Charging LiFePO4 with laboratory power supply

Hello!
I plan to use laboratory power supply for charging 20Ah previously balanced LiFePO4 battery pack. I am going to charge battery pack at 43,2V 10A and this laboratory supply has enough resource for doing that.
My question is following: What will happen when all elements have reached 3.6V and I dont disconnect, switch off or turn down current on my lab supply? Can I ruin my battery pack when leaving it connected at 43,2V 10A when all elements have reached 3.6V?

Thank you!

You dont' say how many cells in series or parallel, or what the charge rate of your cells is, or if you have a BMS, so we cant' answer your question directly.

But you can answer it for yourself:

Take the number of series cells, and the maximum voltage you want on each (HVC), and ensure your power supply is set to no more than that voltage times the number of series cells, and then as long as your cells are always naturally perfectly balanced then they will never be charged to more than that voltage.

If there is ever any imbalance in the cells, then that won't be true, but unless it is a severe imbalance it is unlikley you'll destroy any cells.


If you use a BMS designed to cut off charging when any cell reaches that HVC, or bypass the current around that cell so others can still charge, and then cut off when the pack is fully charged, you don't have to worry about it.



You would also want to set the current on the lab PSU to only the max charging current the total number of parallel cells can take.


If you have a BMS, you need to limit that current to the max the BMS can bypass around a cell that reaches HVC.

Sorry about that. There are 12 cells in series. Each cell is 20Ah 3,65V max(my plan is to charge up to 3,6V). It is ok to charge these cells with 10A continuously. According to the datasheet, the optimal charging voltage is 0.5C

I plan to not use BMS at the beginning and monitor batteries myself while fist times of charging. It is dangerous, but I think I take the risk. For using BMS i should have previously balanced cells anyway because most cheaper BMS-s have low balancing current and they may take too long time to balance. And later if I have all cells balanced after many cycles, they should all stay almost same, and are almost safe to charge with 43,2V. Because then there is a safety voltage of 0.5V to not overcharge any of cells. And 0,5V difference between cells is really hard to come during one cycle, in my opinion based on internet. And after every charge cycle I give a quick multimeter test to pack eo ensure that every cell is ok.

The thing i dont understand is if the battery pack voltage reaches same voltage that my supply gives, what will the current coming from supply do? Will it shrink altough i have set it to 10A with the lab supply knob? Or will it harm battery anyhow?
I undestand that when all cells are balanced, the charging voltage 43,2V is ok to use because then all cells are charged to 3,6V. When i forget to disconnect my power supply for many hours after battery pack has reached 43,2V, will it be a problem to battery pack?

It is hard to explain this problem, because English is not my first language.

kuivati said:

The thing i dont understand is if the battery pack voltage reaches same voltage that my supply gives, what will the current coming from supply do? Will it shrink altough i have set it to 10A with the lab supply knob? Or will it harm battery anyhow?

Click to expand...

Current will always drop as voltage difference between two things connected this way goes down.

So as soon as voltage is equal, there is zero current.

As long as voltage is not equal, then there will be current equal to the difference in voltage divided by the then-present total series internal resistance of the cells in the pack.

Bms no bms how are going monitor the cells ? I would put two 6s sense wires on for a meter like a cellog. Even with a bms I like sense wires for a cellog to check. Without bms I like 42 volts. As try are pretty full after 3.45v so after 3.5v they will race up to a higher voltage very fast. How high how matched are your cells. Go marry them.
Did I say don't over charge per cell. 3.6v. Yes they can take 3.8v but way there is no mah there to care about or above 3.5v lucky to get 17ah of use on a bike.