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charging efficiency by Amps and voltage

Discussion in 'Charging Standards and Infrastructure' started by frequencydip, Apr 18, 2012.

  1. frequencydip

    frequencydip Sig 100 - #52

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    There appears there might be a considerable efficiency in charging your roadster at lower Amps vs high Amps. When I charge at 40 Amps 240v The fans turn on full power and the cooling system runs the entire time. When charging at 12 AMP the fans almost never turn on and just the pumps flow coolant. Therefore it should be more energy efficient to charge at lower amperage. Can anyone confirm that has a separate meter for the car?
     
  2. richkae

    richkae VIN587

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  3. frequencydip

    frequencydip Sig 100 - #52

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    Thanks this is awesome!
     
  4. dsm363

    dsm363 Roadster + Sig Model S

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    I remember that article. Really useful information. I have always been charging at 32A (40A is my max on the UMC anyway) after I read this from Tom's Blog post you referenced above

    Maybe I misunderstood it though.
     
  5. doug

    doug Administrator / Head Moderator

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    There is a certain amount of charging overhead. That is, power used to support the charging (like running the cooling pump, etc) but that doesn't actually go into the battery. A lower charging rate means more time spent charging, and thus more time using power for the overhead. Power * time = energy.
     
  6. markwj

    markwj Moderator, Asia Pacific

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    Amps, volts AND temperature are important. High/Low temperatures and low watts is the worst for efficiency.
     
  7. dsm363

    dsm363 Roadster + Sig Model S

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    I see. So I really didn't have that right I guess. One should always charge at the max then (40A in my case or 70A on a HPC)? I thought lower Amps were nicer to the battery and grid.
     
  8. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    This is like the "Mathematician's Dilemma" problem that you learned in structured programming class. (For those that don't know, here's the problem (as I recall it): A mathematician has forgotten his raincoat and umbrella and now has to walk home. Does he get wetter by running or by walking. Walking gives more time for the raindrops to fall but has less surface area to hit. Running takes less time but the area hit is larger, however the vertical area doesn't get the same number of raindrops per second as the horizontal area.)
     
  9. Robert.Boston

    Robert.Boston Model S VIN P01536

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    Answer: the mathematician calls a taxi.
     
  10. dsm363

    dsm363 Roadster + Sig Model S

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    Didn't they cover that rain question on Myth Busters?
     
  11. Bearman

    Bearman Member

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    Twice, fake rain first time and real rain second time, the second experiment confirmed running is better:
    "REVISITED: You end up drier running in the rain than walking. (From Episode 1)
    CONFIRMED
    When retrying the test in actual rain it was conclusively proven that the running test subject got less wet than the walking test subject. The use of artificial rain in the original test led to a false negative."

    http://mythbustersresults.com/episode38
     
  12. doug

    doug Administrator / Head Moderator

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    As with most things, there are trade offs. Less current is nicer to the battery and the grid, but how much so that it really matters? Based on Tom's data, 40 A seems about the sweet spot, balancing those with energy usage.
     
  13. doug

    doug Administrator / Head Moderator

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    I "proved" this with some overly complicated path integrals many years ago. But if you assume completely uniform and vertical rain, and assume at any given moment a uniform density of rain droplets per unit volume, then the amount of rain you get on your vertical surfaces is determined only by your path length. So for a given path, you get the same amount of rain on your vertical surfaces, independent of the rate at which you move. Where as, of course, the more time you spend in the rain, the more water that accumulates on your horizontal surfaces (e.g., your head).
     

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