How to Balance Batteries in Series – Charge Each Battery Individually

Introduction

When using LiFePO4 batteries, balancing batteries in series is critical for ensuring maximum performance and lifetime. LiFePO4 batteries, recognized for their high energy density, extended lifetime, and great thermal stability, have grown in popularity in various applications.

However, if these batteries are not properly balanced, voltage differences may occur, resulting in lower capacity, probable damage, and degraded overall performance.

Understanding balancing and charging each battery independently is critical to ensuring the life and efficiency of LiFePO4 batteries in series. This article will look at how to balance LiFePO4 batteries in series and the need to charge each battery separately.

What is LiFePO4 Battery Balancing in Series?

LiFePO4 battery balancing in series ensures that each battery in a series connection has the same voltage and capacity before and after linking them. This helps to improve the performance and lifespan of the battery bank by preventing overcharging, over-discharging, or uneven stress on individual batteries.

Balancing LiFePO4 batteries in series can be done by charging each battery individually with a 12V LiFePO4 compatible charger until they reach 100% state of charge and then connecting them in series with a balancer or a protective circuit module (PCM) or a battery management system (BMS) that monitors and equalizes the voltage across them.

Why Balance LiFePO4 Battery in Series?

Here are the reasons to balance LiFePO4 battery in series:

· Improving the performance of the battery bank

Balancing LiFePO4 batteries in series ensures that each battery has the same voltage and capacity before and after linking them. This prevents overcharging, over-discharging, or uneven stress on individual batteries that could reduce their performance and output.

· Extending the lifespan of each battery

Balancing LiFePO4 batteries in series also helps prolong each battery's lifespan by preventing premature degradation or failure. LiFePO4 batteries have a long cycle life, low cost, high safety, and environmental friendliness3, but they can still be damaged by excessive or insufficient voltage.

· Simplifying the charging process

Balancing LiFePO4 batteries in series makes the charging process easier and more efficient. Once the batteries are balanced, you can use a higher voltage LiFePO4 compatible charger to charge the entire set when linked instead of charging each battery individually. This saves time and energy and reduces the risk of overcharging or undercharging any battery.

Preparing for LiFePO4 Battery in Series Balancing

You need to perform the following two actions before balancing:

Choosing the right LiFePO4 batteries for a series connection

Before connecting LiFePO4 batteries in series, you must choose the right batteries for your application. 12V LiFePO4 batteries with the same capacity, voltage, and internal resistance should be used. This ensures they are matched and balanced before and after being linked together.

Check your device's or application's specs to see how many batteries you need to connect in series to get the necessary voltage output.

 

 

Ensuring safety precautions

Working with high voltage and current while connecting LiFePO4 batteries in series may be beneficial if handled appropriately. As a result, you should take various measures, such as:

• When working with batteries and cables, use protective gloves and eyewear.
• Charge each battery independently with a LiFePO4 compatible charger before joining them in series.
• While the batteries are charging or discharging, do not connect or detach them.
• Avoid exposing the batteries to high heat, moisture, or fire. Short-circuit, reverse-polarity, overcharge, over-discharge, or physical damage to the batteries are all prohibited.

Step-by-Step Guide to Balancing LiFePO4 Battery in Series

Now that you’ve taken the safety precautions, it’s time to go through the following steps to balance the LiFePO4 battery in series:

Step 1: Measure the voltage of each battery and identify the highest and lowest ones

Before connecting LiFePO4 batteries in series, you need to measure the voltage of each battery using a multimeter. This will help you identify your set's highest and lowest voltage batteries.

Ideally, all batteries should have the same voltage, but there may be variations due to manufacturing tolerances, aging, or self-discharge. The voltage difference between the highest and lowest batteries should not exceed 0.1V.

 

Step 2: Connect the charger to the lowest voltage battery and charge it until it reaches the same voltage as the highest one

Once you have identified the lowest voltage battery in your set, you need to connect it to a 12V LiFePO4 compatible charger and charge it until it reaches the same voltage as the highest one.

You can monitor the voltage using the multimeter or the charger’s display. This will ensure that all batteries have the same state of charge before connecting them in series.

 

Step 3: Repeat step 2 for the next lowest voltage battery until all batteries have the same voltage

After charging the lowest voltage battery, you need to repeat step 2 for the next lowest voltage battery in your set, and so on, until all batteries have the same voltage. This will balance the voltages of all batteries in your set and prepare them for series connection.

Step 4: Connect the balancer to the batteries and let it equalize the voltage across them

Once all batteries have the same voltage, you can connect them in series using wires and connectors. Make sure to link one battery's positive terminal to another's negative terminal, creating a battery bank with a higher voltage output.

After connecting them in series, you need to connect a balancer to the batteries and let it equalize the voltage across them. A balancer is a device that monitors and adjusts the voltages of individual cells or batteries in a pack to prevent overcharging or undercharging.

You can use a dedicated balancer, a protective circuit module (PCM), or a battery management system (BMS) with a balancing function.

 

Step 5: Disconnect the balancer and the charger and check the voltage of each battery again

After letting the balancer do its job, you can disconnect it and the charger from the batteries and check the voltage of each battery again using a multimeter.

You should see that all batteries have very similar voltages, indicating that they are balanced and ready for use. You can now enjoy the benefits of a higher voltage system with balanced LiFePO4 batteries.

 

Performance and Impact of Balancing LiFePO4 Battery in Series

Balancing LiFePO4 batteries in series significantly impacts their overall performance and functionality. Balancing ensures consistent voltage levels among the batteries, improving efficiency and power output.

Each battery in the series works together seamlessly, minimizing energy losses and maximizing the utilization of the battery pack's capacity by performing the balancing act. This results in enhanced performance, providing a stable and reliable power supply for various applications.

Furthermore, balancing LiFePO4 batteries in series helps to prolong their lifespan. When batteries are unbalanced, some cells may be subject to overcharging or discharging, leading to accelerated degradation and reduced longevity.

The workload is distributed evenly, preventing individual cells from experiencing excessive stress once you’re done with the balancing. This balanced operation promotes uniform wear and tear across the battery pack, resulting in a longer lifespan for the entire system.

When to Balance LiFePO4 Battery in Series?

It would help if you balanced your LiFePO4 batteries in series whenever you notice a significant difference in voltage or performance among them. This could happen due to manufacturing tolerances, aging, self-discharge, temperature gradients, or uneven loading.

Balancing your batteries will ensure they have the same state of charge and capacity before and after linking them, balancing your batteries once a year will extend the battery lifespan and optimize the performance of your higher-voltage system. You should also balance your batteries after long storage periods (more than three months) or if you see a significant performance drop.

 

Final Words

To maximize the performance, lifespan, and safety of LiFePO4 batteries, batteries must be balanced in series. This article demonstrated how to balance LiFePO4 batteries in series and stressed the need to charge each battery independently.

LiFePO4 batteries have gained appeal in various applications due to their high energy density and longevity. However, if batteries are not properly balanced, voltage differences may emerge, resulting in lower capacity, probable damage, and degraded overall performance.

FAQs

Can you charge batteries individually in series?

A single charger with an output voltage equal to the nominal voltage of the battery pack may also recharge a series-connected string of batteries.

How do you balance multiple batteries?

The most effective cell balancing method involves connecting cells with 80% SOC or less in parallel and gently charging them to 100% SOC using a power source (3.6 V for Phosphate batteries, 4.2 V for LiPo or Cobalt cells).

Do batteries in series charge each other?

By connecting many batteries in series, the system's total voltage may be increased; however, this method needs to improve the battery's capacity, just its voltage.

Can I charge 4 12V batteries in series?

There will be no difference in charging time compared to a single battery. To charge more than five batteries simultaneously, connect one 12-volt battery charger across the series connection of the batteries as if each were being charged separately. It's best to charge all the batteries at once.

Can I connect 2 different Ah batteries in series?

The amp-hour capacity of the batteries must match for the connection to work. We highly advise against connecting batteries with different amperage ratings. There may be a charge and voltage variation across batteries because of their different battery management systems and cell counts.