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How hot should the batteries get while charging?

Discussion in 'Model 3: Battery & Charging' started by push2eject, Jun 30, 2020.

  1. CertLive

    CertLive Member

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    Understood but when you factor that into the lifespan of a car and how many times it is charged / discharged faster is it really anything to worry about say over 8 or 10 years?
     
  2. push2eject

    push2eject Member

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    #22 push2eject, Jul 5, 2020
    Last edited: Jul 5, 2020
    It doesn't *always* do it. I think it might only do this extra heating when you charge to high SoC levels. The data below is from another charge session, with SoC ~60%. There is ~45kW going into the battery, and the battery inlet temperature is slightly lower than the battery temperature (~26°C). warm-battery.png
     
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  3. SigNC

    SigNC Active Member

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    Almost every time i've charged on chademo the output of the charger and what's going into the battery are about 8kW off and I can hear the whine of the motor heating. Good to know there are some times it's intelligent about it though.
     
  4. camalaio

    camalaio Active Member

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    Actually, yes. While many will say it's "fine" to use Supercharging exclusively, it's clear that it's detrimental to both the service life and battery performance. Tesla will start limiting your charge rates after certain conditions are reached. This is implied to be based on measurements of the battery (probably some combo of estimated cell capacities, estimated internal resistance, perhaps thermal cycle events, etc.). I have no reason to believe this isn't true, but something as simple as "number of times at a Supercharger" doesn't seem to be the case either.

    Time is a difficult measure simply because some people do 50,000mi in 8 years, and people like me do closer to 400,000mi. The takeaway should be that if your battery is routinely exposed to high heat, its lifetime will suffer. Of course in the case of Supercharging, that's also coupled with high charge rates so the Tesla-specific data is a bit muddled. But this is pretty well understood for Li-ion chemistry in general, and the cells Tesla uses are not currently an exception to that understanding.

    If you want to get the 500,000mi lifetime Elon expects for a Model 3 battery, you cannot:
    • DC Fast Charge often
    • Use Sentry a lot, or use Summon Standby (these use power without adding miles)
    • Live in a battery-unfriendly environment (very cold, very hot)

    Huh. Perplexing. I've always had it heat - low SoC, high SoC. Certainly above 26C as you have there. I can't think of what other variable would be involved though. This is a Model 3 datapoint, right?
     
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  5. Booga

    Booga Member

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    #25 Booga, Aug 7, 2020
    Last edited: Aug 7, 2020
    camalaio - thanks for the details you wrote up in this thread. I've been looking for the in-depth summary like this for a long time. I agree with everything you wrote.

    Two items that stood out include:

    1. Model Y's heat pump and connection to the battery pack could really improve winter comfort. If you've got a warm battery pack, there's a lot more to draw from. The question is going to be... let's say it's 20F outside and you're plugged in, charging to 100% for a road trip. How warm will the car get the battery for this effect? If charging finishes within an hour of your departure, will the 1,000 pound battery pack have enough warmth for this? Will it engage the heat pump during warm up to heat the battery pack even if you're not charging?

    2. Supercharger speeds are designed for convenience and also likely supercharger turnover. Faster charging does make things more convenient for those short on time, but we know it contributes to higher degradation. The other benefit is that during busy holiday seasons, it allows them to handle more cars than they could otherwise service at the supercharger.

    I'm curious to see if the Model Y is able to precondition the battery better than the existing cars without a heat pump. This could obviously be good before you arrive to a supercharger, but also good when you charge at home so the battery can be warm and serve as a source of heat over your road trip.

    The implications of the heat pump and use of the battery pack are large and I can only wonder why Tesla didn't build these in sooner. Maybe they did and ran into limitations we aren't aware of yet. As someone who does a lot of road trips, performance in weather down to 20F is important and I'm hopeful to see data that shows added comfort in the cabin and range from the heat pump. I wonder if we'll see any data before the winter or if we really have to wait till January/February.
     
  6. camalaio

    camalaio Active Member

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    I'm not familiar with what amount of heat could be extracted from the battery, but the heat in the battery at 100% will vary. Fresh off a DC Fast Charger, it'll be above 40C (104F). But if it was Level 2 charging, there's a lot of variables. In Winter, I wouldn't expect it to be warmer than room temp. Probably about 15C (59F). That's not a lot of room for extracting heat for the cabin. That said, if it was charged for a long time at high power in a somewhat insulated space, maybe it gets up to 25C or so? If this is your case with a Model Y, I expect Winter efficiency would be relatively excellent.

    The battery will have much of this heat still an hour later (it won't purposely dump it). Of course, it would lose it faster outside though.

    People are going to have very mixed results with the heat pump because of the above, but it should be better overall. I suspect Tesla didn't do it sooner due to complexity. There's many things simultaneously needing heat or cooling (cabin, battery, drive units) within temperature parameters (efficiency, not sucking too much heat from the pack, etc. Also, AC compressors die often, and this now makes it run effectively all year.
     
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  7. Booga

    Booga Member

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    I see what you're saying. Do you think they would allow dumping heat into the battery pack intentionally as part of the warmup? Maybe it's something that is enabled while on range mode and charging? I see the benefit ahead of a road trip, but maybe I'm underestimating just how much power and time it would take. The simplest is likely still to just have the battery pack finish charging shortly before departure (level 2, home charger).
     
  8. camalaio

    camalaio Active Member

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    It does indeed take a lot of energy to change the battery temperature. They do it automatically if you precondition the cabin and the battery is cold (partly why I think they recommend something ridiculous like preconditioning for at least 30 minutes) at any state of charge and whether or not it is plugged in.

    Otherwise I don't see them purposely exposing something so technical as a user control for heating the battery. Removes the illusion that Tesla universally does the right thing all the time, as well as adds yet another feature they have to test and maintain.
     
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  9. Booga

    Booga Member

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    #29 Booga, Aug 7, 2020
    Last edited: Aug 7, 2020
    Makes sense. Hopefully they release the heat pump for the model 3 - I can make it work for my long drives with its HVAC improvements. There might be a benefit from drawing the battery pack's heat during the winter and that would also help.
     
  10. tilt

    tilt Member

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    Thanks for all this information, camalaio. Very informative. It is interesting get a glimpse into balancing act that Tesla is doing to get charging rates up, wait times down, and not destroy packs.
     

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