Hi everyone.
I want to create a customized UPS system and I will create the electronic boards myself since when available on the market unfortunately it does not fall within the power and space values I need.
My UPS will have the Vin of 24Vdc.
The system will be almost “in-line” in order to avoid “gaps” in power supplies, i.e. from the input I will divide the power supply, one part going directly to the loads and the other part to recharge the 4S lithium batteries (16.8V) ready in case of lack of current to immediately deliver voltage to the load. This will be possible by positioning 2 opposing diodes on the main power supply line (24V) and on the battery line (16.8V).
The battery charging chip must have
Vin =24V
Vout = 16.8V
Charging I = 300mA (I want to recharge them very slowly to prolong their life since they will always remain powered)
Since I want to do everything at home and I don’t trust cheap BMS, I then create an ad hoc BMS through:
- ADC (for reading the voltage of each battery)
- ADC (INA-226 for reading the charging current)
- DB18S20 temperature sensors
- Bipolar MOSFET (driven by the microcontroller which in case of abnormal readings completely cuts the circuit to and from the batteries)
- HY2213-BB3A chip and related resistors for balancing the batteries during charging
The help I ask for is for the chip with which to recharge the batteries (which should preferably be SMD and fairly easy to solder. I can get to QFN-16 but I would prefer SOIC-8 or 16 or an HTSSOP-14).
It is important that the current remains around 300mA (it can vary by 20-30mA but not much more) because the resistors that must be inserted for balancing must be calculated based on the current that must flow inside and therefore on the dissipation that they have (also because once the batteries are 100% charged these R will continue to carry current and therefore I don’t want the energy dissipated and therefore lost into thin air to be too high (I also want a system that is quite efficient from an energy point of view ) ).
Many charging chips also interrupt charging once they reach the maximum value (in my case 16.8V) but this in my case would not be good as after a while (even without being used) the voltage of the batteries will inexorably drop and then a new charging cycle will start and so on; charging cycles shorten the life of batteries.
Let’s say that every 2 days the voltage of a battery drops to 4.1V, the chip will start charging again and therefore within 1 year the battery will have already completed hundreds of charging cycles.
My aim instead is to bring the batteries to 16.8V and always leave the voltage fixed at the ends of 16.8V so that they are always at 100% without ever starting a discharge cycle unless the main 24V line is blown! For the problem of overcharging, overvoltage and overtemperature there is the regulation and control part that would intervene.
Therefore I ask you: do you know and have you ever used chips for charging 4S lithium batteries in any of your projects? If so which ones? As I said above, possibly SMD and quite easy to solder.
Thanks everyone in advance for the help