Electrical – Balancing a large 18650 battery bank

batteriesbattery-charging

I am planning on building an ~60V, ~50A, 18650 battery pack to power a 2 kW electric motor. I've called some electronics stores and it seems like I can get a decent amount of old laptop batteries for free. The obvious problem is that each cell is going to have different lifetimes, capacities, resistances etc. so ill need some way to balance them.

How can I make what is probably going to be the most hack battery ever, as reliable as possible? Should I buy a few BMS's and try and balance each individual cell? should I balance each parallel group? should I not even bother trying this and shell out money for real batteries?

Best Answer

You certainly can have some fun doing this project. Dead Laptop batteries still might have few fairly good cells to harvest. Keep in mind however that the internal cells don't have any protection, so be careful not to short anything at a risk of "rapid venting with fire".

There are some hackers who do this kind of projects and offer their advice, like this one. In most cases take their advice at your own risk, since usually their methods are not backed up by any test nor reliability/safety research. For example, they would boldly connect 18650 cells in parallel in large numbers without any reservations, which doesn't make them overly reliable and long lasting.

For a overview of some challenges in the area, I just found this nice article, which I highly recommend for a start.

Finally, I am afraid you can't just "shell out money for real batteries" and expect you EV bike to fly. One battery doesn't make a EV. You would need a full EV solution for power management, braking recuperation, etc, all sorts of fine engineering.