What Is Cell Balancing

A battery pack consist of multiple cells to achieve desired capacity in a battery pack. The No. of cells can range from few to hundreds or even thousands

cell balancing
All the cells in a battery pack are desired to function equally well all the time, but cells tend to get imbalanced over the period of time with the use. Individual cell may be of a good quality but when multiple cells are inter connected, they may not behave the same all the time. This imbalancing need to get corrected to avoid range reduction and longer life of the battery pack. There are two types of balancing available in the Battery Management System (BMS).

cell balancing

Balancing is the process of equalizing the level of charge in lithium-ion cells on a cell-by-cell basis. There are two ways to do cell balancing such as active cell balancing and passive cell balancing.

Types Of Active and Passive Cell Balancing Methods

01. Passive Balancing:

The primary advantage of passive balancing is the simplicity (and hence, lower cost) of the circuitry involved, compared with active balancing designs. The drawbacks are: Energy is wasted as heat, which could be otherwise used productively, Heat is generated. For fast balancing, more heat is generated, and Battery pack life could be shorter with respect to a pack with an active balancing design.

02. Active Balancing:

An active cell_balancing circuit normally transfers energy from the highest voltage cells to the lowest voltage cells untill all the cells are balanced. This active cell_balancing circuit has a lower cell balancing time and has greater efficiency than the passive cell_balancing circuit. However, this cell equalizing circuit has a huge cost and needs complex system control algorithms for balancing cells.

See the video below, the red colour row has lowest voltage and it is imbalanced. The blue colour row(highest voltage) is transferring energy to bring it at par with other rows. This is active balancing which keeps the battery pack balanced all the time without range falling due to imbalance and increasing the life of the battery pack.

Difference Between Active and Passive Cell_Balancing

SI.NoActive Passive
01. Energy is not dissipated or wastedEnergy is dissipated or wasted
02. Energy is transferred from one cell to another cellThe energy of a cell that has a high state of charge is transferred to a resistor
03. Bulky in sizeSmall size
04. High costLow cost
05. High efficientLow efficient
06.Fast balancingSlow balancing
07. Good thermal managementPoor thermal management
08. Applications: Used in UPS (Uninterrupted power supply), ESS (Energy storage system), EV/HEV (Electrical vehicle).Applications: Used in a portable device, low-power system