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[updated with *] P85D 691HP should have an asterisk * next to it.. "Up to 691HP"

Discussion in 'Model S: Driving Dynamics' started by krisg81, Mar 22, 2015.

  1. krisg81

    krisg81 Member

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    Ok, so have had my P85D for several days now and putting 500+ miles on it, I have observed something interesting here and wanted to get thoughts on it from the crowd here.

    Keep in mind, I traded in my P85 for this.

    First off, the P85D is AWESOME. The launch is killer and the AWD is great. It also handles very well and I am loving the Pilot Cup tires that come on it stock, big thumbs up from me on that department!

    That is also the issue. I love everything about it. That is, until the battery drops below 50%. The power is noticeably reduced. Not by a little, but to where I notice the Insane mode is no longer insane- but rather reduced to what feels like the Sport mode when the SOC is lower. It may even happen sooner than 50%. Know that I rarely noticed any performance difference in my P85 unless the little yellow power reducing line showed up when the battery was really low.

    As it is, the P85D does not feel much faster than my P85 when fully accelerating after 40-50MPH. When it is below 50% battery, I swear.. it feels slower than my P85 did at almost any charge level.. yes, slower.

    I get the P85D hype with the 691HP and I do get how they calculate it, but why I do I feel somewhat cheated this is not a full time 691HP vehicle? If this was a 691HP Lamborghini, Porsche, Ferrari, etc ICE vehicle rated at 691HP, that horsepower claim would be SAE certified and would make that power until the very last drop of gasoline was consumed. Imagine if you bought a 577HP Mercedes E63 AMG that operated much slower when the gas tank was 1/2 full? That would be strange.

    Maybe I don't understand the hardware reasons of why the car must reduce power based on SOC. If I have this bad boy in INSANE mode, then.. STAY INSANE until I decide to charge up! I don't need it to conserve power, this mode should be the advertised 691HP at ALL TIMES. Give me a ECO mode for long range, or just recommend me to use Sport mode when the battery drops- but Elon, there needs to be a mode that can deliver advertised power regardless of battery state. Unless someone can chime in here with the hardware reasons (maybe battery pack cannot output as much power as the charge level drops) then I am slightly disappointed here, especially because the power drop happens so quickly. I wouldn't be complaining if it was dropping below 20%, but 50%? That sucks.

    With that said, I really think this car should be advertised as 691HP* *Up to 691HP with ideal battery conditions
     
  2. hcsharp

    hcsharp Active Member

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    I don't know for sure but there's 2 reasons I can think of. I suspect the heat generated in the battery and motor is too extreme at a lower SOC. When the voltage drops the amps have to increase to maintain the same HP. The amps are a big factor in how much heat is generated and they could be 20% or more higher at 50% SOC. The second possible reason is the voltage sag is too extreme at a lower SOC. If the voltage of a Li cell drops below a certain point it will damage the cell, especially during a high-amp discharge state. You're pulling well over 1,000 amps through your pack and the cell voltage sags due to internal resistance. By reducing power it could be trying to protect your cells from damage.
     
  3. WarpedOne

    WarpedOne Supreme Premier

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    Well, that holds true for all and any car.
    Maximum output power is dependent on many factors, it is common practice to only quote and publish peak numbers.
    I for one doubted 691HP (515kW) is even really available at any one moment as it means 6C drain on the battery. That is muchos high for such high-capacity chemistry.
    It looks like it really is available at some conditions.
    Would you rather only have max 400kW at all times or 515kW at some conditions and 400kW at others?
     
  4. loco

    loco Member

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    #4 loco, Mar 23, 2015
    Last edited: Mar 23, 2015
    Power limit is not as much related to SOC, but rather temperature control. You will find some interesting threads relating to this on TMC. Conclusion is that it's not even a matter of actual heat in the motors, but rather a pre-set time*power limit.

    Took my P85D to a race track yesterday. Wasn't able to complete a single lap at full power (90% charged). Just a few corners and you're at 240kW. Push on and it will be less. Result is lap times similar to Golf GTi, Toyota GT86, Mazda RX8 and the likes. Also drove my Mercedes wagon and got 8 sec/lap less on a 2.5 mile track.

    So, yeah.. "up to 691" would be better and "fastest sedan" is just plain wrong.
     
  5. kennybobby

    kennybobby Member

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    #5 kennybobby, Mar 23, 2015
    Last edited: Mar 23, 2015
    With an 85kWh pack you would deplete it completely in ~8 minutes at the 691 power level assuming no losses, sag, etc., so Real Life is even quicker. How many insane launches can be done with a full pack down to 50% anyway?

    With no losses it only takes ~340 Hp to accelerate 5000 lbs to 60 mph in 3.2 seconds, so any extra is for the power losses.

    The dual motor controller calculates the torque and flux for each motor based upon a switching table lookup and input parameters such as throttle position, traction control feedback, max efficiency, etc...we don't yet know the details of what could be the limiting factors, but if the controller would command full torque and current for both motors then you might experience the 691 if the traction control would allow it.

    Doesn't it seem odd to make a 0-60 in 3.2 and not spin the tires or leave darkies on the asphalt? That's the fun of joy ridin'...
     
  6. krisg81

    krisg81 Member

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    exactly. That's pretty bad if it can't even complete a single lap at full power- do you recall what % the battery was at when it reduced its power (although in your case it seems temp related too)

    in my car the temps were the same, it's just that the car slowed down more and more and the range went down.

    i think the 691HP claim is wrong and maybe it leads into something bigger, like a way to certify claims of horsepower ratings for EV's. Just like the EPA has a gas mileage claim for City and Highway driving, there needs to be HP ratings for all ranges of the battery, or some type of averaging calculation.

    Futhermore, according to the dyno run the P85D did suggests HP never exceeds 400HP to all 4 wheels, but it does have major torque. Once again, HP output and claims needs to be certified by a 3rd party here because of what I've seen on the dyno it should be actually 450HP/691LB-FT torque as there's a lot of torque like a diesel, but combined HP is not as high as their claims, especially on anything less than a full battery.

    also, when accelerating from anything higher than 40MPH you clearly do not feel like you are driving a 691HP vehicle. That power is just not available at anything other than from a stop- if you advertise your car at 691HP then it should be available at all times, in my opinion... Or just advertise its power rating more transparently somehow. Why a S85/P85/P85D feels so similar after 60MPH should be telling of how Tesla needs to re-evalute how they advertise horsepower ratings for the entire fleet.
     
  7. WarpedOne

    WarpedOne Supreme Premier

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    *No car* has max power available at all times.
    Basics.
     
  8. Kbsilver

    Kbsilver Member

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    One of the things that set's Tesla apart from other BEVs is battery protection. I would suspect reduction of max power at a lower charge state is just part of this. When you want to impress your friends, just make sure you have a good charge, all controllable.
     
  9. krisg81

    krisg81 Member

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    I am stumped by your claims. We all love Tesla and our Model S's but let's not lower ourselves to Apple fanboys on things like this.

    I come from an extensive background of heavily modifying vehicles for maximum power output and even tune ICE vehicles on a dyno with HP Tuners and other tuning software.

    Vehicles if tuned correctly will always output within 2% of their peak wheel horsepower if the tune is solid and accounts for detonation and proper fuel. The difference under any condition wouldn't even be noticeable to the driver, only on a dyno. It would stay this way until the last drop of gas in the tank is used.

    while your claim is certainly plausible to a degree, it's such a small difference compared to the drastic difference of the P85D. To the point the car goes from feeling fast to feeling plain out slow. Like buying a 460HP Corvette and once the gas tank drops below 50% then it goes to 230HP. That's the difference here.

    in fact the car should be more transparent during this process. Insane mode should visibly switch at some point when the power switches below a certain metric because it is no longer "Insane" once below 50% battery and should automatically switch to Sport or even an Econo mode, in my opinion.
     
  10. WarpedOne

    WarpedOne Supreme Premier

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    It is not just protection, it is also capability. An empty battery has no power at all, a full one has some maximum power available.
    As SOC drops, maximum available power also drops.

    There are only two possibilities really:
    a) power output is limited at some low value that even a battery at 5% SOC can manage
    b) power is limited by battery SOC (and other things)

    Which option will in general perform better and offer a better value, a or b?

    It is just that "mechanics" of EVs have a different set of limitations. People are used to limitations of ICE cars to much that they don't even see them anymore. Different limitations of EV are more visible as they are both different from ICE's and new.
     
  11. loco

    loco Member

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    The Certificate of Conformity of P85+ states "Maximum continuous rated power: 69kW". Wouldn't make a good advertising slogan ;-)
     
  12. WarpedOne

    WarpedOne Supreme Premier

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    Not just poor advertising slogan but also misrepresentation.
    Noone is limited by maximum continuous power, not in a car on civil roads.
     
  13. David99

    David99 Active Member

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    Batteries are, unlike a gas tank, dependent on the SoC. The higher the SoC the higher the voltage and of course the lower the SoC the lower the voltage. So that's a factor right there. You are loosing 20-30% power depending on the SoC.

    Another big factor, as other have mentioned, is the voltage drop when high power is drawn from the battery. Insane mode also means insane stress on the battery. Tesla has to limit the power when the voltage drops too much for the long term health of the battery. It's unfortunately one of the fundamental disadvantages of batteries. They can't take stress equally over their entire SoC. High power at low state of charge is bad for the battery. For any battery. Drawing 500 kW from the battery is really pushing the limits.
     
  14. apacheguy

    apacheguy Sig 255, VIN 320

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  15. krisg81

    krisg81 Member

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    Excellent response. What you explain here is magnified 1,000% when driving a car like a P85D though- compared to a P85, which wasn't that drastic enough to make a complaint, this is a real problem here when commanding such a price premium for a "performance" model. This "performance" edition is only able to run in "performance" mode for a short period and this is not good at all.

    It just brings me back to the point and topic of the thread, Tesla really needs to re-evaluate how the P85D is marketed and how they advertise 691HP and put some type of disclaimer/asterisk on it. This vehicle is not completely able to perform as advertised for longer than a short period of time- Insane mode needs to transparently state that mode can only run at XX% battery or higher. The website, marketing efforts, technical specs, and even console needs to transparently tell the driver what is happening. I will go as far as state that 691HP is false advertising at this point. This is not like the power reduction in my P85, this is a HUGE drop in performance and the drop happens way too soon.

    - - - Updated - - -

    Understood. With that said, EV's need a completely different way of certifying and advertising horsepower vs ICE cars then. Kind of like MPG vs MPG-E ratings. If there were proper 3rd party companies certifying HP output of the P85D, theres no way they would be cool with the 691HP claim.. because there is not 691HP working at any one moment (as far as I can tell, but the torque from 0-60 is definitely there and Tesla does not advertise the torque specs, just HP) and after hardly any battery depletion it all goes down hill from there. That 691HP claim is fluff IMO.
     
  16. WarpedOne

    WarpedOne Supreme Premier

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    No 'different certification' will tell anything more than current system, rather less.
    Maximum power is a curve dependent on current SOC, current speed and current temperature of battery/inverter/motor.
    No single number can describe that curve in a meaningful way. Stating the maximum number this curves attains at some circumstances is at least correct at exact those circumstances.
    We start to near the torque/power debate.
     
  17. arijaycomet

    arijaycomet Member

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    Then your extensive background would know that modern cars would adjust power output based on a variety of factors. That is to say 91 vs 93 octane (so that Corvette in California won't make the same power as mine in Ohio with 2 more octane points). Additionally, elevation is a huge factory, as would be in general the air density as a result of that elevation. Even if you used the same dynamometer to test the same car (disassembly of dyno, transport across the country with same car, same fuel, and re-test) you'd get different results just based on the air. I think 2% is a big aggressive to assume... I'd expect more variation than that. Not 50% of course...

    I don't think you can call this "marketing fluff" so much as just uneducated public. There becomes a VERY large grey area of what the manufacturer needs to explain versus what the general public needs to learn. The same argument could be made for the 265 miles my 85 is supposed to go. I picked my car up in Ohio in December, and for the next 90-days have averaged around 430 wh/mi. Do you see me on here writing complaints about how the car can't even go but maybe 50-60% of the claimed range?

    No. Because I educated myself first (and this is my 2nd BEV, so I already had experiences for the last two years). But someone who walks into a store and buys a car needing every last drop of that range SHOULD understand that it is EPA rated, in the conditions that the EPA calls out. So while I would agree with you there needs to be more transparency in these figures, the argument as to whose responsibility it should be would vary greatly from one persons' opinion to the next. It would be wise for Tesla to educate their customers, of course... but I think that would be time better spent on matters like range, not horsepower.
     
  18. stopcrazypp

    stopcrazypp Well-Known Member

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    Tesla's hp claim used to be based on the car as a whole (ignoring the power reduction and SOC based variance for the moment). It was around the time of the P85D announcement that they based the hp claim on the motor capability only (same evaluation as SAE: peak power of the motors, not the car package as a whole). This aligns with what a lot of other automakers have been doing in the first place. AFAIK the P85D at the current firmware *NEVER* outputs 691 hp.

    As for the drop, I'm not convinced the P85D drops to a lower absolute level than the P85. I think it's likely it feels that way because our minds are wired to do relative comparisons, so it just feels like it's a bigger drop (because P85D starts higher). I would like to see instrumented testing to see the difference. Although time-wise it's plausible (P85D stresses the battery more so can result in reduced power quicker).
     
  19. krisg81

    krisg81 Member

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    Arijay, those are *environmental* changes due to air density as well as fuel octane rating. SAE certifications give the peak HP rating of the motor based on their testing criteria so we know all motors are rated based on the same testing conditions in order for manufactures to claim those horsepower ratings. Tesla DID NOT confirm to any type of 3rd party testing or certification process. What is occurring here is nothing to due with environmental or fuel/electricity rated changes. The fact of the matter is the car simply does not live up to its horsepower claims shortly after the full charge depleting, no matter what environmental changes occur (although it may worsen of course due to cold weather and any other issues). The car under ideal and perfect conditions will never output 691 advertised horsepower, and if it came close, will drop significantly as the battery depletes, with said battery depletion being the reason for the power loss and nothing else- the loss of available fuel/energy, apparently.

    The only comparison to an ICE vehicle would be saying a ICE drops performance as the gas tank empties, as thats the only thing relatively changing in my ICE vs EV comparison, especially with a P85D. The S85 and P85 are not even worth arguing- its specifically an issue with the P85D. This car is NOT 691HP, does not perform like a 691HP ICE vehicle, let alone any other vehicle with 691HP, and reduces power extremely fast after topping a charge.

    To say this same anomaly happens with an ICE vehicle, with all due respect, is absurd. I can take a 700HP Corvette to the drag strip and run back to back consistent runs there and on a track and the results will be extremely consistent within a small margin of performance, with fuel/energy depletion not being a factor.
     
  20. hcsharp

    hcsharp Active Member

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    Exactly. The OP keeps focusing on the fact that his Corvette will put out the same HP no matter how full his gas tank is but fails to recognize that his ICE cars won't even go into legitimate launch mode until they are fully warmed up (at least not without damaging the engine), are quite susceptible to altitude changes and weather conditions. EVs have none of these limitations.


    Not necessarily. A lower SOC (with corresponding lower voltage) does not necessarily mean you will have a lower power output from the battery. You can increase the amperage draw to compensate for the lower voltage to get the same power output. The problem is with more amps you generate more heat in the power electronics, motor, and battery and begin to exceed the capacity of the cooling system. In addition, as the SOC gets low, you reach a point where the momentary voltage sag from a high-amp draw event can temporarily reduce the battery voltage below or near its minimum safe level. If you don't limit power at that point you will quickly reduce battery life.
     

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