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3.5 hr recharge?

Discussion in 'Roadster: Technical' started by malcolm, Feb 24, 2008.

  1. malcolm

    malcolm Active Member

    Nov 12, 2006
    The usual math goes:-

    240v * 70 amps = 16.8 kW
    16.8 * 3.5 hours = 58,800 kWh… Full pack from empty.

    But the battery cooling required to maintain this consumes a further ~16kWh.

    Andrew’s response: The Recharge Energy of 31kWh/100mi is the electricity you pay for from the grid to recharge your Roadster. It works out to ~75kWh of alternating current (AC) for a full recharge. Our ESS (battery) produces direct current (DC) and holds ~53kWh. The difference between these two numbers is due to charging inefficiencies, including the use of air-conditioning to thermally-manage the battery during charging. to the second comment

    which gives 4.5 hours, assuming that 70 Amps is the limit from the Home Charger.

    Given that Tesla seem to be sticking with the 3.5 hr figure, how is this being done?

    All fairly academic anyway, given that owners may not want to "waste" energy on ESS cooling or may not have 70 Amps available - in both cases they would settle for a lower charging rate with smaller cooling overheads.
  2. TEG

    TEG TMC Moderator

    Aug 20, 2006
    #2 TEG, Feb 24, 2008
    Last edited: Feb 24, 2008
    Some of those figures you posted were ones from me.
    I was just guessing, so it is right to ponder.
    I agree that it seems inconsistent to say 3.5 hour charge is possible if full charge needs 75kWh yet the circuit only provides 16.8kW

    Perhaps there is more to the story. For instance it could be rare for anyone to pull into their garage with the ESS totally empty.
    Also Tesla talked of some pack saving feature to top off at less than full capacity. Perhaps the 3.5 hour charge figure is for a "friendly fill"?

    I dunno.

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