Many projects are usually carried out with a single battery. serial battery connection is required for higher voltages if the charger does not have balancing, deterioration occurs according to the capacity of the batteries, the batteries that are loaded early are overloaded and deteriorated, and this problematic battery, the charging circuit for charging the batteries prematurely finishes charging before the other batteries are charged. For example; We need 12V in our project 3 Li-ion batteries in series with full charge 1 battery voltage 4.2V in this case 12.6V charger for 3 batteries needed We have started to charge our batteries and each battery has a different capacity and occupancy rate Some batteries have an early filling the middle battery in the schematic reaches the limit value of 4.2V and the others are not fully charged in this case the total voltage will not stop charging until the 12.2V charge cycle is 12.6V.
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, the battery will be charged much faster and will be charging in the same way.
The battery balance circuit </ strong> detects the premature battery charge in order to prevent this situation and usually uses resistance as the load. In this case, the battery voltage does not exceed the limit value.
Simple Battery Balancing Circuit
Some of the most frequently used circuits are transistors with simple structure. Some use direct transistor load. Some of them use diode, 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 drawing and SMD materials.
Set up the battery balance circuit: First, set the voltage of your set power source to 4.25V. Set the 1K trimmer slowly until it starts emitting light ( or TL431 REF with 2.5V at the foot. ), the current drawn from the power supply is a value between 100mA and 400mA according to the power of the battery. 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 timpot
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 PNP transistor collector façade. 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.
Published: 2018/06/09 Tags: power electronic projects