My First 220V Public Charging Experience
I've always charged my Nissan Leaf using the 110V trickle charger that comes with the car. Recently, through my own forgetfulness, I needed to use a 220V public charging station, and my impression of the experience is mixed. I didn't have any problems with finding and using a charging station. That was easy. But I was surprised by what it did to my range.
Before getting too far into it, let's back up to the night before. I was coming home from work, and pulled into the driveway with 20% charge left. I remember thinking that I had to plug the car in because it was unlikely that I would make it to work and back the next day on that little charge. Then I remembered that my wife and kids were away at violin camp (those lucky ducks), and I was the only one left to bring the mail in so I better do that. That first thought about charging flitted right out of my brain. I parked the car, walked down to get the mail, and walked right back up into the house, leaving the Leaf unplugged in the garage.
I kid you not, my first thought the next morning when I woke up was OH CRAP! I forgot to plug my car in! Why is it that you vividly remember important things when it's far too late to do anything about them? Anyway, I rushed out to the garage in my skivvies to check, and sure enough, the car was distinctly missing its umbilical cord.
As I was getting ready for the day, I ran over options in my head. I could attempt to make it to work and back on the charge left, but it would be tight. The Leaf tends to lose charge more slowly at the end of the range, and I could drive more conservatively and probably be fine. But I would be much more comfortable if I could charge up at work. Luckily, I had gotten a couple of ChargePoint cards with my new Leaf. I had never made the effort to sign up with ChargePoint when I had my previous Leaf, but the salesman tipped me off that MG&E was doing a study of EV owners so I could charge for free if I signed up for their program.
I checked on the ChargePoint.com site, and there were a couple charging stations in a parking garage within easy walking distance of the office. It was time to give public charging a try. It's not that I was against it; I just never had the need to use it before and charging at home is so much more convenient. After checking the website one more time to make sure the charging stations were available, I was on my way.
Finding the stations was easy, but the first one I found was located in a handicapped parking zone. I'm not sure EV drivers and handicapped drivers are that well correlated right now, so I'm a bit confused on the utility of that setup. Looking a little further up the ramp, I found another station. There was a Ford Fusion PHEV plugged into the 110V trickle charger, but the space next to it was free. I pulled in, plugged in the 220V cord, and swiped my card. The car started charging without a hitch. Cool beans, I thought. I'll come back during lunch and see how it's doing.
When I came back, the car had finished charging to 80%. The meter showed that it had charged for exactly 4 hours. With the 3.3 kW charger, that would have been 13.2 kWh of charge, which is a bit low for charging from 12% to 80% based on my charging log. Normally I get about 4.2% per kWh of charging, which means it should have taken 16.2 kWh to charge that much. Still, I hadn't expected the car to be done charging when I went to check on it, and I didn't think much of the discrepancy. I was quite pleased as I drove over to my normal parking spot by the office and finished out the afternoon at work.
On my drive home I noticed the charge level dropping faster than normal. After only three miles it had dropped 6%. That was a little disconcerting. By the time I had run some errands and returned home, it had dropped 23% in 15 miles. Somewhere in the neighborhood of 15-18% would have been much more typical for that distance. Indeed, I had driven the same route under the same conditions a couple days earlier and only dropped 16% charge on that trip. What was going on?
I decided to not charge that night and see what happened on my drive the next day. I still had 57% charge remaining, so I wasn't too worried that I would get stranded. As it turns out, the battery behaved pretty normally from then on, and I drove 40 miles on 38% of charge before charging up again with my trickle charger. I drove the same 15 mile route again at 80% charge, and this time dropped 20%—not great, but better. By the next charge things were totally back to normal.
So what the heck happened to my battery in the 80% to 55% range of charge with the 220V Level 2 charger? I'd heard other Leaf owners claim that they lose charge faster at the top end of the range, and as they reached 50% and below, they could go more miles on the same decrease in charge. I always wondered why I didn't see something similar with my Leaf. My charge level has always decreased very linearly with miles until the very end, even the few times that I charged to 100%.
Here's what I think happens with the different chargers and the battery. You know how when you pour a beer from a tap with perfect pressure, you can easily fill the glass all the way up, getting beer within an eighth of an inch of the rim and a small amount of head? It's beautiful. The charge from a trickle charger is like that. The charge is flowing into the battery at a slow enough rate that the Lithium ions can be efficiently packed within the chemical structure of the electrodes, resulting in a nice, strongly charged battery over its full range.
Now think about what happens to a beer tap that has too much pressure in the lines. The beer pours too fast and gets churned up in the tap and the glass, resulting in lots of foamy beer with more empty space and less tasty beverage. The L2 charger is more like this because it's dumping charge into the battery much faster. The ions get churned up more, the battery heats up more, and the resulting charge is not as strong as with the trickle charger. You end up with a lot of head in your battery.
Of course, this is not really what's happening in the battery. The electrochemical process is a bit more complicated than that. It's an analogy, but a useful one. The charge at the top end of the range is definitely not as strong, or the battery is not as efficient in that range from an L2 charge. However you want to think about it, it's pretty clear that for the same energy usage, initially the charge level goes down faster when the battery is charged at 220V.
Having the public charging station available was great in this situation, but I wouldn't rely on L2 charging stations for daily charging needs. If you want to get the most out of your battery, you should be charging with the trickle charger whenever you can. It's better for your battery's health, and you'll go farther on a charge. I know I'll be sticking with the trickle charger for my Leaf. Happy charging!