Test # 4
After not being as successful as I would have hoped on my first time test of the superchargers, I decided to try my best to achieve 170 miles of charge in 30 minutes. I had a trip planned to the Sacramento area and planned to charge at the new Vacaville supercharger station. I intentionally filled up at home to only 110 miles of rated range. I hit a couple of slow points of traffic, and had to drive around Vacaville for a few miles, but I successfully arrived at the supercharger with exactly 0 rated range miles. The temperature outside was 60 degrees Fahrenheit or 16 degrees Celsius under sunny skies
At the supercharger there were two other vehicles charging, but I very carefully selected a charger with a different number. At an eight station supercharger for example, there are superchargers 1A, 1B, 2A, 2B, 2C, 3A, 3B, 4A and 4C. Both 2s share some of the circuitry, and your time to charge will be slower if you are using 2A and someone else is charging on 2B. These stations are not lined up in numerical order, so you need to carefully look at the station labels.
Even from the start, I was not too hopeful as the maximum charge was only 107kW. I stayed in the car and took Iphone recordings of the charging every minute. The following is a chart of my charge. I achieved 150 miles of rated range in 30 minutes, lower than the maximum achievable of 170 miles in 30 minutes.
I suspected like my first supercharger time test, I had arrived at another station that was not 100% operational. In reading the Tesla Motors Club forum, my experience is similar to other drivers. Many of us with 120kW capable batteries, are not often seeing the full 120kW charge. It appears that the new Vacaville supercharger was not running at rated capacity.
After my first test, I thought I would email Tesla to get some clarification on the superchargers and how to use them. I received this response to my questions from the Tesla engineering team that I think clarifies a bit on how the charge is distributed.
1. I assuming here that Vacaville like Buellton and Gilroy have some minor issues on the day I arrived. Please correct me if that is not true as the lower rate could have been that there were two other cars charging at the same time.
The first supercharging test you performed starting at 1/10/14 12:37 PM was nearly ideal, since the battery was at a very low state of charge and the temperature of the battery was just a few degrees cooler than optimum, but it didn’t seem to be the limiting factor. The battery was charged from 7.3% state of charge to 50.5% state of charge in just under 20 min. The maximum power you received from the supercharger reached a peak of about 109kW (351V, 311A). At this time we haven’t figured out which charging location or connector you were connected to, but it does seem like the supercharger was the limiting factor. We know for example that Vacaville 3A and 3B are working at about 110kW instead of 120kW due to some maintenance issues. This is quite close to the original advertised charging rate since the battery started out at 7.3% instead of 0% but the supercharger was also working with 8.3% less power than ideal. Under these conditions with a perfectly working supercharger you could see it’s likely possible to receive 50% of your battery energy (132.5mi rated) replenished in only 20 min, which would leave 10 minutes to recharge the additional 37.5 mi and reach 170 mi. We think that 170 mi in 30 min is achievable and actually beatable given the right situation.
2. Other drivers are reporting that they often don’t get a full 120kW when charging. I think it is great the systems are redundant but can we often expect to see these minor issues at the superchargers? I think most folks think of electricity as either working or not, but the superchargers are dealing with power on such a different scale than in our homes.
Certainly we have some superchargers working at reduced power across the network. We are glad to have this feature which allows some parts to fail without making the entire supercharger stop working, but also realize that customers are paying very close attention to the performance of the superchargers. We have a few strategies for this including traveling supercharger technicians and looking at various design improvements we can make.
3. If I am at station 1A and no one is using 1B but other stations are being used, can I get a full 120kW and 170 in 30 minutes?
As you have explained in your article, 1A and 1B are sharing some of their circuitry. If you can use 1A while nobody is charging on 1B, then you can have all the capacity of the supercharger at your disposal. But as you’ve seen a few times now, it’s possible the unit could be providing less than 120kW due to maintenance or the specific power connection at that location, and there are several factors given by your vehicle can also reduce the charging rate.
4. If I am at station 1A and no one is using 1B, what is the degradation if there is one other car charging, two, three, four, six other cars charging, etc… Is this linear? Is this NP-complete?
1A and 1B can affect each other, while 2A and 2B can affect each other, but 1’s and 2’s do not share any hardware so 1A and 2A are completely independent.
5. if I am using station 1A and 1B is occupied for the entire time, how is my charging effected? How much is this dependent on where the other car is in the charging cycle? If the other car also just started charging, he will be pulling more power. So the best case scenario at a busy supercharger would be to choose a charging “partner” that is almost complete?
You are correct that since hardware is being shared between pairs of charging posts, and the rate of charge generally decreases as the battery of each model S becomes charged, choosing a charging “partner” that is at the highest state of charge, or is more close to ending the charge is a good strategy to minimize your total time spent charging. There is a priority given to the car that has been plugged in the longest out of A or B. As the first car completes charging the second car will be allowed to take more power.
Test # 5
I really wanted to try to get 170 in 30 minutes or better, so on another warm day in California, I headed down to the Gilroy supercharger. The temperature was around 75 degrees Fahrenheit or around 24 degrees Centigrade. I managed to start my first test with zero charge, but at that particular station I quickly realized my charge rate was not pulling anywhere near 120kW and closer to 90kW. I was at one of the original four Gilroy superchargers. I quickly aborted the test and drove around Gilroy to get back to zero.
At Gilroy there was another car charging in the larger bank of stations but far on the other side. The newer set of superchargers do not follow the same expected labeling convention and are simply labeled with numbers. I doubt very much the other car was impacting my charge as my maximum rate was 122kW. I had a small interruption because my charge limit was set lower and had to quickly restart the test. My best estimate was 163 miles in 30 minutes.
I am determined some day to get 170 in 30 minutes, and I am getting quite close as I am 96% of the way there.