Active balancing for battery cells
Linear Technology has been addressing the problem of cells in batteries degrading at different rates so affecting the efficiency of the charging and discharging of the battery.
“You’re only as good as your weakest cell,” says Tony Armstrong, LTC’s director of power products.
“The ideal discharge is that all the cells discharge at exactly the same time so all the usable energy in the battery is used,”says Armstrong, “and, ideally,all the cells will charge at the same rate. But. In reality, that rarely happens – cells age at different rates and, if the weak cells discharge before the rest, you’ve got unused energy.”
LTC’s answer is an active balancing chip which compensates for cell mismatch and redistributes energy from higher capacity cells to low capacity cells.
“It takes the energy from the balance of the stronger cells and pumps it into the weaker cells,” says Armstrong, “so all the usable energy is used.”
The same process happens with charging so all the cells charge at exactly the same time and the whole battery pack gets charged.
The company has come up with a couple of chips which can sort the situation out. The LTC3300 bidirectional multicell battery balancer can redistribute charge to and from weak cells to strong cells and vice versa, while the LT8584 active cell balancer does the same job but with integrated telemetry.
Both chips cost about the same and they extend the life of the batteries.
“Big batteries are expensive,” says Armstrong, “you either buy bigger batteries or you use active balancing.”