Sensor to charge battery

I'm doing a project here. I'm designing my own generator using genset and motor to produce 12V of electricity. The main objective of my project is to produce a 12V from the generator. This 12V is used to charge LiPo battery ( 3 cells ). The cable from the motor which produce 12V will be connected to the battery charger then the battery charge will be connected to LiPo battery. So when the LiPo battery is drain to certain voltage, there will be a sensor that detects the draining of the battery and automatically charge back the battery. The power or electricity is obtained from the generator. What kind of sensor should I used to detect the voltage of the LiPo battery ? I can't over charge the battery as it damages the battery. So, I need to figure out a suitable sensor to prevent it from over charge also.

• Which battery charger are you using? What is the accuracy you need to detect the low voltage? Do you have any MCU on board or you need to detect and start charging with discretes or charger IC solution alone? Aug 18, 2019 at 5:49

It would be far far far better to use an premade LiIon 3S charger that to attempt to implement one yourself.

A 3S LiIon battery MUST NOT have an applied voltage of more than 3 x 4.2V = 12.6V.
It is far better in most cases to limit Vmax to 12V or maybe 12.3V.

Maximum current is specificed by the battery manufacturer and is often C/2 or C/1. ie either

C/2 - Ichg_max_mA = battery_mAh capacity /2 or

C - Ichg_max_mA = battery_mAh capacity

What is your battery capacity in mAh or Ah.
What is the maximum power that your genset will produce?
How does the genset regulate the voltage of its 12V output?