Charge a BMS

Hi to everybody.
I am currently working a portable 12Vpowered device so, I am going to use a BMS 3S and still need to choose recharging method for this3x 18650 pack.
During my reseach, I learned that you can not directly apply a 12v to the BMS main output terminal (B+ and B-)! It is a kind of "disappointing" because when you are shopping for those BMS most seller publicated picture with Charge and Discharge and let you think that "naturally" supplying 12v to those pins is going to properly recharge the 18650s batteries:

I think we can all agree on those points:
1. Charging lithium 18650 is more complicate than that, charge must be CC and CV.
2. BMS is not a charging bord, and logically to charge you need a charging board.

Features Required and options retained:
A- Requirements: Visual info of charging and of charging completed, as with TP4056 module...

B- Options available:
1. Use a special 12v lithium wall charger. I came accross those chargers, they got some indicator led to inform you about charging/charge completed. Not really fan of this, I wish to use a standard 12v charger as they are kind of available everywhere...

2. Use 3 x TP4056 IC, and build some custom PCB with those 3 IC, to supply those 3 18650... with 3 indication LED for each 18650...
Or maybe use 3 TP4056 board, but I am runing for space and all this is going to be portable... Anyway to be decided...

3. Use a charge board for BMS : I came accross this board that state it is suited to charge a 3S BMS. I have never used it so do not know what it is worth.





https://fr.aliexpress.com/item/33034553658.html?spm=a2g0o.cart.0.0.21d73c008hx5zI&mp=1

Thx for anyone that would be kind to dig into this subject with me

I would use a standard CC CV PSU going out 12v. Thats how all standard equipment are charged through a bms like that .

I have built many projects like that. Just make sure it hvae CC cv

daromer said:

I would use a standard CC CV PSU going out 12v. Thats how all standard equipment are charged through a bms like that .

I have built many projects like that. Just make sure it hvae CC cv

Click to expand...

hey I was still ajusting the main post ahahahahaha
lol, Thxx for the tip, you are not far, it is actually to build a Portable Lab Power Supply
So I added the info about the board for option 3, you may have some thoughts about it maybe

Thats for charging One cell and not series pack. They cant be powered on same PSU without shorting it out on a series pack. Just get a 12v CC CV PSU that fits

daromer said:

Thats for charging One cell and not series pack. They cant be powered on same PSU without shorting it out on a series pack. Just get a 12v CC CV PSU that fits

Click to expand...

Thx vry much, can you please point me to some 12v CC CV PSU, to kind of know how it looks?

Most electronic psus ourtThere are CC CV. Though CC function are more based on what they can handle max comparing to more complex that have set limits.

On mobile so cant Link right now

use a buck converter, almost all the larger buck converters are cc/cv. With a buck converter you can use any power supply you have including a standard 12 volt charger, but its best to use a laptop charger if you want to charge at higher amps. I have many 3s battery packs and prefer using the buck converters, they give a 3s pack a very good charge. You can find buck converters for less then 15 dollars (less then 5 dollars if bought from china), you adjust the voltage output to 12.6 volts, and most also have a current adjust, in case you want to charge at 2 amps or whatever your preference.

280 watt buck converter, I use this to charge at up to 6 amps. It cc/cv and has voltage and current adjust, works extremely well to charge 3s. I have about 5 of these and are very reliable. Just make sure you use a small fan on it if charging at the higher amps. It has 2 wires input (your power supply) and 2 wires output to your battery.




On my buck converters I added a led volt/amp meter(5 dollars) so I can see the status of the charge in real time. Its not needed but being able to see what the charger is doing is good to have. This one I use to charge a 4s lifepo4.




I just started using buck converters last year, and now use them all the time to charge li-ion, lifepo4 and also my lead acid batteries. Its good to use a balance charger with lithium but if your pack has a bms and is in good balance, buck converters work just as well without having to program anything. Just connect input/output and it starts charging, and it won't exceed the max voltage you set. When the battery is almost full, the amps drop to less then 1 amp which gives the bms balance function a chance to do its job.