Do You Need Passive or Active Balancing for Your Lithium Battery?
More people are interested in battery management systems (BMS). They want to understand the difference between passive and active balancing of lithium-ion batteries. Balancing methods are critical to maintaining battery health, extending battery life, and optimizing battery performance.
In this blog, we will cover the basics of lithium battery balancing. We will explain the difference between passive and active balancing. Finally, we will help you choose the best method for your lithium battery pack.
What is Battery Balancing?
Battery balancing: refers to adjusting each battery in the battery pack to achieve the same state of charge. Because of natural differences in battery cells, no two batteries are exactly alike. Similar to how no two leaves are identical.
Over time, these tiny differences will accumulate, causing imbalances that affect battery performance. If not corrected, this may even pose a safety risk or even cause serious consequences.
Why is Cell Balancing Important for Lithium-Ion Batteries?
Cell balancing is important for lithium-ion batteries. It ensures that each cell in a battery pack charges and discharges equally.
Small differences in how cells form and their age can lead to slight changes in capacity and voltage over time. Without balancing, these differences can cause some cells to undercharge or overcharge. This can shorten battery life and affect safety.
Proper balancing improves the battery’s efficiency. It also extends its lifespan and prevents problems like overheating or capacity loss.
Active vs Passive Balancing
Passive Balancing: Simple, Cost-Effective, but Wasteful
Passive balancing is the more traditional and budget-friendly approach to battery balancing. This method gradually discharges cells with higher voltages using resistors. This discharges excess power as heat to create more charging time for other cells, aligning their charge levels.·How It Works:
Passive balancing uses resistor discharge to lower the voltage in high-charge cells, converting excess power into heat.
·Pros:
Affordable, easy to set up and upkeep.
·Cons:
Limited to the battery with the lowest charge, wasting power as heat. This method works well for small battery packs or low-power uses.
However, it is not suitable for larger, high-capacity packs. The system balances according to the battery with the least charge. It cannot increase the charge of low-capacity batteries. Moreover, the system dissipates all the balanced energy as heat, leading to inefficiency.
·Tip:
The figure shows that we charge battery No. 2 to a safe voltage first. This triggers the protection system of the lithium battery board. Subsequently, it halts the charging process of the battery system. This directly prevents batteries No. 1 and No. 3 from fully charging.
The AA battery limits the full charge capacity of the entire system, resulting in a system loss. To increase the capacity of the battery system, the lithium battery protection board balances the battery during charging.
As shown in Figure 3, when equalization starts, the lithium battery protection board discharges the No. 2 battery. This delays the time it takes to reach the protection voltage value. This will prolong the charging duration for Battery No. 1 and Battery No. 3. This change will improve the whole battery system of power.
However, all the power from the No. 2 battery turns into heat. This causes a lot of waste. The energy dissipation from the second battery represents a system inefficiency and a squandering of power.
The figure shows that overcharging can seriously harm the battery. Overdischarging can also cause significant damage to the battery. Similarly, the lithium battery protection board has over-discharge protection function.
When battery No. 2 discharges and reaches a certain voltage, the protection mechanism activates. This stops the lithium battery from discharging further.
This directly results in the remaining battery capacity of batteries No. 1 and No. 3 not fully utilizing. After balanced startup, we will improve the system. Over release.
·Why does passive balancing generate heat?
Passive balancing generates heat because it dissipates the excess energy of the high voltage battery through resistors. When these resistors release the excess energy, it becomes heat. This heat can build up and require cooling, especially in large battery systems.
Passive balancing is simple and cost-effective. However, the generation of this heat represents an inefficiency in energy management. This makes it less suitable for high power applications or large battery packs.
Active Balancing: Efficient, High-Capacity Balancing
Active balancing uses power transfer, typically through transformer-based systems, to redistribute energy between cells. This technique is more efficient, transferring energy from high-charge to low-charge cells, thus reducing energy waste. Active balancing is well-suited for high-capacity lithium battery packs, such as those found in electric vehicles (EVs).·How It Works:
Active balancing transfers charge between cells, usually by inductive or capacitive methods. Higher-charged cells transfer power to lower-charged ones without creating heat waste.
·Pros:
Minimal energy loss, suitable for large, high-power battery packs.
·Cons:
omplex and costly, requiring additional components like transformers and advanced balancing chips.
In the figure, every 6 strings of batteries form a group. The total power from these 6 strings goes to the battery with a smaller capacity. Inductive active balancing relies on physical conversion and integrates a power switch along with a micro-inductor.
It uses a two-way balancing method to balance the battery. This transfers charge between similar or nearby batteries. It works whether the battery is discharging, charging, or resting. For equalization, the equalization efficiency is as high as 92%.
·Is active balancing better for electric vehicles?
The answer is yes. Active balancing is generally better suited for electric vehicles (EVs). It provides a more efficient and power-saving balancing method.
Active balancing is different from passive balancing. Passive balancing releases energy as heat, while active balancing moves energy between cells.
This process does not generate much heat. Therefore, it can save more power. This energy-saving method is great for large battery packs in electric vehicles (EVs). The main goal for EVs is to keep the batteries healthy and extend driving time.
Passive vs. Active Balancing: Which is Right for Your Lithium Battery?
Experiments have shown that using battery packs with big inconsistencies causes the voltage to change a lot. This leads to lower power performance. At the same time, variability increases, which further exacerbates the differences between battery packs and decreases the battery utilization rate and battery life.
When we find differences in batteries, we should process them to lessen the impact of these inconsistencies. This helps avoid a negative cycle. You cannot completely remove cell inconsistency, but you can reduce it with cell balancing techniques.
Whether you choose passive or active balancing depends largely on your battery needs. Passive balancing is ideal for low-cost, small-capacity applications with limited energy requirements.
Active balancing is most effective for high-power applications where efficiency and performance are important. This is particularly accurate for battery packs of electric vehicles (EV). If you are a DIY EV enthusiast, active balancing is more recommended.
Can we recycle lithium batteries after balancing?
Many people worry about lithium battery recycling. They are concerned about environmental pollution and the release of toxic substances. In fact, whether it is passive balancing or active balancing, it will not affect the recyclability of lithium batteries.
Recycling is important for getting back valuable materials like lithium, cobalt, and nickel. This helps lessen environmental impact and supports the sustainable use of battery materials.
We appreciate your patience and look forward to seeing you in the next blog.
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