Supercharger Time Test

120kW Charging

120kW Charging

I recently went on a road trip throughout California using seven superchargers.  After visits to four supercharging stations, I was not really noticing dramatic improvement with the newly installed 120kW superchargers.  Sitting in the car at the Hawthorne station, I decided at the next three stations to accurately log the amount of mileage I could get in 30 minutes at the next three superchargers.

Before delving into the detailed data I gathered and also data subsequently provided by Tesla, I now feel comfortable writing that I think it is possible with a very empty battery, a 100% fully functional non-busy supercharging station and reasonable weather, I could occasionally charge 170 rated range (EPA 5-cycle) in 30 minutes.

The scenarios where I would envision charging at the maximum rate would be for home to destination trips on boring drives such as Interstate 5 through California with several supercharger stops.  With this kind of driving, one could easily plan their supercharging visits and keep their battery as low as possible.

But I expect to more often be charging closer to 135 miles in 30 minutes as I experienced on my recent trip.  I typically do not just drive on freeways and prefer off the beaten path roads.  When traveling I like to have space and time for the unexpected detour and enjoy the journey.  Keeping the battery at a fuller state of charge for these wanderlust trips will make the trip about the journey not about optimizing the supercharge rates.  So more often, I will likely not be able to carefully plan to have a very empty battery at every supercharger.

The 30 minutes in 170 miles statement currently on the Tesla web page really requires a very empty battery.  Jerome Guillen Tesla VP, WW sales and service responded to my data with the following statement:

“Additionally, that maximum charging speed is valid when you start from a near-empty battery.  Lower still than 18 miles remaining and significantly lower than 40-60 miles remaining.”

In my three station supercharger test, I visited three superchargers and was the only one charging at all three stations in very pleasant California weather ranging from 65 to 75 degrees Fahrenheit.  I arrived at the Buellton station with only 18 rated range miles (15% charge), Atascadero with 63 rated range miles (33% charge), and Gilroy with 58 miles (29% charge).  Tesla did report to me that Buellton and Gilroy were running at less than complete capacity:

“Two of the Superchargers (Buellton and Gilroy) were running at less than rated capacity due to internal components taken offline. There are a series of components in parallel, for redundancy: no offline component will prevent the Supercharger from working, but it will reduce the power out of the Supercharger. In these 2 instances, the max power out of the Buellton and Gilroy Superchargers was 112 kW (not the nominal 120 kW). The Buellton Supercharger was restored to full power on the 20th of December. Work on the Gilroy Supercharger at post 2 has been scheduled for January to avoid causing disruption at the site during the busy holiday travel period.”

The key difference between my results and the 170 miles is that I did not arrive at the stations with a very low battery.  The superchargers can really fill up your battery very fast between zero and 40% full.  After that period, the charge tapers significantly.

Here are my detailed results:

Detailed Data for Time Test at Three Empty Superchargers

Detailed Data for Time Test at Three Empty Superchargers

Tesla supplied the data in the second column “Time of Charge at Max Rate”.  I did not plot my charge on a minute by minute basis.  But the supercharger records indicate that for these three charges, the full power of the supercharger lasted for the listed number of minutes.  For example at Buellton, the car was charging at the 113 kW rate for 10 minutes.

Factors that affect supercharging times:

  1. Initial state of charge
  2. Number of cars charging
  3. Weather
  4. Exact car model (60kW, 85kW, early 85kW with different battery chemistry)
  5. Fully operational supercharging station

Cars with 60kW batteries and some 85kW batteries (built in 2012) will not be able to take complete advantage of the 120kW charge times.  Because of tax implications, I delayed my purchase till 2013 and have a slightly different battery than some of the earliest 85kW cars.  Some of these early owners are not happy that they cannot charge at 120kW.  I think the vast majority of drivers will only be using the superchargers a few times a year.  And for those early buyers the impact of the older battery chemistry will not be that significant:

“For a customer charging from 20% to 90% (more than enough to go to the next supercharger station), the difference in charging time between an early car and a current car is less than 4 minutes!”

The battery itself is a very expensive component in the car.  With Tesla, car owners get regular software updates to the car, and in a year we have seen a lot of nice software improvements.  Asking for dramatic hardware improvements is an unrealistic business model.  I owned a very early Tesla Roadster with plastic knobs and no glove box and was very satisfied with my car and Tesla. I think a little more communication up front on these details will be appreciated by the existing and future customer base.  But having worked in Silicon Valley for many years, I still give Tesla my highest review even with a few missteps here and there.

Tesla has been very helpful and responsive with my inquiries of my charge times.  They pulled my records from the supercharger station and responded with sufficiently detailed data.  In response, they also changed their supercharger web page from stating simply a 30-minute charge with 120kW would give you 200 miles of range (without any footnotes) to now stating 170 miles of EPA rated range (85kWh battery).

I plan sometime in January to drive to the Sacramento area and visit the Vacaville and Folsom superchargers with a very empty battery.


8 thoughts on “Supercharger Time Test

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  2. You state that: “Some 85kW batteries (built in 2012) will not be able to take complete advantage of the 120kW charge times.”

    But this is not true. If you follow the forums threads on TMC, you’ll find there are many of us with 85kWh batteries delivered around April 2013 also have the same 90kW charge limitations (“A” batteries). It’s understandable that Tesla’s continuous improvement program would improve the battery for newer vehicles. But I’m not happy that older cars got “better” batteries.

    • Ken I agree my wording was not the best and is misleading. The thread about 90kW charge times was so large it was almost impossible to follow. Yes, I remember there were folks with cars newer than mine that have lower rates of charge.

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  5. Hi,

    Do you have an S60 or S85? I can’t find the information after searching for a few minutes. It would be so great of you added a picture from the touchscreen while charging. Also I don’t understand your percentage numbers. Did you miscalculate them? If 15.1% is 18 rated miles than 100% is 18*100/15.1= 119 rated miles. There is no Tesla model S with 119 rated miles at 100%. Also if 32.5% is 63 rated miles, then 100% is 63*100/32.5= 194 rated miles. These don’t match. Your 100% rated range can’t be 119 and 190 at the same time. While you are charging you can either display percentage or rated range or ideal range, but not both. What were you displaying? In other words, which numbers on your table are reliable and which numbers are a possible calculation error?

    Can you comment on the weather effect? If the weather is hot, you are on a worse tapering curve. Is that right? How many different tapering curves are there and what heat level do they correspond? Do you have any rough guess?

    Are you absolutely sure there is more than one tapering curve for the same car (your car)? In other words, lets say you supercharge from 15% to 80% in 48 minutes but the same charge takes 39 minutes in winter. This experience would confirm different tapering curve depending on weather. Do you have this kind of experience?

    I have measured 3 tapering curves so far. Here is a picture: but they are from different cars.
    On he following Google spreadsheet; on page “STC Process” there is more info:

    • I have an S85. I think the confusion is I did this test with an early version of the software. Back then the % listed included the extra reserve below zero miles, that’s why all the numbers were skewed up. I also unfortunately have deleted all those screenshots I took. The current percentages start at zero miles; below it was probably like -25 miles / 5kw (I’m just guessing here).

      Weather – all my tests I made sure I was in consistent weather 70 degrees approximately. Colder weather the battery adds energy to heat itself up; hot weather to cool itself down. If the climate control is on, your also pulling energy for that.

      I did charge in 32 degree weather once and it definitely took longer. But it was also very windy.

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