While this has nothing to do with fitness data it is data oriented. My Fiat electric car has given me a new world of data to play with, and as I complete my first year with the 500e, I wanted to share some of the data I have been collecting.
What I learned looking at the data
- The percent charge dashboard indicator is very accurate.
- On average the MPGe indicated on the dash is 17% too high.
- On 1 hour of charging you can drive:
- 3.8 miles if charging at 120V
- 12.5 miles if charging from a 240V TurboCord
- 20 miles if charging from a Level 2 Charger
Each time I charged the car I collected the percentage of charge remaining, the miles driven and the MPGe estimate. When I charged at public stations that provide statistics on the number of kWh charged I tracked that also. The raw data is here.
In trying to look at the accuracy of the charge indicator I needed a known reference to measure against. The only way I found was to use the measurements of ChargePoint charging stations. Whenever I charge the car at a ChargePoint station it will give me an exact reading of the kWh used. I then compare that to the change in the battery charge indicator. The computed kWh is found by:
(ending percentage – starting percentage) * 24 kWh (the battery capacity)
Using this I plot the computed kWh against the measured kWh. Doing this produces:
As you can see the values match very well.
Once I established the accuracy of computing the kWh consumption based on the change in the percentage of the battery charge indicator I could use this to understand the accuracy of the other dash readouts.
Comparing the MPGe (or miles/kWh) estimated on the dash to the values computed, I found that it was the results varies quite a bit. As we can see here the computed MPGe for a given dashboard MPGe, have a wide range.
If we look at the error in each data point and plot that on a histogram we get:
From which I computed the average overestimation of 17%. Even though the dashboard indicator over-estimates the MPGe my actual MPGe after a year of driving was 115 which is higher than the value quoted by Fiat.
When looking at EVSE’s (chargers) they specify the amount of time it takes to fully charge a car. I don’t find this that useful. I often worry that my current charge is not adequate for where I’m trying to go, and I want to know how long it will take to charge to get X extra miles. I found that expressing charge rates in miles of driving per hour of charging to be useful for this. The results above are averages based on 66 partial charges. I did tend to notice that the car will charge slower as it approaches 100% so you can actually get above these rates if you are only partially charging the car.