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Slow Charging

Discussion in 'Model S: Battery & Charging' started by iridium, Mar 9, 2013.

  1. iridium

    iridium Member

    Joined:
    Jul 10, 2012
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    Location:
    Scottsdale, AZ
    Is slow charging better for the battery? On most days I only drive about 30-40 miles. I only need the car recharged by the next morning, so charging at just a few amps would do.. I don't need to charge at 40. Is there any advantage?

    On the lithium polymer batteries I use in rc helicopters this is definitely a good practice.
     
  2. jhs_7645

    jhs_7645 VIN: #3305

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    Jul 1, 2012
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    Location:
    Camas, WA
    There have been gobs of threads dedicated to then best charging behavior (you can search.. I'm feeling kinda lazy right now). The bottom line is that yes, slower charging is a bit better for the battery *BUT* it comes at a cost, and that cost is that the car has to continue to run the battery cooling/management system during the entire charge time which results in a higher cost for the total charge.
     
  3. Twiddler

    Twiddler Member

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    Apr 19, 2012
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    Central TX
    Follow-up question:

    For the times that I know that I need range mode well ahead of time, is it better for the battery to:

    1. Charge at 120V to get to max range - presumably easier on the battery but more time spent at/near full SOC, or

    2. Charge at 220V/40A to spend less time at full SOC, but generate a higher peak temperature in the cells
     
  4. jhs_7645

    jhs_7645 VIN: #3305

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    #4 jhs_7645, Mar 10, 2013
    Last edited: Mar 10, 2013
    Charging @ 120 takes quite a long time, and depending on external conditions (temp etc..) is extremely inefficient and can be difficult to predict the charging rate.

    The best advice I have for charging to 'range mode' is (in order):
    1. Charge to range mode @40A and attempt to time the charge so that it reaches 'full' just as you're leaving so that the battery does not sit for a long time full
    2. If you can't do that (for instance you can't wake up in the middle of the night to start your charge), you can charge in 'normal' the night before, then about 60-90 minutes before you leave flip the car to range mode and finish off the charge to range just before you leave.
    3. If you can't do 1 or 2, you probably want to try charging it at a lower amperage, that will mean that it will sit at 'full' for a shorter time, so that is probably the best third bet, but you should be sure that whatever rate you choose, it's full by the time you need your car. The downside to doing it this way is a) your car's charging system is running for a longer time, and b) you might miss the mark and have to kick up the amperage in the AM anyways.
    4. Of course, #4 is just go ahead and charge in range mode the night before. It's not battery death, but I certainly wouldn't make a habit out of it.

    Hope all that makes sense.
     
  5. Robert.Boston

    Robert.Boston Model S VIN P01536

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    Oct 7, 2011
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    7,842
    Location:
    Portland, Maine, USA
    As long as you're charging below 1C, you're not causing issues. Even for the 40kWh battery, 1C = 40kW, so if you're at 40A 240v, you're only at 0.25 C, way below any point of potential concern. Your RC helicopter has a tiny battery and so needs to charge at a tiny rate in order to stay below 1C.
     

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