quote: Aerodynamic drag only makes up about half of the total resistance at 60 MPH in most vehicles with the rest coming from rolling resistance so by my calculation going from 60 to 80 MPH should consume about 39% more power or from 20 HP at 60 MPH to 28 at 80. Considering the Tesla’s very low coefficient of aerodynamic drag and weight it is likely to be less than half of total resistance at 60 MPH making the HP requirement at 80 some what less than 28.
quote: Lithium batteries don't have the high internal impedance of some of the older chemistries. In fact some lithium chemistries have 1/40,000 the internal impedance of lead acid AGM’s for instance. Kokam quoted a 97% charge recovery at 0.3C charge discharge rate for some of their cells.
quote: Available capacity won’t decline by anywhere near as much as you imagine. Even in the most demanding condition of say successive sprints to 60 MPH.
quote: Initial power demand from stand still would be very low and would rise linearly up to peak power before going into decline. Considering the Tesla’s top speed it might not even see peak power before it reaches 60 MPH.
quote: If we say it does then average draw would be around half of peak. At peak power we would be talking about a 3C discharge rate so on average about 1.5C in the sprint.
quote: I know there are some big flaws in the derivation but in the absence of some better figures it gives an idea of what sort of numbers we are talking about. At a normal cruse of say 60 MPH the discharge rate would be less than 0.2C and at 80 it would still be less than 0.25C.
quote: This is incorrect. As per my example, which is an EXAMPLE to illustrate the exponential increase in air resistance vs speed, if you know how much power it takes to move at a certain speed then you are already accounting for the coefficient of drag. The increase in power would be about the same percentage-wise regardless of the CD, the only difference being that a lower CD would mean less power for a given speed. So your calculation of a 39% power increase is off by a lot.The model S is not light by any stretch of the imagination; it's a 2-ton porker of a car. Granted there are other luxury sedans tipping the scale near or north of 4,000 lbs - Audi A5 comes to mind - but the Audi has an AWD system which the tesla does not.
quote: Tesla uses lithium ion batteries, not the more powerful (and lighter) lithium polymer, likely due to the latter being even less stable than the former, and for that particular battery type 4C is pretty much the upper threshold of discharge that you'd want to subject the cells to.
quote: You're missing a key point that you yourself were quick to point out in your first response - electric motors have full torque from 0 RPM. While a motor at 0 RPM is not producing any power, that does not mean it is not consuming energy. When you floor the accelerator in an electric car, the load will be at or near the full capacity of the system.In the case of the tesla, that means 850+ amps will be drawn from the battery under full throttle, from start and this will taper off as the car slows its acceleration.
quote: No, not really. There relationship between output power and input power is quite rigid. You cannot draw less power from the battery and have the motor put out its full rated 310 kW of power. For the motor to put out 310 kW, it will draw MORE than 310 kW from the inverter, which draws from the battery...this works out to about 4C as explained above.
quote: While the motor is drawing full power from the battery and the car is at a stop, that is 0% efficiency.
quote: The reality of the situation is that right now electric cars are expensive and inferior to their gasoline counterparts.
quote: When characterizing a vehicles drag you cannot disregard the vehicles rolling resistance
quote: You misunderstood my reference to the model S weight. Because the car is heavy and has a low Cd I thought rolling resistance would make up a much larger portion of total drag at 60 MPH.
quote: Total power consumed at 55MPH according to Tesla’s figures is 14.6 kW so if we assume the remainder is solely due to rolling resistance Prr=8.9kW. If we assumed 85% efficiency in the drive...
quote: Gasoline contains about 33.6 kWh per gallon. That means the Tesla pack contain the energy equivalent of 2.5 gallons of gasoline. Any way you look at it it is very efficient at converting that energy to miles.
quote: The key parameter they need to stay below is the core temperature of the cells....Shallower thermal cycling should help cell longevity.
quote: The motor controller acts a bit like a transformer while the controller will always see full battery pack voltage on its input side it will chop the voltage on its output side and even when it is pushing its current limit on its output side its input current will be lower.
quote: It will not draw the full 850+ amps from the battery from the start. Initial amps on the battery side of the controller will be much lower.
quote: You’re talking peaks I’m talking averages. I’m saying that peak power won’t be drawn continuously.
quote: For about a millisecond. While an ICE is idling that is 0% efficient for much much longer. 0% efficiency at 0 RPM doesn’t tell us a lot about what power will be consumed at that point on the curve.
quote: Expensive yes I don't disagree, inferior or not depends on your use case, on what you are hoping to achieve.
quote: Drag is an aerodynamic effect; rolling resistance is a separate thing, and it's effects on the net friction that the vehicle must overcome to accelerate and move is not substantial. You are driving this conversation off topic by fixating on minutia.
quote: No, I didn't misunderstand you. The fact that the car is heavy contributes to its inefficiency. Rolling resistance is largely a factor of the tires - their width and their inflation pressure.
quote: You've already made two 'questionable' assumptions in an effort to make the numbers look "good" or seem right...but lets' examine this with your figures.
quote: Going by what you cite as Tesla's 14.6 kW (20 HP) figure to sustain 55 MPH, we can simply scale up the power required for higher speeds, because:Power:= Work/Time= Force x Distance/Time= Force x VelocityAir resistance is proportional to the square of the speed, and going from 55 to 80 MPH is a 25 MPH increase, or a 1.46 increase in velocity.We square 1.46 to get 2.13, which is the new force.
quote: 14.6 kW x 1.46 x 2.13 = 45.4 kWSo to drive your model S at 80 MPH using your 14.6 kW @ 55 MPH figure, it takes 45.4 kW or 60 HP - your results are off by quite a bit...at this rate your effective range will be around 150 miles, because remember, 45 kW of engine output will draw MORE than 45 kW from the batteries.Like I said before, if you know how much power it takes to go a certain speed, you can figure out how much more (or less) you would need for a change in velocity using some very basic math.
quote: Stepping up the voltage costs efficiency. I do not know what the operating voltage of the model S inverter happens to be, however I am well aware that it regulates its output voltage which is how it controls engine speed.
quote: When I launch a car, I rev the engine up to a specific RPM and drop the clutch. The engine will stay at or near the launch RPM and then increase. There is nothing that says I cannot launch the car AT the redline if my tires have enough traction, thus having the engine producing almost all of its power AND torque from a stop.
quote: The key point is that the batteries will be discharging at 850A or more when the drive program allows 'full power'...and it will be close to full power from a stop if you floor it and have the car in "performance mode".
quote: False. The idling engine is producing torque and therefore power. Simply because the car is not moving does not mean efficiency is 0%.
quote: 0% efficiency means that the electric motor is drawing current but not moving, and since it is not moving it is not producing power so efficiency is 0%. When the motor draws current and does not move, the energy radiates as heat. It is not a difficult concept to fathom, even though it is only for a brief moment.
quote: Tesla is trying to achieve an electric car that replaces gasoline cars, and that's just not happening. It takes too long to charge vs filling up with fuel, using the A/C can have a big impact on range, as can loading the car up with passengers and cargo. Reliability is also in question, and there are already plenty of reports from owners who have experienced problems like the car completely shutting off (while being driven) and being unable to start.
quote: Really, well all those poor fools buying low rolling resistance tires are just wasting their money then.
quote: The energy consumption of a vehicle virtually all comes back to two factors. Weight and aero drag. First you say weight will make a car inefficient then you totally disregard it in this calculation. So which is it, is weight in or is it out. Does weight generate a drag force which must be overcome or can we say its basically zero so we can just ignore it.
quote: A bit too basic unfortunately. It seems to have escaped your attention that aero drag scales with the cubic function of velocity when it comes to power requirements and including all the drag that doesn’t scale will dramatically exaggerate your figures.
quote: I told you exactly what the aero drag power requirements were at 55 MPH yet you choose to ignore that and generate more nonsense. If I apply a bit of reducto ad absurdum to your argument that all drag is aero drag and therefore scales to the square function of velocity then at zero velocity the car would exist in a frictionless state with only its inertia to resist motion if on a level surface. You would have no trouble pushing a 4700lb car with your pinky finger. It only takes a small force and a bit of time to overcome inertia.
quote: Actually I’ve been trying to tell you that it regulates its output amperage and it controls motor torque not speed. EV’s would be hard to drive if the motor controller and accelerator position regulated motor speed.
quote: EV’s don’t work that way. The power provided at a full throttle launch will ramp from some initial value required to overcome losses up to peak power at peak power RPM and speed.
quote: Wrong. Peak amps is only drawn from the battery at peak power. Peak power occurs around 7000RPM. Peak torque is a band from 0 to7000 RPM. 7000 RPM by my calculation would occur around 57 MPH. Don't forget EV's control torque. You don't get "full power" but full torque when you floor it.
quote: And that idling torque is totally consumed internally overcoming pumping losses and bearing friction.
quote: Actually I was thinking more about what their customers were hoping to achieve. Personally I would like to get off blood oil.
quote: I didn't disregard weight.
quote: Weight has already been accounted for by the baseline value, which I scaled.
quote: It's really very simple and I'll repeat it for you: if we know how much power it takes for a vehicle to move at a certain speed on a level surface, we can use a simple scaling formula to ascertain the power required at higher or lower speeds.
quote: False. The primary resisting force is aerodynamic drag. Again, your fixation on minutia in an effort to obfuscate the real point only makes you look like someone who can't accept that they were wrong.
quote: Verbal diarrhea is not the mark of someone who knows what they're talking about. You seem to be sliding into a pit of repetition peppered with stupidity. Next thing we'll have you telling us that climate change affects the Tesla's efficiency because vegetable.
quote: That's incorrect. It uses a PWM type of speed control, which limits voltage. Current limiting is an automatic result of pulsing the drive voltage at lower frequencies when the car is moving at lower speeds, and higher frequencies when the car is moving faster. The pwm system allows for "real time" feedback on what the engine is doing and allows its performance and response to be tuned.
quote: If you were to simply make a direct "always on" connection to the motor from the inverter, the car would probably have trouble gaining traction.
quote: FYI direct current limiting causes the excess current to be bled off as heat. That would be a very inefficient method of regulating the engine speed...and incidentally it's why tesla uses a PWM speed control. And yes, it's called a SPEED CONTROL not a torque control.
quote: I'm quite aware of the differences; but you've cleverly managed to miss my point yet again. The point I was making, is that while electric cars may have "full torque" from 0 RPM, launching a gasoline car from a stop can be done in such a way that you have nearly full power and torque from a stop. It's called launching for a reason.
quote: Since the inverter regulates the motor using a PWM type of system, full throttle doesn't equal a full-on connection between the motor and power source. The entire powerband is regulated, and that means the power is always pulsed, i.e. on and off.
quote: The problem with people like you is that you believe you know what you're talking about but don't. Do you think that the motor spinning at 7,000 RPM in free air (no load) will draw the same current as it would pushing the weight of the car down a drag strip (full load)?
quote: Please shut up about your idiotic and incorrect calculations and moronic theories about how electric motor drive systems work. You really do not know what you are talking about here and it's just getting tedious repeating myself.
quote: The amount of power consumed by the belt driven accessories is minimal at idle. Torque is not consumed; it is transferred.
quote: Oh yes you did. I for one happen to understand that zero squared is still zero.
quote: Yes but you than scale it with total disregard of weight solely as a function of speed.
quote: Repeating the same flawed argument over and over again doesn’t make it correct.
quote: I don’t accept I’m wrong because I’m not and I have proved it. Minutia it’s not. Have you ever tried to push a 4700lb vehicle?
quote: Who said anything about current limiting with an additional load? The Back EMF of the motor and the resistance of the windings can be used to control the current if you chop the voltage accordingly. I find it really hard to believe that you think you cannot control the torque output of a motor. Really?
quote: I didn’t miss the point. The point was redundant. Just because you can have full power and massive torque and convert your tires to smoke at launch doesn’t mean that EV’s must have full power available at launch. They don’t and they don’t need to unless the objective is to make lots of expensive smoke.
quote: When you get abusive do people pay more attention to what you say? Does it improve your credibility?
quote: When a system is in equilibrium, i.e. idling at a constant RPM, any torque produced by the engine must be matched by an equal and opposite torque or the engine would not be in a state of equilibrium and would either be accelerating or decelerating. When the drive is disengaged that torque will be predominantly internal losses. Physics 101. I’d be interested to hear your take on where that torque is being transferred to.
quote: If you are calculating the approximate power required for a car to move at a certain speed without knowing the power required to move at ANY speed in the first place, then weight would be part of that equation...but since we already knew how much power it takes to move the car at a given speed, weight has already been factored, and therefore we can scale power, as I did. Not sure how many times I have to repeat this until you get it.
quote: so get over it and learn some basic math while you're at it.
quote: quote:Minutia it’s not. Have you ever tried to push a 4700lb vehicle?
quote: Oh that's a new one - you restate things I've said and then try to present it as what you've been saying all along. LOL Nice job, but you are still not grasping the basic functions of an electric motor and its respective speed controller.
quote: In an EV we don't want to control the speed of the motor but the torque it puts out. If the accelerator position controlled speed the vehicle would be very difficult to drive. Hence the motor controller manipulates the current by manipulating the voltage but the voltage doesn't bear any direct relationship to the accelerator position. None of this is in disagreement with what you have said I’m just trying to add a different perspective. As for load when you encounter a hill the driver must adjust the accelerator pedal to maintain speed (as you currently do in your ICE powered car) increasing the current to maintain the voltage.
quote: Actually it's not redundant, because it completely shatters the whole "full torque from zero RPM" line that the ignorant EV humpers cite as a major benefit of electric motors over gasoline engines...apparently they don't know how to launch a gasoline car to maximize its acceleration and assume that all acceleration happens off-idle...and if you launch correctly your tires will hook and you will accelerate quite nicely.
quote: I'm hardly being abusive...maybe you're just too whiny and thin-skinned.
quote: You probably spent hours writing this statement, even soliciting your asian friends for help, only to end up "not getting it".Your previous statement attempted to portray the engine accessories as requiring all or most of the torque of the engine at idle - which is false. The power steering pump, the water pump, alternator and A/C unit combined place a relatively minor parasitic load on the engine, whether it's idling or at its redline.Yes, I'm sure you thought you are brilliant for pointing out newton's 3rd law, but that is obvious that was never in question or in doubt.Torque is a force, so it is transferred rotationally along an axis. It is not "consumed". Power is consumed, and power is torque x RPM.
quote: An axle spinning at a certain RPM being driven with a fixed amount of torque can continue turning so long as the load placed on the axle does not exceed the amount of torque which is driving it...however if you increase the load on the axle without increasing the torque, the RPM will decline. Get it? That is power being consumed - the torque does not change.Go back to school.
quote: Because weight doesn’t change with speed, the drag force due to weight doesn’t change with speed.
quote: Therefore the power consumed due to weight scales linearly with velocity or is proportional to mass times velocity.
quote: The drag force due to aero drag scales with the square of velocity. Therefore the power consumed due to velocity (aero drag) scales with the cube of speed or is proportional to velocity cubed.
quote: Adding the results of the linear function and the cube function creates a third function in which mass and velocity still feature separately. That third function is NOT proportional to the square of speed. Mass times velocity is NOT a constant and so cannot be factored out along with the other constants when figuring out proportionality. I’m not wrong about this.
quote: That went straight over your head. The Tesla’s weight and tires will result in a rolling resistance of 56lb force. If you think that is insignificant to the point of being practically zero when compared to aero drag then what else can I say. Either you can’t understand or you won’t understand and neither of these makes you look good.
quote: An EV is not like one of your model aircraft and the correct terminology is Motor controller specifically so people like you won’t become confused. I posted this on the 4/16/2014 in this thread so it is what I have been saying all long.
quote: The advantage of full torque from zero is not having to have a clutch (or torque converter).The advantage is not having to have a clutch. It’s a mechanical simplification.
quote: In the case of Tesla the range of the motor is so broad that it also doesn’t need a gearbox and can make do with a single reduction ratio. A further mechanical simplification. The net result of this is lower weight better reliability and reduced cost.
quote: So if torque is not consumed and power is consumed and power is torque x RPM then really it is just RPM that is being consumed?? LOL. You’re funny.
quote: All that and you still haven’t said were torque in an idling engine is being transferred to.
quote: How does it feel Eric being bested by a “dim-witted buffoon”. Nothing in this world is free Eric not even cheap shots.
quote: We're not talking about economics, skippy, the point was that electric power generation is inherently inefficient...and the fact that you totally veered off topic is basically you conceding that I PWNED your pathetic liberal arguments in favor of electric cars.
quote: While an electric motor does a great job of converting electrical energy into mechanical work, when you consider the fact that the the fuel consumed to generate said electricity is far greater than the energy wasted by gasoline and diesel engines as heat, we can clearly see the SCAM that is being perpetuated by the whole "green energy" political agenda.
quote: It all fits into the broader left-wing agenda of deception, the notion that "climate change" is caused by human activity and supported by dim-witted buffoons like yourself, who fail to realize that being educated today is more of a liability than an asset.
quote: I just find efficiency of generation secondary to anything that has real world effects.
quote: So efficiency should really only be considered within a single fuel type unless you apply some sort of compensating factor.
quote: By the way you did bring up energy independence in your side bar. Electric car = 100% US sourced energy, ICE age car = 30% US sourced energy, 70% imported energy. +1 for the EV
quote: Like I said where I live 70% hydroelectric generation. No fuel consumed there just falling water. Most of this generating capacity was built prior to environmentalism becoming fashionable. No green agenda involved. No tax breaks for EV's here either.
quote: Oh WOW, just WOW. So education and the educated are the enemy. I guess that means ignorance is an asset.
quote: Abusive name calling and personal attacks add nothing to the debate and really only serves to depreciate your cause.
quote: People usually resort to this behavior because they have lost the rational argument and are basically trying to create an emotional fist fight where they try to wound with words rather than admitting defeat.
quote: When you start calling me a dim-witted buffoon for occupying a position I haven’t well that shot misses the mark by a mile. While I can admire a never say die atitude I do read these outbursts as victory.
quote: You have to exclude the inconvenient fact that electricity generation is inherently inefficient
quote: Efficiency is not an end in itself but a means to another end. Its good EV’s are efficient because their batteries can be smaller and because they use electricity that someone has to pay for but that is where it stops at the plug.
quote: Thank you for playing.