What are you talking about? IMO the Model S still looks better, than the Model 3.
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PMAC vs induction motor for model 3
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What are you talking about? IMO the Model S still looks better, than the Model 3.
Rashomon
Member
No, it's not. What is of interest is CdA, the effective frontal area, not Cd, which is just a dimensionless number that only tells you how much one shape is better than another. You also have to know how big that shape is. Kilowatts consumed at a given speed are proportional to CdA times V-cubed.
The V-cubed absolutely kills EVs as speed increases. ICE cars, not so much, because the gasoline engine efficiency is also increasing substantially with increasing load. But that also means you can't have acceleration and good mileage easily in an ICE car; ideally, the peak engine power is only 2 or 3 times the cruise power requirement if you're optimizing for fuel economy (cough, cough, Prius). When you get to acceleration numbers anywhere close to a P100D MS, an ICE vehicle's fuel economy typically puts it on the Gas Guzzler Tax list.
I agree with you! I was talking about the cars in that list {except Tesla, I have an S aS well
Ioniq also looks kind of nice, not as good as the 3 and the S, but better than the X, for example.
You cannot safely assume that and here is why. All AC induction motors induce voltages in the rotor "windings" (hence the name induction motor). The rotor is constructed with shunts (shorting bars) that conduct the current generated by the induced voltage in the shorting bars. The field must rotate at a different rate than the mechanical rotation of the rotor in order for the voltage induction to occur.
Now here is the relevant detail answering the OP question. Since the Tesla drive motors are inducing voltages in the rotor and the shorting bars are not superconducting the resulting current flow results is rotor voltages that differ from the remainder of the motor frame. Any drive imbalances also result in rotor shaft to frame voltages. As a result the motor armature shaft *must* be electrically grounded to the motor frame or else it would result in capacitive arcing. When the rotor shaft grounding is insufficient, then arcing occurs through the armature shaft bearings (we are talking high currents here) and that results in pitting in the bearing races. As a result, over time these bearings get very rough running since the races are no longer smooth and the bearings would eventually need replacing since they are self destructing. The motor drive unit "growling" that some Tesla drivers have experienced could be caused by the armature shaft bearing arcing, as described above.
Here is one reference, there are plenty more: http://www.est-aegis.com/js/AEGIS_HVAC_White_Paper_JohnstoneSupply.pdf
SageBrush
REJECT Fascism
Thanks for the reply, but it sounds like something that if it had been present, would have been corrected once it was known. By that I mean that it is not generic to AC induction but a QC problem.
Brando
Active Member
NOTE: difference is 25% (1 out of 4 miles)
or 33% better as in 4 miles vs only 3 miles
Considering the difference with gas cars, it is even smaller, and how you drive may well be a bigger factor, right?
SageBrush
REJECT Fascism
Brando
Active Member
weight would seem #1 factor (directly related to the amount of work that is needed) Model S heaviest
(seems curious eSMART and i-MiEV aren't city mileage winners - why would that be?)
aerodynamics #2 directly related to highway miles
friction? I'd suspect very small difference as all use very similar bearing. Tires??
Rashomon
Member
Well, now that PMAC has been confirmed, I'm willing to bet the next major update of the MS/MX line includes a PMAC motor on at least one axle -- but maybe not both. Tesla may well add a PMAC motor at the front for efficiency under a number of operating conditions, while using an AC induction motor for high-acceleration at the rear axle that can also be shut down with no cogging drag for highway cruise. Of course, there may be cost and control issues I'm overlooking, but the next big update on the luxury line will be very interesting, I'm sure.
Other way around. You want to use PMAC for acceleration, and IM for highway cruising.
Or to keep it simple, just transplant the model 3 propulsion system into the Model S/X en mass... If the model 3LR can get 310 miles with a 75kw pack with decent acceleration, what can a model S get with a 100kw pack do? 400 miles????? Whatever special sauce they are using in the model 3, Elon is probably trying to down play it so it doesn't hurt current model s/x sales. The next big thing in the s/x line will include the special sauce of the model 3. Lets see how long it takes for Tesla to incorporate these things. A 400 mile range model x would fulfill pretty much all of my use cases. In other words, when that happens, the situation of "shut up, and take my money" will occur for me
Or to keep it simple, just transplant the model 3 propulsion system into the Model S/X en mass... If the model 3LR can get 310 miles with a 75kw pack with decent acceleration, what can a model S get with a 100kw pack do? 400 miles????? Whatever special sauce they are using in the model 3, Elon is probably trying to down play it so it doesn't hurt current model s/x sales. The next big thing in the s/x line will include the special sauce of the model 3. Lets see how long it takes for Tesla to incorporate these things. A 400 mile range model x would fulfill pretty much all of my use cases. In other words, when that happens, the situation of "shut up, and take my money" will occur for me
You will actually get less highway range, all things being equal. EPA range might increase due to the way it measures... it overemphasizes city driving with a lot of acceleration and deceleration. PMAC motors are much better in that driving pattern than IM. But at 70-80 mph on the highway, IM is more efficient. So do you care that the EPA range is higher or that your actual long distance range is higher? Remember, the Model 3 is a much smaller and lighter car so a lot of efficiency gain is due to the form factor. I suspect that EPA range would increase more on the X, but actual realistic highway range will drop significantly. There are also other trade-offs for high power. It will be interesting to have a 100D with IM front motor and PMAC rear motor to capitalize on the differences between the two.
"EPA tests have previously shown that reducing vehicle weight is one of the best ways to improve fuel economy, with a 1-percent improvement per 100 pounds of reduced weight. As Autoblog details, a study by the Aluminum Association found that eliminating 10 percent of vehicle weight improved fuel economy by 4.1 percent, while cutting 20 percent of weight improved fuel economy by 8.4 percent. It’s not clear if EVs follow exactly the same formula, and we’d expect some slush even between gasoline vehicles. Still, it’s clear that at least some of the Model 3’s improved range on a smaller battery is courtesy of having less junk in the trunk."
EPA Reveals How the Tesla Model 3 Gets 310 Miles of Range - ExtremeTech
curb weight of cars:
3,814 lbs. (Model 3 Long Range) // rear wheel 75kw
4,647 lbs. s85 rear wheel
aprox 800lbs difference. hence, aprox 8% of the range will be cut from a hypothetical model 3 with the weight of an s85 because of the weight according to the epa.
range (epa):
310 miles - model 3lr
265 miles - s85
.... so with the special sauce, a updated model s 85 with model 3's special sauce could get around 285.2 miles of range (310*.92). Only a 7% increase in range as compared to the original 265 miles. I guess you are right. Penalties of weight does really affect the overall range. As you mentioned, to increase range, something like a a 100D with IM front motor and PMAC rear motor would really be amazing. That might take a few years though. Hopefully, I'm wrong and it's will take only a few months to implement this
Actually, haven't they been working on the model 3 for a while? They probably know about this efficiency already. They might already be working on a front IM and back PMAC model s/x. Maybe, this october they will announce such an update for the s/x??? hahahaha... that would be amazing.. They truly would be "not your typical car manufacturer"..Ooof - even though they hedged "It’s not clear if EVs follow exactly the same formula, and we’d expect some slush even between gasoline vehicles.", this quote shows a disappointing lack of understanding of the physical principles behind the numbers.
The base study was done on ICE cars with conventional brakes. Vehicles with regenerative braking drastically change the equation (weight is a significantly smaller factor than for vehicles without regenerative brakes)
The primary mechanism that drives increased fuel consumption is obvious: Accelerating a heavier car takes more energy (i.e., consumes more fuel) than accelerating a lighter car.
But that's not where the story ends.
Here's a "Gedankenexperiment'; Let's say you take two identical cars on a long airport runway, load one with 400 lbs of extra weight, accelerate both of them to 60 mph then let the cars coast in neutral. What you will find is that the heavier car will coast quite a bit farther than the lighter car. This is because the 400 extra lbs give it more inertia to overcome the wind resistance and other sources of friction. So the extra energy you put into the car came back to a degree in the form of extra distance traveled.
Let's change the experiment slightly - instead of letting the lighter car coast, we have the driver apply just enough throttle to stay beside the heavier car. What we'll find is that the total amount of fuel consumed by both cars will be very similar - it will represent the energy lost to wind resistance, mechanical friction in the drivetrain and rolling resistance. Most of these factors will vary very little with the weight of the car.
So basically, the weight in this scenario was not a big factor. So where does the disadvantage for heavier cars come from?
The real source of varying fuel economy by weight is braking. Why? Because the formula for how much energy the brakes need to "dump" is similar to the formula for accelerating the car - it varies proportional to weight. Braking a car that's twice as heavy from 60 mph to 0 mph requires removing twice as much energy. Unlike our previous example, where the energy we used to accelerate the car is reused during the coasting phase to keep the car moving, in this case, the energy gets released into the atmosphere as heat from the brakes (i.e., it is wasted).
The part that the article misses with its analysis is that regenerative braking allows a very significant portion of the braking energy to be preserved and reused. How much of an effect this has depends on the round-trip efficiency - i.e., the amount of energy lost in charging the battery during regeneration, and then pulling the charge back out of the battery to move this car.
I couldn't find good numbers on round-trip efficiency, but found a reference to a Tesla blog, which suggested it might be around 64% (based on 80% charging efficiency and 80% efficiency of the motors drawing energy from the battery).
Based on this, you would expect the numbers from the article to be off by about a factor of 3. So instead of increasing fuel economy 8.4 percent through a 20% weight reduction, an electric vehicle with regenerative braking would increase its economy only around 2.8%. (This assumes that substantially all of the electric car's braking is regenerative - if the car is panic braked a lot, YMMV).
The real explanation for the Model 3's efficiency advantage is simpler, IMO: It's a smaller car, meaning it has less wind resistance. Since in practical conditions wind resistance predominates as the main source of frictional losses above 30 mph, this is likely to be the main factor in efficiency tests.
(source: Fuel Economy)
No, aerodynamics plays a big role, but it isn't really that big until above 50 mph and not dominant until above 65-70 mph in a Model S due to its excellent aerodynamics. You can see this:
https://www.tesla.com/sites/default/files/blog_attachments/the-slipperiest-car-on-the-road.pdf
Aero horsepower on a Model S at 70 mph is 14, or 10.44 kW. It's about 50% of the overall energy required at that speed, depending on what else is going on (HVAC primarily). In less aerodynamics cars, the effect is stronger at lower speeds.
In a Model S versus a Model 3, it's about energy losses during acceleration as well as regenerative braking. You can try this yourself if you own a Model S or X. There is a very large energy average consumption difference if you keep the acceleration to under 80 kW (107 hp) and maximize the 60 kW regenerative braking. Note that an Ioniq only has 88 kW (118 hp).
Aerodynamics are not dominant at 30 mph, but definitely becomes dominant lower than 65 mph. I estimate aerodynamic losses become dominant in Model 3 at 45-47 mph and Model S at just over 50 mph. It looks like I'd need to double the tire losses have to the aero start to be dominant at 65 mph.
Here's my most recent power vs speed graph for Model 3.
My interpretation of dominant wasn't when it becomes the biggest of the factors, but exceeding 50% of power... ie. the majority of where the power goes. If you add up the other 3 that you have, it is about 65 to 70 mph where aerodynamics becomes the majority of the power.
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