BMS question


2019-10-12 9:18 am

I'm currently working on a DIY bluetooth speaker. The amplifier that I've chosen needs about 12V for 2x20W speakers that I'm planning to use. The part I don't understand is the 18650 battery management. Most of them have a nominal voltage of 3,7V and maximum voltage of 4,2V. If I understand correctly, using 3S2P configuration would make an 11,1V - 12,6V battery pack, which is good for the amplifier. However, most of the BMS circuits I'm able to find have an over-discharge cutoff at 2,5V. At 3S2P configuration 7,5V would be way too low for the amplfier. Would those BMS's keep the voltage between 11,1V- 12,6V or not? Or is there any way too keep the voltage somewhere around 12V?

For example:
(Title says 11,1V-12,6V, however in the description over-discharge protection for each cell is 2,5V)
3S 40A BMS 11.1V 12.6V 18650 lithium battery protection Board with balanced Version for drill 40A current-in Battery Accessories from Consumer Electronics on | Alibaba Group
Here you can see the specifications for the nowadays Sanyo Panasonic 18650.

Chemistry starts to be weak below 3V per cell. The 2.5V setting is just an emergency mechanism, not a convenience mechanism.

You may consider making a monitor circuit with a low power or micropower comparator IC and some resistors and capacitors. But the main question is: Does the amplifier misbehave or just shut down below a certain voltage? An adjustable power supply may be required to test that.