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Why doesn't Tesla sell an option that fills the "frunk" with a battery for more range

Discussion in 'Model S' started by calisnow, Nov 21, 2015.

  1. calisnow

    calisnow Active Member

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    I just thought of this today - yes the extra cargo capacity is great, but why not an option of an extra supplemental battery pack either in the frunk or that uses up some of the trunk space in the rear? Is there an engineering reason I haven't thought of or would nobody buy it?
     
  2. DougH

    DougH Active Member

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    I see the start of a 500+ page thread.
     
  3. glenhurst

    glenhurst Member

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    Elon and others at Tesla have said they could build a car with a 500 mile range right now, but it would be prohibitively expensive. I don't think space is the issue.
     
  4. Max*

    Max* Autopilot != Autonomous

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    You put a small battery in the frunk, add a ton of weight (reduced range) and sell it for $10k more to get a net extra 15 miles range.
     
  5. AMPd

    AMPd Active Member

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    Weight distribution would be horrible
    Car is made to have a crumple zone in case of collision
    Too expensive
     
  6. eye.surgeon

    eye.surgeon Member

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    Not to mention the suspension and brakes are engineered to a certain weight. A significantly heavier battery would require reworking those.
     
  7. pmadflyer

    pmadflyer Member

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    Rumor has it that the microwave compartment in the rwd cars was for additional modules, similar to the two that are stacked at the front of the current pack. The area wasn't needed to get to 85 kWh, and was left open.
     
  8. MikeL

    MikeL some guy

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    Seems more like something BMW, Audi etc. are all going to need because they don't/won't have a SuperCharger network :smile:
     
  9. StaceyS

    StaceyS Member

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    I'm sure it could be done, but I see a number of cons with this that outweigh the pros:
    1) Additional weight
    2) Higher center of gravity
    3) Greater weight leverage (mass beyond the front and rear wheels negatively affects handling)
    4) Risk of severe battery damage in the event of a collision
    5) Adds more battery form factors (keeping it all under the floor supports battery pack swapping, and common vehicle platform sharing)
    6) Adds added wiring and high voltage disconnect complexity
    7) Adds costs (and probably at a higher rate per kwh than the flat pack under the car).

    I'd rather just have the carrying capacity and let advances in battery technology over time give me greater range in the compact form its in now. Its my current goal to own this Model S long enough to justify upgrading the pack at least once.
     
  10. Ben W

    Ben W P85 #61, Roadster #108

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    There are diminishing returns when adding extra batteries.

    Consider the 70D vs 85D. The extra 15kWh yields 21.4% more battery capacity, yet only adds 12.5% more range. Some of this may be due to the extra weight. (Curb weight 4721lb for 70D, 4849lb for 85D.) Possibly also due to testing with 19” vs 21” tires. I’d be curious to know the exact specs the EPA used for the tests.

    The real win will come with improved cells. I’m a bit surprised they haven’t retested the EPA range with the 90D, if only because so many news articles “get it wrong” and mistakenly assume the EPA has actually measured the 90D to have no improvement over the 85D.
     
  11. tstafford

    tstafford Member

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    Great idea for an aftermarket enhancement. Maybe we should do a Kickstarter.
     
  12. Aljohn

    Aljohn Member

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    #12 Aljohn, Nov 22, 2015
    Last edited: Nov 22, 2015
    It's is simply the law of diminishing returns. Given the same technology, the weight and cost won't yield significant range. Tesla has always said, technical advances will allow for added range. The electric car is not new, the early models (no I wasn't there) as shown on Leno's Garage used lead acid batteries. The weight of the batteries limited the range of the vehicle causing their lost popularity to Gasoline. Even ICE manufacturer's calculate the size of the gas tank for a given range of approximately 300-350 miles highway. It is the acceptable "sweet spot" for range vs. weight. Same the Air Planes, the altitude on long-range planes is limited until they burn off the excess fuel. On shorter range (STL's), they place enough fuel to get to the destination and a safety margin. Filling tanks to the max will make flying less efficient . Same with current technology batteries -- added weight diminishes range per added unit.

    A battery in the Frunk would also change the weight distribution of the car, affect handling as well as reduce the front "crumple zone". The last thing you would want is a litheon ion battery crushed in an accident --- they don't like heat and pressure. Also, keep in mind the battery is cooled, so placing a "small battery" up front would need additional cooling capacity along with added collision protection -- i.e. another titanium cover, if even feasible.
     
  13. Navyguy

    Navyguy Dreamer

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    The current weight of the full battery is only about 700lbs. of the nearly 5K pounds the car weighs. DOUBLING it is just expensive not impossible. if they added a battery half the size at only 300lbs they would easily get 35-45% more range out of it. there are cars that weigh over 5500 lbs One Mercedes benz I believe as well.


    I think they said the battery (the upgrade is expensive. but its a small upgrade) is a huge portion of the cost. DOUBLING it. would probably tack on at least 50K becuase honestly motors are cheap to make and theres not much in the car. the tech in it is not worth 50K but at 150K price of the car. its prob 30% battery at a min.
     
  14. DougH

    DougH Active Member

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    Look who's back.
     
  15. Navyguy

    Navyguy Dreamer

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    I think you can find the bat specs online, at least for the 60 or 40Kw version, they are not much different than like 10K lithium Ion AA sized batteries all wired up with liquid cooling etc. its not like a standard LiPoly battery thats soft like you would see in an RC car or plane. there are some small batteries like that - that can produce nearly the same amperage as the battery in this car. some that have over 100C (100 times the capacity) and if you wire some 12S batteries in P you could have some massive voltage and amps. the only thing about lipo / soft packs is there volatility impacts can make them go boom.

    LiPo 11,000 6S 22.2v Battery Pack


    904 of those would double the current capacity, at a cost of 350K dollars hahaah. although at retail I assume theses have easily a 100% markup. in qty and direct, or made by tesla. would be fraction of that but still prob at least 80K if not 100K




    EDIT: Actually you would have 22Kw/h sorry not 180 (originally forgot to change the 18 to 22volts)
    it would do the trick btw and at 40C it would (by chemistry) be able to deliver 40x capacity which is 40million amps hahaahah. At least the Math works out that way.


    OH and yes I am back. I got banned for saying the G word and the A word really? lol Oh well.
     
  16. benf

    benf Member

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    The upgrade from 85kw to 90kw is $3000, or $600/kwh. The cost of a new 90kw pack is $25,000, or $277/kwh. Let's just use a round number and estimate low and say this new frunk pack would be 45kwh @ $300/kwh = $13,500. This assumes that the R&D for this completely new pack is free, it drops right in with no issues, and somehow just works. Of course that is impossible, so then you have to figure out:


    1. What's the R&D cost for this new pack?
    2. What is the cost of the other modifications to the Model S to make it work?
    3. What is the cost of re-crash-testing the Model S?
    4. Etc.

    Let's just pretend you could accomplish all of the above including the base $13,500 cost of the pack for $20,000 even. We know that 50% more capacity won't give you 50% more range. Let's say it gave you 35% more range, or about 90 miles. Would you pay $20k for 90 miles? For some that might be an easy yes, for others, less so. Some people are paying $3k for ~15 miles right now with the 90kwh upgrade, so there's clearly a market for it (I personally don't understand paying $600/kwh but to each their own).

    But then we have to get back to reality. Would you pay $20k for 90 miles, worse handling, a significantly reduced safety rating, and no cargo space in the front? Particularly for the safety reason, I doubt Tesla would even offer you the choice. But I'd think most people would say no anyway. I certainly would not want ~350 pounds of batteries to try to come smashing through my dash in an accident.
     
  17. aus

    aus Member

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    That is true for now, but keep in mind VW also owns Audi, Prosche, Bently and they have a ton of money, despite some SERIOUS fines/lawsuits that will come soon. I could easily see VW producing a pretty vast network for all their brands to use. It's just a matter of time when they decide to get serous about electric power.

    Does the battery pack really only weight 700 lbs???
    The new S class is around 4,750 lbs and BMW 7 series around 4,400; depends on which engine it has
    .
     
  18. Aljohn

    Aljohn Member

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  19. Jaff

    Jaff Active Member

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    Back then, there also was a rumor that the "microwave" compartment was to house the extra motor when Tesla would be retrofitting the Model S to AWD.


     
  20. yobigd20

    yobigd20 Well-Known Member

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    the original intended purpose of the "cubby" in the non-D frunk was for extra battery packs. they didn't think they could fit all 85kW in the battery pack but they did. there are also published patented designs from tesla for dual battery pack system (lithim ion + metal air). I can't remember if they showed the placement of those in the frunk though.
     

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