What Is Passive Balancing And Active Balancing?

When multiple cells with unequal voltages are connected in series, charging or discharging them without a balancer decreases the lifespan of the batteries. Battery equalizers or balancers help in improving the durability of a battery pack. They monitor and regulate the charge across the batteries.

You can find them in laptops, electrical vehicles, computers, and similar devices using lithium battery packs. For instance, automobiles require large battery stacks to provide high output power. Each individual battery present in the stack should contribute equally in an ideal scenario.

However, due to various reasons, all these batteries cannot produce equal power as they age, despite their same physical size and chemistry. Even though their physical shape and size are the same, their total capacities, self-discharge rates, internal resistance, and many other such parameters can be different. Apart from these, the battery can age differently, having a significant effect on battery life. Enquire now to purchase rechargeable battery packs from our online store.

Types Of Battery Balancers

When you use balancers, they help in improving battery life cycles along with utilizing the power of all the batteries in the stack optimally.

There are two different types of battery balancers

1) Passive battery balancer

2) Active battery balancer

As battery balancers are also known as equalizers, they are often referred to as passive battery equalizers and active battery equalizers and still mean the same as above.

Passive Balancing

In a new stack of batteries, you might start with the same capacity but as the battery ages, their general aging and degradation process vary leading to a difference in capacities. Passive balancing helps in balancing the capacity difference between the cells.

Top balancing and bottom balancing are two possibilities with passive balancing. Top balancing refers to cells reaching 100% SoC (State of Charge) through energy shunting using a parallel path that consumes the current for balancing the charge between cells. Bottom balancing bleeds the energy of the cell with higher SoC to balance it with the lower SoC to make them equal. In both cases, energy is spent as heat and the balancing time also increases.

A weak battery is quick to charge as well as discharge and the strong cells hold the charge well. During run-time, this becomes a limiting factor as you cannot utilize the complete capacity of the strong cell. This is where passive balancing comes in handy. It works by equalizing the voltage of all batteries in the stack to that of the lowest battery capacity. It is done by connecting the high voltage cell to a dummy load that drains the high voltage.

Fig 1.1: Passive balancer set-up

Fig 1.2: Balanced batteries and switch-off using a balancer

The set-up and operation are simple and inexpensive as very little equipment are necessary to achieve passive balancing. All you need is a resistor connected in parallel to every cell and a switch (Fig 1.1). The resistor activates and drains the voltage when there is an unbalanced voltage in between the cells. Once the voltages are balanced, the process is switched off using the switch (Fig 1.2).

Advantages

• The advantage of this process is that the batteries can charge to their full capacity and maintain balanced voltage.
• Long-term self-discharge current mismatch is correctable using passive balancing.
• It is a low-cost method that keeps your batteries healthy.

Disadvantage

• The run-time of the battery-powered system does not improve.
• The discharge resistor wastes energy in this process.

Active Balancing

Active balancing maximizes the system run-time and allows efficient charging. However, it is expensive and requires a sophisticated setup when compared with passive balancing.

Through active cell balancing, the energy is redistributed rather than wasting it during both charging and discharging. It is achieved by replenishing the weaker cells with the help of stronger cells during the discharge.

The weaker cells draw energy from the stronger cells as they deplete which extends the time of depletion. Meaning the total usable charge is way higher than the capacity of the weak cell.

We have two types in Active battery equalizer

1)         Induction Based

2)        Capacitor based

Battery Equalizer or Balancers are available in different ratings Eg. 1.2A, 2A, 5A, 10A, etc., They are available in non-Bluetooth battery equalizer and Bluetooth battery Equalizer. Among them 4s,8s,6s,14s,16s,21s are popular configurations in industries and some of have LED indicators to show functioning and some don’t. Heltec is one of the popular companies in this area.

For more in-depth information on active balancing, check this article.

Advantages

• When cells are balanced actively, less heat is generated, which helps in maintaining the safety of the battery better.
• The charge time decreases in comparison to passive balancing.
• Also, the usable charge increases when using passive balance for the same set of batteries.

Disadvantages

• Expensive when compared to passive balancing.
• Architecture is complex and has a large footprint.

Why Is Balancing Important?

Apart from maintaining an optimal battery life cycle, balancing is also important for the safety of the battery. Lithium batteries are sensitive to mistreatments such as overcharging, overheating, or improper charge levels making them susceptible to chemical damage.

When the cells are not unbalanced and do not coordinate charging voltage among themselves, they are vulnerable to various failures. It can result in reverse polarity, thermal runaway, or internal gassing.

To avoid such damage and hazardous effects that occur due to variation in charge, balancers are important.

Summary

Batteries in a stack are monitored during the process of cell balancing, be it active or passive. It is to ensure that the batteries are maintained at a healthy SoC.

A properly maintained SoC extends the battery life along with providing an additional layer of protection from overcharging or deep discharging. Passive balancing dissipates excess charge while active balancing redistributes it.

Balancers are useful in Lifepo4, Li-ion, LTO, and any other cell Chemical compositions including lead Acid batteries

Please follow the link for Sriko products for battery equalisers and battery balancers. We are the best online store for electronics in the USA and provide quality products for you. If you have any queries about balancers or batteries in general, feel free to comment. Our experts are happy to answer your questions.