The post discusses a relatively easy lipo battery balance charger circuit which is designed to continuously scan and charge the connected cells of the battery.

The idea was requested by Mr. Schindler and Mr. Emil Jan Thomas Baticulon.

 Charging 6 Li-Po Packs

The concepts are very well written, concise and clear. Thank you so much for the deep coverage of the charging subject.

Have you encountered the need to charge several identical lipo packs regularly? I have that very need, it is time consuming to recharge 6 high power packs containing 4 cells each every few days.

I propose a single cell charger that scans all cells via the balance plugs and serves up the requirement per need during a partitioned interval of the scan period.

Arduino sketch, shift registers, discrete coupling and a plan to stitch it together... there is where I bid you to guide me to a viable implementation. If you'd be so kind?

Charging 18650 Li-Ion Pack

Good day,

I just recently found your blog and upon further reading your post it's very helpful with or without electronic background and i appreciate your work.

I have a project in mind but I am stuck with it, My idea was how can I charge 13pcs 18650 li-on battery in series connection with balancing charger?. Can you help me with it and add this to your work?

Thank you,

The Design

As shown in the following diagram, the proposed lipo battery balance charger circuit can be implemented rather effortlessly using a couple of IC stages.

Let's try to understand how the circuit is intended to function:

The second diagram below is the relay driver stage which needs to be repeated 10 times and the base of the BC557 associated with the red spots of the relevant BC547 stages from the first circuit below.

Control Circuit Diagram

I forgot to show resistors on the bases of the transistors, make sure you put them, 10K would be OK...

Relay Driver Schematic

If the cells are 3.7V rated, the opamp preset is adjusted such that its output pin#6 just goes high when the charge level across the cell reaches around 4.2V.

How to Set up the Balance Charger Circuit

For setting this up, a sample 4.2V may be fed at the shown preset's upper lead, and the preset slider adjusted to make pin#6 of the opamp just high (positive).

  1. With all the positions connected as depicted in the diagrams and power switched ON, let's assume that at the onset pin#3 of the IC4017 is high which in turns activates the associated BC547, BC557 and the connected relay contacts.

  2. Cell#1 now begins charging, which drags down the supply voltage across the preset pin#3 of the opamp to may be say 3.4V or whatever may be the initial discharge level of the cell#1.

  3. While this happens, pin#3 of the opamp experiences a lower potential than it's pin#2 ensuring a low signal at its pin#6 and the pin#14 of the IC 4017.

  4. As cell#1 of the lipo battery charges, the terminal voltage of this cell slowly increases until it reaches the stipulated 4.2V mark.

  5. As soon as this happens, pin#3 of the opamp also is subjected at this voltage forcing its output pin#6 to go high, which in turn prompts the IC4017 to shift its pin#3 logic high to it next pin#2, toggling the driver stage of this pin into action.

  6. The above shift activates the charging of the second cell of the lipo battery in the same manner as it did for the first cell.

  7. The process now continues and repeats itself by scanning and charging the cells in steps continuously.

  8. Thus the lipo battery cells are maintained with optimal charging level through the above explained lipo battery balance charger circuit as long as the circuit remains connected with the lipo cells.

Parts list for the above diagram:

All resistors are 10K, preset is 10K, all transistors are BC547, zener diodes are 3V/ 1/2 watt

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