Electric Vehicles

I can tell a story of two vehicles.

A friend of mine had a self-built e-bike that went past my self-built e-car as if it were a road sign. :)

However, I can relay a word of caution: he used the lightest and best drone batteries (LiPo batteries) for it. They are incredibly good at burning, when helped a little to start the process. On one nasty day, he had to throw the flaming e-bike out of the garage door. Not much remained of the bike. Fortunately he had a smoke alarm and didn't charge unattended.

As for my e-car - it drove some 12 000 more kilometers, but eventually the charger malfunctioned. It didn't realize the battery was full and overcharged the cells. Needless to say, it was a cheap Chinese charger.

Instead of LiPo batteries, the car used LiFePO4 batteries. The safety valves opened and blew out electrolyte vapour, but nothing shorted and nothing caught fire. After another hour of cooking, maybe it would have, though.

I stopped the process, cooled down the cells and sorted them later by the level of damage. They lived a second life of 4 years as the auxiliary (outdoor) battery bank of my house, when it was freshly built. Some of them still hold charge, but in general, they're about to retire.

Lesson 1: different chemistries have different risk levels. If you can't or don't wish to have battery monitoring, choose a safer battery chemistry.

Lesson 2: redundant charge termination systems were missing. It's easy enough to install some. Always do it. Don't count on the charger to finish charging. Install a secondary board and suitably rated MOSFET / relay to cut the connection if cells go unbalanced, if temperature rises, or if voltage rises beyond full charge.

And of course, don't charge unattended. Sleeping == unattended.