Its been about a year since I built my Bafang conversion e-bike and I still enjoy riding the bike. I am impressed with how powerful the 750 watt motor is and the range the 840wh battery provides. However, the Bafang conversion is missing one key feature that I’ve become very used to on my Bosch e-bike. That is a continuous range estimate on the control display. Without a range estimate provided by the e-bike system, you have to guess the range left in the battery based on your experience.
So it finally happened. I ran out of juice while riding the Bafang. I must admit it came as a surprise. I started the ride with 3 out of 5 bars displayed on the battery indicator. Three out of 5 bars means I should have somewhere between 40-60% of the battery’s charge left. However, after about a mile into my ride the battery dropped to 2 out of 5 bars meaning I had a 40% charge. Still, I wasn’t worried sine I was planning an out and back ride. I simply planned to turn around when, or before, I reached 1 bar. My plan was to use 1 bar going out and 1 bar to return. However things didn’t go as planned.
To my surprise, about 10 miles (16 km) out while climbing a hill the battery dropped to 1 bar. Only 10 miles (16km) on 1 bar? That was unusual. Still I wasn’t worried. I just turned around and headed home. If I used 1 bar going out the remaining bar should get me home. Right? Wrong! Only a few miles more while climbing a short steep hill the battery indicator started flashing empty. No way! I should get more than 15 miles (24 km) on a battery that was at least 40% charged when I started. Was the Battery Management System saving power to protect the battery from completely discharging? There was no way to tell. Not willing to take a chance on damaging my battery, I shut off the power and started pedaling my dead e-bike home unassisted. Luckily it wasn’t as hard as I expected. The motor didn’t add much drag and the additional weight was only noticeable on climbs. About half way home I turned on the system again. What was happening? The display showed 1 bar again and I was able to make it home on assistance level 1. In my opinion, not having a continuous range estimate is a BIG DESIGN DEFICIENCY in the Bafang system, especially when for some unknown reason the first half of a charged battery provides a lot more miles than the last half of the charge.