Is Tesla Limiting Supercharging Speed The Right Choice?

Tesla Superchargers

JUL 18 2017 BY EVANNEX 30


Tesla Superchargers


Tesla recently caused a fuss with its decision to limit the Supercharging rate for vehicles that have racked up numerous DC fast-charging events. A similar stir erupted a few months ago when the company used an over-the-air update to limit the use of Launch Mode (in response to owner outcry, Tesla later removed the software limitation).

In both of these cases, however, the company is not trying to spoil anyone’s fun – on the contrary, its goal in controlling Supercharger speed is “to ensure that our customers have the best experience at Superchargers and preserve as much vehicle range as possible.”

Fast charging stresses a battery, and doing it too often or at too high a rate can shorten a battery’s useful life. Tesla explained in a statement:

“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 article comes to us courtesy of EVANNEX (which also makes aftermarket Tesla accessories). Authored by Charles Morris.

Some vocal owners become incensed at any limitations on the way they use their Teslas. However, everyone wants to maximize their battery’s lifespan, and most will accept Tesla’s engineers’ explanation that, if a particular pack meets certain conditions, it’s prudent to limit the Supercharging rate. The inconvenience is minimal. “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,” says Tesla.

In any case, the controversy has inspired many owners to learn a bit more about how fast charging events affect a battery over time. Jeffrey Jenkins, writing in Charged, recently offered a detailed discussion of the issue, which we’ll briefly summarize here.

Tesla Superchargers

Tesla Model S and X vehicles supercharging

As Tesla explained, many things can reduce the lifespan of a battery pack, including charging at a high C rate. The C rate is the rate at which a battery is charged or discharged, relative to its maximum capacity. For example, if a battery is being charged at a rate of 1C, it will reach a full charge in 1 hour. Increasing the current increases the C rate, and decreases time to full charge. Charging at high C rates causes chemical changes to the battery cells that can eventually reduce their lifespans.

If you frequently charge at a high C rate, after a few years, the battery can’t take as much current as it used to, at least not safely and efficiently. It’s analogous to the effect alcohol has on a human body – steady moderate use won’t hurt you, and even an occasional binge won’t cause permanent damage, but frequent benders over a period of years certainly will.

Another factor that affects battery life is temperature. For maximum life, batteries need to be operated within an optimal temperature range. Excessive heat can shorten life (as some Arizona LEAF owners learned), but so can excessive cold.

As the 19th-century Swedish scientist Arrhenius discovered, the rate of a chemical reaction is dramatically affected by changes in temperature. At lower temperatures, a battery’s internal resistance increases, and lithium ions in the electrolyte have a greater tendency to come out of solution and deposit onto the electrodes – a process called plating out. This is bad news, because not only does it permanently decrease capacity, but it can eventually cause a short circuit, with disastrous results.


Tesla vehicles Supercharging

The tendency for lithium to plate out is more pronounced at higher charge/discharge rates, so one potential solution is to limit current at low temperatures, as Tesla alluded to in the statement quoted above. Automakers are secretive about their battery pack designs, but it seems likely that there are numerous temperature sensors throughout a Tesla pack, and that those sensors communicate with the charger during Supercharging.

Maximizing battery life isn’t the only reason for Superchargers to monitor the charging process – safety is another. Tesla’s Superchargers aren’t just power outlets that passively deliver electricity – they keep tabs on many different parameters as a vehicle charges, in order to keep your battery safe, durable, and working as intended.


Source: Charged

*Editor’s Note: EVANNEX, which also sells aftermarket gear for Teslas, has kindly allowed us to share some of its content with our readers. Our thanks go out to EVANNEX, Check out the site here.

Categories: Charging, Tesla

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30 Comments on "Is Tesla Limiting Supercharging Speed The Right Choice?"

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Super Charging is thus that & with less than 1% effected. Tesla is correct. No where did Tesla state you can Super Charge fast at every charge. Customers need to be more understanding of the limitations. Others like the car i have do not even offer supercharging fast.

Tesla wants to limit the number of fast DC charging to protect the battery. Why? Is it to keep customer satisfaction high? Is Tesla trying to keep the battery in satisfactory condition to make it to the end of the warranty period? Is Tesla trying to keep negative press from happening because owners abuse their batteries by performing too many fast DC supercharging? Should Tesla just back off and let owners drive and charge their cars anyway they want. After all the owners own the car, thus the name ‘owners’. Tesla does not own the car anymore yet appear to want to take action on an owner’s car to either keep up Tesla’s image or protect Tesla from having to replace a battery under the warranty period. Imagine Ford or any other manufacturer telling someone they cannot constantly abuse their muscle car’s engine by always revving to max RPM’s all the time while the car is still under warranty. After warranty, do what you want to your car. So, I am in Tesla’s camp for now. First, I would want my battery to last forever, though I know it won’t…If tesla can help with that, great. Also, if Tesla is… Read more »

Battery capacity is not covered under Tesla’s warranty, so they are not doing this for financial reasons.

FYI, this isn’t just Tesla. My Leaf will slow chademo speeds if I charge too much about it. I can even get a printout at my dealership telling me if I’ve been abusing fast charging too much.

Fine and all for the “good of the car”, but Tesla should have made this widely known and not so secret. Nowhere on their supercharger page does it even discuss the negatives of using it too much or keeping the battery pack at a too high a percentage either.

Manufacturers rarely go out of their way to describe in great detail the limitations or negative qualities of their products.

In a perfect world, they would do so. We don’t live in that perfect world. In this world, it’s not reasonable to expect Tesla to anti-sell its own products, which would make them less competitive with other auto makers’ products.

I agree that Tesla is doing the right thing but I think they can go about it in a better way. For example, shift the choice to the user (via an on screen prompt) with strong advice that it is better to restrict their car. Make it clear that if they decide to ignore it then the vehicle will be permanently flagged as such and will be taken into account for related warranty issues and these marks will be clearly visible to potential future owners of this car.

People will think twice when their warranty is at risk and/or it could impact the value of their when they sell it.

What you appear to be suggesting is that voiding the warranty should be a matter of degree, not an either/or situation.

I can’t imagine that any responsible person at Tesla would agree. The engineers would point out that the average person would not have the expertise to make an informed decision about that. Heck, probably even most electrical engineers wouldn’t have sufficient knowledge of li-ion batteries to make an informed choice. Also, the Tesla bean-counters would point out that there isn’t any degree of voiding the warranty; it’s either voided, or not.

Voiding the warranty, or not, is a binary, either/or case, which disallows your suggestion that users should be able to pick their own degree of how much the warranty is voided.

Mil — If you want to void your warranty, go for it. Just don’t expect Tesla to HELP YOU void your warranty.

That’s like taking your brand new BMW to your local BMW dealership and asking them to install some sketchy bootleg ebay aftermarket performance parts that will absolutely void your warranty, and then being surprised when they tell you they won’t install it.

Typically car makers won’t assist you in voiding your warranty.

What Tesla should really have is a Supercharger setting in the car that defaults to slower, from Day 1, but has a selectable option to increase the charging speed.

That helps prevent degradation while ensuring the user has the option of selecting the fastest charge setting when they feel they need it.

Trouble is, the average user will always select the fastest rate available, regardless of whether they need it. And then you are back where we are today. I don’t think the average driver even cares to learn such nuances about their car. They just want to jump in and drive. An EV should be easier to own and operate, not harder!

The average customer doesn’t routinely fast charge with direct current (DC).

Education is the albatross Tesla has had to wear. I think that is most of what’s going on, and I agree what they have done through updates, while in an adverse performance direction, is small. I understand it as limiting inputs (charging to 90KW) and outputs (~10KW drops for P90DL’s, to ~480-500KW). People still freak out. Maybe it is because Tesla freely makes these changes through an “Update” process they boast about.

Perceived or real, most people consider the biggest advantage of Tesla just that – the ability to DC fast charge the car conveniently and often.

The second part nails the concern for me. I don’t really like how much visibility and control Tesla has over a vehicle that someone has purchased and legally owns. And others are downright violently against it. This could hurt Tesla’s image in the long run as they try to sell hundreds of thousands of Model 3s every year.

“…the ability to DC fast charge the car conveniently and often.”

The problem here is that people are not going to agree on what is “often”. The person who makes only 3-4 trips outside the Tesla car’s normal range in a year would have a very different opinion of what constitutes “often” than all the guys who bought their Model S for the purpose of driving from L.A. to Las Vegas three or four times a month.

“What Tesla should really have is a Supercharger setting in the car that defaults to slower, from Day 1, but has a selectable option to increase the charging speed.”

And thus default to increasing the amount of time the average Teslae spends sitting at a Supercharger… thus increasing unnecessary clogging of the system, and making Superchargers less useful for all Tesla car owners?

Nope, Tesla is doing the best thing for everyone by doing things exactly as they are now: Maximize charging speed as far as possible without prematurely degrading the car’s battery pack, and slowing charging only on those cars in danger of premature aging.

Clarkson — The problem only impacts 1% of cars, and there is zero problem with the rest of the 99% of cars charging at full rate.

So the default should be for the 99% of cars that aren’t affected. It only makes sense to limit the 1% of cars that is actually affected.

Temperature thing is nonsense, unless Tesla engineers are total morons. Car won’t charge without the battery pack being in optimal temperature. A short drive to Supercharger would’ve warmed it up / cooled it down, and thermal management will continue to keep the battery in optimal temperature throughout charging regardless of ambient.

Same is true with SparkEV and just about all other DCFC capable EV other than Leaf and eGolf. It seems the article was written by Leaf driver.

“Temperature thing is nonsense…”

That’s odd, I thought you knew a lot about EVs and EV battery packs, Sparky. Apparently I was wrong.

“It seems the article was written by Leaf driver.”

It seems your comment was written by a Tesla basher.

If you think Tesla would dump peak kW of power into the battery while it is too cold / too hot, you must think Tesla engineers are morons. I give Tesla more credit; that’s Tesla praising not Tesla bashing.

In case of Leaf / eGolf, they have no choice since they lack active thermal management. By talking about supercharging in too cold temperature, author of this article is talking about Leaf, not Tesla.

I’m a Leaf basher, tainted by vast majority of my negative experience with EV due to Leaf (ie, waiting almost 30 minutes at DCFC for Leaf charging at 3 kW using 50 kW charger).

Really, Sparky, you’re doubling down on your obviously incorrect assertions?

Let’s look at just one thing you posted:

“…thermal management will continue to keep the battery in optimal temperature throughout charging regardless of ambient.”

Now Sparky, you know this isn’t true. You yourself have posted charts and graphs showing the tapering off of Supercharging a Tesla car. If the battery was “kept in optimal temperature throughout charging”, then there would be no need to taper off the charging until the pack reached about 60% charge.

Contrariwise, you yourself have posted data showing that if a Supercharger starts at maximum power, it will start tapering that off after just a few minutes. In other words, it starts reducing the power to the pack as soon as the pack heats up.

Have the intestinal fortitude to believe your own analysis, dude.

Tapering power is part of TMS. If the temperature is going to go up even with tapering, there’s no point in tapering. In effect, pack will never see unsafe high temperature thanks to TMS: active cooling + tapering.

Article also talks about fast charging in too cold temperature, which is another nonsense. Tesla pack would never be subject to too cold fast charging. Charging power would be used to warm the pack to safe temperature before actual charging would begin.

SparkEV does this, so I assume Tesla engineers are at least as competent. You shouldn’t assume Tesla engineers are morons.

I found with my Roadster that driving at moderate speeds only manages to keep the battery from getting colder. Even after extended driving, the battery had to be warmed using the resistance heater for around 45 minutes prior to any charging.

I’d assume the more modern batteries in the “S” or “X” would self-heat even less in moderate driving, and therefore would need to heat prior to charging.

But that is not what is being discussed here, since my Roadster would not allow CHARGING at ANY rate until the battery was at least 34 degrees F. Driving the car was allowed down to around -10 degrees. Beyond that, the car would self-heat prior to running.

Seems reasonable. Especially with any car they have a guaranteed buy back rate of. I know they cancelled that but I presume cars sold before it was cancelled would still have the guarantee?

This is the bottom line: it’s a new technology business and Tesla is at the cutting edge of it. No-one else charges such large batteries, or charges them at such a high rate. Just think how far behind Porsche are starting with the Mission E. They are struggling to get the car out in the first place and aren’t even close to learning these daily operational nuances. Tesla is pioneering the business.

We have to allow them room to conduct research.

For once, an article has answered the question it raised in a very thorough and factually correct manner, so I have nothing relevant to add.

Kudos to Charles Morris for writing an article showing far more understanding of the engineering principles than we usually find in popular press articles!

Thank you, Evannex!

To me it’s just another side effect of the supercharger “all you can eat” flatrate. With a mandatory fair-use rule e.g. limiting supercharger use to 10% of total charge, it would have been clear to all customers that supercharger abuse is not tolerable, not only but also from the technical aspect.

This problem goes away at busy Tesla sites since when 2 cars are connected to 1 charger bay as is what happens during busy-hours, the charging rate is limited by what the charging bay can put out anyway. If the charging rate is in danger of some cases as being ‘too high, too often’ as illustrated by Tesla’s statement, it rather puts the lie to many commenters here saying it is trivially easy and at little expense or complication to increase the charging rate to 200 kw, 350 kw, 1000 kw, 2000 kw – pick your own number. I would assume, the smaller the battery, the sooner this problem would manifest itself. Those of us with BEV’s with relatively large batteries (my bolt essentially has 65 kwh) and no fast charging can rest assured we’ll never has this problem since the charging rate is always 1/10th C or less. And even 120 kw charging on a hot day isn’t really 120 kw. I would imagine the refrigeration system in an “S” or “X” is relatively large to be able to successfully remove much heat, and therefore the amount of juice actually being put in the battery is only a fraction… Read more »
If anyone is interested, JB Straubel has published youtube videos detailing all of the variables Tesla uses to complexly calculate something as seemingly simple as charging a battery. dozen temp sensors, resistance, cell chemistry, cell age, module, pack, historical life, vibration, air pressure, humidity, and A/B stall power splitting, individual charger rack coupling, ground testing, voltage/amperage control, power grid restrictions, list goes on. Tesla has already been limiting SC power ever since they deployed it. They are simply tweaking the variables. Every time they introduce a new cell, module, pack design they start off with cautious limits, then increase them. Check out the 90d charging graph comparisons on the internet. It sounds like the increased too much for some use cases, and are backing down. I believe Elon and JB said the goal is 500,000 miles to >80% SoC for a pack. That’s an old quote, so they may have changed the goal. The issue for owners is not really that it’s being controlled, but the lack of why it seems slow. And is there something they can do about it, which is possible. Today there is limited info to a user. when it’s really cold or really hot a… Read more »

Tesla should make it more clear that Supercharging degrades batteries. I bet this problem is only for those who live close to a Supercharger and always use it just to save money on their electricity bill. Superchargers are intended for people doing long distance travel and not for everyday use instead of home charging.

I have no sympathy for those who abuse the system and tie up supercharger locations for those legitimately in need. Their warranty should be voided and the warranty should clearly state a maximum number of supercharging cycles to void the warranty.

““This change due to age and usage may increase total Supercharge time by about 5 minutes”

I heared 50% less power?!

“and less than 1% of our customers experience this,” says Tesla.”

Of course, because the batteries are still quite young, also in the meaning of mileage.
Often it seems for me like the Model S/X is not the only car.
AFAIK the Model 3 will get batteries with smaller capacities (at least not the 100kWh) + I will be more affordable, so it will be used more often by commuters who don’t have an other car and if they come home lately, there was a problem with charging over night or some sort of “emergency”…
In other words: All this will lead to more fast charging.

“For example, if a battery is being charged at a rate of 1C, it will reach a full charge in 1 hour.”

*LOL* 1C means like a 22kWh battery charging at 22kW -> 1h for 0->80% (and then much slower, look e.g. at the Zoe price-list).


I really hope the Model 3 cells are better, ive personally tested the 3.4Ah cells out of a tesla pack and theh dropped to 88% capacity after just 100 cycles charging at the equivalent of 50kW (not very fast).