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Charging limit—should it be tied to anticipated use or 90%?

Discussion in 'Software and Firmware' started by jsanford, Jun 27, 2018.

  1. jsanford

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    So the delivery center said to charge at 90%, but the manual said something to the effect to charge enough to fit the battery use.

    Most weekday driving for me is under 40 miles. Does to make sense to keep charging to 70-90% each night? I’d love for Eloise to last as long after she’s paid for as her predecessor.
     
  2. Dr. J

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    Most people will say it doesn't matter as long as you don't leave the car at a very high charge for a long period of time. When I get my car, I intend to cycle it close to 50%--say, charge to 60%, then plug in every night. You probably want a little cushion beyond 40 miles per day, but: 40/310 = 13% / 2 = 6.5%, survey says charge to 56.5%.

    Not the best source of info, but: http://batteryuniversity.com/index.php/learn/article/how_to_prolong_lithium_based_batteries

    Cycle life as a function of
    depth of discharge.*
    A partial discharge reduces stress and prolongs battery life, so does a partial charge. Elevated temperature and high currents also affect cycle life.
     
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  3. Rich M

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    Excellent info!
    This chart from the link is the most helpful:
    [​IMG]

    75% - 45% best represents my daily commute usage (70 to 45 really). Good to know that will result in one of the lower degradation rates.
    Elon retweeted one of his battery tech guys at one point, who stated the battery is happiest at 50%. I will post if I can find the conversation.

    I'm not going anywhere far this weekend, and will likely leave the car plugged in with charge limit set to 55%.
     
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  4. Dr. J

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  5. garsh

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    I'm planning to charge to 80% normally. I don't need that much range for my daily commute, but there are many times that I'd like to run an extra errand on the way home, and I can't do it with my Leaf. It's good to have some buffer.
     
  6. PandaM3

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    +1 I just charge to 80% nightly as well. I have a 50 mile round trip commute. However 80% of battery capacity is more than enough range with 250 miles.

    For example, just yesterday (a Saturday) I planned to go to RPM Tesla in the AM for my CF spoiler install and my wife came along since she wanted to go to the “premium outlets” to take advantage of the 70% off Kate Spade sale while draining my accounts at the same time. Any how our day started in Santa Ana with the Tesla at 250 miles of range. Drove down to Rancho Santa Margarita in what I call “Panda Race Mode” (drive settings set to normal steering and normal acceleration) at fairly aggressive speeds. You see I was thinking we where just going to the Outlets in San Clemente... when we got back into the car after RPM installed the CF spoiler my wife turns to me and says the Kate Spade outlet is in Carlsbad (North San Diego). So I stuck in in EAP, “Panda Chill Mode” (my drive settings set to chill acceleration + comfort steering), and just hang out in traffic for the next 1.5 hours. Fast forward and we make it back to our home in North Santa Ana with about 120 miles left on the range when my friend rings me up and wants to see my Model 3 so he can decide if he wants white (he really wanted to see if the rear bumper missmatch is really obvious)... so we all go out to dinner in Newport Beach and back with around 80n miles left on the range. (With me exhausted and the car still with plenty of range) Plugged it in last night and within hours I’m back to 250 miles of range so my wife can take it tow work this AM.

    That being said... 80% is more than enough for us.
     
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  7. GDN

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    Good articles and information. Seems even 90% is a bit high if you don't need it on a daily basis, per the reads. We just happened to hit about 75% on the first moving of the bar - gets about 235 miles of range when charged. Daily commute is 10 to 12 miles or maybe 30 if I get to drive it once in a while. 75% is plenty for weekends too. We don't usually go too far. If we do, will have to make a temp adjustment.
     
  8. PNWmisty

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    And that is the best reason to be able to charge at 48 amps at home. You can charge to a lower level on a daily basis and top it up more quickly if your plans change and you need to add some range.
     
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  9. jsanford

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    Thanks everyone for the links. This is great information! I’ve been charging to 70% which has been more than enough.

    Might be a good thread to make sticky? Or add to a FAQ listing?
     
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  10. sakaike

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    Question: If my normal usage is low, (20-30 miles per day), and if I charge in a 35%-65% range, are there battery cells that never get “exercised” and is that good or bad for the overall longevity of the battery pack as a whole?
     
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  11. KFORE

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    The battery is constantly being balanced. There is no need to worry about this. You want to keep the battery near 50% constantly for best longevity, but in reality, just don't keep it at 100% for longer periods of time and you're fine.
     
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  12. PNWmisty

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    Under that kind of usage, the battery will last for decades. Even the short-range batteries of the Model 3 will likely have a very long lifespan under that low impact scenario.
     
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  13. KarenRei

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    #13 KarenRei, Jul 4, 2018
    Last edited: Jul 4, 2018
    It is always being constantly balanced, but there is an issue wherein if you never bring a battery pack toward the extreme ends of its cycle range it can throw off your SoC measurements. Li-ion state of charge is generally done with coulomb counting, which tends to drift over time, so it gets recentred based on voltage and other factors that are less reliable general measures of SoC but not effected by drift. These are most unambiguous near the ends of the SoC range, so the occasional deep cycle tends to improve SoC estimation accuracy significantly.

    Li-ion discharge voltage curves are very flat outside of the endpoints, and consequently the SoC-related differences in voltage are swamped by effects such as temperature, aging, etc on voltage.

    (Caveat: Given that Tesla battery management is a lot more advanced than that which you find in general consumer electronics, I imagine that they have a lot of other tricks up their sleeve for helping make SoC measurements more precise. They could subject random cells to deeper cycles (Model 3's "giant motherboard"-style BMS should allow for this), they could measure internal resistance changes, and probably a number of other things.)
     
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  14. PNWmisty

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    Can you speculate on what a SoC estimate that was inaccurate due to drift over time would impact besides the reported SoC and miles to empty?

    In other words, do you think it would affect charge rate (or is this done by battery temperature and the rate of acceptance) and would it affect the 100% charge capacity (or would this be recalibrated as the charge approached 100%)?
     
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  15. KarenRei

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    #15 KarenRei, Jul 4, 2018
    Last edited: Jul 4, 2018
    Should only affect reported range remaining. It can cause things like peoples' cars dying when they still show range remaining. I don't know the details of how Tesla manages their topping charge, but one approach that one battery pack that I worked with used was to measure the waste heat being generated by the charging process. Once the input energy matched the waste heat, the cells are refusing to accept more charge and you're at 100%.
     
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  16. Thunder7ga

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    I don't get the car for 2 more weeks, but been calculating what I should charge to based on my typical commute. I do about 150 miles a day so I will use ~50% of the battery every day. So, was thinking about keeping it in the 80%-30% range.
     
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  17. Quicksilver

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    I don't drive very much daily so I set mine to about 50%. When we were on vacation for a full week, I left Quicksilver plugged in with a 50% charge. I don't expect to increase the charge percentage unless I anticipate a road trip coming up.
     
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  18. littlD

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    I'm a 20%-80% guy. Matches what I've found works for preserving my Smartphone battery on my Pixel 2.

    Totally support whatever percentage you feel is best for you and your needs.

    Currently, I'm without a working home charger (my 5 year old Voltec bit the dust), so it's my local SC for now, and charging to 80% every few days is a lot more convenient.

    Once I have a new Tesla Wall Connector on a 60A line, I'll be back to plugging in each night.

    With several SCs well within reach when I travel, I may never charge to 100%. And boy is charging to 100% a slow affair!
     
  19. dhrivnak

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    Are you sure of that? On the Roadsters you need to above 85% for any balancing. At the lower states of charge there is little difference in voltage between 50 and 75%.
     
  20. reallove

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    I live in a state where I don't get different rates for day vs night electricity usage. I don't commute (work from home) and I only drive the car a few times a week to do grocery shopping or visit friends. I leave the car always plugged in when at home, with battery at about 65%.
     
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