Hello,
I am currently working on creating a DIY balancing module for the Lithium-ion battery pack. I work according to the scheme in the link below.
It is a small power bank (4S). The entire module would be controlled by arduino. The module consists of an optocoupler, mosfet and power resistor. The digital pin arduino will be connected to the optocoupler input TLP621-2 via a 270 ohm resistor and then to the GND arduina. Recommended current for optocoupler is, according to datasheet, 16-20mA, so I chose 270R. When arduino is connected to optocoupler, 4V voltage is applied to MOSFET gate BUK98150-55A, which switches + and - batteries through a power resistor, which will discharge energy when reach 4V (battery operating voltage 3.0-4.0V for optimal life) pending other cells will be 4.0V. Charging is then terminated.
The only part that is not clear to me is the resistance between G and S of MOSFET. I have read that this resistance is related to the required switching frequency. The lower the resistance, the greater the switching speed potential. However, with longer switching, a small resistance between G and S would lead to the destruction of MOSFET, so the vast majority of people use a 10k resistor and with longer switching even 100k. But there is a minimum resistor that must be there for the MOSFET to work properly. Can someone please briefly explain?
Can you please tell me if the scheme is correct? Will the balancer work in hardware terms? Is the resistance between G and S optimal? I must add that the batteries shown in the illustration are connected in series. Two more (4S pack) will be connected to them.
MOSFET and optocoupler datasheet
Mosfet
Thank you very much for your answer.
Sincerely, Tom