Battery Circuit Diagrams

# BALANCING LI-ION LI-POLYMER BATTERIES BATTERY BALANCING CIRCUIT Schematic Circuit Diagram

#### Introduction to Battery Protection Circuits and Balancing for Li-ion, Li-Po, and LiFePO4 Batteries

In addition to discussing “Li-ion Battery Charge Integrators MCP73831 TP4056” and their relevance in charging, protection, and balancing of Li-ion and Li-Po batteries, I will provide further insights into this critical topic.

#### Managing Multiple Batteries

In most projects, a single battery suffices. However, when higher voltages are required, the need for serial battery connections arises. Without an integrated balancing feature in the charger, battery capacities can deteriorate. The batteries that reach their full charge earliest end up being overburdened and undergo premature wear and tear. As a result, the charging circuit erroneously concludes the charging process for these particular batteries before the rest have completed their charge cycles.

#### Balancing in a Practical Scenario

For instance, consider a scenario where we need 12V for our project, requiring three Li-ion batteries connected in series. With each battery reaching a full charge voltage of 4.2V, the charger must provide 12.6V in total. When we initiate the charging process, each battery, having distinct capacities and levels of charge, follows its individual charging trajectory. In this context, some batteries might reach the 4.2V limit more quickly than others, causing an imbalance. The middle battery in this setup could hit the 4.2V threshold while the others remain incompletely charged. Consequently, the charging process persists until the total voltage reaches 12.6V, which can lead to uneven wear and performance degradation in the batteries.

After charging, the battery will exceed the middle battery limit voltage. 4.4V will be charged. The other batteries are not fully charged. They are left at 4.1V but the total voltage is 12.6V.

We use our batteries when we charge them with a charger that does not have a new balancing circuit. Depending on the condition of the battery, it will be charged much faster and in the same way.

Battery balancing, the ripping circuit detects prematurely charging the battery to prevent this condition and usually uses resistance as the load. In this case, the battery voltage does not exceed the limit value. The charging circuit continues charging until the other battery is charged.

There are many sophisticated systems for battery balancing , especially the Texas Instruments BQXXXX series battery protection, balancing integrators are often used in Laptop batteries, the other company that produces a more affordable variety is SII Semiconductor ( I think the company has changed hands by ABLIC Inc. )

#### SIMPLE BATTERY BALANCING CIRCUIT

The most frequently used circuits are transistors with simple structure. Some use direct transistor load. Some of them use diodes, load resistor, diode. In the following circuit, BD140 PNP is used as transistor load. TL431 REF can be precise voltage adjustment with trimpot connected to the foot.

There is no need to use this circuit for a single battery. One of the balance circuits is used for each battery in the serial connection Three serial Li-ion battery connection schemes for 12.6V;

For the circuit testing, we can think of the dimensions as perforated platelet lead test purposes, which can be done in much smaller sizes with regular PCB drawings and SMD materials.

#### Adjusting the battery balance circuit:

First, set the voltage of your regulated power supply to 4.25V. Turn the 1K trimpod until it starts to give light (or see 2.5V at the TL431 REF lamp). Meanwhile, look at the current drawn from the power supply. A value between 400 and 400 is sufficient. I use 300mA for the 18650 Li-ion battery

Basically, TL431 REF should be resistance setting as 2.5V in the foot. If you use full value resistor, you do not need trimpot, but easiest is to use multi-turn trimpot.

In this circuit, the direct BD140 transistor is used as the load. In some applications, 1W … 2W 5 … .10-OHM resistor or series 3 … 4 1N4007 diodes are connected to the collector of the PNP transistor. I did not use it in the tests, but if you use the BD140 transistors with a 1K trimmer you need to connect a small cooler, you can make more precise adjustments, and the voltage divider 15K, 22K resistors are better than 1% tolerances.

#### Utilizing Simplified Circuit Variations

In the simplified version of the circuit, a resistor is directly connected to the series-connected diodes, or it can be employed as a direct transistor load without additional components, as shown in the initial schematic. An extra transistor is often added for the LED indicator, enhancing stability. However, this indicator can be connected either at the transistor collector or omitted entirely.

This uncomplicated system finds application in the charging adapters of various devices, particularly in products like models, model cars, boats, and helicopters available in the market. It’s a common feature in these chargers.

In more intricate designs, advanced integrated control stabilizer circuits are employed. Some even incorporate microcontroller-controlled systems. For instance, the S8209B integration from SII Semiconductor products offers a viable yet not overly complex solution for these applications.

The battery stabilization cycle does not repair the problematic battery or make it perform better, but it prevents the battery from getting worse and causing more damage to the better battery. It is necessary to use in series connected …

#### UNLESS YOU USE THE BALANCE CIRCUIT?

There is a low chance that you sometimes have a lot of difference between the batteries and the battery pack does not have a problem for a long time.

By measuring, you will be able to identify the batteries that will cause the least problems and connect them in series, but I think that the seller will allow this and I need to sort out something like this in the article ” Matching the Transistors “.

For example, there are 10 unused Li-ion batteries in your hand. Overwrite the voltage of each battery that measures the voltage of all, then connect the load, repeat the measurement and write the voltage on the load onto the batteries. Be careful that you can connect and use series of batteries that have no load and load voltage or that are close to each other.

These batteries have very little unloaded voltages, but their voltage on the load is very different. This battery can not see our work for serial connection. You can use 15-OHM 2W resistor as load.

On used pillars; Fully charge all of them and do the same measurement a few days later..

Finally, you can recharge the batteries separately if the serial connection is frozen and recharged but it is possible.

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