I finally finished creating all the charge speed versus temperature graphs for fast charging my electric motorcycle. The data was collected already but I had to transform them into these graphs for presentation.
Riding and charging on B-roads
The B-roads scenario is riding roads with a speed limit of either 70 or 90 kph (often switching between both) and some short 50 kph sections crossing town centers. Average speed is often around 65 kph when riding like this. Sport or other riding mode, more or less re-gen, doesn’t make much difference.
A quick conclusion is that you should be fine when riding at 25°C weather limiting 30 to 80% charges at 50A (takes 30 min) and riding for as long as possible in between using just that 50% of the battery. That will work all day or as long as you need it to on non constant highway speeds and keeps your battery between 30 and 40°C.
At this point your battery will leave chargers being at around 40°C which is just 1°C away from the yellow battery indication. If you really want to charge as fast as possible you could start the day with a full speed charge since then you start with a 24°C battery temp (or slightly higher from riding). That will render the below graph. But it will only work for the first charge of the day.
Note that all you’ll gain is 5 minutes this way… So might not be worth it. On the other hand it doesn’t make much difference for the next charge if you do or don’t. So why not. No matter how you started your first charge you’ll likely be at 40°C after the charge anyway.
Now the next question is what happens to the battery temp while riding! Well the good news is that it does cool down. Just not by as much as I’d like it to. Here you’ll find the biggest difference in the weather cause the higher the difference between your 40°C battery temp and the weather the faster it will cool down.
At 24°C weather the below graph is how the battery cooled down while riding. It took around 2 to 3 °C per hour of riding. So starting a ride at 40 °C requires 2 hours of riding for it to go down to 34°C again giving us just (or barely) enough room for our next 30min 50A charge (see first graph).
On B-roads I can manage an average consumption of 60Wh/km which will render me a 266 km range (=16.000/60). Using only half of the battery is still a range of 133 km. Riding at around 65 kph average speeds is like 2 hours riding. Hence the 3*2 °C degrees drop.
Riding and charging on highways
Riding on highway speeds is another story cause the constant higher current demand from the battery, compared to non highway riding, also introduces heat. So there is no such thing as a quick first charge of the day plus you simply can’t ride for 2 hours on highway speeds to let the battery cool down enough.
Highways in Belgium are mostly limited to 120 kph speeds, some sections are at 100 kph. In the Netherlands most highways are limited to 100 kph already and I think Belgium is heading into that direction also.
To cover as much distance as possible with at least battery used as possible while still riding fast enough for traffic is a challenge. I find that riding 110 kph on the display, that is 100 kph real speed, seems to be a good balance. That way, if I do my best riding smoothly and tucking in a bit (not full tuck) I’m able to cover 100 km in 1 hour with just 50% of the battery used.
That puts us right on the sweet spot to get those 30 to 50 % SOC charges in 30 minutes at 50A or 15 kW charge speed. Only downside is that the log I pulled showed that the battery temp was already at 32 °C just by riding. Charging at 50A limits gives me this result.
Just over 30 minutes and also just over that 40 °C so yes this was showing a yellow battery. Just out of curiosity I also looked up a charge where I didn’t limit the charge speed after highway riding. That day I started charging at an even higher 35 °C battery temp.
After 10 minutes the battery already reached 40 °C and the charge speed even drops just below the 15kW or 50A setting I picked manually in the other graph. Charge time is almost identical at just over 30 minutes. The main difference is that we are at 43°C at the end of the charge, really limiting our options for the next charge. I’ve seen as low as 7kW charge input after a full day (500km) of highway charging and riding.
Now honestly on highway riding I think you’ll always end up heating the battery over time, even at 50A charges. The issue here is that you can only drop the battery temp 2 to 3 °C after riding for 1 hour before reaching the next charge.
So even if you limit to 50A and you manage (somehow) to stay at the 40°C batt temp in the end you’ll still start your next charge at 37°C at best. Just leaving not much room for that charge.
On B-roads this is luckily not as much of an issue. And most people don’t get these bikes to ride highways anyway. Even I rarely do more than 1 charge on highway rides.
There was an interesting comment on FB about the specs when the new plus battery was announced. It was talking about a battery temperature up to 55 °C. So it might just be that the charge algorithm wasn’t adapted for this new battery.