Charging LiOn battery pack

Ramussons

Joined May 3, 2013
1,409
This is an ad for a 12 volt LiOn battery pack that has inbuilt BMS.
https://www.amazon.in/MAEntTM-Lithium-Rechargeable-Industrial-Equipment/dp/B07WZW3TYK?th=1

The manufacturer also offers a recommended charger that outputs 12.6 volts CC/CV.
https://www.amazon.in/MAEntTM-Battery-Lithium-Constant-Indicator/dp/B07Y27RKLL?th=1

My question is, if the battery bank has an inbuilt BMS, what is the need for a CC/CV charger?
Can I not simply float the battery across a 12.6 volt power supply with a load?
Of course, the power supply must have sufficient current capacity to charge the battery bank and supply the load.

Thanks.

Alec_t

Joined Sep 17, 2013
14,313
Can I not simply float the battery across a 12.6 volt power supply with a load?
You probably could, providing (a) the pack is fully charged before you put 12.6V on it and (b) you don't mind the reduced battery life resulting from keeping it at full charge indefinitely.

Oguzhan17

Joined Feb 19, 2021
4
CC/CV guarantees a determined maximum current during CC (constant current) phase.

Imagine your batteries are around 11,1V and you will start charging them. Let us assume that you connect this 12.6V charger. If the total resistance between your batteries and the power supply (this includes the output resistance of the charger, resistance of the cable between the charger and the battery pack and the internal resistance of the battery) is around 0,05 Ohm, the charging current will be (12,6V - 11,1V) / 0,05 = 30A. This can be too much for the cells (I actually do not know, I did not check the charging details of the cells).

So, you CC/CV charger will make sure that it does not charge the battery pack with a higher current than you set. Or if you do not want to use a CC/CV charger at all, you can indeed use a typical 12,6V power supply but in that case I would just insert a small series resistor to its output to limit its charging current. That can be also a nice option.

Ramussons

Joined May 3, 2013
1,409
What is the role of the BMS built into the battery pack? Is that the one to manage the charging currents and protect against under voltage, over voltage, ...?

Audioguru again

Joined Oct 21, 2019
6,691
Since the ad for the battery does not say BMS then it does not have one.
A Lithium battery must never have a power supply over-charging it all the time.
Please go to battery university.com and read about how a lithium-ion battery charger detects a full charge then shuts off to avoid over-charging damage.

Oguzhan17

Joined Feb 19, 2021
4
What is the role of the BMS built into the battery pack? Is that the one to manage the charging currents and protect against under voltage, over voltage, ...?
View attachment 278088
The role of BMS can be balancing the cells. Imagine if you have 4 series connected cells and your battery voltage is 12V, ideally each cell should be 3V. However, sometimes imbalance between cells may occur. One of the cells may be 3.2V while the other one is 2.8V. In this case BMS can balance these cells (it can be either passive or active balancing depending on the application but it is not that important at this point, eventually it balances).

So, BMS may not have a responsibility to protect against overvoltage or overcurrent. Its responsibility may be only cell balancing.

bassbindevil

Joined Jan 23, 2014
828
The BMS doesn't manage charging. It does provide protection from catastrophic overcharging, short circuits, and discharging to below a safe voltage. It should include balancing, but not always.

The description says:
" Built-in BMS protection,With overcharge, over discharge, short circuit protection "
So, probably no balancing. If the cells are good quality and well-matched, that may not be a problem, but I'd prefer the pack to include a balance connector so voltages could be verified and if necessary plugged into a balancing charger.

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