I have been keeping a log of all my runs on my board, which is using my own motor controller. I have been logging gps info, date, travel time, travel speed, # of teeth in motor gear, battery pack configuration, mAh/km, Wh/km and average power over the runs. Here’s a link to the google sheet with all the results (https://docs.google.com/spreadsheets/d/1eorvXba_T8MIPB3ofDTwA8SjOiL4x7r-A7Iy1rNPU9M/edit?usp=sharing), select the “Gen2.1 deck” sheet from the bottom of the page.
I wanted to test the ratio of travel speed and energy spent per kilometer, so I decided to do 3 runs without any kind of duty cycle limitation, AKA full speed runs and then do another 3 runs with a 70% duty cycle limit. My battery pack is a 6S4P configuration made with LG MJ1 cells.
So in theory, with the 70% duty cycle limit the board should only go about 70% the speed than without the limit or simulate the motor seeing only a 4S battery. This test was meant to actually see how the results behave.
I have this benchmark route that I ride when I want to see how a board behaves over long distance. It is a there-and-back route, which means environmental effects such as wind have lessened effect and overall the terrain averages a flat plane (uphills become downhills on the way back and so on…). The route doesn’t have any lights and is generally a very quiet piece of road. This allows me to keep my duty cycle at the maximum for about 99% of the run.
After I come home I then let the battery rest a bit and then charge it with a RC charger in balance mode and log the charged capacity and then interpolate the other variables from that based on the travel time and distance.
Results are: non-limited runs: 23.1 km/h avg; 13.1 km; 521 mAh/km; 11.6 Wh/km; 267 W avg power 23.1 km/h avg; 17.0 km; 509 mAh/km; 11.3 Wh/km; 261 W avg power 23.0 km/h avg; 18.0 km; 506 mAh/km; 11.2 Wh/km; 258 W avg power
85% duty limited runs: 20.5 km/h avg; 13.0 km; 445 mAh/km; 9.9 Wh/km; 203 W avg power 20.6 km/h avg; 14.5 km; 432 mAh/km; 9.6 Wh/km; 198 W avg power 20.4 km/h avg; 17.0 km; 422 mAh/km; 9.4 Wh/km; 191 W avg power
70% duty limited runs: 17.7 km/h avg; 13.0 km; 356 mAh/km; 7.9 Wh/km; 140 W avg power 17.5 km/h avg; 13.0 km; 400 mAh/km; 8.9 Wh/km; 156 W avg power 17.3 km/h avg; 18.0 km; 374 mAh/km; 8.3 Wh/km; 143 W avg power
Averages: non-limited: 23.1 km/h; 512 mAh/km; 11.4 Wh/km; 262 W avg power 85% limited: 20.5 km/h; 433 mAh/km; 9.6 Wh/km; 197 W avg power 70% limited: 17.5 km/h; 376 mAh/km; 8.4 Wh/km; 146 W avg power
Conclusions: Comparing the 70% duty limit to the non-limited results we can deduce some things.
23.1 km/h * 0.7 = 16.2 km/h; I went faster at 17.5 km/h, which I think can be explained by lower voltage droop across the battery, because lower continuous current and the non-linearly behaving aerodynamic drag (relatively lower drag at lower speed).
512 mAh/km * 0.7 = 358 mAh/km; I spent a bit more capacity per kilometer with 376 mAh/km, but I believe some of this can be attributed to the cold temperature, especially on the latter 2 duty limited runs when it was almost below freezing and most likely was if wind chill would be factored in. Taking a look at the LG MJ1 cells’ datasheet (https://eu.nkon.nl/sk/k/Specification%20INR18650MJ1%2022.08.2014.pdf) they spec the temperature effects on the battery the following:
I’m not 100% sure, but this might have had an effect on the result. Although it still shouldn’t cause the cell to use extra energy. Or maybe it was because I did go a bit faster when comparing the average speeds then what was predicted and that’s what caused the extra energy expenditure.
11.4 Wh/km * 0.7 = 8.0 Wh/km. 8.4 Wh/km This result follow the same conclusion logic as the mAh/km one, but clearly shows less energy spent per kilometer, meaning that going at lower speed gets you more range
262 W * 0.7^2 (<- power needs to factored in this way) = 128 W. 146 Watts average power shows that indeed my average power consumption was higher and therefore my mAh/km and Wh/km should have been a bit higher than the straight calculations show. Question is that what would the results have been if I had been traveling at the 16.2 km/h average speed rather then the 17.5 km/h I did with the 70% duty. Would the rest of the results fallen in line in that case? Are the results much more linearly linked to the speed rather than the duty cycle?
Summary: The results were overall very close to the estimated values and show how much the travel speed impacts your energy expenditure. I’m pretty happy that the results were within 10% of the calculated values. I can use this information in the future to make a bit more educated decision on what kind of battery pack I’m going to build regarding speed and range.