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Charging slower

Discussion in 'Model S: Battery & Charging' started by Dexter, May 8, 2015.

  1. Dexter

    Dexter New Member

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    Hi all. I'm a new Model S owner. I remember reading somewhere that charging at a lower current is better for the battery than a higher current. So when I plug in the car to charge at night, I set the current to the minimum needed for the car to finish charging as close as possible to the time I leave for work in the morning. Doing this will hopefully help to slow the rate at which the battery's capacity decreases over time. Any thoughts on this?
     
  2. davewill

    davewill Member

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    An excess of caution. No harm, but probably no help either.
     
  3. TexasEV

    TexasEV Active Member

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    Not necessary at all. If you read that somewhere, it wasn't written by Tesla. Tesla designed the battery to be charged at 40-80A with the onboard charger, and much higher amps at the supercharger. It's less efficient (more expensive) to charge at lower amps and doesn't significantly help the battery. As I've suggested in previous posts, let the battery management system manage the battery.
     
  4. bhzmark

    bhzmark Active Member

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    Search for the thread that concludes that if you are not in a rush it is better to charge at 56 amps with a hpwc instead of 80 to distribute a lower load over both chargers and keeping temp of the battery down. Can't hurt. Might help.
     
  5. TexasEV

    TexasEV Active Member

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    If the OP is calculating the minimum current needed so the car finishes charging just before he needs it in the morning, he's charging at less than 40A. It may help his anxiety but it's not helping the battery. Some owners try to make this more complicated than it needs to be. Just plug the car in every night and let it charge, as long as it's not charging to 100% when you don't need it to.
     
  6. bhzmark

    bhzmark Active Member

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    It's simple. Set the max amp at 56 amps. Set the time to charge at 3 or 4 am or whatever works so it is charged in time. Not complicated.
     
  7. jgs

    jgs Member

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    You mean can't hurt other than

    ?
     
  8. Dexter

    Dexter New Member

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    Thanks for everyone's thoughts.

    I'm not clear though on why it would be less efficient to charge at lower amps. Given the same voltage, I would think that charging at lower amps is more efficient for a couple of reasons: 1. Less resistance in the conductors = less electricity wasted. 2. Lower battery temp = less waste heat (maybe this second reason is the same as the first?)
     
  9. jerry33

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

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    It's the loss in the wiring before it gets to the car. Anything above 30 amps is reasonably efficient. Below 30 amps is where the real hit is.
     
  10. spottyq

    spottyq Member

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    #10 spottyq, May 8, 2015
    Last edited: May 9, 2015
    On the tesla charging page http://www.teslamotors.com/charging#/calculator there is a calculator which can determine the power usage needed to charge the battery.

    The resistance in the conductors probably isn't so high, because these same conductors (except for the UMC) can handle 120KW at supercharger, so they shouldn't break a sweat at 22kW let alone 11kW (yes I know that it's the current and not power that causes heat)

    AFAIK, the biggest difference is the thermal management system which has to run longer if charging at a lower rate. (certainly so when the battery needs to be heated instead of cooled)
     
  11. Todd Burch

    Todd Burch Electron Pilot

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    You want to charge in the 40-60A range, all else being equal. 40-60A is nowhere near enough to significantly reduce the life of the battery.

    The battery is 60-85 kWh, so [email protected] is only about 1/4C for the smaller 60 kWh battery (see this link for an explanation of "C"). If your battery is larger, or the current is lower, the "C" rate is even less. (This charge rate is not going to cause any harm to the battery whatsoever). Charging at less than about 40A means that charging takes longer, so the losses through the wiring (such as heat due to resistance of the wire), and losses from the car being "awake" longer take up a greater percentage of the energy used for charging. Charging at higher rates generates more heat in the battery/wires due to the higher current, plus the car may need to actively cool the battery. In those cases additional energy is lost.

    Experimentally, the 40-60A range (assuming 240V) has been found to be the most efficient at getting power from the wall into your battery.
     
  12. linkster

    linkster Member

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    i like it! The car, tires, and batteries are too expensive (to me) not to deploy every strategy to increase the service life. We have charged at 24A for nearly 50K miles where passive cooling to the pack is sufficient and since the S is mostly idle on the weekends it rests at 50% SOC.
     

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