I live in Shenzhen, and electric scooters/bikes are extremely popular here. Having been riding one myself for a couple years, I completely understand why – the weather is great for it 11 months out of the year, and you can drive anywhere. Literally. Sidewalks, highways, overpasses, underpasses, buildings – if it fits, you sits. Combined with a low cost of ownership ($300-$500 for a bike) and basically free charging its a no-brainer.
Unfortunately, most bikes run on sealed lead acid (SLA) batteries that are heavy, and lose capacity after a few hundred recharges. My bike is about 18 months old now, and is starting to show its age – I used to get 30km per charge, and now I’m lucky to get 15. I could replace the batteries with new lead ones, but if I’m gonna get under the hood I might as well upgrade it at the same time.
I’ve been reading quite a bit about lithium based batteries on awesome sites like Endless Sphere, and have gathered enough information that I feel ready to give it a shot. For the first pack, I’m thinking to go the nice, safe route AKA LiFePo4. Safer than your standard lipo batteries, but a bit heaver. Considering I’m coming from the land of SLA batteries it will be a net weight reduction regardless.
Of course living in Shenzhen and buying stuff off Taobao, you have to be on guard. Especially with stuff like batteries where its easy to make a claim. The first thing I did was source a battery tester. This will measure the actual capacity of the battery (measured in amp-hours (aH)).
The tester is pretty simple – two clips to hook up a battery and two terminals to hook up a big fat power resistor. This one can handle discharges as small as 0.1A @ 2v and as large as 20A @ 60v which means I can test both individual cells as well as entire battery packs. Awww yeah.
I’ve started to order a bunch of different batteries and will be testing their capacity one by one. Once I find a reliable supplier then I will design the battery pack, install it, and hopefully my bike will be back to new (and hopefully even have a bit bigger range!) Will try to post an update with the next step.
Continue on to read Part 2 – Battery Selection.