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Watts Per Mile Guess?

Discussion in 'Charging and Infrastructure' started by Dan Detweiler, Nov 8, 2016.

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  1. Dan Detweiler

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    The news that Tesla will be crediting 400 kW per year for new cars has me wondering. Elon said that this should equate to about 1000 miles of range. Unless I am screwing something up, that means he is assuming 400 watts per mile. What are the general thoughts as to the electrical consumption for the Model 3? I was thinking that being a smaller car (granted, that doesn't necessarily mean lighter), more aerodynamic, more efficient battery chemistry, etc. that we might see usage significantly lower than that. Am I missing the mark here? What do you all that know a hell of a lot more about such things than I do think?

    Dan
     
  2. Rick59

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    Don't count me as part of the 'smart' group but I've read many articles that refer to about 300 watts per mile. So that would make about 1,300 miles.
     
  3. Topher

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    kWh = kiloWatt-hours NOT = kW or kiloWatt.

    Telsa is gifting us with 400 kWh. Cars use a certain number of Watt-hours per mile.

    That said:
    Going from a drag coefficient of 0.24 to 0.21 will reduce power required for high speed travel by 12.5%.
    Reducing the frontal area by 10% (guess) will reduce power required for high speed travel by 10%.
    Reducing the weight by 20% (Elon hint) will reduce power lost to braking by 20%.

    If the Model S gets 300 Watt-hours / mile, a Model 3 should get about 240.

    Thank you kindly.
     
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  4. Badback

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    Power lost to braking???
     
  5. Dan Detweiler

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    Thank you for the vocabulary lesson, it is appreciated. There are very few things I understand less about than electricity and its use. Pay bill, plug into socket, machine runs. Don't pay bill, unplug from socket, machine doesn't run. That's the extent of my electrical knowledge!

    Dan
     
  6. Topher

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    Sure. Every time you slow the car down, you transform kinetic energy into heat in the brakes and energy in the battery through regeneration, and heat in the system through inefficiency in regeneration. If you estimate the distance between successive braking events, you get a power loss: 1/eff * [1/2 * Mass of car * velocity^3 * regen eff / distance between brakings]. As you can see from that equation, reducing mass directly reduces braking losses. Did you have a more specific question?

    Thank you kindly.
     
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  7. EBelly

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    It is possible that Elon was talking about the present fleet and Model ☰ will get more than 1000 miles.
     
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    Your original statement made it sound like no regen was happening.
     
  9. Topher

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    It did? Ok.

    Are there people who think that because a car has regenerative braking that it losses no energy when it brakes? That would be a misconception that we should address.

    Thank you kindly.
     
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  10. Michael Russo

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  11. Topher

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    I suspect that this depends greatly on a lot of things, like how balanced the charge in your pack is, which you have no way of knowing. Please don't expect this sort of thing.

    Thank you kindly.
     
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  12. Hezekiah

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    It's funky how going from watt-hours per mile throws me off, instead of thinking of miles per kWh.

    My guess is that the M3 will get 3.5-4.5 miles for each kWh.
    Currently, the S gets around 3 depending on usage, and the bolt gets around 4. So I've read! It would be nice if the EPA would do miles per kWh like they do MPG.

    I really hope that the model 3 can up that mpk and that distance supercharging stays around for life. EV's are almost as expensive as ICE cars on the highway. A new car (I'm thinking Carolla-like car) gets 40 mpg highway. Then at $0.15 per kWh it will cost $2.40 to go 40 miles in an S, even more the faster you drive.

    Highway is worse case-scenario of course. But it makes the point, electricity isn't free! Given current S information, and 30mpg city for a corolla, it's $1.29 to go 30 miles in the S. Of course, the S is much, much, bigger than a Corrolla, I'm just getting ready for the model 3, which will have to be compared to such a car if it's going to be "a car for the masses"
     

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