So I don't consider this a resolution of any kind to the situation, more of a direct slap in the face to those who actually know what we're talking about.
The comparisons to SAE don't make any sense and are just as bad as Tesla's own obfuscation of the issue with JB's blog post. There is no "SAE Gross Power" methodology for an EV (not that's I'm aware anyway), so let's just stop assuming what that methodology will be. For SAE measurements on an ICE, does the fuel source change between SAE Net and SAE Gross measurements? Pretty sure the ICE still gets fed gasoline (or diesel or whatever fuel it's supposed to use). If it were fed something more exotic for gross testing I think people would have a problem with that. It seems pretty reasonable to figure that an eventual SAE gross vs SAE net for EVs will have the same fuel source as well: the actual battery that it will be powered from.
Saying that an EV should be tested with the motors run from a power supply, which has little to no voltage drop or power loss like a battery would have, is like saying that we should test ICE vehicles on nitrous oxide and advertise those power numbers. Would it be reasonable of an ICE manufacturer to do that? I would think not. Why should Tesla get to swap out their fuel source to get better numbers then? Seems pretty unreasonable to me, yet this blog post claims Tesla rated the car's performance without accounting for the battery... one of the most important parts of an EV's power train.
Accessory loads are negligible in an EV, specifically the Model S, so I personally don't care if they're included or not. We'll just give Tesla the full usage capability of the resistive heaters (~8kW), A/C (~5kW), and DC-DC (~3kW) combined as a handicap regardless and it's still < 20kW/~26HP. So lets shoot for 665 HP / 496 kW then. Does the car do that? Nope.
JB pretty much lost all credibility with me whatsoever when he wrote: "Defining electric power in terms of horsepower is not very intuitive." I thought this man was an engineer? Everyone with any familiarity with electrical engineering knows that 1 HP = 746W. This has been the way it's been for long before Tesla Motors was conceived. Yet it's not "intuitive" to do simple multiplication or division to convert W or kW to or from HP? This is coming Tesla's god d**n Chief Technical Officer for crying out loud.
Even from a technical perspective, stripping away the crap, this post is misleading at best. "With the P85D the combined motor shaft power can often exceed the battery electrical horsepower available." Now again, I remind you that this is Tesla's CTO. Why would he use the word "often" in this sentence? This man knows the maximum capability of the battery pack. He knows that it is never able to meet the "combined motor shaft power" of the motors. "Often" implies that it can at some point. If it can, and he can give me the conditions under which I can get my car to feed 691 HP worth of energy from the pack to the motors, by all means do so and you will never again hear from me on this topic. I'll even buy a P90D+L as part of my apology. Since I know this is impossible with the P85D's stock battery pack (and likely the P90D's), I'm pretty sure saying "often" here is a lie... misleading at best.
Overall, this blog post appears to be nothing more than fluff and obfuscation of a few key facts deliberately aimed at a target audience who isn't going to be familiar with the technical aspects and is going to just take Tesla at their word, as usual, just like we took them at their word when they sold us a car that put out 691 HP.
I do find it interesting and a bit amusing that this is the second blog post from JB addressing deficiencies of the P85D, both regarding issues I have been very vocal about (initially the efficiency issue, and more recently the horsepower issue.... neither of which has been resolved by the blog posts, although the efficiency issue is much less of an issue than it used to be).
For some data to munch on: In some testing I've done of cells from the P85 packs I have for my solar project I've been able to measure the internal resistance of the cells pretty well. So I whipped up this chart of what the maximum horsepower output of the 85 kWh pack will be at various SoC using that data and the associated voltage drops extrapolated out to the full 85kWh pack level. Interestingly enough, and essentially confirmation that the data and methodology is correct, it matches to within a few percent of all REST max kW readings I have for my P85D using the 1300A number. The P85 is limited to 1200A, for reference. I brought the graph out to the 1500A Elon Musk claimed the P85D could pull with the (so-far vaporware) Ludicrous hardware updates.
You'll see that at 100% to 60% SoC (the only ranges I have sufficient data for so far) that the P85 will always have enough power available at or below it's maximum amperage (1200A) to output 100% of it's rated and advertised horsepower (417 HP or somewhere near there). The P85D, however, never has enough power available from the battery to even get close to it's advertised power. It drops ~75HP from 100% to 60% SoC. That's ~15% of it's actual power output lost in the first 40% of the discharge of the pack. I don't have enough data to accurately show data for lower SoC's with certainty like I do with these, however the data I do have suggests that a P85D at 50% SoC or so can actually have less power than a P85 (with slightly more charge). That's pretty sad. Drive 120 miles and lose 100+ HP. lol.
Not to say that this isn't expected. This aspect of the situation I fully understood from day 1. (Max power available at 100% SoC). Granted, my testing is done at room temperature. There may be some wiggle room with heating the pack at an optimal temperature at an optimal SoC for lowering the internal resistance of the cells slightly, but it would take nearly a 100% decrease in internal resistance for the 85kWh pack to put out 515 kW @ 100% SoC voltage @ 1300A. Considering these are batteries and not superconductors, I'm going to say that this is impossible. I'm also going to point out that the same is impossible of the 1500A Ludicrous upgrade, which would get us up to about 600HP at best. (Edit: Note: I have *zero* data for the cells used in the 90 kWh pack. It is entirely possible that their internal resistance is lower than the cells in the 85 kWh pack, thus boosting performance for the 90 kWh pack per amp more than the 85 kWh pack.)
Back on topic, after filtering the nonsense, Tesla has essentially admitted that they used misleading numbers when advertising the P85D with this blog post. They posted a number they knew the car could not produce. They never made anyone aware that the car could not produce this power. An asterisk next to "691" linking to this same blog post back in October 2014 might have saved a lot of headaches... but would certainly have dulled sales for Q4'14.
So I don't consider this a resolution of any kind to the situation, more of a direct slap in the face to those who actually know what we're talking about.
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Even if the P85D had put out 691 hp at the motor shafts combined it would still not be that at the wheels.
Very little actual data on the P90DL yet but the REST data collected by Pete shows 456 KW or 611 hp. The VBOX show 50 hp more at the wheels than the P85D which is what you'd expect with 55 to 60 hp more at the battery.
This is the most concise way of putting it. It feels about as misleading as what VW did, except that with VW there actually is some configuration possible where the car is really putting out the numbers claimed. The only reason Tesla isn't in trouble is because the numbers it misleadingly claims are not subject to regulation in the US. They may very well be subject to regulation in jurisdictions with strong consumer protection laws and stricter rules on misleading advertising.
Andyw2100
Well-Known Member
There's very little I can add to the excellent technical posts sorka and wk057 have already made in this thread. But I will point out that the table was set, so to speak, for us expecting significantly more power in the P85D than in the P85 at the D launch event. Musk, speaking at that event, said very clearly that the P85D would have "about half again as much power" as the P85. (You can start watching the video below at 4:13 to see and hear this for yourselves.)
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Kilowatt
Member
Fantastic post and summary of the problem, wk057!
Tesla Staff - read it once and then again. And again. Then go back to your executive management team and make them have a good think about next steps. This is not a VW grade scandal - but almost imho.
Should note that I'm extremely happy with my P85D overall. Not so much about the L upgrade and cost under these circumstances, though.
stopcrazypp
Well-Known Member
The analogy is not 100% perfect, but the crux of the analogy is that under SAE Gross power, the number given is supposed to reflect the engine, not the system as a whole. This is similar to how "motor power" focuses on the motor. The difference between gross power and net power is 25-30% (sometimes higher). The difference between the motor power 691hp and the battery power at 550hp is 20%. If you throw in inverter/motor losses then it'll pretty much be in the 25-30% range. The analogy seems like a good fit to me.
The fuel analogy you use doesn't work that well, because in all cases, whether it be a power supply, the stock battery, a custom battery, or some other DC source, all of them is using electricity. All the motor inverter cares about is getting that DC electricity (the motor cares about getting the AC). Whereas an engine is very different running different fuels.
This is not obfuscation, just an observation that for a better part of a century (until the switch to net power starting in the 1970s), this was a horsepower standard that was accepted by everyone and has similar implications as Tesla's "motor power" rating. This is a counterpoint to those that claim that all horsepower standards for cars must reflect the system as a whole.
Straubel also seems to be saying the current European standard is similar.
What he said is completely true. There is a noticeable section in the rev range of the motors where the available battery power is more than the motors can output. When it reaches ~40mph, that is when the power "plateaus" in the P85D and the battery is the limiter. That is the "often" part.
I think you guys are overly focused on looking only at the peak power and forget that the power band is not just represented by one number.
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I care for 30K USD worth, that's what it cost me to exchange my perfectly functioning S85 with the P85D on the advertised 691HP (700 Europe), an advertised number that has now not only been pulled back but also explained not to be true. It might be a trifle in your household, but in mine it's a small fortune.
the problem is if we simply rated dual motor ev's peak hp as the peak power draw from the battery then two cars with the same hp rating could have massive performance differences, yet the customer would buy the one with the most hp
long term this will be settled on the race track. some ev's may be more suited to drag races and some ev's may be more suited to race tracks. the model s has no competition yet. until there is actual competition in the ev space tesla will continue to spin hp numbers. long term all hp figures will be removed from the tesla website forcing customers to compare actual performance. you have to remember tesla is still an underdog and the people we are at war with do not play fair.
long term this will be settled on the race track. some ev's may be more suited to drag races and some ev's may be more suited to race tracks. the model s has no competition yet. until there is actual competition in the ev space tesla will continue to spin hp numbers. long term all hp figures will be removed from the tesla website forcing customers to compare actual performance. you have to remember tesla is still an underdog and the people we are at war with do not play fair.
I think a huge portion of the problem is that, while Tesla and wk057 know the actual output of the battery, the inverters, and the motors, Tesla lives in a world where they compete against ICE vehicles that are rated differently because their systems are different. Even though there is a direct mapping of kW to hp, that doesn't capture the qualitative difference between Tesla's drivetrain and ICE competitors. For example, there was that UK review where they compared an Aston Martin with a P85 and the P85 was very much quicker even though the Aston has something like 550 hp. Tesla has to sell against these ICE vehicles all the time where the hp numbers do show up somewhere in the drivetrain but never really makes it to the road. So they chose a spec that is true in some sense, but misleading. But it better captures the qualitative experience - an ICE vehicle with 550 hp usually doesn't accelerate like a P85D with the curb weight of the P85D.
I do wonder if the cells can output a higher amount of current for a very short period of time.
I think Tesla should not have attempted this disception, even the truth is misleading in a different way. The result of 0-60 in 3.2 or 3.5 should speak for itself. The difference in the qualitative difference between the electric and ICE drive trains should be a matter of education, but when has Tesla waited for others to understand?
I do wonder if the cells can output a higher amount of current for a very short period of time.
I think Tesla should not have attempted this disception, even the truth is misleading in a different way. The result of 0-60 in 3.2 or 3.5 should speak for itself. The difference in the qualitative difference between the electric and ICE drive trains should be a matter of education, but when has Tesla waited for others to understand?
Tesla seriously should hire you for their obfuscation staff if they haven't already. You're the master, and even better than JB. Hats off to you for trying to pick my post apart and make it sound like I don't know what I'm talking about.
Just like JBs post, its simple to go through and point out why you're simply wrong, but I'm not going to bother. You're a big part of the reason that I stopped posting in the first place. You and others will try to twist anything to suit and defend Tesla's position regardless of facts and must have the last word in all cases so that it artificially inflates your position that has no technical merit whatsoever.
Back off duty.
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