Wesley's Tool-Box

I keep a detailed log of my Bolt EV drives to gain insights to the questions I wanted answers to. One of them was this feeling that the drivable range was getting lower on a cold day despite the fact that I drive without having the heater on. Since my EV driving habits became consistent after driving for about half a year, I decided to analyze one full year's of driving from February 2019 to January 2020 to spot a trend between the ambient temperature and the car's efficiency ("fuel economy").

The results above speak for themselves. Even if you don't use a heater, the car's efficiency will certainly drop as the outside air gets colder. This is largely because the air itself becomes more dense, increasing resistance. Using a heater will impact efficiency on top of this. Meanwhile, driving at an average trip speed of about 50 km/h (30 mph) yielded about 1 to 1.5 km/kWh better efficiency than at about 80 km/h (50 mph). Again, less air drag meant better outcome.

If you want to know how the data points were chosen, please read on.

My two most common driving patterns happen on expressways and intercity roads. The former are usually for the long distance family trips. The latter are used in the routine errands between Naju and Gwangju for groceries or movie-going. Downtown driving is done mostly by my wife and there are no records of time or temperature, so they were not analyzed.

As all trips start and end within cities, the most significant and fastest road type used must take up at least 75% of the entire distance for a sample to be representative of a type. And to minimize impacts of traffic jams, average speed of a trip had to be at least 70 km/h for expressway and 40 km/h for intercity. Driving under rain or snow were also out in order to avoid other weather factors. Additionally, expressway trips had to be at least 100 km long and the intercity trips had to have no significant deviations from the most common 22 km-long route I take. Use of heater was completely avoided, while air conditioning was used very sparingly if needed and took up less than 1% of the battery consumption.

In the end, 108 samples spanning a total distance of more than 10,600 km were chosen out of the 27,000 km total distance covered during the period. The real life driving conditions did still create some variability, but the trends were clearly present. I can now use this analysis to better plan for future trips.

- or, why do I get "too much power" error with my drive and how do I fix it? -

With iOS 13, native support of USB external storage was introduced to iPhones. Files stored externally can be accessed from the Files app included in the OS. Other apps can do it as well if it can connect to this Files app. Sadly, modern iPhones' external port of choice is Lightning, which means you either buy a storage device with a Lightning port or get an adapter to connect a USB device. This is where things get complicated.

I bought a Lexar MicroSD to Lightning Reader (part # LRWMLBNL) more than three years ago. It connects directly to the Lightning port and I can open files using a dedicated app. Apple MFI certified storage can supposedly work with the iOS 13's Files app, but that wasn't the case here despite the certification. Adding insult to injury, its app had not been updated in more than two years - the screen resolution and the file sharing functions were outdated. I needed a different solution.

Apple sells many types of USB adapters, one of which is the Lightning to USB Camera Adapter you see above (US$29). It can be connected to a camera for transferring photos and videos, hence the name. Other devices could be plugged in as long as the OS recognizes it, like keyboard, MIDI equipment, or Ethernet adapter. iOS 13 expands this to general storage and mouse.

So I bought this adapter expecting that any low-power storage devices like USB flash drives and memory card reader could be plugged in directly for my file management uses. Boy was I so wrong. Of the multitudes of flash drives and card readers I own, all of them, save for one, caused the "too much power" error you see here. This was bizarre because they shouldn't consume enough power for this to appear. There had to be a reason and a way around this, so I decided to dig in.

On June 1, 2019, my Bolt EV had its first birthday. As it moved around more than 24,000 kilometers, I kept a detailed log to make continuous analysis of the car's conditions and characteristics. Many people including myself are interested in how an electric vehicle fares over the years, so this should provide some good insights.


I used to drive around 1,000km per month on average before getting a Bolt EV. But you can see that it has doubled since. Cheaper fuel costs was a major factor (less than 1/10 that of gasoline), with some "new car curiosity" thrown in. Efficiency suffered in summer and winter due to the extreme temperatures, which affects battery performance and climate control use. Largely speaking though, fuel economy had been improving because I've been adjusting my driving style to be smoother in order to go further before recharging. This proved to be helpful in long-distance trips.

The three lines at the bottom of the graph depict the battery capacity as calculated by various means. The battery degradation is a major concern for many, so I kept track of this closely as well. Going by the reported values, my Bolt EV originally had 58.63kWh of usable capacity (65.14kWh raw) and had 55.98kWh usable (62.20kWh raw) by 24,099.4km. This is a degradation of 4.52%. Assuming linear progression, the battery would have exactly 70.0% of capacity left after 160,000km. This is in line with the industrial average warranty and shows that my Bolt EV's battery is in a reasonably good condition so far.

So why did I have three lines here? It stems from the fact that the Bolt EV doesn't tell you its battery health outright. One of the Parameter ID (PID) readings from the OBD-II port (#2241A3) correlates directly with battery capacity, but interpreting the number has been up for debate. So I decided to find an interpretation that I was comfortable with.

Korea's Ministry of Environment (ME) has been aggressively expanding its network of DC Fast Charging (DCFC) stations throughout the country, with more than 1,100 new chargers being installed and operating in pilot mode since early this year, accounting for nearly 40% of total. I was fortunate enough to live close to one of such stations (and a 100kW version at that), which let me test out the charging characteristics of my Bolt EV without costing me a dime.

Although the chargers are supposed to switch to normal paid operation starting mid-May as the firmware updates are deployed in a staggered manner, I was able to observe what the close-to-ideal charging situation would be before this happened to the nearby charger. The following graphs plot the data I recorded.

It should be noted that the ME chargers have either a 40-minute or a 41-minute time-out. This was done to prevent a single person from hogging the charger for too long. Therefore, I did these charging sessions during the early hours in the morning when no one else was around in order to have as close to continuous charging as possible. This led to a bit of "blips" in the graph (64% - 41st minute / 88% - 82nd minute), but it did not affect the overall picture that much.


Charging speed is largely dependent on the battery's State of Charge (SoC), so it helps to see the data as its function. As you can see, the charging current remains more or less constant at a given "zone", then drops down a step after a certain level of SoC is reached.

The actual charging power will slowly increase in a zone because the charging voltage rises. This is a direct reflection of the the voltage of the battery cells themselves, which rise as the energy is filled up. The 288 cells are arranged as 96 groups in series of 3 cells in parallel, so there would be nearly a 100-fold difference between the cell voltage and the charging voltage.

Another major factor in the speed is the battery's temperature. Assessing multiple charging sessions, it became apparent that it should be around 24 to 27°C at the beginning in order for the Bolt EV to enter maximum current (roughly 150A before 50%). If it's colder, it will start out a bit slower, then ramp up to 150A as the battery heats up to about 24°C. If it's too hot (more than 30°C), the charging current caps to 95A to prevent overheating.


For someone who's waiting for the car to fill up, the time it takes for each of those charging zones is also quite important. So this is a graph showing the same data, but plotted as a function of time. Key numbers are distilled into the following table.

To make a quick comment about the displayed and actual SoC, the two meet at around 75% mark, with the displayed getting larger above and the actual getting larger below. At the extremes the two differ by about 4%, showing the buffer for preventing over-charging or over-discharging.

The power and current values are as seen from the charger. The values from the vehicle's subsystem were about 96% of these, showing the losses inherent in the charging process. Further losses occur as the energy ends up inside the battery, so we end up with a bit more than 10% loss in total.

The advantage of using a 100kW (500V x 200A) charger is apparent only for the first 50% of charge, and is not a huge one at that. 50kW chargers in Korea supply either 110A or 120A maximum current, so the charging speed of 1.06%/minute should extend to below 50% SoC when you use them. Hence, you'll shave about 10 minutes off the session with a 100kW charger instead of a 50kW one if you're starting from 10% charge left. You can thank Bolt EV's highly conservative charging regime for this.

So what's the takeaway from all these information? Probably a good basis for forming a charging strategy during a long-distance trip. To minimize charging times, you should keep the car's SoC between 10 to 20% minimum and 70% to 80% maximum, with each charging session lasting about an hour at most. The last 25% alone takes an hour to charge, so a full charge is not a good strategy unless you're going to a place where the chargers are sparse. Meanwhile, the ambient temperature during charging should be as close to 20°C as possible. Hopefully, you can find a charger within a building or under a shade.

When I have to charge my Bolt EV in the dark, such as outdoor charging in the middle of the night, the lack of illumination on the charging port makes it hard to plug the charging cable correctly. I saw a video about fixing this with an LED strip, so I decided to try it myself as well. I bought an LED dog collar online for about six bucks (KRW 6,900) that would get the job done.


The collar had a Micro-USB port for charging, and came with a short cable to facilitate it. After I finished charging it (the indicator turned green, from red) I went down to the parking lot.