2013 Tesla Model S: How Quickly Does a Supercharger Charge?
October 7, 2013
A couple of months ago I made a lame attempt to measure how quickly a Tesla Supercharger dumps electricity into a 2013 Tesla Model S battery. I was hoping to figure out how much downtime to expect on a long trip because I'm planning to take our Model S on my annual year-end holiday trip to Oregon as soon as the Supercharger network expands and connects the dots.
But my visit to the Hawthorne Supercharger at Tesla HQ was a spur of the moment decision. I hadn't really worked out a procedure before I arrived. And my results were inconclusive because of the comings and goings of other cars charging in adjacent spots.
Since then I've worked out a simple method, and a couple weeks ago I tried it on a short weekend trip to Monterey. The site was the new Supercharger in Buellton, California, and I was able to get clean data because no other Tesla vehicles were charging while our car was there.
We arrived with 38 miles left on the range meter and promptly plugged the supercharger into the car. I immediately took an initial screen grab of the Tesla app with my iPhone then walked with my wife to a nearby restaurant.
From the comfort of our booth I took additional screen grabs every 5 minutes while we had a relaxing lunch. The app displays range, voltage and charging amps, everything I'd need for analysis later.
Charging commenced at 10:49 a.m. but I took another grab at 10:50 a.m. so it'd be easier to keep track of the 5-minute intervals. Besides, charging ramps up gently in the first minute or two, so an extra data point wouldn't hurt.
The app reports charging speed in "miles per hour" and its peak reported rate of 291 mph came at 11:00 and 11:05 a.m., exactly 11 and 16 minutes from the start, respectively.
But 291 mph turns out to be a little misleading. For one, it's an instantaneous figure that you can't use to predict when the battery will be full. This rate isn't sustainable for more than a few minutes. The charging rate starts off high and then tapers off.
I divided miles added by minutes passed and got 273 mph at 11:00 and 281 mph at 11:05. Theses cumulative numbers trail behind the instantaneous ones reported by the app because of the slow ramp-up in the first minute.
In the end, our Tesla battery reached a full charge (normal range mode) in 59 minutes, during which time 193 miles of range were added. That's an overall average charge rate of 196 miles per hour, and we pulled out of the parking lot with 231 miles on the range meter.
Here's what my data looks like graphed out. The x-axis is time in minutes and the y-axis represents many things. The 0-300 scale stands for charging rate in "miles added per hour waiting" if you're looking at the blue line, it's good-old driving range in miles when looking at the green line and it shows kilowatt-hours added per hour if you're looking at the red line.
Yes, I know that "kilowatt-hours per hour" is longhand for kilowatts. But the volume of an EV battery, its "gallons," if you will, is given in kilowatt-hours (kWh) and this exercise seeks to understand how much time it takes to refill the tank. Kilowatt-hours per hour seems like the best way to communicate what's going on here even though your math teacher would mark off points if you failed to simplify kWh/h to kW.
Our red line is the best one to follow if you want to see how a Supercharger interacts with the battery. As we saw on the app, the peak charging rate occurs about 10 minutes in, after which it rolls off. The max rate at the top of the curve is 89.9 kW, which makes perfect sense because the Buellton chargers have big "90 kW" stickers on them.
Tesla boasts of 120 kW chargers on their Supercharger Web page, but they must be a work in progress. I've visited five Supercharger locations, two of them open less than a month, and have yet to see a 120 kW unit. They'll undoubtedly be faster, but I expect the roll-off curve will look about the same, albeit hiked up by some 33 percent.
The "miles per hour" blue line is nothing more than Tesla's attempt to restate the red line in a less nerdy format. And it truly is a handy way to think about it. A Tesla Model S charges at 3 mph on 120V home current, 18 mph on our Level 2 Chargepoint back at work and something like 50 mph on our new Tesla HPWC. Yeah, this 90 kW Supercharger is fast, and the 120 kW ones will be even faster when they finally arrive.
For now, I'm assuming I'll have 90 kW Superchargers for my planned trip north to Oregon. If they're spaced 200 miles apart, I'll need to plan on one hour of downtime for every 3 hours of driving, which won't disappoint my wife and kids one bit.
I can cut that down to 40 minutes if the Superchargers are spaced closer together and take full advantage of the fact that the first two-thirds of the charge time delivers 80 percent of the juice. No use waiting for the bitter end if the slowest 20 percent of the charge isn't strictly necessary to get to the next Super-oasis.
Dan Edmunds, Director of Vehicle Testing @ 9,271 miles