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Charge Tapering

Discussion in 'Model S: Battery & Charging' started by TomServo, May 31, 2015.

  1. TomServo

    TomServo Member

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    I'm trying to gather all my facts/data before buying my CPO Tesla and have read how the charge rate slows at some point. If I set my charge capacity to say 80% on an 85kW MS will I bump into the tapering?

    If if so about where does the tapering start at, 70%, 75%. Also if charging with a Level II EVSE does charge tapering ever occur?

    Thanks in advance.

    PS: I'm coming from 40 months of Volt ownership and there are no special charging rules/procedures. It likes to be in the plug 24/7 with a FULL charge so I will need to relearn some things.
     
  2. Stoneymonster

    Stoneymonster Active Member

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    Tapering only occurs during supercharging, and is a continuous curve as the charge state increases, but gets more rapid as you crest 50%. Even toward high states of charge, supercharging is much faster than Level II, however.
     
  3. Doug Darby

    Doug Darby Member

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    Yes you may see some tapering off of the charge rate at 80%. Thats how all high end chargers work with lithium batteries. Just out of curiosity, why are you concerned about how and when the charge rate tapers off?
    It occoured similarly on my 2012 Leaf I drove for almost 3 years.

    I experience tapering off of the charge rate at home using my HPWC as well as at Superchargers.
     
  4. TomServo

    TomServo Member

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    I'm keeping the 2013 Volt (paid off) and will use my CC LCS-25 Level II EVSE for my home charging needs, and was wondering if it would charge any slower that the 10MPH it charges at now.

    So if I only encounter this with HIGH SPEED charges like Tesla S/C's I just need to understand its impact on charging times vs range I can get during trip charging sessions.

    Thanks
     
  5. TexasEV

    TexasEV Active Member

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    The LCS-25 supplies 20A at 240V which should give you more than 10 miles/hr. At 40A the car gains 29 miles/hr so at 20A it should be about half that. There won't be any significant tapering issues until the last few miles.

    Regarding superchargers there is a curve on the Tesla supercharging web page:
    Supercharger | Tesla Motors
    It takes almost as long to go from 80-100% as it does from 0-80%. When supercharging, only take the time to go over 80% if you need it to get to the next supercharger or to your destination with a comfortable reserve.
     
  6. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Let me state this a little differently, the charge power is the smaller of the charger power available and the ability of the battery to safely accept charge (the taper). Let's look at a few cases or an 85 kWh Model S, where the battery is not too hot or too cold:

    • The 120 kW power limit on a Supercharger is hit at about 10% SoC (State of Charge); before that the power is limited by the 120 kW Supercharger per stall limit (even on a 135 kW Supercharger), and after that the charge power is limited by the taper.
    • With a full power CHAdeMO, the maximum charge rate is about 48 kW at 85% SoC, when the taper kicks in.
    • With an 80 Amp, 240 Volt HPWC and dual chargers, the taper starts at about 97-98% SoC.
    • With a 40 Amp 14-50, the taper starts at about 99% SoC.
    • Etc.


    As you can see from the above, taper is most noticeable with a Supercharger, but you can hit the taper at high SoC with all but the slowest chargers.
     
  7. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Charge tapering occurs even on a Level 2 EVSE, but if you're charging at 10kW you won't see the taper kick in until you're above about 98% SOC. At a Supercharger, the charge rate holds pretty steady up to about 45% and then falls off rather dramatically. Working from memory, a charge that begins at 20% SOC with 117kW will drop to about 55kW by the time you reach 60% SOC. You'll still be above 10kW even at 95% SOC.
     
  8. RiverBrick

    RiverBrick Active Member

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    I like your way of putting it. Would it also be true to say that HVAC use can hide tapering? For instance, if the amount of power being used to charge the battery has dropped from 120 kW to 90 kW, but cooling systems are running full blast, will the dash display something several kW more than 90 kW?

    This often comes into play in the Winter where at 97% the Model S is still taking the max a 14 kW L2 station can provide because most of the power is for heating.
     
  9. S4WRXTTCS

    S4WRXTTCS Active Member

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    #9 S4WRXTTCS, Jun 2, 2015
    Last edited: Jun 2, 2015
    Under normal circumstances you won't hit the charger taper with the Level II EVSE, home charging, etc. You won't because you'll set the charge limit to 80%. The only reason you'll use 90-100% (where the charge taper comes into play with Level II or home charging) is if you're range charging right before a trip.

    Like the Volt the Tesla likes to be plugged in 24/7. The whole "a plugged in Tesla is a Happy Tesla thing".

    The Tesla handles all the management for you.

    The only thing to know is that a FULL charge is only for occasional use. I might be totally mistaken about this (due to lack of evidence/knowledge), but I don't believe most companies allow you to use 100% of a Lithium ion battery. Where instead they set the maximum somewhere below it, and they pretend that the lower amount is 100%. That way on something like an iPhone it will quickly charge to "100%" without any noticeably long charging time. Tesla does allow you to use the 100% amount for range charging.

    All lithium batteries have charge taper. It's simply a function of how they charge. They accept less and less current from the charger, and they're charged from current control voltage sources. The only reason you would never hit a charge taper is with a really small source current.

    I'm not sure why anyone is concerned with charge taper outside of charging time.
     
  10. Incredulocious

    Incredulocious '11 LEAF –> '13 RAV4 EV

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    #10 Incredulocious, Jun 2, 2015
    Last edited: Jun 2, 2015
    No, no electric car let's you use the battery's entire capacity as this would be detrimental to the battery. A reserve is held back at the bottom and at the top. The useable capacity of the battery is what you can address when you charge to 100% in extended/range mode. On the 85kWh Model S, I believe folks have computed that to be just under 80 kWh. (Not sure about that number. On my RAV4, 41.8kWh is useable in extended charge mode out off the battery pack's 48 kWh size.)

    Here's one of several threads on the topic in this forum:
    Real Usable Battery Capacity

    Here's somebody else's calculated estimate along with a pretty diagram:
    http://nickjhowe.com/tesla/modelsguide.html

    png_base642ceb9023f4bb7cba.pn.png

    On a related note, it's been determined through CAN bus decoding and testing on the RAV4 EV (Tesla battery/motor) that Toyota "hides" normal capacity degradation by adjusting the 80% used for normal charging and letting the extended charging mode take most of the hit:
    Toyota Rav4 EV Forum SOC%, kWh, Rated Range

    Has anyone determined yet if Tesla does something similar between normal and range mode?
     
  11. AmpedRealtor

    AmpedRealtor Active Member

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    Tapering doesn't affect my 80A HPWC charge rate until I hit ~97% SOC.
     
  12. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Exactly!

    Here is a picture of my MS going into the taper while I was preheating the car 's interior, getting ready for a winter hypermile adventure. If you look at the power that the car was consuming during the taper, you can clearly see the difference in power drawn with the cabin heating on and off. I purposely turned it on and off to watch the graph on a TED that is dedicated to my HPWC.

    This last bit of charge 90% to 100% took over 2 hours. This was on a much early version of software in the MS (1.5 years ago?), and starting with a cool battery...

    Range Charge Complete w heat.png
     
  13. S4WRXTTCS

    S4WRXTTCS Active Member

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    #13 S4WRXTTCS, Jun 2, 2015
    Last edited: Jun 2, 2015
    To clarify I only meant the top end. Where they allow you to charge all the way to 100% during a range charge. The reason I brought that up was the OP mentioned the Volt specifying FULL charge, but the Volt leaves a buffer at the top. They call it a full charge, but internally to the battery it's not full. It does not have a "RANGE MODE".

    I didn't mean 100% as in going all the way down to zero because not only would that be really bad for the batteries, but I'm not sure all the Motor electronics would even run properly. It would be like my Evolve Longboard where it suddenly cuts out (low battery voltage protection), but then goes again. Where if you give a buffer like my Boosted board does you get a nice smooth operation all the way till the buffer hits. They both have battery protection (you don't want to go below a certain voltage per cell), but they do it differently.
     
  14. Incredulocious

    Incredulocious '11 LEAF –> '13 RAV4 EV

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    Well, that's part of what I was describing. My understanding is that there is still a reserved bit at the top end on the Model S that is unreachable even with "range" charge. Or in other words, the battery could be made to take more charge but you're not allowed to, like with the Volt and other vehicles. (I should mention that the idea of 80%/100% charge levels or "range" or "extended" charge levels is present on other vehicles. Though, interestingly, Nissan dropped the ability to specify 80% charge levels after a couple of years on the LEAF in an apparent desire to get better published EPA range estimates.)
     
  15. TomServo

    TomServo Member

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    Awesome feedback, essentially I'll just Plug and Play and try to keep the SOC between 10% and 80%. I'm expanding my purchase decision to 85kW cars. So now I'll have to delay my purchase a few months to gather the additional funds.

    I truly appreciate all your info and time bringing me up to speed on this issue.

    Cheers
     
  16. ljwobker

    ljwobker Geek.

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  17. Rocky_H

    Rocky_H Member

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    I'm pretty sure that's not correct about the Model S battery system. At the end of a full range charge, it's down to 2 amps and 1 amp for some unbelievably boring amounts of time, and it would not be going nearly that slowly and low current if it weren't at the top end. Also, Tesla would not have to be warning people to drive fairly shortly after doing a range charge if it weren't really full.
     

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