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Tesla needs 200kW Superchargers for A+B pairing and future proofing.

Discussion in 'Charging Standards and Infrastructure' started by ratsbew, Feb 18, 2016.

  1. ratsbew

    ratsbew Member

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    #1 ratsbew, Feb 18, 2016
    Last edited: Feb 18, 2016
    I was just thinking about Supercharger congestion and charging speeds. To me, it seems like the rollout of 200kW (or greater) Superchargers would go a long way to combating Supercharger crowding because if all stalls are taken, this would give both A and B stalls at least 100kW of power and more cars per hour moving through the stations. Also, as larger batteries (or higher C rate) are rolled out in the future that can accept faster charge rates it would allow single cars to charge faster (up to 200kW or whatever the battery limit is).

    As it stands now a 135kW Supercharger (the biggest I'm aware of) can only charge two cars simultaneously at about 67.5kW each.

    Another possibility would be redesigning new stations so that there is no A+B and that the Superchargers could flow power to whatever stalls are occupied.
     
  2. lolachampcar

    lolachampcar Active Member

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    I'm kinda amazed there exists a nationwide 135 KW fast charging capability but I guess more is (almost) always better.
     
  3. AlMc

    AlMc 'Senior Moments' member

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    IIRC, JB indicated that he felt it would eventually be possible to half charge in less than 10 minutes. I certainly believe faster charging trumps larger battery packs.
     
  4. roblab

    roblab Active Member

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    Without spending time checking all the charts and charging protocols that have been posted about A pack vs B pack charging, etc, I remember that all packs charge at peak for only a few minutes at the beginning of the cycle, and almost immediately start tapering off, so that a 120 kW pack will be charging slower than a 90 kW pack in a short time.

    When a car pulls in to charge, the car in the paired stall is probably already leaving more than enough to charge car #2 at full, and if not, will be shortly. The fear of waiting seems to dominate, but in reality, it's a mostly imagined fear.

    The cars already move through, or *should*, in about 20 - 30 minutes. If eight stalls are rotating every 30 minutes (two stalls rotating every 8 minutes or so), I doubt if having a few more kW available will speed things up much at all since the only time one needs full power is the first minute or so.

    Already I have heard rumors of 150 kW and more, but Tesla is already so far ahead of this game it's not funny. And for most of the week, most charger pairs are not occupied.
     
  5. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    It'd cost more.
    More powerful transformer.
    More chargers and cables.
    And maybe most importantly: higher demand charges.
     
  6. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    There's a balance to be struck between Tesla's demand charges (highest simultaneous power consumption), transformer size and cost, etc. With the exception of some specific sites in California, I think there's a good balance today.

    200 kW superchargers would require larger transformers (right now the majority I've seen are 500 kVA, they'd have to go up to 750 kVA or 1 MVA). That, in turn would cost more to Tesla in the form of equipment costs and/or demand (highest simultaneous load). The load just isn't there outside some specific stations - yet.
     
  7. green1

    green1 Active Member

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    Keep in mind that unless you arrive basically empty, you aren't likely to be able to charge faster than that anyway. I would bet that if Tesla dug up stats on it they'd find that the cars wanting to pull more than is available is not all that common, and even in cases where it happens it probably adds very little time to the session as it resolves fairly quickly as the battery his the taper anyway.

    That said, in the future I agree they will need to increase the available power, I just doubt we're really there yet.
     
  8. ratsbew

    ratsbew Member

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    Isn't this the main reason for stationary storage on site? "Trickle Charge" the storage battery to avoid demand charges and then release that energy into the cars when they show up.
     
  9. astrotoy

    astrotoy Member

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    Is there a technical reason why the charging algorithm cannot be changed to extend the higher charging rate to longer into the battery charge, so the charge to say 60 or 75% occurs faster? That would free up chargers faster, making everyone wait a shorter time. The longer charging time for the second car into the unit is more than made up by having first cars finish faster and reducing the likelihood that you will be the second car into the unit.
     
  10. green1

    green1 Active Member

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    Yes, the technical reason is that it's bad for the battery. The higher the state of charge, the slower you need to charge to not damage things.
     
  11. deonb

    deonb Active Member

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    So you can chose between 200kW going across 2 cars, or let's say - typical station - 800kW over 8 bays.

    Or you can use that exact same 800kW and distribute it at 135kW over 12 bays.

    Uhh... Yeah, I'd take the extra 4 bays rather than the extra 3 minutes it will save charging.
     
  12. Cyberax

    Cyberax Member

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    The technical reason is "not letting the battery to explode". And simply using a more powerful cooling system won't help.

    Unfortunately, the only cure for this are better and bigger batteries.
     
  13. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Yes. But, they have to figure out the correct amount of storage to meet peak demand at lowest cost.
    And of course that's another cost.
    Anyway, the point is that with their current set-up each Supercharger cabinet is sized to provide max charge rate, and then pairing is used to provide additional charging at little extra cost. Because of tapering, 1-Supercharger-per-stall is cost-inefficient. It's better to add pairs, rather than beef up each pair. Only when max rate increases should Tesla up Supercharger power.
     
  14. Kim.T

    Kim.T Member

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    This is a chart of my 70D charging. In Denmark/Germany we have 135kW SuC. I get a max of 116kW but only for a couple of minutes (until the SoC is approx 15%).
    Ladetider.jpg
    If my SoC is 60% the car is only charging at 50% = 56kW. It would be nice if the it could charge with more kW in a longer period.
     
  15. green1

    green1 Active Member

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    Yes, it would be nice, however it's not related to the Supercharger not having the capacity (as you can see at the start of the chart, it has plenty of capacity) It's all about the battery chemistry.

    Now we don't know if Tesla is being too conservative with their tapers, or even too aggressive, Tesla hasn't been completely open on exactly what the chemical makeup of their cells is, and most of us aren't battery engineers. That said, it seems likely that Tesla also wants to charge as fast as they can safely do so, so I fully believe Tesla when they say that they can't charge faster without harming the battery.

    The only real hope is that over time, as batteries continue to improve, that new cars will be able to hold a higher charge rate for a longer period of time. Only once that happens (and by a relatively significant amount) does it make sense to upgrade the chargers to put out more power than they do now.
     
  16. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    If users arrived with 0% in the battery and leaving with 80%, according to Tesla, they would need 40 minutes without charging limits. Here is the chart at Supercharger | Tesla Motors

    Supercharger Charge Profile.png

    In a near worst case situation, there is a queue of cars all needing that charge rate. My guess is that after they fall into a new a car arrival at the halfway point in the charge, it will add only 5-10 minutes to each car's time. By the time the car has been charging for 20-25 minutes the power draw will have dropped to 60 kW or less from a peak of 120 kW. 135kW - 60kW = 75kW. That means the new car starts with 75kW instead of 120kW, but that power will rise as the more charged car's power continues to fall, leading to my 5-10 minute assertion.

    If all that is added is 10 minutes in a worst case situation, then I favor 135 kW Superchargers and more of them than 2/3 as many 200 kW Superchargers. In the real world, it's not just a site power limit, but 135 kW is pretty darn good for now, and not that much of a limit...

    By far, most of the time, there are multiple stalls open on arrival. On the few occasions where I have arrived and seen my power limited, I just surveyed the site and found a stall that was not sharing or sharing with an almost fully charged car. In almost 10,000 of miles of Supercharger driving, I have never had a Supercharger-sharing power-limit that delayed me.
     
  17. freds

    freds Member

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    It's been my recent experience that on long trips with multiple charging stops that you arrive at the intermediate chargers basically empty and the last charge session has you arriving at your destination the same way. So when you do arrive at a super charger your car is ready to charge at maximum rate.
     
  18. trils0n

    trils0n 2013 P85

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    I guess increasing the power of the superchargers would decrease congestion in the rare situation where: all stalls are full, all cars have arrived roughly at the same time, and all very low charge. I think this situation is pretty rare, so it probably isn't worth it at this point. It would also reduce charge times/improve experience when users(an increasing amount of users do this) plug into a paired charger that is already in use and get a reduced rate, instead of plugging into an unpaired charger. It might also be possible to change the wiring of the Superchargers to allow shuttling of power from unused chargers to any of the plugs, to eliminate this pairing penalty. Who knows if it would be worth the extra wiring though.

    In the future, it might be worth it to expand SC capability if the location is constrained on number of charging slots, but not total electrical feed capacity, and frequently full. This will probably also be a rare situation.

    I'd think it would almost always be better to add extra stalls/chargers with the extra required power than to expand power requirements to make existing stalls faster.
     
  19. ReddyLeaf

    ReddyLeaf Member

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    I agree, more stalls will always be better. Here's a thought experiment: Is there a benefit to three stalls sharing the 135 kW? That's 45 kW each avg (that's Chademo territory and likely close to 2 hrs for a full charge, not the best for travel, but not bad over lunch, dinner, shopping, movie, etc.). The first vehicle to arrive in the 3-pair gets up to 135 kW, the 2nd gets what's left (probably at least 30 kW no matter what due to the time delay and taper of the 1st vehicle), then the 3rd gets the dregs.

    Perhaps somebody with more understanding of the theory behind the bank teller problem can help with this. My simplistic brain says it would be better, but I don't know by how much. Certainly there will be an impression of "better" (people will feel better about having their car sitting in an actual charging stall and receiving at least some charge rather than sitting in a line of 5 or 10 people waiting to get to the stall).

    Thinking about it a bit more, I think this will only help in very high use areas where a significant fraction of the cars charge above 80%. Given Kim T's graph above, the 70D receives less than the 45 kW average after 75%. Thus, the benefit to 3-stall pairs over 2-stall pairs really only occurs when two of the vehicles are over 50%, and probably really one when they both exceed 75%. Perhaps Tesla could do this at malls when the Model 3 arrives, but as others have said it might be cheaper to sprinkle 50 HPWC's (or J1772's) throughout a parking lot, with each unit capable of reaching 4-8 parking spaces.
     
  20. Kbra

    Kbra Member

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    I think the attempt at battery swap stations was supposed to help mitigate some of the overloading of SCs and expedite those that are in a rush or maybe dont want to wait in line as they get more popular. However the quite test run and likely higher cost deterred people from pursuing it any further. Maybe it will be revived in the future.
     

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