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Impact of high amp charging on Model 3 battery life

Discussion in 'Tech Talk' started by voip-ninja, Sep 27, 2017.

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  1. voip-ninja

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    #1 voip-ninja, Sep 27, 2017
    Last edited: Sep 28, 2017
    In the FAQ Tech Talk thread an interesting point came up with someone indicating that they choose to charge their Tesla below the full 40 amp charge rate possible on their home outlet, instead choosing to throttle the charging speed to 15 amps since they can still get the charge level they need and hope or expect that this will have a positive affect on long term performance of the battery.

    I think that this is a subject worthy of further discussion in order to better understand two issues;

    1. Does voluntary reduction of charge rate in home charging scenarios prolong battery life?
    2. Does capping charge to a below max range value prolong battery life?

    This is what I believe we know about this at this time. When time permits I will start quoting and linking sources.

    1. Elon Musk when pressed on the question of what charge level home owners should charge to for daily driving in order to get maximum longterm life of the battery is quoted as saying "around 80%". I believe this was something he posted to Twitter.



    2. Tesla have published information that indicates that owners that charge frequently at high charge rates at super charger stations can expect a small amount of battery wear to result. Super charging though has no impact on warranty which has a maximum allowable battery reduction of something like 1-2% per year.

    3. Initial survey information from Model 3 owners does not appear to show any correlation between battery degradation and type of charging done.

    http://www.pluginamerica.org/surveys/batteries/model-s/faq.php

    4. Private Model S/X rental/taxi operator in the Southern California area that rents a large fleet of Model S/X cars charge exclusively on super chargers (taking advantage of the bundled "free" supercharger access) and some of their vehicles have over 100,000 miles on them with no observed extra wear on battery life.

    http://www.greencarreports.com/news...0k-and-300k-miles-still-humming-along-happily

    It is worth noting that the operator did have one Model S that had its battery completely replaced under warranty during the unlimited mile 8 year battery warranty, it would no longer take a charge. It's hard to say what would happen if a regular owner ran into this problem after 8 years since their battery was basically dead and would have cost $20,000 to replace out of pocket.
     
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  2. garsh

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    Charging at low rates is less efficient. There is some amount of fixed overhead involved with charging. So keep that in mind as well. It will cost you slightly more to charge at lower rates.
     
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  3. voip-ninja

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    Thanks, that's definitely a valid point worth mentioning. The "overhead" of charging at 10/15/20 amps is noticeably higher than doing faster charging at 30-40 amps.
     
  4. Model34mePlease

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    Is there any reason to believe that AC charging is any worse for the battery than SC (DC) charging at equivalent power-to-the-battery rates. If not, then I would predict that AC charging has inconsequential effect on degrading the battery since the AC charge rate is vastly lower than SC rates.
     
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  5. Tom Bodera

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    I agree that overhead(Phantom Drains) and DC conversion efficiency (Which is better above 15 amps) is better at higher rates. However as you approach the higher rates or max rating on the AC cable (80% of max Safety factored), the cable should in theory begin to heat which would decrease efficiency. So if you have a 40 Amp charger on a 50 amp rated wiring, would not charging at 30 Amps be most efficient?
     
  6. Rusty

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    The charge will be slightly more efficient with lower amps. This won't add up to much for one charge, but over the life of the car can add up to several bucks.
     
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  7. voip-ninja

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    In the thread I created for this specific discussion it was pointed out that charging is actually more efficient at higher amps on a 220V line, not less efficient. Maybe we could discuss it further there.
     
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  8. Rick59

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    For the lazy people (like me), what's the name of the thread?
     
  9. voip-ninja

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  10. Frank99

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    Perhaps you'd have lower resistive losses because the wire is cooler, but you'd have to charge 25% longer, meaning that the electronics are taking power while controlling the charging for 25% longer. Is that worse for efficiency than resistive losses in the wire? One can't make a blanket statement here; you'd have to measure the two different situations and see.
     
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  11. EvanLin

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    #11 EvanLin, Sep 27, 2017
    Last edited: Sep 27, 2017
    I think electronics use much less power than charging, just like "turn off screen/headlight" vs. "driving 10mph slower" to save energy.
     
  12. arnis

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    Overhead at speeds below 3kW charge rate is too high for long term use (below 230V 16A). Though all EVs support at least that speed.
    Cooling draw (overhead) at speeds above ~30kW also starts to increase in some cases (very warm pack with thermal management).

    Degradation speed hardly varies at AC charging (3-22kW). Maximum charging speed of Model 3 batteries vary according to pack size.
    We can expect 100kW and 75kW respectively to be the upper ends for Model 3 battery packs. Charging those with onboard charger that is rated up to 10kW is far far away from maximum charging speed potential.

    General guidance should be to charge fast. In case of local energy production or storage, no faster than these can cope.
    Daily rapid charger usage will speed up degradation process (slightly), even with actively cooled packs.
    In terms of long term savings, EV's should always be charged with cheapest electricity possible. Local is the best,
    cheapest night tariff is next.

    PS. It appears Tesla has smaller onboard charger for standard range Model 3. Cheaper to produce and also makes
    maximum charging rate (C value) between two packs very similar.
     
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  13. garsh

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    I wasn't able to find numbers for a Tesla, but I found several reports about the charging overheads for the Nissan Leaf.

    Level 1 (120v, 12 amps): 78% efficient
    Level 2 (240v, 16 amps): 91% efficient
    Level 2 (208v, 30 amps): 91% efficient
    CHAdeMO (500v DC, ~100 amps): 93% efficient

    So it looks like there may be some minimum level of charge rate required to overcome the majority of overhead losses, then other factors become more important in calculating charging losses. Hopefully we can dig up similar reports for a Tesla.

    Sources:
    http://www.mynissanleaf.com/viewtopic.php?t=8583
    https://avt.inl.gov/sites/default/files/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf
    https://www.researchgate.net/profil...ency-of-quick-DC-vehicle-battery-charging.pdf
     
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  14. Brokedoc

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    This is VERY useful. I didn't read the full articles but presumably the same efficiency for Level 2 16amps and 30 amps does not account for heat loss. @PTFI has already noticed significant heat of the charging cable @ 36 amps to the point that he makes sure the cable is not coiled and can dissipate heat faster.

    Another user had commented about length of charge as a factor contributing to degradation of battery chemistry but, if true, this must be a minor factor because Tesla recommends daily charging even for people who drive very little and leaving the charging cable plugged in when on extended periods of inactivity.
     
  15. garsh

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    You might be confusing "length of charge" with "being plugged in". Being plugged in without charging will have no effect.
     
  16. Brokedoc

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    #16 Brokedoc, Sep 28, 2017
    Last edited: Sep 28, 2017
    Yes. The terms used are not precise. Based on my X, I would say that leaving the car plugged in results in intermittent charging due to phantom loss about every 6-12 hrs because my app sends me notifications that charging is complete. Therefore leaving the car plugged in does increase the time of charging.

    Also, is length of charging that deteriorates battery chemistry purely a function of time or is it the typical measurement of amp-hours which is a clearly known issue that all rechargeable batteries have a limited lifespan in terms of charge cycles. Li-Ion batteries have the advantage that the charge cycle can be fractional when calculating battery lifespan (i.e 10 charges of 20%=2 charge cycles) whereas older chemistries such as Ni-Cad were not (10 charges of 20%=10 charge cycles)

    Battery deterioration is unavoidable and multifactorial. I love these scientific discussions and I would love to see experiments showing the effect of each variable. Time charging, age of batteries, Current, Heat, charge cycles. Also, I suspect the cold winter weather in NY may be preservative for battery life but reduce battery capacity during the colder months (I remember somewhere storing unused alkaline batteries in the fridge prolongs shelf life). There must be some sweet spot where we can balance our charge rate to overcome efficiency losses, not generate too much wasted heat, and maximize battery lifespan. This sweet spot will vary for everyone based on their charge capacity at home and the distance of their typical commute and the amount of time they have at home to charge (or the hours that their utility drops the rate).
     
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  17. JWardell

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    Folks, the generalization of higher charge rates being more efficient is not necessarily true. It all depends on the efficiency and design of the AC to DC converter, in this case the chargers built into the car just above the battery.
    Most AC to DC converters are most efficient at their maximum current rating. And the 3 is getting two different ones depending on model. The standard will charge most efficiently at 32A while the long range will charge most efficiently at 40A, but less efficiently at 32A than the standard battery charger.
    Of course if your wires and connections are not oversized to handle the higher current, then resistance will turn larger currents into heat in the wiring and drop the efficiency, adding another variable to the equation.
    And of course DC charging through superchargers and Chademo bypasses the AC to DC battery chargers in the car, and therefore depend on the efficiency of the huge transformers at the site.
     
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  18. Model34mePlease

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    Am I misunderstanding these numbers or does AC to DC conversion really only lose a maximum of 2% efficiency?
     
  19. Model34mePlease

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    That is an interesting observation given that the new UMC will only charge at a maximum of 32A
     
  20. voip-ninja

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    Well, it could also be a play to try to improve sales of the wall charger by artificially lowering the max charge rate achievable via 50 amp circuit and 40 amp wall outlet. Hopefully though they had a less nefarious reason.
     
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