Good points.
Two years ago I saw JB give
this talk during which he showed this slide:
http://www.teslamotorsclub.com/attachment.php?attachmentid=2931&d=1317772965
Concluding that most the time spent charging was using the MC120 (not called the spare connector) and thus 120V, 12A was good enough for most folks. Can anyone remember why this data might be biased?
Depending on when the data was collected, it may have only included the first 200 owners, which I'm sure would skew the data because all of those Roadsters included an HPC, and I'll bet that group has different demographics than the larger owner community. I'm a little surprised there isn't a bigger spike at 40A for all the Roadster owners who saved half the cost of an HPC by getting an MC240 or UMC for charging in their garage and on the road. That does make it look like the data is exclusively or mostly from the very early Roadster owners.
Regardless, the data has very limited utility. Data doesn't lie, but people can easily draw wrong conclusions from it.
The chart tells us nothing about how any individual owner charges their car. It also only shows how people charge given what the Roadster allows, the cost of the various charging units, the state of public charging infrastructure, and how those together limit what's practical and convenient.
From the chart, it's easy to conclude that about half of Roadster charging is done with a 70A HPC with the car set to take all 70A. Does that mean people need 70A charging in their garage? Definitely not, that's just what happens if you buy an HPC, throw it on the wall and plug the car in without thinking about any possible benefits of charging at a lower current setting. However, some of the 70A charging is happening on longer road trips where 70A is critical. That chart doesn't give us any idea how often owners would benefit from even faster charging. It also doesn't tell us how often the Roadster gets left in the garage because of a lack of available public charging at sufficient rates to not be a huge pain.
The chart shows a big chunk of charging at 120V/12A. How many owners were satisfied with 120V charging? What portion of that is because people were pissed that Tesla changed the HPC from included in the base price to a $3,000 add-on? How many owners were waiting for the MC240 or UMC be become available? What portion is due to owners not having access to 240V where they park their car? What portion of that is people going on
road trips and getting by just fine on 120V charging?
We got our LEAF two weeks ago and just got our J1772 charging station installed and inspected today. We've been charging on 120V and it's been totally adequate. It would be even easier with the Roadster where I could do my normal 20-to-40 mile daily driving and get charged overnight. If I do a long 150-mile drive, I can still add 40 to 50 miles of charge overnight and have plenty for typical drives until I build back up to a full charge over the next several days. Does that mean 120V would work for every Roadster owner? Definitely not.
To be clear, I'm really disappointed that the LEAF has an anemic 3.3 kW on-board charger. I think it's stupid they didn't max it out at the full 19.2 kW that the J1772 standard supports. With that, you could charge a LEAF faster than a Roadster from just a simple, cheap Level 2 station.
I think it's much more interesting to look at the charging behavior of a single owner, so how about me? To create the following chart, I used the new data aggregation feature added by my log parser that RichKae is using to collect data for his
battery longevity study.
The above chart shows the number of hours spent charging at different current levels, with 120V showing at half the amperage, including time spent with the current tapering off near the top of a charge, over a period of 2 years and 19,000 miles. If you want to play along, look at the chart and see what you can tell about how we charge our Roadster. Below, I'll tell you what the chart means and what it doesn't say.
We used to charge at 40A at home because that was more than fast enough for overnight charging while staying away from low current levels that are less efficient, and it reduced the load on our panel. We've owned a RAV4-EV since 2008, and we generally set timers so we don't charge both at the same time, but lowering the Roadster's current level to 40A means we're using less than 70A even if the Roadster and RAV are charging at the same time.
After I did my
analysis of charge rates and efficiency, I concluded that charging at 32A had nearly the same efficiency as higher current levels, was still plenty fast, and further reduced the load on our panel, and was maybe a tiny bit nicer to the battery pack.
In all this time, I've only charged our Roadster at home at 70A once, for the charging efficiency study. (We have used it to charge the Roadsters of friends passing through town on long trips, our quiet contribution to charging infrastructure, but that's not reflected on the chart.) So basically, the 70A charging is all on road trips.
But the spike at 70A only tells part of the road trip story.
Some of the 40A charging is on the road, some of which was fine at 40A getting us charged while we did something fun, some of it was painful, killing time at an RV park.
The 70A spike doesn't tell you that driving from Seattle to Portland used to be painful, requiring staying in the right lane to do 55-60 mph while dodging the big trucks. That drive got so much more pleasant when we got an HPC installed at the midpoint of the drive at the Burgerville in Centralia. Now we can blast down the road at whatever speed is appropriate, pop into Burgerville for a quick bite and 20 minutes of charging, then cruise the rest of the way to Portland with no SOC stress. With a bit longer stay, we could even do the drive comfortably with a standard mode charge.
The charts says nothing about how adding a 70A HPC in Ellensburg made the 310-mile drive from Seattle to Coeur d'Alene, Idaho, very doable with just a long lunch break partway through the drive. It would be even better with another charging opportunity between Ellensburg and Spokane.
The charts also says nothing about all of the road trips we just don't even consider in the Roadster because of charging stations we don't have. If we want to do a drive like that, we need to rent gas-burner. Tesla seems to think the range on the Roadster is so large that no one needs to charge away from home. That's true for most people's daily driving, but it's just not true if you want an electric car to completely replace a gas car.
The Roadster is not a great car for long drives. The ride is rough and noisy. The passenger doesn't benefit from the fun driving factor, making the car less suitable for long drives with someone else. I assume the Model S will be much better as a car, especially for the passengers, so road trips will be even more constrained by charging infrastructure. Tesla has to get this right, and they won't get it if they just look at aggregate Roadster data and ignore what Roadster owners tell them we want.
I think the 10 kW on-board charger option is dumb. Although most everyone will be totally happy with 10 kW at home, especially with the big battery pack that can handle occasional long drives and still be fine for the next drive even if not fully charged the first night back home. The Model S seems like it will be a great road trip car, even with base 160-mile battery. You only get the advantage of the big battery once per day, after that it's all about charge rate. Tesla will not be able to cover the whole country with quick chargers along the route to every small isolated community where people have friends and relatives they want to visit. For those trips, owners will want the maximum charge rate possible and it will always be easier to fund maxed out Level 2 chargers than DC fast chargers at strategic spots. It'll just make owners mad if they get the 10 kW on-board charger and then want to drive somewhere not covered by Tesla's promised fast charge network.
Actually, seriously. I also think that SAE should consider using Tesla's connector, they don't have a backwards compatibility problem. I'm sure the optional CHAdeMO ports on the Leaf could also be retrofitted, or at least replaced, with Tesla plugs. Not sure if that has a better chance than a snowball in hell, but the Tesla connector appears much better, so I think that's the direction to take.
