Long time since the last post. I have been working on a lot of projects but I haven’t posted much on the blog.
Here is the project I am working on at the moment. It’s cell balancer for Li-ion / Li-Mn /Li-po cells. Basically it detects if a cell goes above a pre-set voltage during charging and “activates” the mosfet and power resistors in the circuit, draining/bleeding the charging current allowing the cell to stay at or below the pre-set voltage. Depending on the resistor (and mosfet) used it’s possible to set the maximum bleeding/draining current. In the video above the maximum draining currents turned out to be 1.3-1.5 A.
It’s very important for all the lithium chemistries that the single cell don’t go above a certain voltage to avoid damage. In case of Li-ion / Li-Mn /Li-po cells it is recommended not to go over 4.2v per cell. I set my balancer to activate at 4.15v per cell.
Some of you would say: “why don’t you just use a BMS?”. Well, BMS, especially for bicycles and motorbikes have limitations. In particular the charging and discharging current, and most importantly the balancing current, which is normally set to 0.3 A or less. Therefore using a standard BMS can take several hours or days to balance an unbalanced battery pack. The circuit above is designed to speed up the process when bulk charging.
I will have new pcb ready in a few weeks as the one I am currently using has a design error. The current boards are 5s.
Please comment if you have any question or contact me if you are interested in having one of the boards to test it on your setup.