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Supercharging a a low capacity battery

Discussion in 'Model 3' started by JeffK, May 7, 2016.

  1. JeffK

    JeffK Active Member

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    With superchargers starting to be 135 kW and maybe up to 150 kW sometime in the near future what effect will this have on smaller capacity batteries like in the Model 3.

    Current Models 70 (75) and 90 charge at less than 2 C, but if the Model 3 battery comes as a 50 kW version then you'll be well above 2 C and closer to 3 C. What are your thoughts about the impact this might have on battery life or will the new batteries handle that kind of charge rate?
     
  2. seattlite2004

    seattlite2004 Member

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    From the vids bellow, the smaller Model S battery takes much longer to charge than the bigger batts. So regardless of input, seems the larger batt will charge faster. Gonna be a bunch of M3s clogging up the stations...S and X folks are gonna get ticked....

     
  3. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Charge rate is best thought of as [rated] miles per minute/hour rather than kW (or kWh/h which is the same as kW). Since the Model 3 will have better efficiency (Wh/mile) that effect will likely fully counteract the fact that charge rates in kW may be lower. In fact I believe the Model 3 will supercharge quicker on average than Model S or X when measured in miles restored power hour of charging.

    That said, between different Model 3 battery sizes the one with the larger battery will charge faster.
     
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  4. JeffK

    JeffK Active Member

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    I like using C to describe charge rates... especially when talking about battery lifespan. I'm not talking about range or efficiency here, I'm purely talking about the lifespan of the battery.

    It's nice to see that the superchargers will automatically lower the charge rate as the batteries charge.
     
  5. Johan

    Johan Took a TSLA bear test. Came back negative.

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    C is decided by chemistry, not size. One 18650 cells with some 12Wh of capacity charges at the same C rate as the whole pack does regardless of size.
     
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  6. JeffK

    JeffK Active Member

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    #6 JeffK, May 7, 2016
    Last edited: May 7, 2016
    I think we have different definitions of a C-rate
    C with regards to charging is the charge rate of the battery it's not determined by chemistry. A battery is typically made of multiple cells. C is defined as battery capacity divided by 1 hour.

    1 C for the 60kWh battery is 60 kW
    1 C for the 80kWh battery is 80 kW
    etc.

    discharge is the same
    if a 60kWh battery and an 80kWh battery are discharging at a 80kW then the 80kWh battery is discharging at 1 C while the 60 kWh pack is discharging at over 1.33 C
     
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  7. Johan

    Johan Took a TSLA bear test. Came back negative.

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    You are misunderstanding. Charging at 1C means recharging the entire battery from empty to full in one hour. Charging at 2C it takes only 30 minutes. Charging at 0.5C takes two hours. But these would be average C rates over the entire cycle. In reality the charge starts out with a higher C rate and then has to taper to a lower and lower rate as the battery gets fuller. The shape of the curve of possible C rate as a function of state of charge (basically voltage) is decided purely by the chemistry. Total pack size is irrelevant (as long as the charger can keep up and give enough volts and current, otherwise that would of course limit the charging process).
     
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  8. JeffK

    JeffK Active Member

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    I'm not misunderstanding at all... The shape of the curve is determined by software is what you're really saying. Chemistry has nothing to do with it. You can certainly pump a Li-Ion battery at 3 C from empty until full it's just not healthy for the battery.

    The videos seattlite2004 posted show the software controlling the charge rate dynamically based on voltage/temperature etc.

    The Tesla firmware is what makes the pack size irrelevant.
     
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  9. Johan

    Johan Took a TSLA bear test. Came back negative.

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    If it's not healthy for it then it's disingenuous to say it can be done. Of course it can be done but with rapid degradation. And of course it's "software" controlling the actual curve being used to charge.

    But please listen to the point I'm making: the only thing that governs how aggressive a charge curve it is possible for the software to charge the battery with while still sustaining acceptable cycle life is the chemistry and also pack design with regard to temperature control.
     
  10. eloder

    eloder Member

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    Efficient cars regain range faster, by virtue of driving more miles kwh per kwh. While the efficiency gains probably won't counteract the larger battery, it will help out in some manner.
     
  11. david_42

    david_42 Member

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    The 60kwh battery in the Model S is older technology, that impacts the maximum charge rate. I suspect the Model 3 battery to have much the same charge times on a Supercharger as the newest Model S batteries.
     
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  12. lklundin

    lklundin Member

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    Apologies for interjecting and for being so pedantic.

    But there is a difference between a physical unit and a physical quantity.

    'Length' is a physical quantity with SI-unit 'meter' (and a whole lot of alternative units).

    This relatively new way of seeing the world is hampered by some languages.

    English, for example, has words such as 'voltage' and 'mileage' which blurs this important distinction.

    Similarly, I would like to point out that regardless of how it is actually defined or used, the charging rate of a battery, which is often called the C-rate, or just C, is a physical quantity, with unit 1 divided by time (e.g. 1/h).

    This is important because '1C' as found in 'Charging at 1C' really is the SI-notation of 1 Coulomb, i.e. the electrical charge from a constant current of 1 ampere for 1 second. (As such a battery charged so it holds 1Wh at a voltage (!) of 400V holds an electrical charge of 9C).

    Although the above quote is quite common usage, it really is better to not confuse the charging rate with its unit.

    I guess a pedantically correct phrase would be: A charging-rate of 1/h means ...

    I will now go back up in my ivory tower, so the actual discussion over charging rates can continue. :)
     
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  13. David99

    David99 Active Member

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    Elon mentioned in a public meeting that the Supercharging rate is conservative. The battery can be charged much quicker and with a stronger cooling there would probably be a lot more room. The limitations we see with the Model S now don't necessarily apply to future cars. The superchargers are designed to max out at the current power. The wiring isn't capable of much more power.upgrading those would be a major task.
     
  14. SageBrush

    SageBrush Active Member

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    The GM Volt might be instructive here, since AFAIK the issues related to high C battery operation apply equally to discharge and charge.
    The Volt battery (Gen1 anyway, IIRC) is 16 kWh but I'll guess that daily driving averages about 1C with lots of 2 - 5 C experience, and seems to holding up well so far after 4 years. That suggests that occasional SC use should not be a problem, even before I consider the superior Tesla system for heat control.
     
  15. George S. Bower

    George S. Bower New Member

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    I think we could expect the same C rate for the smaller kwh pack unless Tesla goes to a different anode. From what I've been able to determine the anode construction, material etc is what defines the recharge speed--as opposed to cathode-- and I don't think Tesla will be changing the anode construction.
     
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  16. George S. Bower

    George S. Bower New Member

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    I don't think you can assume the same C rate for charge and discharge. In other words a battery that has a high discharge C rate does not mean it will have a high charging C rate. As I said above I think when talking recharge the anode drives it while in discharge the cathode drives it.
     
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  17. Johan

    Johan Took a TSLA bear test. Came back negative.

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    This is correct. For Tesla's batteries the capability to discharge quickly is 3-4 times greater than charging.
     
  18. Jeff N

    Jeff N Active Member

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    #18 Jeff N, May 8, 2016
    Last edited: May 8, 2016
    As a general rule, the inherent cell discharge rates are usually loosely about twice the discharge rates in lithium ion EV battery packs but not always -- the 2016 Chevy Malibu hybrid's 1.5 kWh pack is specified to charge at a slightly higher rate (65 kW) than discharge (52 kW) or roughly at 35C and 43C peak rates. Those are vastly higher C rates than in the Volt or Model S and as far as I know it is mostly, but not entirely, due to differences in cell construction. In practice, pack charge rates are often limited by charging station and equipment capability in larger pack vehicles like a Tesla or a Bolt EV.

    Another factor, in addition to cell cathode and anode chemistry, electrolyte chemistry, and pack cooling design, is the construction of the cell itself. Cells can be designed in ways that maximize power C rates (power density) or in ways that maximize energy density. Generally speaking, designs that maximize energy density max have reduced power density.

    The bottom line is that we don't know yet how all of these different factors will result in specific charging rates for the Model 3. Some differences in the Model 3 may tend to increase power density while other changes may tend to increase energy density at the expense of power density.

    Without knowing more, the best starting point is to assume the rates achieved by the modern Model S packs and then scale to the appropriate pack size. In other words, a 55 kWh base Model 3 will probably charge at about the same peak rate and charge curve as the more recent builds of the Model S 60 pending further specific pack and cell design information.
     
  19. Jeff N

    Jeff N Active Member

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    Oops, I meant to say the discharge rates are twice the charge rates.
     
  20. WarpedOne

    WarpedOne Supreme Premier

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    Volt 1/3 of capacity reserved i.e. not available to use.
    Its battery capacity will need to degrade under 70% for theoretical chance to measure a difference in cars behavior. Volt is a hybrid that automatically starts the ICE when it sees fit so the driver is even hardly pressed to notice the difference.
    So, volt is not instructive here at all.
     

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