I’ve got a Bluetooth speaker project I have been tossing around in my head - it’s kind of a ridiculous one, but one I want to do because I can. I have a pair of 3.5″ full range speakers, and plan on getting a 6.5″ subwoofer to match. I already have a Bluetooth amplifier board on the way - so I need to choose the cells and BMS to outfit it with, but I’m still learning about lithium batteries, and could use some guidance. I guess I need help knowing how to appropriately charge the battery pack I build too.
The board I ordered is listed as 12v-24v. 24v would allow for lower amperage, and thinner wire. I also have a 12v/24v charger, however its lithium setting is “lifepo4”, so I’m not sure if that means I couldn’t use the charger if I get li-ion cells.
My first question - the cells I’m currently looking at are 21700 li-ion cells - some are rated at 15a, while there are also some 45a cells I have in mind. I don’t need 45a output, rather I need to understand BMS selection to be able to decide what I need in a call. Do I want a BMS with a high current rating, to allow the cells to operate to their potential, or a BMS with a lower current rating to keep the cells from exceeding their safe rating? Or both? There is a 20a BMS I have in mind at the moment - if it will still protect 15a rated cells, then I would likely grab those cells. If it being rated at 20a means that it will NOT adequately protect the 15a cells, I would make the jump to the 45a cells, as I really don’t need 45a of output - as much as my speaker driver selection may make one think otherwise, I don’t plan to run the speaker THAT loudly.
These are li-ion cells with a nominal voltage of 3.6V and a max voltage of 4.2V. The BMS I am looking at is a 7S BMS, so the total nominal voltage would be 25.2V Is the nominal voltage the voltage I should be considering when matching it to the amplifier board’s power, or should I be using the maximum voltage, meaning I should instead look for a 6S BMS?
Lastly, the charging - can I use my lifepo4 charger on the li-ion battery pack, or do I need to figure out a different option, like a DC wall wart? Or does having a BMS make that not so much of a concern.
Thanks for any help you can offer!
