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How much more does a fully charged MS weigh?

Discussion in 'Model S' started by traxila, Feb 1, 2013.

  1. traxila

    traxila Member

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    Thought it would be fun to know how much weight the electrons actually add to the car.

    Is a fully charged MS measurably heavier than one running on empty?

    Thanks.
     
  2. richkae

    richkae VIN587

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    I think the answer is 4.641 mg assuming a nominal battery voltage of 375 volts and an 85kWh car.
     
  3. NielsChr

    NielsChr Member

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  4. traxila

    traxila Member

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    Thanks, guys! Love the math.

    My figuring as well was that it would be measured in grams.

    I think on a visceral as opposed to ethereal level, that is hard to fathom. I could imagine the glazed looks on most people faces trying to digest stuff like this in today's ICE world.
     
  5. pete8314

    pete8314 Vendor

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    Fascinating stuff. And an ICE car with 17 (US) gallons on board would weigh an additional 103.24 Lbs, or 46829 grams.
     
  6. ElSupreme

    ElSupreme Model S 03182

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    That is all good and peachy but those electrons just move to the other side of the battery. You need to use E=MC^2 to determine the mass differential. We did it before I'll look for the link.

    or you can just put 85kWh into WolframAlpha
    85kWh in g - Wolfram|Alpha

    Ends up being 0.000003405 grams! So not grams but mircograms.
     
  7. NielsChr

    NielsChr Member

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    maybe some point in futre your could fit the 85 kwh pack in a nut shell - or even load the car once in a lifetime in a larger pack and drive almost for ever.

    think about old fasion floppy discs (80 kb) and now you got a memory microSD card witch holds 64Gb data - back 20 years ago this was pure fantasy
    at same time size have shrinked a factor 100 - that is total a improvement of aprox 100.000.000 times.

    Im not saying its going to happen to battery storage, just saying it might happen at some point as demant of better battery are pressent and huge amount is invested into this field.
     
  8. Doug_G

    Doug_G Lead Moderator

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    Actually the car doesn't get a net charge - there are no more electrons in the car after it is charged than before. It simply stores energy. If it was a supercapacitor this would be done via charge separation; a battery does something similar with chemistry.

    E=mc^2 applies.

    From Mass-energy equivalence - Wikipedia, the free encyclopedia one gram equals 25.0 million kilowatt hours.

    85 / 25,000,000 = 3.4 micrograms.

    Edit: Darn El Sup beat me to it!
     
  9. Bound466

    Bound466 Member

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    Like a wind-up toy with a spring, after the toy is wound up it weighs the same as before, except it has potential energy now that can be discharged. Of course, e=mc^2 applies (mass energy equivalence) so that stored energy has a very small weight as ElSupreme identifies.
     
  10. NielsChr

    NielsChr Member

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    your right - electron has not been filled, just moved.
    E = mc^2
    m = E / c^2

    1 [kwh] = 3.6x10^6 [J]
    c = 300.000.000 [m/s]
    1 Tesla charge [Tesla*] = 85 [kwh]
    1 [kg] = 1 [J] / (1 [m^2]/ 1 [s^2])

    m [kg] = (85 [kwh/Tesla*] * 3.6x10^6 [J/kwh])/300.000.000 ^2 [m/s]
    m [kg] = 3.06x10^8 [J/Tesla*] / 9x10^16 [m^2/s^2]
    m [kg] = 0.34x10^-8 [J/Tesla*] / [m^2/s^2]
    m [kg] = 0.34x10^-8 [kg/Tesla*]
    m = 0.0034 [mg/Tesla*]
    3.4 microgram
     
  11. Bound466

    Bound466 Member

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    Actually, I'm just thinking that a battery may not be potential energy, it may be chemical energy. But the concept still applies.
     
  12. fiksegts

    fiksegts Active Member

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    My P85 on the scales.... 4,690....

    tesla-model-s-weight-2.jpg
     
  13. JohnQ

    JohnQ Active Member

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    Extra credit to Niels for showing his work.
     
  14. woof

    woof Model S #P683 Blue 85 kWh

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    But was it fully charged at the time?
     
  15. metafor

    metafor Member

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    Note that having a positive potential (charged) battery doesn't necessarily mean you added electrons. It just means that you added some electrons to one side and took away some from the other side of the barrier, causing a potential difference between the two. So aside from whatever asymmetries that exist in a LiON cell (how much there is, I don't know), there should be no difference in weight :)
     
  16. ToddRLockwood

    ToddRLockwood Active Member

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    I nominate this thread for Question of the Year.
     
  17. aviators99

    aviators99 Model S - R140

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    With a name like Niels, would you expect anything less??
     
  18. wraithnot

    wraithnot Model S VIN #5785

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    I'm pretty impressed how many people on this board know enough science to answer this question correctly. Very different than the previous car club I was a part of!

    I'm really curious how people on other EV forums would do with this question. Is anyone willing to post a similar question on the Chevy Volt forum, the Nissan LEAF forum, the Fisker Karma forum, etc. and report the results? (you would obviously change the name of the EV to match the forum)
     
  19. Doug_G

    Doug_G Lead Moderator

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    Of course you realize a Tesla is a unit of magnetic flux density, usually denoted B...
     
  20. wraithnot

    wraithnot Model S VIN #5785

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    We could keep score based on how many responses before someone get the right answer. In our case, ElSupreme nailed it on the fifth response. Of course, this will only work if no one gives away the answer on the other forums :)
     

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