For a while, we’ve been meaning to talk about the power difference as a result of battery charge level. So we thought the best way to illustrate this was to use our Dynapack dyno to just show the raw power at the wheels. at different charge levels. Special thanks to Kyle from Clean Technica for giving us a poke to get this test done, we probably wouldn’t have done it without him expressing interest in this!
We started our test at 15% battery charge. To ensure the motor and battery was adequately warmed up, we went for a 20-minute drive from 20% SOC with a lot of full acceleration followed by full regen to warm both the battery and drive unit. This was followed by a one-hour soak period to allow the heat to dissipate equally to match the following runs which would have one-hour intervals between them.
The first dyno pull at 15% really showed how low the power was compared to our previous 80% test as expected, so we knew right away it was going to be interesting to see how the power increased with charge – whether it was linear or not.
After each dyno pull, we plugged the car in and charged it at the full 32A the portable charger provides. This results in around 7kW going into the battery, or a 0.1C charge rate. Not enough to add any additional heat to the battery. We then did a dyno pull every 15% – so that is 15%, 30%, 45%, 60%, 75% and 90%.
After the 90% pull, we decided to see if there would be any additional power at 95% SOC. Since it was getting late we didn’t give the drive unit a ton of time to cool down (only the 30 minutes or so between pulls), so it is possible (however unlikely) that the drive unit was still too hot to deliver full power. Either way, the 95% pull did not produce any additional power, in fact, it was slightly (1-2hp in spots) lower than the 90% SOC run. It’s not included in the graph below simply for clarity.
The reason we didn’t test at 100% or closer to 0% is simply due to the fact that it’s obvious what the trend looks like, and we thrash this battery enough on the racetrack we don’t need to be running it at extreme ends of the spectrum. There’s really no need to be running the battery down below 15% or above 95%. The degradation too battery life is just too significant.
The really nice thing about our Dynapack dyno is how incredibly consistent the dyno itself is. Because there are no rollers and the hubs are directly coupled to the dyno, there is almost no variance from run to run. From my experience with this machine over the years, I have full confidence that the dyno readings do not fluctuate more than 0.5% +/- on each pull. It is very common for us to do dyno pulls where the graphs are virtually indistinguishable when you lay one over the other.
So without further delay, here are the dyno graphs overlaid on each other. I’ve also added ground speed in km/hr to the X-Axis so you can look at this in terms of Motor RPM or speed. If you like miles per hour, we’re sorry. But Canada and the rest of the world enjoy metric 🙂
Here’s the full video of the test. Enjoy!