Why is Tesla limiting the charging rate at Superchargers?

Tesla Supercharger

What’s this? Tesla is limiting my Supercharging rate, saying I’ve been fast-charging too often? It’s an outrage! I signed up for unlimited Supercharging forever! Splutter…argh..ack! ack! [falls backward, clutching at chest]

Not so fast. Calm down and let Tesla explain. Yes, the vehicle software will limit the Supercharging rate for vehicles that have racked up too many DC fast-charging events. No, this is not intended to limit your Supercharging enjoyment, but rather to protect the battery.

For a while now, some Tesla owners have been complaining on the forums that their charging rate at Superchargers has been reduced. Many factors affect the charging rate, so it was hard to isolate the reason until one Tesla owner took a road trip on which he used several different Superchargers, and never experienced a rate above 90 kW (the top charging rate is 120 kW). He took the issue to the Tesla Service Center, and the technician’s response reads in part: “Once vehicle has been DC fast charged over a specified amount, the battery management system restricts DC charging to prevent degradation of the battery pack. According to Tesla engineers, this vehicle has seen significant DC fast charging and now has permanently restricted DC charging speeds. Important to note, Supercharging will always still be available to the vehicle and the battery pack has not yet experienced significant degradation due to the amount of DC fast charging performed on the pack up until this point in time.”

It seems this particular owner has been using DC fast-charging almost exclusively, which is far from the usual scenario – he has used CHAdeMO 245 times, and Superchargers “50 to 60” times.

Nonetheless, the discovery sparked a firestorm on the forums, similar to that which erupted after Tesla used an over-the-air update to limit the use of Launch Mode. The company responded with a statement explaining the reason for limiting charging speed:

The peak charging rate possible in a Li-ion cell will slightly decline after a very large number of high-rate charging sessions. This is due to physical and chemical changes inside of the cells.  Our fast-charge control technology is designed to keep the battery safe and to preserve the maximum amount of cell capacity (range capability) in all conditions. To maintain safety and retain maximum range, we need to slow down the charge rate when the cells are too cold, when the state of charge is nearly full, and also when the conditions of the cell change gradually with age and usage. This change due to age and usage may increase total Supercharge time by about 5 minutes and less than 1% of our customers experience this.

Tesla is not slowing down charge rates to discourage frequent Supercharging – quite the opposite.  We encourage our customers to use the Supercharger network at their discretion and we committed to doubling the number of worldwide chargers just this year.  We also want to ensure that our customers have the best experience at those Superchargers and preserve as much vehicle range as possible – even after frequent usage.

As Electrek notes, there are several ways in which Tesla’s software limits performance in order to increase durability or safety, and most of them are not detectable. When they are, however, better stand back and watch the sparks fly.

 

Source: Electrek

  • Vincent Wolf

    So indeed why buy a Tesla to get into their supercharging network if for ‘battery protection’ events is limits charging to 90 kW or less? If your taking a trip across the country I sure would want the charging to be as fast as possible and am NOT willing to wait an extra half hour each time to charge because Tesla feels this is a ‘no no’. Screw that. Just one more reason why I am cancelling my model 3 reservation. Tesla won’t allow reservationists to order what they want (AWD) until years later and by then the rebate will be gone, and then they lie about charging rates saying they get 130 kW and that’s misleading since they are ‘throttling back’ anytime you try to take a long distance trip!

    No thanks Tesla your really ticking me off with your lying, your arrogance, your fairness ‘doctrine’. Bye.

    • Pat Campbell

      If you are going across country, my guess is you will not be supercharging at each stop. Chances are you will be L2 charging overnight at hotels and at L2 chargers elsewhere. Still, thanks for cancelling.

    • Lance Pickup

      I agree with you in principle, but I really think you missed some important points in the article:

      1) “This change due to age and usage may increase total Supercharge time by about 5 minutes” Not sure where you got your “30 minutes” figure.
      2) “130 kW and that’s misleading since they are ‘throttling back’ anytime you try to take a long distance trip” ANY time? I doubt a single trip across the country would put you into the realm of being limited. The user mentioned in the story has fast charged 300 times. Even if you took an annual cross country trip, you’d still probably only rack up about 20-30 fast charges a year.
      3) Not related to the article, but “Tesla won’t allow reservationists to order what they want (AWD) until years later” Years???? Granted, you may be right about the tax credit though, although since I think it will be more of a 6-12 month delay for AWD, I doubt the credit will be 100% phased out.

    • dogphlap dogphlap

      Tesla do not throttle back anytime you try to take a long distance trip.
      If you don’t like the way Tesla do business you definitely should not buy one.

    • Kelly Hart

      Show me where you can charge at a non supercharger that goes even close to 90kW

    • davidwhittlesey

      “This change due to age and usage may increase total Supercharge time by about 5 minutes and less than 1% of our customers experience this.”

      What time zone are you in where 5 minutes = half hour? And you are a “1%’r? Bugatti is working on an EV. Wait for that.

    • LAKIN

      That’s OK, Vincent. I’m sure you’ll find exactly what you want, when you you want it, from any one of of the many manufacturers who are committed to an EV future.

  • Ed

    I have been floating the idea that perhaps what Tesla will do next is put a larger battery in the car than the marketed rating, say, a 110 kWh battery that is marketed as a 100 kWh unit. The car would never charge beyond 100 kWh, so charging time to any level will be faster, and any degradation up to 9% would be invisible over the life of the car. Doing this wants to wait for higher power density and lower cost cells…but that may be just around the corner with the 2170.

    Also, in theory, the higher 140 kW Supercharger charging rate might be used to further accelerate the charging time for these batteries. Anyone else share this view?

    https://uploads.disquscdn.com/images/90086e1c0dc9cd0fb5c80c4de5f9642a10258221577d28fcdd179f5bf17d11c4.jpg

    • wardmundy

      Ha! Tesla is doing just the opposite. Buy 90kWh and you get 78kWh.

    • Lance Pickup

      Well they already did with (temporarily) with the 60kWh battery that was really 75kWh software limited to 60 (and upgradeable if you wanted to go to 75kWh). They’ve since canned the 60kWh option.

      I doubt it will ever make sense to do this on a regular basis, particularly at the top end.

  • wardmundy

    Reminds me of the promised “unlimited data” on my cellphone plan. And it turns out the 90kWh battery is more like 78kWh. Ick!

  • Lance Pickup

    Not sure I’m really buying it. The story sounds plausible, but I don’t think the raw number of fast charges is what matters, as much as the heating effect of those fast charges, which is going to differ from user to user. And besides which, Tesla can always throttle the charging rate dynamically when the battery approaches excessive heat levels. So even though they are saying that it’s for the health of the battery, I do actually think it’s to discourage high usage users to not Supercharge as much, similar to how cell phone companies throttle high bandwidth users. The difference is that apparently once you cross whatever threshold they’ve set, that’s it!

    Kind of reminds me of Nissan’s range increase for the LEAF. Nissan had to set their official EPA range based on how most people would charge their cars. When the LEAF came out, there was an option to charge to 80%, and that’s in fact what the user’s manual recommended. So as a result, most people routinely charged their cars to 80% and so they had to quote the range for an 80% charge. But then they got rid of the 80% charge option (saying that they didn’t see any degradation due to 100% charging) and suddenly they were able to “increase” the range of their cars without doing a damn thing to it!

    So I’m a bit skeptical that they are being 100% honest here.

    • http://ChargedEVs.com/ Christian Ruoff

      Understand the skepticism, but we think Tesla is being honest here. Heat plays a role but its mostly about the electrochemistry happening in the cells. The adverse side reactions get worse after a large number of high rate charging events. We’re working on a report to explain more.

      • davidwhittlesey

        Looking forward to the report. The more details the better. Battery technology is the key to widespread EV adoption of all types of transportation.

  • Freepat 75014

    I fully understand the technical points here but still this hardly questions the other Tweets of Elon on next Gen Supercharger v3 last December. For him, the German Porsche led 800V CCS SuperCharger standard, finally translated into up to 350KW AC (With a 150KW step also available), would be for children toys… Since that we all expect Tesla future SC v3 to deliver up to 500KW or even 600KW versus 120KW to 145KW today, while the best 100KWH Tesla models S & X today are limited to 120KW maxi peak charge, by Software, if I got it right (Means they have set a # 1.2*C charge capping).
    So the question now is what Tesla car could ever use that next gen SCv3 power when available ? And the arguments documented here are very-very bad indications for current models S & X at least.
    And that triggers other questions, like : Will the new #30% more efficient Tesla 2170 cells, to be used in Model 3 and PowerPack2, but then will be expanded to new Models S & X by end of 2017 too… Will this 2170 cell be capable to accept much more Cs than current 18650 cells used in Models S & X, that seam limited to 1.2C (120KW for 100KWH). Knowing Model 3 that uses new 2170 cells will have a maximum 75KWH pack, and a minimum between 50KWH and 60KWH. Connecting it at full power to future SC v3 that would have say 350KW to 600KW power, would require these 2170 cells to be capable to accept 4.66*C to 12*C, means # 10X versus today 1.2C on 18650 cell based Model S & X…. That already seam at their limit after only 50 to 60 x Supercharger charges and 245 1000KM day trips per year with my family, that I’m holding my Model X 100D PO till I understand how that will work and if I should wait for next 2170 Cell up-dated Model X launch later this year, to benefit SC v3 as much as possible. There is a gap in Tesla disclosed datas on SC v3 and 2170 cell that needs to be addressed here ASAP.

    • Mark Treveil

      SCV3 – what is it good for…. well trucks might be one answer.
      As for throttling: well the whole TM recharge process is throttled – you only get near max power at <20% battery charge.
      Preventing battery damage = prolonging the life of the battery, and is something TM have worked hard on. They continually refine to reflect the results they are seeing in the field. Personally I still get 116Kw sometimes into my S85 which has 60k KMs on the clock and supercharged the majority of the time these days.

    • davidwhittlesey

      Wait for the 2170’s to be used in the Model X. Realistically, it may charge a bit faster but it won’t be nearly 5X. Maybe 1.5X. The many tech papers you (and I) read span a wide range of chemistry’s, life cycle expectations, energy densities, safety tolerances, etc… Wouldn’t it be awesome if LTO cell could be made at 250+ kW/Kg??? Those kind of battery specs are still a few years away, unfortunately.