An Overview of Active cell Balancing: Layman’s guide

Electronic devices often use multiple cells connected in series for powering the applications. Each battery in the battery pack tends to age differently because of operating conditions and production tolerances. It causes an imbalance between the cells of the battery pack.

If these differences are not taken care of using an equalizer, the battery pack cannot work to its full capacity, and its safety is also compromised. Such a situation is avoided through balancing.

What is balancing?

When cells are out of balance the battery pack cannot accept or deliver power. In the initial stages, the weak cell limits the whole pack’s performance and renders the battery pack useless if it continues without balancing.

Balancing ensures that the SoC (State of Charge) of each battery in the cell is the same by managing the charge distribution. It helps in protecting the cells when they operate out of the bounds of normal operating conditions.

There are two types of balancing – passive and active. Passive balancing expends charge from batteries having too much charge and disperses bleeding energy as heat. It is a simple and inexpensive process but not as efficient as active balancing. Active balancing works by moving the charge from high voltage cells to the low voltage cells.

Why Is Active Balancing Necessary?

Without a balancer, after each charge and discharge, the differences between battery parameters are magnified, leading to quick deterioration of the battery pack. The whole battery can fail prematurely or become weaker due to the overstress it experiences because of these differences. However, by equalizing the charge in the battery chain using active balancing, it is possible to extend the battery life.

Active balancing prevents battery damage, allows optimal battery usage, and provides overcharge protection. The circuits related to this arrangement are implemented either in the battery or the charger. Lithium ion battery chemistries work more efficiently using active balancing techniques than passive types.

Active Balancing – How It Works?

An active battery balancer or equalizer uses an inductor, or a capacitor to balance the batteries. Cell-to-cell, pack-to-cell, or cell bypass implementations are utilized for active cell balancing.

Cell Bypass Equalization

Few cells reach their maximum SoC quicker than the other cells in the battery pack. In this method, the current bypasses high cells and continues charging the other cells till they reach their maximum SoC. This method is less sophisticated as well as pocket-friendly. However, the battery’s overall efficiency should be good and it is implementable only after at least one of the cells reaches maximum SoC. This process starts towards the end of the charging process.

Cell-to-cell equalization

The energy is passed from a cell to its adjacent cell when lower energy storage is detected. It is an effective method of balancing when compared with cell bypass but it is a slow and complex process.

Cell-to-Pack Equalization

Here the distribution happens from the most charged battery in the pack to the remaining cells equally. Even pack-to-cell distribution is possible and here the weaker cell receives from the other cells in the pack. This method has the lowest efficiency among the three methods mentioned here and the complexity is also high.

Implementation of active equalization

Each of these cell balancing methods is implementable in multiple ways. For instance, cell-to-cell balancing uses capacitors. Initially, the capacitor is connected to the strong cell for charging and then switched to the weak cell to discharge. As the charge is shuttled this method is referred to as capacitor shuttling.

This method involves energy loss as the capacitor consumes energy while charging and discharging. Also, charge transfer happens only between adjacent cells. The long process of charge, switch, and discharge cycle consumes more time than other methods.

Inductors when used in the place of capacitors for moving the charge between adjacent cells, improve the efficiency of the process. Though it is faster, it still has a few other downsides. The charge is transferable only from higher to lower cells, diode voltage drops and the switching losses are a few of the important points of concern.

All in all, active cell balancing is possible in various methods and each method has a few advantages and disadvantages. They differ in speed, efficiency, or other performance aspects.

Manufacturers of Active Balancers

While there are several manufacturers in the market for battery equalizers, Heltec is one of the most popular among them. There are several variations of these balancers from rating to type. They are available in the following types.

• Non-Bluetooth battery equalizer
• Bluetooth battery Equalizer

They usually come with a rating of 1.2A, 2A, 5A, 10A, and so on. The popular configurations are 4s,8s,6s,14s,16s, and 21s. Few of them come with LED indicators that show functioning.

Both Lithium battery compositions such as Lifepo4, Li-ion, and LTO as well as any other cell Chemical compositions such as Lead Acid batteries utilize this technology.

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Benefits of Active balancing

Through active balancing offers several benefits along with improving the performance of the battery pack and increasing its life cycle.

In charging state:

• Control over the charging process
• Avoid cell overcharging
• Balance the batteries in the charging state
• Checks the battery temperature

In discharging state:

• Limiting the maximum output of the cell pack
• Avoid battery deep discharging
• Balance the batteries in the charging state
• Checks the battery temperature

Summary

In short, balancing modifies the level of charge in batteries in a cell-by-cell manner. Using an active balancing approach, you can achieve the maximum potential of the cell. Another good reason to use active balancing is to increase the lifespan of a battery.

However, it has a large footprint and is a complex solution. Various battery compositions have different needs and when appropriate balancing is applied, the efficiency of the application is improved.