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2018 Bolt EV Premier
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Discussion Starter · #1 ·
My Bolt EV reached the 1 year milestone a couple of days ago, so I gathered up all the data I've been collecting over all these times and made some graphs and analyses.

First of all, the car has been driven for 24,099.4km (14,974.7 miles) for its first 365 days. It's not quite as extensive as some, but I used to only drive less than half that per year when I had ICEVs. I would like to think that it's a nice "average" sample as the warranty goes for 8 years / 160,000km (100,000 miles) and that means 20,000km per year.

Anyhow, I have an OBD-II port scanner and I've been logging some key PID data every time I take the car for a spin. Two things were in focus - fuel economy and battery health. The main analyses were posted on my blog, but I'll make some key comments about it here.

http://tool-box.info/blog/archives/2791-Assessing-one-full-year-of-Bolt-EV-driving.html



Fuel economy part is more or less expected. I had dips in summer and winter, but overall I've been honing my driving techniques and things have been improving in general. My personal goal is to get a minimum of 7.0km/kWh (4.35mi/kWh) even on highway driving and it's been working out fine so far.

Battery capacity part is interesting. As many of you know, there had been a debate on interpreting the PID 2241A3 numbers. My initial take was to multiply by 0.035 for the raw capacity, then multiply that by 0.92 for the usable capacity. The rationale was that the raw PID number was the electric charge in 0.1Ah increments (e.g. 1760 = 176Ah), so you'd multiply the nominal voltage for the raw capacity. Then, there was that Reddit post that indicated that GM put a 4% buffer on top and bottom, so that the actual usable capacity is 92% of raw. So that's where the 0.92 multiplier comes in.

But now I have one year's worth of data that can be used to revise these numbers as needed.



This shows how the Displayed SoC and Raw SoC are related based on all my data points. It seems to be more or less a quadratic curve, and there's actually a 5% buffer in each extreme, not 4%. So the multiplier should be 0.9 instead.



Now, I need to make sure that I'm not just guessing the battery capacity without any basis in reality. I need to know what the car thinks of it. That's where the orange and green lines come in. Here's a snippet from the blog:

In order to infer what the car thinks of the battery capacity, I need to see how much the battery charge drops after a certain amount of power use. The car's dashboard shows the battery's State of Charge ("Displayed SoC") in 5% steps. MyChevrolet app and OBD-II PID #228334 are more accurate - 1% and 0.4% steps, respectively. Meanwhile, the infotainment screen displays the energy spending in 0.1kWh steps. Putting these two together, you get the orange "Disp. SoC-based Capacity" line. If you use the raw SoC data from OBD-II PID #015B instead and multiply the result by 0.9, you get the green "SoC-Based Capacity" line that nearly matches the orange line.
The 0.9 multiplier does its job well with the two lines, so I need to make the blue line work with it as well...

Nominal voltage of a lithium polymer battery is 3.7V and there are 96 packs in series, so the resulting voltage comes to 355.2V.

1,751Ah x 355.2V = 621,955.2Wh ~= 62.20kWh

This would be the raw capacity for the value of 1,751, and the usable capacity would again be multiplied by 0.9, resulting in 55.98kWh. Data derived from this calculation shows up as the blue line, or "Reported Capacity". You'll see that this fits the orange and green lines pretty well, but in a steadier manner. So this is my interpretation of the battery capacity data from the OBD-II PID.

PID #2241A3 x 0.03552 = Raw Capacity
Raw Capacity x 0.9 = Usable Capacity
So that's it. Based on these assessments, my battery health is...

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.
As for the battery cycles, here's the graph.



I'm trying to recharge when there's about 10 to 20% left, and charge to 100% most of the time. It's been working out alright.
 

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"Fuel economy part is more or less expected."

Fuel economy? I believe that is totally wrong as the Bolt does not use any, so the "economy" is infinite.

It better to use "energy" instead as all vehicles need a form of energy to move.
 

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12/16 build, 2017, white LT
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"Fuel economy part is more or less expected."

Fuel economy? I believe that is totally wrong as the Bolt does not use any, so the "economy" is infinite.

It better to use "energy" instead as all vehicles need a form of energy to move.
Since well over half of all US, and global, electricity is still produced by fossil fuels...coal, natural gas, and oil

https://www.eia.gov/energyexplained/images/charts/electricity-generation-by-major-energy-source.png

https://en.wikipedia.org/wiki/World_energy_consumption

I find "totally wrong" to be totally wrong. :)
 

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Since well over half of all US, and global, electricity is still produced by fossil fuels...coal, natural gas, and oil

https://www.eia.gov/energyexplained/images/charts/electricity-generation-by-major-energy-source.png

https://en.wikipedia.org/wiki/World_energy_consumption

I find "totally wrong" to be totally wrong. :)
Yup, where I live my fuel economy would be miles per lb of coal burned. Even when looked at this way with production efficiency, line losses from transmission, transformer losses for voltage step up and step down, I still use significantly less fossil fuel in my Bolt than I do in my Miata.

Keith
 

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Improper terms will be used for quite some time. We still even compare our cars power to horses... People in EV's will talk about hitting their gas pedal and filling up their tank with electricity. It still makes me cringe when people don't know the difference between a kW and kWh.
 

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2018 Bolt EV Premier
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Discussion Starter · #6 ·
"Fuel economy part is more or less expected."

Fuel economy? I believe that is totally wrong as the Bolt does not use any, so the "economy" is infinite.

It better to use "energy" instead as all vehicles need a form of energy to move.
Good thing that you brought it up. I used "Fuel economy" as a general automobile term since that's a widely accepted concept. Forgive me for using an outdated word in an EV forum.
https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles
https://www.fueleconomy.gov/feg/Pow...2017&year2=2018&vtype=Electric&srchtyp=newAfv

You can consider "fuel" in the EV as "electricity" here as that's the equivalent energy source. Still, I do agree that the term "fuel" should be replaced with "energy" eventually. Unfortunately, "energy economy" means something different altogether. Perhaps "energy efficiency" would be used in the place of "fuel economy" for the general public in the long term.

Terminologies aside, I was wondering how everyone else's battery was doing. Folks over in the Korean forum thinks mine's degraded a bit more than expected.
 

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I wouldn't worry about terminology much anyhow. The gas pedal on modern cars doesn't control the flow of fuel anyhow, it controls the airflow (which is what it throttles, hence throttle). The computer injects fuel based on how much airflow you've allowed into the engine.

People that know about energy conversions and efficiency ratings will get what you're talking about, and those that don't never really had an interest to know anyhow.
 
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